AKADEMIA GÓRNICZO-HUTNICZAIM. STANIS�AWA STASZICA W KRAKOWIE

Fa ulty of Ele tri al Engineering, Automati s, Computer S ien e andEle troni sDepartment of Tele ommuni ationsDIPLOMA THESISMaster'sAn analysis of multi-rate mode of IEEE 802.11 EDCA wirelessnetworks using the ns-3 simulatorAuthor: Rafaª SrokaSpe ialization: Ele troni s and Tele ommuni ationsSupervisor: dr in». Marek Natkanie

Cra ow 2011

I hereby de lare that this thesis is a work of my own, and that only sour es ited in the bibliography have been used.O±wiad zam, ±wiadomy odpowiedzialno± i karnej za po±wiad zenie nieprawdy,»e niniejsz¡ pra � dyplomow¡ wykonaªem osobi± ie i samodzielnie i »e niekorzystaªem ze ¹ródeª inny h ni» wymienione w pra y.

Kraków, 10th of September 2011

To my Parents

Contents1 Introdu tion 11.1 The aim of the thesis . . . . . . . . . . . . . . . . . . . . . . . 11.2 Thesis stru ture . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Wireless LAN 32.1 Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Frame Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2.1 Frame �elds . . . . . . . . . . . . . . . . . . . . . . . . 63 Multirate Capabilities of the Physi al Layer 103.1 802.11 Lega y . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2 802.11b and Complementary Code Keying . . . . . . . . . . . . 113.3 802.11a/g and Orthogonal Frequen y Division Multiplexing . . . 123.4 802.11n and Spatial Division Multiplexing . . . . . . . . . . . . . 134 Medium A ess Control Proto ol 144.1 Distributed Coordination Fun tion (DCF) . . . . . . . . . . . . . 154.2 Point Coordination Fun tion (PCF) . . . . . . . . . . . . . . . . 154.3 Hybrid Coordination Fun tion (HCF) . . . . . . . . . . . . . . . 164.3.1 Enhan ed Distributed Channel A ess (EDCA) . . . . . . 164.3.2 HCF Controlled Channel A ess (HCCA) . . . . . . . . . 165 Enhan ed Distributed Channel A ess 185.1 Tra� Di�erentiation . . . . . . . . . . . . . . . . . . . . . . . 185.2 Enhan ed Distributed Channel A ess Fun tion (EDCAF) . . . . 195.2.1 Ba ko� pro edure . . . . . . . . . . . . . . . . . . . . . 205.2.2 Transmission Opportunity (TXOP) . . . . . . . . . . . . 215.2.2.1 EDCA TXOP . . . . . . . . . . . . . . . . . . 215.2.2.2 Multiple frame transmission . . . . . . . . . . . 235.3 Transmission Retries and Collisions . . . . . . . . . . . . . . . . 235.3.0.3 Retransmissions . . . . . . . . . . . . . . . . . 235.4 Blo k A knowledgement . . . . . . . . . . . . . . . . . . . . . . 246 Dynami Rate Adaptation in IEEE 802.11 WLANs 276.1 Multiple Transmission Rate Support . . . . . . . . . . . . . . . . 276.2 Rate Adaptation Algorithms . . . . . . . . . . . . . . . . . . . . 276.2.1 ARF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27v

6.2.2 AARF . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.2.3 CARA . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.2.4 RBAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 316.2.5 SampleRate . . . . . . . . . . . . . . . . . . . . . . . . 326.2.6 Minstrel . . . . . . . . . . . . . . . . . . . . . . . . . . 346.2.7 RRAA . . . . . . . . . . . . . . . . . . . . . . . . . . . 356.2.8 AARF-CD . . . . . . . . . . . . . . . . . . . . . . . . . 366.2.9 AMRR . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.2.10 Onoe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 The ns-3 Network Simulator 397.1 Design Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 397.1.1 Simulation Engine . . . . . . . . . . . . . . . . . . . . . 407.1.2 Pa kets . . . . . . . . . . . . . . . . . . . . . . . . . . . 407.1.3 Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417.1.4 NetDevi e . . . . . . . . . . . . . . . . . . . . . . . . . 417.1.5 Channel . . . . . . . . . . . . . . . . . . . . . . . . . . 427.1.6 Helpers . . . . . . . . . . . . . . . . . . . . . . . . . . . 447.2 Ar hite ture of 802.11 Implementation . . . . . . . . . . . . . . 447.2.1 Wireless Channel . . . . . . . . . . . . . . . . . . . . . . 447.2.2 PHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457.2.3 MAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467.2.4 802.11e style QoS support . . . . . . . . . . . . . . . . . 467.3 Implementation of Rate Control Algorithms . . . . . . . . . . . . 478 Analysis of QoS Provisioning in Multi-rate EDCA WLANs 498.1 Common Assumptions . . . . . . . . . . . . . . . . . . . . . . . 498.1.1 Channel onditions . . . . . . . . . . . . . . . . . . . . . 498.1.2 EDCA Parameter Set . . . . . . . . . . . . . . . . . . . 498.2 S enario 1. Mean transmission delay. BSS topology. . . . . . . . 508.3 S enario 2. Mean transmission delay. IBSS topology. . . . . . . . 578.4 S enario 3. Throughput. BSS topology. . . . . . . . . . . . . . . 618.5 S enario 4. Throughput. IBSS topology. . . . . . . . . . . . . . 658.6 S enario 5. Pa ket loss per entage. BSS topology. . . . . . . . . 688.7 S enario 6. Pa ket loss per entage. IBSS topology. . . . . . . . . 748.8 S enario 7. Bit error rate. . . . . . . . . . . . . . . . . . . . . . 758.9 Implementation Issues . . . . . . . . . . . . . . . . . . . . . . . 1009 Con lusion 1019.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102vi

Bibliography 103

vii

List of Figures2.1 Independent Basi Servi e Set (IBSS) topology . . . . . . . . . . 42.2 Basi Servi e Set (BSS) topology . . . . . . . . . . . . . . . . . 42.3 Extended Servi e Set (ESS) topology . . . . . . . . . . . . . . . 52.4 MAC frame format . . . . . . . . . . . . . . . . . . . . . . . . . 52.5 Frame Control �eld . . . . . . . . . . . . . . . . . . . . . . . . 62.6 Sequen e Control �eld . . . . . . . . . . . . . . . . . . . . . . . 82.7 QoS Control �eld . . . . . . . . . . . . . . . . . . . . . . . . . 94.1 MAC layer ar hite ture . . . . . . . . . . . . . . . . . . . . . . . 145.1 EDCA operation model . . . . . . . . . . . . . . . . . . . . . . 185.2 EDCF timing diagram . . . . . . . . . . . . . . . . . . . . . . . 225.3 Message sequen e hart for Blo k A k me hanism . . . . . . . . 256.1 Flow hart of the Automati Rate Fallba k algorithm . . . . . . . 286.2 Flow hart of the Collision-Aware Rate Adaptation algorithm . . . 306.3 RBAR Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . 327.1 Modules of the ns-3 network simulator . . . . . . . . . . . . . . 407.2 Wi�NetDevi e ar hite ture . . . . . . . . . . . . . . . . . . . . 437.3 Partial inheritan e diagram for rate- ontrol lasses . . . . . . . . 478.1 BSS simulation topology . . . . . . . . . . . . . . . . . . . . . . 518.2 Mean transmission delays of the �ows in IEEE 802.11a BSS network. 538.3 Mean transmission delays of the �ows in IEEE 802.11a BSS net-work (y axis adjusted). . . . . . . . . . . . . . . . . . . . . . . . 538.4 Mean transmission delays of the �ows in IEEE 802.11b BSS network 548.5 Mean transmission delays of the �ows in IEEE 802.11b BSS net-work (y axis adjusted) . . . . . . . . . . . . . . . . . . . . . . . 558.6 Mean transmission delays of the �ows in IEEE 802.11g BSS network 568.7 Mean transmission delays of the �ows in IEEE 802.11g BSS net-work (y axis adjusted) . . . . . . . . . . . . . . . . . . . . . . . 578.8 IBSS simulation topology . . . . . . . . . . . . . . . . . . . . . 588.9 Mean transmission delays of the �ows in IEEE 802.11a IBSS net-work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598.10 Throughput of the �ows in IEEE 802.11a BSS network . . . . . . 638.11 Throughput of the �ows in IEEE 802.11b BSS network . . . . . . 638.12 Throughput of the �ows in IEEE 802.11g BSS network . . . . . . 648.13 Throughput of the �ows in IEEE 802.11a IBSS network. . . . . . 67viii

8.14 Pa ket loss per entage of the �ows in IEEE 802.11a BSS network. 698.15 Pa ket loss per entage of the �ows in IEEE 802.11a BSS network(y axis adjusted). . . . . . . . . . . . . . . . . . . . . . . . . . . 708.16 Pa ket loss per entage of the �ows in IEEE 802.11b BSS network(y axis adjusted). . . . . . . . . . . . . . . . . . . . . . . . . . . 718.17 Pa ket loss per entage of the �ows in IEEE 802.11b BSS network 718.18 Pa ket loss per entage of the �ows in IEEE 802.11g BSS network 728.19 Pa ket loss per entage of the �ows in IEEE 802.11g BSS network(y axis adjusted) . . . . . . . . . . . . . . . . . . . . . . . . . . 738.20 Pa ket loss per entage of the �ows in IEEE 802.11a IBSS network 748.21 S enario 7 topology . . . . . . . . . . . . . . . . . . . . . . . . 768.22 Throughput in IEEE 802.11g saturated network with �xed BER (1) 788.23 Throughput in IEEE 802.11g saturated network with �xed BER (2) 798.24 Throughput in IEEE 802.11g unsaturated network with �xed BER(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818.25 Throughput in IEEE 802.11g unsaturated network with �xed BER(2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828.26 Delay in IEEE 802.11g saturated network with �xed BER (1) . . 848.27 Delay in IEEE 802.11g saturated network with �xed BER (2) . . 858.28 Delay in IEEE 802.11g unsaturated network with �xed BER (1) . 878.29 Delay in IEEE 802.11g unsaturated network with �xed BER (2) . 888.30 Pa ket loss in IEEE 802.11g saturated network with �xed BER (1) 908.31 Pa ket loss in IEEE 802.11g saturated network with �xed BER (2) 918.32 Pa ket loss in IEEE 802.11g unsaturated network with �xed BER(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 928.33 Pa ket loss in IEEE 802.11g unsaturated network with �xed BER(2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 938.34 Jitter in IEEE 802.11g saturated network with �xed BER (1) . . . 958.35 Jitter in IEEE 802.11g saturated network with �xed BER (2) . . . 968.36 Jitter in IEEE 802.11g saturated network with �xed BER (1) . . . 988.37 Jitter in IEEE 802.11g saturated network with �xed BER (2) . . . 99

ix

List of Tables3.1 IEEE 802.11 a/b/g data rates and parameters . . . . . . . . . . 103.2 IEEE 802.11n data rates and parameters . . . . . . . . . . . . . 113.3 OFDM PHY parameters for 802.11 a/g PHY . . . . . . . . . . . 124.1 EDCA A ess Categories . . . . . . . . . . . . . . . . . . . . . . 165.1 UP-to-AC mappings . . . . . . . . . . . . . . . . . . . . . . . . 195.2 Default values of EDCA Parameter Sets . . . . . . . . . . . . . . 205.3 Retransmission parameters of EDCA . . . . . . . . . . . . . . . 246.1 List of symbols used in CARA �ow hart . . . . . . . . . . . . . 316.2 Symbols used in SampleRate transmission time formula . . . . . 336.3 AARF-CD parameters . . . . . . . . . . . . . . . . . . . . . . . 377.1 MAC low models of the ns-3 network simulator . . . . . . . . . . 467.2 ns-3 MAC high models . . . . . . . . . . . . . . . . . . . . . . . 468.1 Log-distan e propagation model parameters . . . . . . . . . . . . 508.2 Mean transmission delays in IEEE 802.11a/b/g BSS networks. . . 528.3 Mean transmission delays in IEEE 802.11a IBSS network. . . . . 598.4 Throughput [Mbit/s℄ in IEEE 802.11a/b/g BSS networks . . . . 628.5 Throughput [Mbit/s℄ in IEEE 802.11a IBSS network. . . . . . . . 668.6 Pa ket loss per entage in IEEE 802.11a/b/g BSS networks. . . . 688.7 Pa ket loss per entage in IEEE 802.11a IBSS network . . . . . . 748.8 Throughput in IEEE 802.11g saturated network with �xed BER. . 778.9 Throughput in IEEE 802.11g unsaturated network with �xed BER. 808.10 Delay in IEEE 802.11g saturated network with �xed BER. . . . . 838.11 Delay in IEEE 802.11g unsaturated network with �xed BER. . . . 868.12 Pa ket loss in IEEE 802.11g saturated network with �xed BER. . 898.13 Pa ket loss in IEEE 802.11g unsaturated network with �xed BER. 918.14 Jitter in IEEE 802.11g saturated network with �xed BER. . . . . 948.15 Jitter in IEEE 802.11g unsaturated network with �xed BER. . . . 97x

List of A ronyms3GPP 3rd Generation Partnership Proje t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42A-MPDU Aggregated MAC Proto ol Data Unit . . . . . . . . . . . . . . . . . . . . . . . . . . 13A-MSDU Aggregated Medium A ess Control Servi e Data Unit . . . . . . . . . . . 8AC A ess Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16ACK A knowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13ADDBA Add Blo k A knowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24AID Asso iation Identi�er. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7AIFS Arbitration Interframe Spa e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20AIFSN Arbitration Interframe Spa e Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20AP A ess Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3API Appli ation Programming Interfa e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39ARF Automati Rate Fallba k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10AARF Adaptive ARF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29AARF-CD Adaptive Auto Rate Fallba k with Collision Dete tion . . . . . . . . . . 36AMRR Adaptive Multi Rate Retry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38BEB Binary Exponential Ba ko� . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29BER Bit Error Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48BPSK Binary Phase Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12BSS Basi Servi e Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3BSSID Basi Servi e Set Identi� ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7CCA Clear Channel Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30CARA Collision-Aware Rate Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29CBR Constant Bit Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100CCK Complementary Code Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12CFP Contention-free Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7CRC Cy li Redundan y Che k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5CRI Computing Resear h Infrastru ture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39CS Carrier Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15xi

CSMA/CA Carrier Sense Multiple A ess with Collision Avoidan e . . . . . . . . 14CSMA/CD Carrier Sense Multiple A ess with Collision Dete tion . . . . . . . . 41CTS Clear to Send . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15CS Carrier Sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15DA Destination Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7DCF Distributed Coordination Fun tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14DELBA Delete Blo k A knowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25DIFS DCF Interframe Spa e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20DQPSK Di�erential QPSK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12DR Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10DS Distribution System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3DSSS Dire t Sequen e Spread Spe trum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10EDCA Enhan ed Distributed Channel A ess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1EDCAF Enhan ed Distributed Channel A ess Fun tion . . . . . . . . . . . . . . . . . . . . 1EOSP End Of Servi e Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8ERP-OFDM Extended-Rate PHY OFDM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45ESS Extended Servi e Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4E-UTRAN UMTS Terrestrial Radio A ess Network . . . . . . . . . . . . . . . . . . . . . . 42EWMA Exponential Weighted Moving Average . . . . . . . . . . . . . . . . . . . . . . . . . . . 34FCS Frame Che k Sequen e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5FHSS Frequen y-Hopping Spread Spe trum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10HC Hybrid Coordinator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8HCCA HCF Controlled Channel A ess. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16HCF Hybrid Coordination Fun tion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16HR/DSSS High Rate DSSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11HT High-Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9HTC High-Throughput Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5IBSS Independent Basi Servi e Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3IR Infrared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11LCP Link Control Proto ol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42LTE Long Term Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42xii

MAC Medium A ess Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1MIMO Multiple Input Multiple Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13MMPDU MAC Management Proto ol Data Unit . . . . . . . . . . . . . . . . . . . . . . . . . . 8MSDU MAC Servi e Data Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6MTL Maximum Tolerable Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35NIC Network Interfa e Controller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41NSF National S ien e Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39OFDM Orthogonal Frequen y Division Multiplexing . . . . . . . . . . . . . . . . . . . . . . 12OOP Obje t-Oriented Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39ORI Opportunisti Rate In rease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35PC Point Coordinator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15PCF Point Coordination Fun tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15PHY Physi al Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45PPP Point-to-Point Proto ol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42PRNG Pseudo-Random Number Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40PS Power-Save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6PS-Poll Power Save Poll proto ol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7QAM Quadrature Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12QoS Quality of Servi e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1QBSS QoS BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17QLRC QoS Long Retry Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23QPSK Quadrature Phase Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12QSRC QoS Short Retry Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23RA Re eiving STA address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7RBAR Re eiver-Based AutoRate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31RRAA Robust Rate Adaptation Algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35RTS Request to Send . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15SA Sour e Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7SER Symbol Error Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31SIFS Short Interframe Spa e. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20SGI Short Guard Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13xiii

SP Servi e Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8STA Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3TA Transmitting STA Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7TC Tra� Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8TID Tra� Identi�er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8TS Tra� Stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8TXOP Transmission Opportunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8UAN Underwater A ousti s Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42WDS Wireless Distribution System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3WLAN Wireless Lo al Area Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1WNIC Wireless Network Interfa e Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Wi-Fi Wireless Fidelity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

xiv

Chapter 1Introdu tion1.1 The aim of the thesisThe aim of this thesis is to arry out the study of Quality of Servi e (QoS)provisioning in multi-rate IEEE 802.11 wireless networks based on Enhan edDistributed Channel A ess Fun tion (EDCAF). The work overs the simulationanalysis of su h QoS fa tors as throughput, mean transmission delay, per entageof lost pa kets and jitter in networks of various physi al layer types of IEEE802.11 standard utilizing di�erent rate adaptation algorithms.In this thesis, a set of rate ontrol me hanisms is extensively evaluated interms of their performan e in wireless networks based on EDCAF. To a hievethis goal, simulation analysis is arried in the ns-3 network simulator and itsresults are dis ussed in detail.1.2 Thesis stru tureThe stru ture of the thesis an be divided into three parts. First part des ribesthe fundamental topi s onne ted with network topologies and proto ols of IEEE802.11 wireless lo al area networks and overs the related work. After an insightinto Wireless Lo al Area Network (WLAN) ar hite ture, the multirate apabilitiesof di�erent Physi al Layers are dis ussed, as well as hannel a ess methodsde�ned by Medium A ess Control (MAC) proto ol. Topi s dis ussed in the �rstpart are ru ial for understanding the rate ontrol algorithms and QoS issuesdis ussed in the next parts.In the se ond part, the fo us is given to QoS extensions that ome withIEEE 802.11e Enhan ed Distributed Channel A ess (EDCA). These are tra� di�erentiation using A ess Categories and EDCAF, that ontrols the a essto the medium. Aspe ts of transmission retries, ollisions or multiple frametransmission are overed here. The deep overview of dynami rate adaptationte hniques is presented with an emphasis put on rate adaptation algorithms su has ARF, AARF, CARA, Minstrel and others, and their theory of operation. These ond part of the thesis in ludes also the extensive overview of the ns-3 networksimulator, its apabilities, features and limitations. The simulator is used in thesimulation analysis in the third part of this work.1

Third part overs simulation analysis of the multi-rate mode of IEEE 802.11EDCA ompliant wireless networks. Di�erent types of networks, utilizing variousrate ontrol algorithms and di�erent Physi al Layer models are being evaluated.Networks of wireless stations utilizing EDCA in multi-rate environment are beingtested in terms of mean transmission delays, pa ket loss ratio and throughput.Finally, detailed on lusions are presented as well as the overview of theimplementation issues that aroused during the simulation development in ns-3.

2

Chapter 2Wireless LANThis hapter ontains the fundamental knowledge about Wireless Lo al AreaNetworks (WLANs), whi h is ru ial for understanding further, more sophisti- ated topi s. First se tion gives fo us to network topologies present in WLANsand introdu es the nomen lature whi h is utilized in latter parts of the thesis.Se ond se tion presents the general format of the IEEE 802.11 frame, its om-ponents and their role in various s enarios, with the emphasis put on the Qualityof Servi e features.2.1 TopologiesWLAN ar hite ture des ribes the proto ols, hardware and software elements thatbuild the network system. Topology of the WLAN may be dynami and hangein time. Wireless stations an roam, hange their lo ations, be ome too distantfrom the transmitter to su essfully ommuni ate. The 802.11 standard familydes ribes the omponents of the WLAN system as sets and supports three typesof them [18℄. The following se tions des ribes wireless network topology sets indetail.Independent Basi Servi e SetIndependent Basi Servi e Set (IBSS) network topology onsists of wireless sta-tions that ommuni ate between ea h other dire tly, without an a ess-point asdepi ted in Figure 2.1. This type of network is also alled an ad-ho network.Of ourse, to su essfully transmit data, every Station (STA) must be within thetransmission range of the other STAs. IBSS model de�ned by the standard doesnot involve onne tion with outside network.Basi Servi e SetAs shown in Figure 2.2, Basi Servi e Set (BSS) topology is omposed of anA ess Point (AP) and a number of end stations. Stations are asso iated withthe AP that is onne ted to the Distribution System (DS) - typi ally a wirednetwork infrastru ture. However, a Wireless Distribution System (WDS) an3

Figure 2.1: Independent Basi Servi e Set (IBSS) topologyalso o ur, therefore a WDS is formed by multiple APs inter onne ted using802.11 WLAN [26℄.All STAs and the AP utilize a single frequen y hannel. Transmission betweentwo end stations takes pla e via the AP - sour e STA sends a frame to the AP,by then the AP forwards it to the destination STA.

Figure 2.2: Basi Servi e Set (BSS) topologyExtended Servi e SetTwo or more inter onne ted BSS ells ompose Extended Servi e Set (ESS).The ells are linked over the DS as shown in Figure 2.3. The DS is usually awired IEEE 802.3 Ethernet LAN. APs are responsible for forwarding tra� fromone BSS to another. STAs in ESS an freely roam between BSSs.4

Figure 2.3: Extended Servi e Set (ESS) topology2.2 Frame FormatsEvery MAC layer frame onsists of three main parts: header, body and frame he k sequen e omponent. MAC header in ludes frame ontrol, duration andaddress �elds whi h are mandatory, and optional QoS information and High-Throughput Control (HTC) �elds. Frame body, with its variable length, ontainsinformation a ording to the type and subtype of the frame. Frame Che k Se-quen e (FCS) �eld is �lled with IEEE 32-bit Cy li Redundan y Che k (CRC)information [1, 2℄.HT

ControlFrameControl

Duration/ ID

Address 1 FCSFrame Body

Octets: 2 2 6 0-23124 46 6

Sequence Control

2

Address 2 Address 3

6

Address 4QoS Control

2

MAC Header

4Figure 2.4: MAC frame formatA general MAC frame format a ording to [1℄ is shown in Figure 2.4. The�rst three �elds, whi h are: Frame Control, Duration and Address 1 as wellas the last �eld ontaining FCS information are present in all frame types. Other5

�elds are optional and appear in spe i� frame types and subtypes.2.2.1 Frame �eldsFrame Control �eldFrame Control �eld de�nes the fun tion of the frame using 2 bit Type sub�eldas shown on Figure 2.5.Bits: 4 1 2 1

Protocol Version

Type Subtype To DS

1

From DS

1

More Flag

1

Retry

1

Pwr Mgt

1

More Data

1

Protected Frame

1

Order

Figure 2.5: Frame Control �eldA single frame an be either a ontrol, data or management frame. What ismore, every frame type may also indi ate a de�ned subtype (4 bit Subtypesub�eld). For instan e frame of Management type an de�ne a subtype ofAsso iation request.The Proto ol Version sub�eld spe i�es the number of urrent version ofthe standard, whi h is zero.Frame Control �eld indi ates also whether the frame is exiting the DS oris destined for the DS (To DS and From DS �ags). The More Fragment �aginforms the re eiver about possible fragmentation of the urrent MAC Servi eData Unit (MSDU). The �ag is set to 1 when there is another fragment of theMSDU to re eive.The Retry sub�eld is set to 1 in frame that is being retransmitted and setto 0 in all other ases. This helps the re eiver to distinguish between possibledupli ates of the frame. If the value of the Power Management sub�eld is equalto 1 this indi ates that a STA is in Power-Save (PS) mode while the value of 0informs of a tive state of the STA. Frames that originate from AP have this �agset to 0.AP may inform the STA that it has more MSDUs or MMPDUs destined forthat frame in its bu�er by setting the More Data �eld value to 1. The Prote tedFrame �eld is set to 1 in all data and management frames of Authenti ationsubtype. Frame Body �eld is su h frames is prote ted with ryptographi en ap-sulation algorithm. The Order �eld is set to 1 when the non-QoS frame arriesdata using Stri tlyOrdered servi e lass. In all other ases it is set to 0.6

Duration/ID �eldThe information stored in this 16 bit �eld is di�erent in di�erent types of frames.The Duration/ID �eld may arry the Asso iation Identi�er (AID) of the STAwhen frame subtype is set to Power Save Poll proto ol (PS-Poll). When theframe is transmitted by a non-QoS STA within Contention-free Period (CFP),the value of this �eld is �xed and equal to 32768 (all bits set to 1). In all other ases, the Duration/ID �eld arries the information about the expe ted timethe frame ex hange will take (in mi rose onds). This duration is used in the hannel reservation me hanism by the transmitting devi e. However, the valuethat is stored as a duration varies slightly depending on the spe i� frame type(f.e. ontrol frames and management frames sent by QoS STAs insert in theDuration/ID �eld di�erent duration values).Address �eldsThe four 48-bit address �elds present in the MAC frame may in lude 5 di�erentIEEE MAC addresses:• Basi Servi e Set Identi� ation (BSSID) - the address identifying the BSS.In IBSS the address is omposed of randomly generated digits with theindividual/group bit set to 0 and the universal/lo al bit set to 1.• Sour e Address (SA) - the address of the MAC entity the MSDU originatesfrom.• Destination Address (DA) - the address identifying the �nal re ipient orre ipients of the MSDU.• Transmitting STA Address (TA) - the address identifying the transmitterthat sent the frame over the wireless medium.• Re eiving STA address (RA) - the individual or group address of immediatere ipient STAs.Address 1 �eld in ludes RA, the address of the single re eiver (in that aseframe is alled dire ted or uni ast frame) or group of re eivers of the MPDU.Address 2 spe i�es the TA - the address of the STA MPDU originates from.Address 3 depends on the type of the frame. Address 4 is used only when datatransmission o urs over a WDS. Contents of this �eld are di�erent in di�erenttransmission s enarios (f.e downlink or uplink transmission) and depend on thevalues of To DS and From DS bits in Frame Control �eld [26℄.7

Sequen e Control �eldEvery transmitted MSDU, Aggregated Medium A ess Control Servi e Data Unit(A-MSDU), or MAC Management Proto ol Data Unit (MMPDU) has a sequen enumber assigned. The sequen e number is stored as the part of the Sequen eControl �eld as shown in Figure 2.6.Fragment Number Sequence Number

Bits: 4 12Figure 2.6: Sequen e Control �eldThe value of the Fragment Number sub�eld is by default equal to zero.However, when MSDU or MMPDU is fragmented, �eld is �lled with fragmentnumber. If the frame is retransmitted, its sequen e and fragment numbers remainun hanged.Frame Body �eldThis �eld is variable sized. Its maximum length is determined by the maximumlength of the MSDU or A-MSDU and additional en ryption overhead. The min-imum size is 0 o tets. Information arried by this �eld depends on the type andsubtype of the frame spe i�ed in Frame Control �eld.QoS Control �eldThe stru ture of QoS Control �eld is shown in Figure 2.7. The 3 bit Tra� Identi�er (TID) �eld in ludes information about the Tra� Category (TC) orTra� Stream (TS) to whi h data arried in Frame Body �eld belongs.The End Of Servi e Period (EOSP) sub�eld is set to 1 by Hybrid Coordinator(HC) to inform the re eiver that urrent Servi e Period (SP) has ended. In allother ases the value of this �eld is set to 0.The A k Poli y sub�eld arries the information about the a knowledgementpoli y that is being urrently utilized. An MSDU an be sent using four types ofpoli ies: Normal A k, No A k, No expli it a knowledgement or Blo k A k.Frames sent by the HC in BSS that arry QoS data with CF-Poll in luded usethe Transmission Opportunity (TXOP) Limit sub�eld to spe ify the time limiton a TXOP the STA is granted after re eiving the frame.The Queue Size sub�eld is used by non-AP STA to inform the re eiver aboutthe length of the queue of frames for given TC or TS that are waiting in a bu�er.8

TID EOSP

Bits: 4

Ack Policy Reserved TXOP Limit

1 2 1 8

TID EOSP Ack Policy Reserved AP PS Buffer State

TID 0 Ack Policy Reserved TXOP Duration Requested

TID 1 Ack Policy Reserved Queue Size

(a)

(b)

(c)

(d)(a) QoS (+)CF-Poll frames sent by HC; (b) QoS Data, QoS Null, and QoS Data+CF-A k frames sent by HC; ( ),(d) QoS data frames sent by non-AP STAsFigure 2.7: QoS Control �eldThis information an be useful for the AP in determining the TXOP duration forthe sending STA. The STA may inform the AP about its desired TXOP durationby setting the value of TXOP Duration Requested sub�eld.The AP may use AP PS Buffer State sub�eld to give the non-AP STAinformation about the urrent PS bu�er state asso iated with that STA. Su hinformation may in lude the AC of the highest priority tra� present in the bu�er,total bu�er size, or �ag indi ating whether the AP PS bu�er state is spe i�ed.HT Control �eldThe HTC �eld is an optional �eld and is present only in HTC frames. QoS dataand management frames as well as Content Wrapper frame that onform to IEEE802.11n standard draft [1℄ in lude this High-Throughput (HT) Control �eld.FCS �eldThe Frame Che k Sequen e (FCS) �eld ontains a 32-bit Cy li Redundan yChe k (CRC) al ulated over �elds present in MAC header and Frame Body�eld. Value stored in this �eld is al ulated by the sender of the frame. Re eiverof the frame re al ulates the FCS number using �elds in the re eived frame. Ifthe FCS number al ulated by the re eiver di�ers from the value already storedin the frame, a transmission error is assumed.9

Chapter 3Multirate Capabilities of thePhysi al LayerData Rate (DR) is the physi al apa ity available to transmit the network tra� [9℄. DR expresses the devi e's raw data transmission apability at the Physi alLayer (PHY) level. IEEE 802.11 a/b/g/n PHY proto ols ome with a set ofdi�erent data transmission rates. The number of available rates depends on theproto ol and varies from 2 in the original version of the IEEE 802.11 wirelessnetworking standard to 16 in 802.11n [1℄. The brief view of 802.11 a/b/g/ndata rates and parameters is depi ted in Table 3.1 and 3.2.Although the standards do not state the algorithm of the rate sele tion,various rate ontrol me hanisms like Automati Rate Fallba k (ARF) or Minstrelhave already been developed and deployed in real devi es. Rate ontrol algorithmsare des ribed in hapter 6.Table 3.1: IEEE 802.11 a/b/g data rates and parametersStandard Frequen y[GHz℄ Modulation Bandwidth[MHz℄ Data rates [Mb/s℄802.11b 2.4 DSSS 20 1, 2, 5.5, 11802.11a 5 OFDM 20 6, 9, 12, 18, 24, 36, 48,54802.11g 2.4 OFDM,DSSS 20 1, 2, 6, 9, 12, 18, 24,36, 48, 543.1 802.11 Lega yThe original version of 802.11 standard (IEEE 802.11-1997 or Lega y) was pub-lished in 1997. The spe i� ation introdu es two possible transmission rates of 1and 2 Mb/s utilizing 2.4 GHz arrier frequen y and 20MHz wide hannels. Data an be transmitted using Frequen y-Hopping Spread Spe trum (FHSS), Dire t10

Table 3.2: IEEE 802.11n data rates and parametersMIMO streamChannelwidth[MHz℄ 1 2 3 4802.11n 20 6.5, 13,19.5, 26,39, 52,58.5, 65 13, 26, 39,52, 78, 104,117, 130 19.5, 39,58.5, 78,117, 156,175.5, 195 26, 52, 78,104, 156,208, 234,26040 13.5, 27,40.5, 54,81, 108,121.5, 135 27, 54, 81,108, 162,216, 243,270 40.5, 81,121.5, 162,243, 324,364.5, 405 54, 108,162, 216,324, 432,486, 540802.11nwith SGIenabled 20 7.2, 14.4,21.7, 28.9,43.3, 57.8,65, 72.2 14.4, 28.9,43.3, 57.8,86.7, 115.6,130, 144.4 21.7, 43.3,65, 86.7,130, 173.3,195, 216.7 28.9, 57.8,86.7, 115.6,173.3,231.1, 260,288.940 15, 30, 45,60, 90, 120,135, 150 30, 60, 90,120, 180,240, 270,300 45, 90, 135,180, 270,360, 405,450 60, 120,180, 240,360, 480,540, 600Sequen e Spread Spe trum (DSSS) or Infrared (IR) PHY. However, the IR modedid not a hieve a ommer ial su ess.In FHSS, a set of ommuni ating STAs hange hannel they operate on aftershort periods of time. The hannel sele tion pro ess relies on the pseudo-random hannel frequen y list and is utilized by all STAs in the set that parti ipate inthe ommuni ation.In DSSS, STAs of the same set use a �xed hannel. To avoid interferen esdi�erent spreading odes are applied in this mode [45℄.3.2 802.11b and Complementary Code KeyingPublished in 1999 IEEE 802.11b standard des ribes the hanges and additionsto the original 802.11 spe i� ation and introdu es Higher-Speed Physi al LayerExtension.The standard extends the set of available transmission rates with two newvalues of 5.5 and 11 Mbit/s and uses High Rate DSSS (HR/DSSS). The ar-rier frequen y of 2.4 GHz as well as hannel width of 20 MHz remained the11

same. Higher rates are possible due to the 8- hip (instead of 11 hips in DSSS)Complementary Code Keying (CCK) modulation s heme with 11MHz hippingrate. Symbols are en oded with Quadrature Phase Shift Keying (QPSK) andDi�erential QPSK (DQPSK). The 802.11b was the �rst standard that a hieved ommer ial su ess due to its popularization under the Wireless Fidelity (Wi-Fi)name [45℄.3.3 802.11a/g and Orthogonal Frequen y Di-vision MultiplexingThe 802.11a and 802.11g standards in reased the maximum transmission rate to54 Mbit/s. Both PHYs use Orthogonal Frequen y Division Multiplexing (OFDM)but distinguish in arrier frequen ies. Frequen y of 2.4 GHz is used by 802.11gand 5 GHz by 802.11a.Total number of 52 OFDM sub ariers an be employed, with Binary PhaseShift Keying (BPSK) or QPSK or 16 or 64-Quadrature Amplitude Modulation(QAM). Data transport is realized with 48 sub arriers while 4 sub arriers ontainpilot symbols.Possible modulation s hemes and data transmission rates for 802.11 a/g areshown in Table 3.3.Table 3.3: OFDM PHY parameters for 802.11 a/g PHYData rates [Mbit/s℄Modulation 20 MHz hannelspa ing 10 MHz hannelspa ing 5 MHz hannelspa ingBPSK 6 3 1,5BPSK 9 4,5 2,25QPSK 12 6 3QPSK 18 9 4,516-QAM 24 12 616-QAM 36 18 964-QAM 48 24 1264-QAM 54 27 13,512

3.4 802.11n and Spatial Division MultiplexingThe 802.11n amendment was published in 2009. The new PHY proto ol omeswith the signi� ant improve in throughput and range when ompared with olderstandards. To a hieve this bene�ts, the standard introdu es multiple spatialstreams and wider hannels as well as e� ien y me hanisms su h as frame ag-gregation or Blo k ACK.All older standards used 20Mhz wide hannels. STAs onforming to 802.11n an also use hannels of 40MHz width and up to four spatial streams to transmitdata. The spe i� ation in orporates the idea of Multiple Input Multiple Output(MIMO) and multiple antennas. A MIMO sender STA an send multiple spatialstreams of data to the re eiving MIMO STA within the same hannel. Thiste hnique is alled Spatial Division Multiplexing and allows for multipli ation ofthe raw data rate of a single stream. 802.11n STA utilizing the maximum numberof four spatial streams an send data at 600 Mbit/s. The 802.11n data rates (inMbit/s) and parameters are depi ted in Table 3.2 [9℄.Short Guard IntervalShort Guard Interval (SGI) me hanism that omes with the spe i� ation animprove the data rate by redu ing the symbol time from 4 µs to 3.6 µs. De reaseof the gap between symbols leads to 10 % in rease in the raw data rate.Frame aggregationA-MSDU and Aggregated MAC Proto ol Data Unit (A-MPDU) me hanism arefurther enhan ements that in rease throughput. The �rst allows for groupingthe MSDU frames whose destination and sour e addresses are the same. Thelatter introdu es A-MPDU whi h is omposed of a group of MPDU subframesthat in reases the maximum size of the frame to 64000 bytes.A knowledgment (ACK) frames an be also aggregated with the Blo k ACKproto ol. The idea of this me hanism is to send a single frame to a knowledge agroup of frames whi h leads to de rease of the a knowledgement overhead. Thesize of the ACK frame has been redu ed to 8 bytes from the lega y 128 bytes[9℄.13

Chapter 4Medium A ess ControlProto ol

Distributed Coordination Function (DCF)

PointCoordinationFunction(PCF)

HCFContention Access(EDCA)

HCFControlledAccess(HCCA)

802.11e HCF

Figure 4.1: MAC layer ar hite tureThe IEEE Medium A ess Control proto ol de�nes a me hanism for wireless hannel a ess whi h allows for multiple a ess of the STAs. The proto ol baseson the set of oordination fun tions that determine when a STA an send orre eive frames. The main hannel a ess method is Distributed CoordinationFun tion (DCF) known as Carrier Sense Multiple A ess with Collision Avoidan e(CSMA/CA). The ar hite ture of 802.11 MAC sublayer is depi ted in Figure 4.1.The IEEE 802.11 MAC provides all ore fun tionalities of the MAC layer,whi h (a ording to [26℄) are:• determining when to transmit/re eive frames,• de�ning frame formats,• se urity support,• QoS provisioning, 14

• mobility support,• error ontrol.Not listed but very important in wireless networks is also the power-managementme hanism. Su h a me hanism is used for ontrolling interferen es and enhan -ing signal quality to save mobile STA's battery power.4.1 Distributed Coordination Fun tion (DCF)Distributed Coordination Fun tion (DCF) or CSMA/CA is the mandatory wireless hannel a ess fun tion that must be implemented on all STAs.Before every transmission attempt, a STA has to sense the arrier and he kwhether it is busy. If the medium is idle, the transmission o urs. DCF handlesa short gap between onse utive frame transmissions so the STA has to wait a ertain amount of time after ea h sent frame. This assures the possibility forother STAs to send data. If the STA senses that the medium is busy, it waitsuntil the urrent transmission ends. Then, the STA sele ts a random ba ko�interval after whi h it attempts to he k the hannel and (if the medium is idle)transmit the frame.Above-des ribed pro ess an be enhan ed with RTS/CTS pro edure. Re-quest to Send (RTS) and Clear to Send (CTS) short ontrol frames sent by there eiving and transmitting STAs allow for redu ing frame ollisions.4.2 Point Coordination Fun tion (PCF)Point Coordination Fun tion (PCF) is the optional wireless hannel a ess fun -tion that utilizes two me hanisms - virtual Carrier Sense (CS) and a ess priority.PCF an be employed in the infrastru ture BSS network on�guration. Themethod uses a Point Coordinator (PC), a polling master whi h is implementedon the AP and assignes the right of transmission to STAs de iding whi h one an transmit within the given time. PCF an be des ribed as a poll-and-responseMAC.PCF has not emerged in ommer ial produ ts. This is due to problems withQoS provisioning and di� ulty for the implementation. However, the 802.11eMAC that introdu es extensive QoS support was developed by enhan ing PCFand DCF.

15

4.3 Hybrid Coordination Fun tion (HCF)Hybrid Coordination Fun tion (HCF) is de�ned in IEEE 802.11e that omes withextensive QoS support. The method extends DCF and PCF with QoS me h-anisms and is ba kward ompatible with original MAC. There are two hannela ess me hanisms in HCF:• HCF Contention-based Channel A ess or EDCA• HCF Controlled Channel A ess (HCCA)The �rst one is based on DCF while the latter on PCF. STAs that do notsupport QoS, do not implement HCF.4.3.1 Enhan ed Distributed Channel A ess (EDCA)In the EDCA approa h, tra� is divided into eight di�erent User Priorities (UP)that des ribe di�erent types of tra� like voi e or video. When a MPDU arrivesat the MAC layer, the UP of the MPDU is mapped into one of four a ess ategories (ACs) [26℄. Table 4.1 shows symbols and the des ription of the ACs.Table 4.1: EDCA A ess CategoriesA ess Category (AC) Des riptionAC_BK Ba kgroundAC_BE Best E�ortAC_VI VideoAC_VO Voi eFrames labeled with ACs ontend for the hannel. Of ourse, ACs of voi e andvideo tra� have the priority sin e real-time streaming media are more vulnerableto delays. EDCA is extensively des ribed in Chapter 5. The in�uen e of thetransmission rate sele tion on the EDCA-based network parameters is evaluatedin Chapter 8.4.3.2 HCF Controlled Channel A ess (HCCA)In the HCCA approa h, when a frame needs to be transfered with a parametrizedQoS poli y, a Tra� Stream (TS) is set between the re eiver and the transmitter.16

The TS an be established between AP and QoS-STA or between two QoS-STAs. However, to make the TS work, the STAs and the AP of the BSS haveto ex hange the set of tra� hara teristi and QoS parameters su h as:• nominal MSDU size,• mean data rate,• maximum burst size,• delay bound.The AP has to utilize an admission ontrol algorithm to e�e tively steer thesetup pro edure of the TSs in the BSS. After the su essful ex hange of tra� hara teristi s and QoS parameters the Hybrid Coordinator (HC) (equivalent ofthe PC in PCF) establishes the desired TS using HCCA [26℄. The HC an bedes ribed as the entral oordinator, an AP that oordinates all other STAs inQoS BSS (QBSS) [45℄.

17

Chapter 5Enhan ed Distributed ChannelA essThe IEEE 802.11e amendment that introdu es HCF, spe i�es two di�erent QoSenhan ement me hanisms - HCCA and EDCA. This hapter extensively des ribesEDCA and its role in QoS enabled networks. EDCA derives from DCF and isrequired for time prioritized QoS servi es. The idea of EDCA operation is depi tedin Figure 5.1 and is explained in the following se tions.

AC_BK EDCAF

1

2

AC_BE EDCAF

0

3

AC_VI EDCAF

4

5

AC_VO EDCAF

6

7

virtu

al collision resolution

User

priorityTransmit queues

for ACsPer-que EDCAfunctions

Transmissionattempt

priority

Figure 5.1: EDCA operation model5.1 Tra� Di�erentiationWithout QoS support, all STAs that ontend for the medium in a BSS aretreated equally. To make STAs a ess the hannel and send MPDUs in a more ontrolled way, EDCA introdu es tra� di�erentiation. The 802.11e station is alled a QSTA while a BSS supporting QoS a QBSS. Tra� that is generated by18

a single STA an be assigned a priority - User Priority (UP) - that des ribes itsimportan e. Tra� marked with higher UP should be transmitted �rst, omparedto the tra� labeled with lower UP (with one ex eption shown in Table 5.1).In general, real-time streaming media tra� like Voi e over Internet Proto ol(VoIP) or Video on Demand (VoD) where low delay values are ru ial is labeledwith higher UPs.There are eight di�erent UPs that an be mapped to four ACs using s hemeshown in Table 5.1. Table 5.1: UP-to-AC mappingsUP AC Des ription1 AC_BK Ba kground2 AC_BK Ba kground0 AC_BE Best E�ort3 AC_BE Best E�ort4 AC_VI Video5 AC_VI Video6 AC_VO Voi e7 AC_VO Voi e5.2 Enhan ed Distributed Channel A ess Fun -tion (EDCAF)Every AC has a orresponding independent instan e of Enhan ed DistributedChannel A ess Fun tion (EDCAF) whi h derives from DCF and extends itsoperation with QoS apabilities.ACs an be treated as queues, independent MAC entities that utilize enhan edDCF fun tion but with di�erent sets of parameters like inter-frame spa e orwindow size [49℄.The EDCAF parameters di�er on the AC and are used to tune fun tion'sbehaviour in ompeting for hannel a ess. The EDCA parameters are a quiredfrom the QAP in sele ted Bea on, Probe Response and (Re)Asso iation Responseframes and are utilized among all QSTAs in the QBSS. This ensures that EDCAFinstan es of the same AC on di�erent QSTAs use the same EDCA parameterset. If there is no EDCA parameters information in above-mentioned frames, thedefault values (shown in Table 5.2) are assumed.19

Table 5.2: Default values of EDCA Parameter SetsAC CWmin CWmax AIFSN AIFS∗ TXOPlimitLega y 802.11 15 1023 2 34 µs -AC_BK 15 1023 7 79 µs 0/0AC_BE 15 1023 3 43 µs 0/0AC_VI 7 15 2 34 µs 6.016/3.008 µsAC_VO 3 7 2 34 µs 3.264/1504 µsDefault values of EDCA parameters based on [2℄. (∗) indi ates dependen y on PHY,here 802.11b/802.11a are sele ted.In DCF, hannel is onsidered idle when no transmission o urred during DCFInterframe Spa e (DIFS) duration. DIFS an be al ulated using Formula 5.2,where Short Interframe Spa e (SIFS), is the small time interval between the lastsymbol of the previous frame and the �rst symbol of the subsequent frame. SIFSvalue is �xed per PHY. Thus, a STA has to examine the medium for DIFS timeinterval to de ide whether it an transmit.EDCAF sense the hannel for Arbitration Interframe Spa e (AIFS) durationwhi h is di�erent, depending on the AC. The minimum value of the AIFS is DIFS.However, it an be in reased with Arbitration Interframe Spa e Number (AIFSN).Smaller values of AIFSN, whi h is hosen by the HC, give the AC a higher priorityin a essing the medium. The AIFSN value should be greater or equal to 2 fornon-AP QSTAs and greater or equal to 1 for QAPs.DIFS = SIFS + 2 · Slot time (5.1)

AIFS[AC] = SIFS + AIFSN [AC] · Slot time (5.2)5.2.1 Ba ko� pro edureAfter determining that the hannel is idle, STA starts a ba ko� ounter. Whenthe ounter hits zero, STA waits one slot interval and starts transmitting data.The initial value of the ba ko� ounter is random but is taken from intervalde�ned by the minimal size of the ontention window (CWmin). Another pa-rameter - CWmax - spe i�es the maximum size of the window that annot be20

ex eeded. Smaller CWmin and CWmax result in higher priority in hannel a ess.However, if there is more then one QSTA utilizing the same AC, the probabilityof a frame ollision is greater for smaller CWmin and CWmax values [45℄. Thesize of the ontention window is in reased when transmission failure o urs butnever ex eeds the value of CWmax. The size of the window after i number offailures is des ribed by Formula 5.3.CWi = min[2i(CWmin[AC] + 1)− 1, CWmax[AC]] (5.3)5.2.2 Transmission Opportunity (TXOP)In EDCA, AP ontrols the a ess to the medium by assigning a ertain amountof time to the STA that is about to transmit. During this time interval theSTA is granted an uninterrupted medium a ess and is allowed to send MSDUs.This small amount of time is alled a Transmission Opportunity (TXOP). TXOPis de�ned by two values: starting time and duration. There are two types ofTXOPs:

• EDCA-TXOP - a quired using ontention-based hannel a ess,• HCCA-TXOP or polled TXOP - a quired via ontrolled medium a ess bythe HC.5.2.2.1 EDCA TXOPQSTAs are informed of the maximum value of a TXOP by the HC using aTXOPlimit parameter in an information �eld of the bea ons generated by theQAP. If the TXOPlimit is set to 0, single MSDU or MMPDU an be sent forea h TXOP.QSTAs have to ensure that the transmission of the MSDU with sele ted PHYrate will not ex eed the TXOPlimit and fragmentate the MSDU when needed.However, the TXOPlimit an be ex eeded in following situations:• when a MPDU is sent with lower PHY rate then the rate sele ted in theinitial MPDU transmission attempt,• for retransmission of an MPDU,• for the �rst transmission of an MPDU if any previous MPDU in urrentMSDU was retransmitted, 21

• for broad ast and multi ast MSDUs.The EDCAF of the sele ted AC an perform one of the following a tions:• start a transmission of a frame,• de rease the ba ko� ounter,• start a ba ko� pro edure if an internal ollision o ured,• stay idle.However, to start a transmission of the frame, several requirements must bemet. First of all, there must be a frame available to sent at the EDCAF. What ismore, orresponding ba ko� ounter has to have a value of 0. Finally, the AC of ahigher UP is not allowed to start transmission of a frame. When all requirementsare met, the EDCAF is granted the permission to begin a transmission sequen e.When the EDCAF instan e initiates the frame ex hange it is given an EDCATXOP. Figure 5.2 [49℄ shows the EDCF timing diagram that illustrates the trans-mission of the frames with 3 di�erent priorities i, j, and k where i is the highestand k the lowest priority. Smaller values of AIFS and CW guarantee a higherprobability of su ess in ontending for the hannel a ess.

AIFS[i]

Busy Medium Back-off Window

CW[i]

AIFS[j] CW[j]

AIFS[k] CW[k]

Defer AccessDecrement Backoff as long

as medium is idle

Back-off Window

Back-off Window

CW [i] < CW [j] < CW [k];AIFS[i] < AIFS[j] < AIFS[k]Figure 5.2: EDCF timing diagram22

5.2.2.2 Multiple frame transmissionWhen there are two or more frames waiting for the transmission in the AC que andthe AC was granted a EDCA TXOP, a QSTA may transmit multiple frames duringthe same EDCA TXOP. In su h a ase, all frames must be assigned to the AC forwhi h TXOP was a quired - frames of other ACs are not allowed for transmissionduring other AC's EDCA TXOP. However, a QSTA is permitted to send the ad-ditional frame during the same TXOP only if the additional frame's transmissionduration in reased by the expe ted a knowledgement response frame transmis-sion duration do not ex eed the remaining hannel o upan y timer value. Whenabove-stated requirement is ful�lled, QSTA may transmit the additional frameafter waiting a SIFS time.A QSTA must announ e the intention of sending multiple frames during thesame EDCA TXOP. To do so, the Duration/ID �eld of the frame is appropriatelyset.5.3 Transmission Retries and CollisionsA ontention between di�erent EDCAFs of the same QSTA may o ur whentheir ba ko� ounters hit the value of 0 at the same moment and both EDCAFshave a frame available to transmit. In su h a ase, a virtual ollision is assumedand ba ko� pro edure is started. The EDCAF of the AC with higher priority isgranted the right of transmission while other EDCAFs a t as if a ollision tookpla e on the medium.5.3.0.3 RetransmissionsA QSTA utilizing EDCA me hanisms implements two retry ounters for ea hAC. These are QoS Short Retry Counter (QSRC) and QoS Long Retry Counter(QLRC), both with initial values of 0. QSRC and QLRC ount retransmissionsof the frame and determine the number of frame retransmissions after whi h theframe is dis arded. All retransmitted MPDUs have their Retry �eld set to 1.After ea h su essful transmission the ounter is reset to its initial value.To hoose whi h ounter, QSRC or QLRC, should be in reased at the timeof transmission failure, the size of the MSDU or MMPDU is examined. Forunsu essful transmissions of MAC frames whi h length is less then or equal todot11RTSThreshold, the AC's QSRC value is in reased. Similarly, for framesbigger then dot11RTSThreshold, QSTA in reases the value of QLRC.Sin e real-time streaming voi e and video tra� are more vulnerable to delays aused by retransmissions, AC_VO and AC_VI require smaller retry ounters thenAC_BK and AC_BE. 23

The maximum number of possible retransmissions is limited by the parame-ters:• dot11ShortRetryLimit for QLSR,• dot11LongRetryLimit for QLSR.When one of the ounters rea hes the maximum value des ribed by the pa-rameters, the MSDU or MMPDU is dis arded. The ounters are also in reasedwhen internal virtual ollision o urs in the EDCA hannel a ess pro edure.Table 5.3 shows the parameters dis ussed in this se tion and its default values.Table 5.3: Retransmission parameters of EDCAParameter Default valuedot11RTSThreshold 3000dot11ShortRetryLimit 7dot11LongRetryLimit 4dot11EDCATableMSDULifetime 500 µsWhen a MSDU arrives at the MAC, QSTA starts a transmit MSDU timer.The timer is used to measure, how mu h time the MSDU waits for the trans-mission. When the timer rea hes the maximum value des ribed by parameterdot11EDCATableMSDULifetime, the frame is dropped.5.4 Blo k A knowledgementThe introdu ed in IEEE 802.11 amendment Blo k A knowledgement (Blo k A k)me hanism an be used in both EDCA and HCCA. The me hanism allows fora knowledging a number of MPDUs with one ACK frame whi h improves overalltransmission e� ien y and redu es overhead generated by ACK frames.QSTAs that support Blo k ACK me hanism may use one of its subtypes:• Immediate Blo k ACK - for high-bandwidth, low-laten y transmissions,• Delayed Blo k ACK - for medium-laten y transmissions.Figure 5.3 shows a frame ex hange with Blo k ACK me hanism. Add Blo kA knowledgment (ADDBA) Request/Response frames are used to initiate thetransmission and set up Blo k A k parameters su h as Blo k A k Poli y and24

Bu�er Size while Delete Blo k A knowledgment (DELBA) frame is used to sig-nal the end of Blo k A k operation. However, before the transmission utilizingaggregated ACKs begins, QSTAs have to on�rm that they support the me ha-nism by examining the Delayed Blo k A k and Immediate Blo k A k apabilitybits in the re eived frames.Tear D

own

Data & Block Ack

ADDBA Request

ACK

ADDBA Response

ACK

QoS Data MPDU

BlockAckReq

BlockAck

DELBA Request

ACK

Setup

Originator RecipientFigure 5.3: Message sequen e hart for Blo k A k me hanismThe EDCA ontention takes pla e only on e, before the �rst frame of theblo k s heduled for transmission. After the ontention has been won the wholeblo k is sent as well as Blo kA kReq frame that ontains the a knowledgmentrequest. Re eiver responds with Blo kA k frame with the ACK information25

about ea h frame of the blo k, so the originator an retransmit frames that werenot in luded in the Blo kA k response frame.During one TXOP, QSTA an send a burst of MPDUs separated by SIFS.The transmitter is allowed to send Blo k and Blo kA kReq frames in di�erentTXOPs. What is more, also the frames that build the blo k an be splited a rossdi�erent TXOPs.It has been shown that TXOP and Blo k A k features that ome with IEEE802.11e an signi� antly enhan e the overall throughput in high data rate trans-mission networks while they are rather not useful in low data rate environmentswith low TXOP values [43℄.

26

Chapter 6Dynami Rate Adaptation inIEEE 802.11 WLANs6.1 Multiple Transmission Rate SupportAll standards des ribing IEEE 802.11 PHYs support data transmission using dif-ferent transmission rates. Although the multi-rate apabilities are learly spe -i�ed, listing available transmission modes, standards do not de�ne a parti ularrate ontrol algorithm, leaving its implementation and deployment to the Wire-less Network Interfa e Card (WNIC) manufa turer. Rate ontrol features an beimplemented either in a software driver or realized in hardware omponents ofthe devi e.6.2 Rate Adaptation AlgorithmsThe la k of prede�ned standardized rate sele tion me hanism led to the reationof various rate ontrol s hemes. This se tion in ludes extensive overview of themost known algorithms, fo using on those evaluated in the further, simulationpart of the thesis.6.2.1 ARFThe ARF rate ontrol algorithm was introdu ed by A. Kamerman and L. Mon-teban in 1997 and is used in Lu ent's WaveLAN II devi es [22℄. In ARF, trans-mitting devi e ounts re eived and missed ACK frames in order to sense hannel ondition and adjust the data rate. Generally speaking, ARF de reases the ratewhen onse utive ACKs are missed in a row and in reases it after ounter ofsu essfully re eived ACKs hits appropriate value.Theory of operationWhen a STA starts transmitting frames, ARF sets initial rate to 2 Mbit/s. Ifthe ACK for the transmitted frame has not been re eived for the �rst time, theSTA retries to send it using 2 Mbit/s. However, when also the se ond ACK is27

missed, ARF de reases the rate to 1 Mbit/s and �res a timer. If 10 onse utiveACK are su essfully re eived or timer expires, ARF swit hes to higher datarate - 2 Mbit/s. When STA does not re eive ACK after upgrading the rate, itimmediately falls ba k to 1 Mbit/s and ontinues normal operation. Figure 6.1presents des ribed above ARF s heme using a �ow hart.!ransmission

START

Missed ACK

Increase received ACK

Set missed ACK to 0

Received ACK > 10

or

Timer has expired

Missed ACK > 2

Set rate to 2 Mb/s

Set rate to 1 Mb/s

Start timer

Increase missed ACK

Set received ACK to 0

Initial rate: 2 Mb/s

Initial missed ACK: 0

Initial received ACK: 0

YES

NOYES YES

YES

NO

NO

Missed ACK

NO

Figure 6.1: Flow hart of the Automati Rate Fallba k algorithmEnhan ed ARF s hemeIf more then two data rates are used, a system utilizes enhan ed ARF s heme,whi h is analogi al to that presented above. When two onse utive frames arenot re eived, STA de reases the trasmission rate to the next lower rate and startsthe timer. Similarly, when 10 ACKs are re eived or timer expires, the transmissionrate is in reased. First transmission after raising the data rate must be su essful28

or the rate is dropped to its earlier value.6.2.2 AARFThe Adaptive ARF (AARF) rate ontrol algorithm was initially des ribed in [25℄and was designed to work in a low-laten y systems as well as to improve perfor-man e of ARF [22℄, on whi h the algorithm is based. The main idea of AARF isto enhan e ARF operation by dynami ally hanging the number of su essfullyre eived ACKs that triggers the in rease of the transmission rate a ording tothe hanges of hannel onditions.Performan e issueA ording to reators of AARF, ARF ine� iently deals with stable hannel on-ditions. To outline this issue a simple example an be onsidered. STA operatesat 1 Mbit/s rate, su essfully sending data through stable transmission medium.However, transmission at 2 Mbit/s auses hroni frame losses. In su h an envi-ronment, ARF will set the rate to 1 Mbit/s. Furthermore, it will also ontinuallytry to use a higher rate, sending every tenth, probing frame at 2 Mbit/s hopingthat transmission with higher rate will be trouble-free. This s enario illustrateshow ARF, in a spe i� but stable onditions may ause regular transmissionfailures.Theory of operationAARF addresses above-dis ussed performan e issue by ontinuously hangingthe threshold of su essfully re eived ACKs at run-time. Threshold is adaptedusing Binary Exponential Ba ko� (BEB) [30℄. When a STA fails in transmittingthe probing frame, it immediately de reases its rate to the previous, lower valueand multiplies by two the number of su essful transmissions that triggers thein rease of the data rate. The maximum value of the threshold is bounded to 50.However, AARF's behavior is di�erent when two onse utive frames are missed- the threshold in su h a situation is set to its initial value of ten.6.2.3 CARAThe Collision-Aware Rate Adaptation (CARA) algorithm was presented by J. Kimet al. in 2006 [23℄. CARA, unlike other rate adaptation te hniques, is able todete t the reason for missed ACK frame, indi ate whether this loss happeneddue to frame ollision or hannel errors, and rea t appropriately.29

Theory of operationCARA introdu es two methods of di�erentiating ollisions from hannel errorsthat underlie operation of the algorithm: mandatory RTS Probing and optionalClear Channel Assessment (CCA) Dete tion. The algorithm is similar to ARFand as its prede essor utilizes onse utive transmission failures and onse utivesu essful transmissions ounters.Sin e RTS frames are small-sized and transmitted at solid rate, reators ofthe algorithm assumed that the probability of the RTS frame transmission erroris negligible.After su essful RTS/CTS transa tion, a STA is onsidered to have a guaran-tee that the following transmission will o ur without ollisions. Hen e, any trans-mission failure after su essful RTS/CTS ex hange must be aused by hannelerrors. Performing RTS/CTS transa tion before every data transmission wouldassure no frame ollisions but would be extremely ine� ient, adding signi� antRTS/CTS overhead. RTS Probing me hanism deals with that issue by pursuingRTS/CTS ex hange only when transmission failure o urs.�ransmission

START

m ≤ P

Missed ACK

RTS/CTS

m++

n=0

NO

SuccessFailure

NO

YES

YES

YES

m == M

NO

n++

m = 0

Increase

rate

Await MPDU

n == N

YESNODecrease

rate

Transmit frame

Figure 6.2: Flow hart of the Collision-Aware Rate Adaptation algorithm30

Table 6.1: List of symbols used in CARA �ow hartSymbol Default value Commentn - onse utive su ess ountm - onse utive failures ountM 10 onse utive su ess threshholdN 2 onse utive failure threshholdP 1 probe a tivation thresholdFigure 6.2 presents simpli�ed s heme of CARA operation. Related symbolsare des ribed in Table 6.1.When MPDU arrives, CARA examines whether the ounter of onse utivetransmission failures hit its limit or the size of the MPDU ex eeds given threshold.If one of these events o urs, the RTS probing pro edure is started. RTS/CTStransa tion may fail - if so, ounters remain un hanged. However, when RTSprobing su eeds, frame is sent with the urrent transmission rate. Now, STAawaits an ACK frame - if it gets it, ounter of su essful transmission is raised byone and the ounter of transmission failures is set to zero. When the number ofsu essful transmissions hits the threshold (by default 10), the rate is in reased.Though, when an ACK frame is missed, failure ounter in reases its value andthe number of su essful transmissions is reset. If the onse utive transmissionfailure ounter hits the threshold (by default 2), the rate is dropped to the nextlower available value.CARA an also use the optional, CCA Dete tion te hnique to distinguishframe ollisions from errors introdu ed by the hannel. In this approa h, afterthe transmission of the frame, after SIFS, CARA probes the hannel using CCA.If the hannel is in use and the STA re eived no ACK for the transmitted frame,CARA assumes that ollision o ured - in su h a ase ounters remain un hanged.6.2.4 RBARThe Re eiver-Based AutoRate (RBAR) proto ol was introdu ed in 2001 by G.Holland et al. in [21℄. The Algorithm hooses the rate during the RTS/CTSpro edure - loser to the real transmission time.In RBAR, ontrary to other algorithms su h as ARF or CARA, rate sele tionis performed by the re eiver STA. This fa t, a ording to the reators of RBARallows for the better, more a urate estimation of hannel onditions sin e varioussigni� ant signal parameters like Symbol Error Rate (SER) or signal strength an31

be a essed by the re eiving hardware.However, sender STA is the one that hooses the transmission rate. Thus,information about quality of the hannel should be sent ba k to the sender STAto allow it to adjust the rate. This transmission however, may introdu e anoverhead as well as potential syn hronization issues due to transmission delays.Theory of operationTo allow RBAR to work e� iently, minor hanges of 802.11 frame formats mustbe implemented. Modi� ations of RTS and CTS frames are shown in Figure 6.3.FrameControl

DurationDestinationAddress

FCSSourceAddress

FrameControl

DurationDestinationAddress

FCS

FrameControl

Rate & Length

DestinationAddress

FCSSourceAddress

FrameControl

Rate & Length

DestinationAddress

FCS

Rate Length Rate Length

Octets:

Bits:

2 2 6 6 4 2 2 6 4

4 12 Bits: 4 12

RTS Frame CTS Frame

(a)

(b)

(a) Original 802.11 RTS/CTS frames (b) Modi�ed RTS/CTS framesFigure 6.3: RBAR FramesIn order to hoose best transmission rate, the re eiver STA analyzes the RTSframe at the time of its re eption. Re eived RTS frame in ludes rate value hosen by the sender pursuant to some heuristi - f.e the most re ent rate. Afteranalyzing the information about hannel, re eiver estimates the transmissionrate for the forth oming frame. When appropriate rate is sele ted, sender STAis noti�ed about it in the CTS frame and an appropriately set the transmissionrate and a ordingly adjust its ba k-o� timer. However, original CTS frame doesnot ontain any �eld that an be used for arrying su h information and slight hanges of original 802.11 are ne essary.6.2.5 SampleRateSampleRate algorithm [13℄ is one of three rate ontrol algorithms of MadWi�Proje t [7℄. In SampleRate, rate sele tion is done after examining average pa kettransmission time of re ent samples. Rate with the smallest average transmission32

time is hosen. Contrary to many other rate ontrol me hanisms (f.e ARF, CARA,AARF) SampleRate does not assume that higher rates are less solid and robustthan lower rates. Thus, to sele t the optimal transmission rate, the algorithmperiodi ally performs a transmission using rates other than the urrent rate. Thisis done to olle t information about pa ket transmission times at di�erent ratesand estimate the optimal rate.Theory of operationWhen a STA begins to transmit data, SampleRate sets its rate to the highestavailable rate and he ks whether four onse utive failures o urred - if so, rateis de reased until frames are su essfully transmitted. To obtain pa ket trans-mission time samples, every tenth frame is sent at random rate - one, pi kedfrom the list of available rates. However, if four onse utive frames have notbeen a knowledged for the spe i�ed rate, su h a rate annot be used in sam-pling operation. What is more, the rate annot be pi ked when its su essfultransmission time ex eeds the average frame transmission time of the urrentrate. This redu es the number of rates that have to be he ked. Sample rateuses the following formula for transmission time al ulation (related symbols aredes ribed in Table 6.2):txtime(b, r, n) = DIFS + backoff(r) + (r + 1) · (SIFS + ack + header +

n · 8

b)Table 6.2: Symbols used in SampleRate transmission time formulaSymbol Commentb bit-rater number of retriesn length of the pa ket in bytesDIFS 50 µs in 802.11b, 28 µs in 802.11a/gSIFS 10 µs in 802.11b, 9 µs in 802.11a/ga k 304 µs using 1 Mbit a knowledgments for 802.11b and 200

µs for 6 megabit a knowledgmentsheader 192 µs for 1 Mbit 802.11b pa kets, 96 for other 802.11b bit-rates, 20 for 802.11a/g bit-ratesba koff(r) al ulated using the table in Figure 2-233

Every sample that algorithm uses for its estimations is valid for a �nite timeinterval of ten se onds - this guarantees that old, outdated information aboutpa ket transmission times are not onsidered. If during the algorithm run, av-erage transmission time of one of the rates be omes lower than the averagetransmission time of the urrent rate, SampleRate immediately hanges the ur-rent transmission rate to that rate.6.2.6 MinstrelThe Minstrel algorithm [4℄ is a part of MadWi� rate ontrol algorithms suite. Itwas designed by D. Smithies and released in 2005. Main idea of Minstrel is basedon SampleRate algorithm [7℄ (dis ussed in earlier se tion) and uses ExponentialWeighted Moving Average (EWMA) in rate sele tion pro ess.Theory of operationSimilarly to SampleRate, Minstrel he ks rates that di�er from the optimal bysending frames with randomly pi ked rate in order to gather statisti al informa-tion. After olle ting data the most su essful rate is hosen. To sele t themost su essful rate, Minstrel examines the measure of su essfulness using theformula 6.1.Measure of su essfulness = Ptransmissionsuccess ·megabits transmittedelapsed time (6.1)Every 100ms algorithm pro esses olle ted information using EWMA al u-lation, tra ing the su ess history of ea h tested rate. After doing so, best rateis sele ted and set. EWMA al ulation makes the information about the givenrate more smooth. By default, EWMA s aling fa tor is set to 75% whi h meansthat algorithm uses 75% of the old information and 25% of the new. Probabil-ity of su ess is al ulated every 100ms for ea h rate that is being tested usingformulas 6.2 and 6.3.

Ptransmissionsuccess =25 · Psuccessthistimeinterval + 75 · Pold

100(6.2)

Psuccessthistimeinterval =number of pa kets sent su essfully this ratenumber of pa kets sent this rate (6.3)34

6.2.7 RRAAThe Robust Rate Adaptation Algorithm (RRAA) was designed by H.Y. Wong etal. in [47℄. Inventors of the algorithm implemented a short-term loss ratio me h-anism that improves estimation of the hannel's onditions and further sele tionof the transmission rate value.Theory of operationRRAA measures the hannel onditions by tra king the frame loss ratio. Toqui kly rea t to the hanges of the transmission medium, frame loss ratio esti-mation is performed within a time window (by default 5 - 40 frames). RRAAintrodu es a set of parameters:• Estimation window size - the number of transmitted frames that triggersthe re al ulation of the loss ratio. The size of the window is in reased forhigher rates that transmit more frames in the same time when omparedto lower rates.• Maximum Tolerable Loss threshold (PMTL) - the threshold for rate de- rease.• Opportunisti Rate In rease threshold (PORI) - the threshold for rate in- rease.Estimation window size, Maximum Tolerable Loss (MTL) and Opportunisti Rate In rease (ORI) are spe i�ed for ea h rate. The loss ratio is al ulated usingthe Formula 6.4, where the number of lost frames and the number of transmittedframes are summed over the estimation window.

P =number of lost framesnumber of transmitted frames (6.4)Algorithm starts with the maximum rate, al ulating the loss ratio after theappropriate number of frames is transmitted. Afterwards, if the loss ratio islarger than PMTL, the rate is de reased. Similarly, when the loss ratio is smallerthan PORI , the transmission rate is in reased to the next available value. A newestimation window is started after every rate hange.

PMTL for the rate R is al ulated using the Formulas 6.5 and 6.6 where R−is the next lower rate and α is a tunable parameter.P ∗(R) = 1−

Throughput(R−)

Throughput(R)= 1−

txtime(R)

txtime(R−)(6.5)35

PMTL = α · P ∗(R), α ≥ 1 (6.6)The threshold for rate in rease, PORI is al ulated similarly using Formula6.7 where PMTL(R+) stands for the PMTL of the next higher transmission rate:PORI =

PMTL(R+)

β, β ≥ 1 (6.7)RRAA introdu es also an Adaptive-RTS feature. The me hanism keeps tra kof the number of transmissions utilizing RTS/CTS transa tions. Only limitednumber of su h transa tions an be performed within a time window (RTS win-dow). When frame transmission fails, value of the RTS window is in rementedallowing RTS/CTS transa tion to be performed. This limits the overhead ausedby the RTS/CTS frames, avoids the problem of RTS os illation and suppresses ollision losses.6.2.8 AARF-CDThe Adaptive Auto Rate Fallba k with Collision Dete tion (AARF-CD) algorithmwas initially des ribed by F. Maguolo et al. in [27℄. Algorithm is based onAARF me hanism and extends its rate sele tion pro edure by adding informationa quired from RTS/CTS transa tions.Theory of operationAARF-CD uses the same adaptation s hema as AARF, utilizing BEB algorithmto hose the threshold value of onse utive su essful transmissions that triggerthe in rease of the rate. What reators of the AARF-CD added to their solutionis a ollision dete tion using RTS/CTS transa tions - this solution is also put intopra ti e by CARA rate ontrol algorithm. The numeri al values of parametersused in the des ription of the theory of operation of AARF-CD are shown inTable 6.3.The de ision of employing a RTS/CTS me hanism is made before every trans-mission by examining the RTS ounter. When the RTS ounter (rtsCounter)is greater than zero the RTS/CTS pro edure is started. Su essful re eption ofthe CTS frame de rements the ounter by one. However, missing a CTS framedoes not ause any hange in nSu ess, nFailed and rtsCounter ounters.The value of the RTS ounter an be rised in several situations:36

Table 6.3: AARF-CD parametersSymbol Comment Possible valuesnSu ess Conse utive su ess ounter 0 - ThSu nFailed Conse utive failure ounter 0 - ThSu rtsCounter Conse utive RTS/CTS handshakes ounter 0 - RtsWndRTSWnd Number of onse utively transmissionsusing the RTS/CTS me hanism 1 - 40ThFail Number of onse utive failures requiredin order to de rease the rate 2MinThSu Minimum su ess threshold value 10ThSu Number of onse utively su ess requiredto in rease the rate MinThSu - 60ThFailRe Number of onse utive failures requiredwhen a new rate is tried in order to de- rease the rate 1• after the number of su essful transmissions spe i�ed by su ess ounter(nSu ess) hits appropriate limit (ThSu ). This triggers the in rease ofthe rate and sets the rtsCounter to RTSWnd value.• when transmission failure o urs without using RTS/CTS pro edure. Valueof RtsWnd is doubled in this ase.Loss of the data frame results in in reasing the onse utive transmissionfailure ounter nFailed. In the event of nFailed rea hing the failure limitThFail, the rate is dropped to the next lower value, nSu ess is reset andThSu is set to MinThSu . However, after the rate is rised, if nFailed hitsThFailRe threshold the rate is de reased and value of ThSu is doubled.AARF-CD vs CARABoth AARF-CD and CARA use RTS/CTS transa tions to di�erentiate transmis-sion failures aused by hannel errors from those aused by ollisions. Althoughtheir operation in that matter may look similar, there is a signi� ant di�eren ebetween them when it omes to the sele tion of the right moment to performa RTS/CTS operation. CARA does not perform RTS/CTS pro edure wheneverthe rate hanges while AARF-CD swit hes it o� on rate de rease and turns it onwhen the rate is in reased. 37

6.2.9 AMRRThe Adaptive Multi Rate Retry (AMRR) was presented in tandem with AARFby M. La age et al in [25℄. The algorithm is based on Madwi�'s rate ontrolalgorithm and introdu es me hanisms derived from AARF. The main idea ofAMRR is to in orporate a Binary Exponential Ba ko� (BEB) me hanism into itsrate sele tion s heme.Theory of operationAfter N sent frames, AMRR sends a probe frame using a higher rate. If thetransmission is su essful, the rate is in reased and the value of N is restoredto its minimum. However, when two onse utive transmission fail, the rate isde reased. The BEB me hanism is used to spe ify N, whi h de�nes the numberof pa kets that must be sent between two onse utive probing frames. If thetransmission of the probe frame fails, the value of N is doubled [29℄.6.2.10 OnoeThe Onoe rate ontrol algorithm one of four algorithms implemented in theMadWi� driver [6℄.Theory of operation [46, 33℄The initial rate is set (11 Mbit/s in 802.11b, 24 Mbit/s in 802.11a/g) with reditequal to 0. When less then 10% ACKs are lost in the time window of 1 se ond,the redit is in reased by one. Of ourse, at least ten frames must be transmitted.If more then 10 % of the transmitted frames need retransmissions, the redit isde reased by one.The rate is in reased when the value of the redit rea hes 10. Onoe performsrate de rease when more then 50% of the frames were lost during the period ofthe time window. However, after the lowering of the rate, the previously sele tedrate is not hosen again for the period of 10 se onds. After every hange of therate, the redit is zeroed.What an be on luded from the Onoe's theory of operation is that a singlerate in rease an be performed after 10 se onds of uninterrupted transmission (inthe most optimisti ase). This behaviour makes Onoe more suitable for stable,robust networks, where hanges of the onditions of the hannel does not o urto often sin e Onoe's ability of fast rate adaptation is limited.A ording to [29℄, Onoe is not used in pra ti e today sin e its on ept of therate sele tion is not apable of working su essfully sin e parti ular rate odesuse not equal en odings. 38

Chapter 7The ns-3 Network SimulatorThe ns-3 is a simulation environment apable of simulating various aspe ts of omputer networks in luding data �ows, various network proto ols, large-s alesystems or QoS aspe ts. The proje t is a free, open-sour e initiative started onJuly 1, 2006 and is funded as a part of the National S ien e Foundation (NSF)CISE Computing Resear h Infrastru ture (CRI) program. It is li ensed underthe GNU GPLv2 li ense, whi h makes it publi ly available primarily for resear h,development and edu ational use.Simulator ame into being as a su essor of the ns-2 simulator that wasreleased in 1996 and still remains in a tive use. However, reators of ns-3 de idedto design and develop a new major version of the simulator, that will providesupport for 64-bit ma hines as well as improved ease of use and s alability, whi hwere ru ial issues of ns-2. Developers of the new simulator planned to reuseas many of ns-2 models as possible in order to preserve ba kward ompatibility.However, that fun tionality has not been a hieved [20℄.The ns-3 is a dis rete-event simulator whi h means that states of the systemthat is being simulated hange not ontinuously but due to the happening ofspe i� events. Dis rete-event model presumes that, regardless of the ontinuityof time, in a given interval of time, only a �nite, ountable number of events an emerge. That fa t gives a opportunity to boost up the simulation pro essby presenting hanges of the model that have been aused by the o urren e of�nite number of events [44℄.7.1 Design OverviewThe ns-3 simulation ore and models are implemented in C++ programminglanguage. Almost all of the ns-3 Appli ation Programming Interfa e (API) isalso exported to Python, therefore simulations an be de�ned either using C++programs or Python s ripts. Sin e the ns-3 environment is an obje t-orientedsystem, it onforms with regular Obje t-Oriented Programming (OOP) prin iplesand patterns of design - ns-3 obje ts an be de lared and used applying normalC++ rules. Figure 7.1 depi ts modules of ns-3 simulator.39

Helpers

Routing Internet Stack Devices

Node Mobility

Simulator Common

Core

High-level wrappers

Mobility models (static, random walk, ...)

Node, NetDevice, Address types, Queues, Socket, IPv4

Events, Scheduler, Time arithmetic

Packets, Tags, Headers, PCAP file writing

Smart pointers, Attributes, Callbacks, Tracing, Logging, Random VariablesFigure 7.1: Modules of the ns-3 network simulator7.1.1 Simulation EngineCore of the simulator onsists of lasses that determine the engine of the sim-ulation environment. Those lasses are used by all proto ol, hardware and en-vironmental models. Core lasses deal with su h ru ial matters like memorymanagement or error handling. Furthermore, they provide a Pseudo-RandomNumber Generator (PRNG), whi h is often extensively utilized by simulations.Random numbers an be obtained from instan es of ns3::RandomVariable lass. Unfortunately, in urrent version of simulator (3.10) there is no possibilityof using external pseudo-random number generators, whi h an be onsidered asa slight limitation.Another fun tionality supplied with ore lasses are Callba ks. Callba kme hanism allows for alling of a fun tion of the external model without anyspe ial inter-module dependen y, thus it provides a solution for passing informa-tion between di�erent simulation models during the simulation run.7.1.2 Pa ketsImplementation of a pa ket model is a ru ial matter in every network simulator.Although simulation results will never be as reliable as results of resear h arriedout on real network, ina urate model may lead to signi� ant dis repan y be-tween out omes of simulations and measurements ondu ted in real world. Ea hinstan e of ns-3 Pa ket lass holds a byte bu�er, sets of byte and pa ket tags40

as well as metadata. The former ontains header and trailer data of a pa ket.This is a mirror-like image of bytes that ompose above-mentioned parts of areal network pa ket. Metadata portion of the Pa ket implementation identi�esheader and trailer types in luded in the byte bu�er. Byte tags are used to mark asubset of bytes while pa ket tags sti k a label on a pa ket itself. A good exampleof su h a tag is QoS lass id (ns3::QosTag), whi h an be set on a pa ket toindi ate its belonging to the spe i� type of tra� .7.1.3 NodeThe network node in ns-3 is represented by ns3::Node. Su h a network node an be treated as a single omputing devi e. Name of the lass was taken fromGraph Theory sin e ns-3 developers wanted users not to asso iate its name withthe Internet network - that may have happened if the lass was named hostor end system. An instan e of ns3::Node may be ompared to a shell of a omputer, to whi h user an add various fun tionalities provided by peripheral ards, proto ol sta ks and appli ations.7.1.4 NetDevi eNetwork interfa e of the Node is represented by NetDevi e lass. This lassis a equivalent of hardware Network Interfa e Controller (NIC) with appropriatesoftware drivers installed and ready to use. Node may have multiple NetDevi esset up. Ea h of them, managing onne tions with Node and Channel obje ts.The ns-3 provides di�erent types of NetDevi es that spe ialize in di�erent typesof networks and di�erentiate in behavior. Main NetDevi es that ome with ns-3bundle are:• BridgeNetDevi e - virtual network devi es that simulates a bridge. Class onforms with IEEE 802.1D standard in the implementation of data planeforwarding me hanism and is used for onne ting multiple LAN segments.• CsmaNetDevi e - CSMA virtual network devi e similar to Ethernet de-vi e. However, Ethernet uses Carrier Sense Multiple A ess with Colli-sion Dete tion (CSMA/CD) whi h is not fully implemented in ns-3 sin eCsmaNetDevi e does not model ollision dete tion.• EmuNetDevi e - this virtual network devi e gives a possibility of usage ofa real network interfa e in the simulation. After binding EmuNetDevi e tospe i�ed interfa e that exists on the ma hine, simulation pa kets an besent and re eived over a real network.41

• LteNetDevi e - virtual network devi e apable of modeling basi LongTerm Evolution (LTE) network devi e. Using this NetDevi e models of3rd Generation Partnership Proje t (3GPP) UMTS Terrestrial Radio A essNetwork (E-UTRAN) infrastru ture LTE networks an be established.• MeshPointDevi e - virtual network devi e that simulates a mesh point ina WLAN mesh networks based on IEEE 802.11s draft. MeshPointDevi eworks as a asing for multiple network interfa es that work under the sameMAC-layer routing proto ol.• PointToPointNetDevi e - virtual network devi e that models an inter-fa e that utilizes Point-to-Point Proto ol (PPP) to arry data to anotherPointToPointNetDevi e on the other side of the link. However, thisNetDevi e does not implement Link Control Proto ol (LCP).• UanNetDevi e - virtual network devi e used in Underwater A ousti s Net-works (UAN) models.• WifiNetDevi e - virtual network devi e apable of simulating a wirelessnetwork interfa e ontroller. Using WifiNetDevi e one an model in-frastru ture and ad ho networks based on IEEE 802.11 standards. The lass is extensively used in simulation part of the thesis where various sim-ulation s enarios of QoS networks are evaluated. Figure 7.2 depi ts thear hite ture of the lass.7.1.5 ChannelCommuni ation hannel an be des ribed as a physi al transmission medium,through whi h signals arrying information �ow, or as a logi al path over a phys-i al medium, established between transmitter and re eiver. Every transmission hannel has its own hara teristi s, a set of attributes, that determine its opera-tion in tele ommuni ation system. Attributes, whi h des ribe a hannel an bevarious, for instan e laten y, attenuation, bit errors or bandwidth.The ns-3 provides wide range of spe ialized hannel models that inherit frommain Channel lass. However ompli ated and sophisti ated hannel modelsare, they are all responsible for managing ommuni ation and data �ow betweennodes.The way of ex hanging information and stru ture of the transmission mediumdepends stri tly on the type of simulated network. For instan e, in wirelessnetworks, the model of the hannel is a three-dimensional spa e, full of obsta les.In Ethernet or point-to-point networks, the transmission hannel is simply a model42

WifiNetDevice

NqstaWifiMac

MacLow

WifiPhy

WifiChannel

DcaTxOp MacRxMiddleDcfManager

ForwardUp

ForwardUp

ForwardUp

Receive

Enqueue

ReceiveOk/ReceiveError

StartTransmission

SendPacket

Send StartReceivePacket

Listener

Listener

Send

DCF function implementation

Packet queue, packet fragmentation, packet retransmission

Active probing, association state

machine

RTS/CTS/DATA/ACKtransactions

Figure 7.2: Wi�NetDevi e ar hite tureof wire. The ns-3 omes with variety of hannel models, nevertheless new ones an be simply implemented by inheriting from Channel lass. Main ns-3 hannelmodels are:• PointToPointChannel - instan es of this lass model a simple point topoint link. The onne tion is similar to full duplex operation of links uti-lizing RS-232 standard.• CsmaChannel - a lass modeling a CSMA hannel with Delay and DataRateattributes that an be a essed to spe ify medium hara teristi s. CsmaChannelsimulates a broad ast medium in a bus topology - transmitted pa ket isre eived by all devi es that are onne ted to the hannel.• WifiChannel - model of a transmission hannel of 802.11 wireless net-works. Contains propagation delay and propagation loss models. Instan eof this lass an be used to inter onne t network interfa es modeled byWifiNetDevi e. 43

• WimaxChannel and SimpleOFDMWimaxChannel - lasses that model atransmission hannel in 802.16-based WiMAX networks.7.1.6 HelpersDevelopers of ns-3 de ided to smooth the way of reating a simulation by intro-du ing the helper API. So- alled 'helper' lasses make writing of ns-3 ode easierand more transparent to read or analyze. Instead of oding the simulation modelfrom s rat h using low-level API, helpers shorten this pro ess by automati allymaking adequate onne tions, setting data �ows between instan es of various lasses, setting attribute values et . Of ourse everything that an be donewith helpers an be done using low-level API alls. Simulations of 802.11 net-works utilize several helper lasses in luding WifiHelper, WifiChannelHelperor QosWifiMa Helper.7.2 Ar hite ture of 802.11 ImplementationOne of the goals of ns-3 proje t is to keep pa e with the rapid growth in wirelessnetworking, therein many variants of IEEE 802.11 network systems [20℄. Im-plementation of Wi� model in ludes urrently several models of physi al layersin luding models based on 802.11a/b/g spe i� ations.Modeling wireless, 802.11 based network relies stri tly on Wi�NetDevi ewhi h inter onne ts all WiFi-related obje ts su h as hannel (ns3::WifiChannel),physi al layer (ns3::WifiPhy) or MAC layer (ns3::WifiMa ).7.2.1 Wireless ChannelWifiChannel lass is responsible for modeling 802.11 hannel between ommu-ni ating WifiNetDevi e network interfa es. It allows user to spe ify propagationdelay and loss models for simulated hannel. By default, ConstantSpeedPropagationModeland PathLossPropagationModel are used. The former spe i�es a delay modelin whi h the propagation speed is onstant, equal to the speed of the light. De-fault propagation delay model an be hanged to RandomPropagationDelayModelwhere propagation delay is random, de�ned by uniform distribution U(0:1.0).The latter PathLossPropagationModel lass models the propagation loss througha transmission medium due to the path loss. Variety of propagation loss models an be used as a repla ement of the default model, in luding Nakagami fastfading, Rayleigh or Friis models.44

7.2.2 PHYThe ns-3 provides a set of physi al layer models, in luding IEEE 802.11a/b/gstandard ompliant models. The most onvenient way of setting a standardWifiNetDevi e should use is via helper lass WifiHelper. In that ase SetStandard(enum WifiPhyStandard standard) fun tion enables user to set standard toone of the following:• WIFI_PHY_STANDARD_80211a - a model of physi al layer onforming toIEEE 802.11a spe i� ation. Implementation of that model is des ribedextensively in "Yet Another Network Simulator" [24℄.• WIFI_PHY_STANDARD_80211b - IEEE 802.11b ompliant model, imple-menting High Rate extension of the Physi al Layer (PHY) for the DSSSsystem (Clause 15 of IEEE Std 802.11, 1999 Edition) [2℄.• WIFI_PHY_STANDARD_80211g - IEEE 802.11g ompliant model, employingExtended Rate PHY extension, Extended-Rate PHY OFDM (ERP-OFDM)(Clause 19, Se tion 19.5 of IEEE Std 802.11g-2003) [2℄.• WIFI_PHY_STANDARD_80211_10Mhz - model onforming to IEEE 802.11OFDM PHY spe i� ation for the 5 GHz band with 10 MHz hannel band-width (Clause 17 of IEEE Std 802.11a-1999) [2℄• WIFI_PHY_STANDARD_80211_5Mhz - model onforming to IEEE 802.11OFDM PHY spe i� ation for the 5 GHz band with 5 MHz hannel band-width (Clause 17 of IEEE Std 802.11a-1999) [2℄.• WIFI_PHY_STANDARD_holland - on�guration of the PHY des ribed byHolland et al. in [21℄, whi h introdu es RBAR rate ontrol me hanism.Proposed algorithm requires 802.11 frames to be slightly modi�ed.Apart from above listed PHY models simulator provides support for severalfun tionalities des ribed in IEEE 802.11n spe i� ation [1℄, however implementa-tion of a omplete 802.11n model is still underway. Already implemented featuresare:• A-MSDU Frame Aggregation• HCF• TXOP• Blo k ACK 45

7.2.3 MACImplementation of MAC layer is divided to two omponents - high and low.Low models in lude DCF and EDCAF implementations while high models areresponsible for bea on generation, probing and asso iation state ma hines. Table7.1 presents a syntheti view of hara teristi s of the lasses modeling MAC lowmodels. Table 7.1: MAC low models of the ns-3 network simulatorClass Chara teristi sMa Low RTS/CTS/DATA/ACK transa tionsD fManagerD fState DCF fun tion implementationD aTxop pa ket queue, pa ket fragmentation, pa ket retransmission,transmission of frames using the DCFEd aTxopN pa ket queue, pa ket fragmentation, pa ket retransmission,QoS operationsSimulator ontains three MAC high models, ea h of them des ribing parti ularelement in the wireless network topology. A single WifiNetDevi e an operatein AP, non-AP STA or ad-ho mode. Ea h of these modes is modeled by adi�erent lass as shown in Table 7.2.Table 7.2: ns-3 MAC high modelsClass Mode Chara teristi sApWifiMa A ess Point bea on generation, asso iationStaWifiMa Station a tive probing, asso iation statema hine, automati re-asso iationAdho WifiMa Station in IBSStopology, ad-ho mode no bea on generation, probing, orasso iation7.2.4 802.11e style QoS supportAll des ribed above MAC high models implement a QosSupported attribute.Utilizing this parameter, a 802.11e QoS support an be introdu ed to the simu-46

lation. In that ase tra� an be divided into four di�erent ACs: AC_VO, AC_VI,AC_BE or AC_BK.Every pa ket that goes through the MAC layer an be labeled with the ACTID using a QosTag lass. By default, without earlier marking of pa ket's TID,every pa ket is onsidered to be a member of best e�ort a ess ategory (AC_BE).7.3 Implementation of Rate Control AlgorithmsEvery lass that models a rate adaptation algorithm and manages transmissionrate inherits from WifiRemoteStationManager (Figure 7.3) and adds additionalfun tionality based on the spe i� ation of the algorithm.

ns3::WifiRemoteStationManager

ns3::ArfWifiManager

ns3::AarfcdWifiManager

ns3:: AarfWifiManager

ns3::AmrrWifiManager

ns3::CaraWifiManager

ns3::ConstantRateWifiManager

ns3::IdealWifiManager

ns3::MinstrelWifiManager

ns3::OnoeWifiManager

ns3::RraaWifiManagerFigure 7.3: Partial inheritan e diagram for rate- ontrol lassesSimulator, in its 3.10 version omes with ten, already implemented rate on-trol algorithms.• ConstantRateWifiManager - simple rate ontrol manager that uses al-ways the same, onstant transmission rate for every data and ontrol frame47

sent. Data rate must be supported by PHY and an be spe i�ed by settingDataMode attribute.• ArfWifiManager - lass implementing ARF rate ontrol algorithm intro-du ed by A. Kamerman and L. Monteban [22℄. ARF implementation inns-3 utilizes a pa ket-based timer instead of time-based timer - initiallyproposed in algorithm's des ription.• AarfWifiManager - rate ontrol manager based on AARF algorithm de-s ribed by M. La age et al. [25℄. ns-3 implementation of AARF was writtenby one of its inventors - M. La age.• Aarf dWifiManager - lass implementing AARF-CD algorithm proposedby F. Maguolo et al.[27℄. Algorithm's implementation was written byMaguolo in the very early development version of the simulator.• AmrrWifiManager - lass implementing AMRR rate ontrol algorithm.AMRR was originally des ribed by M. La age et al. [25℄ and implementedby himself in ns-3.• CaraWifiManager - rate ontrol manager based on CARA rate ontrolalgorithm introdu ed by J. Kim et al. [23℄. CARA me hanisms wereimplemented by F. Maguolo - the reator of AARF-CD - in prototypestage of ns-3 development.• MinstrelWifiManager - lass modeling the Minstrel rate ontrol algo-rithm. ns-3 implementation of that algorithm was ported from the onedeveloped as a part of the Madwi� Proje t [4℄.• OnoeWifiManager - rate ontrol manager based on the algorithm devel-oped by Atsushi Onoe. This me hanism is used as the default rate ontrolalgorithm for the MadWi� driver. Implementation relies on publi ly avail-able sour e ode of Onoe algorithm implementation [6℄ whi h is a part ofthe Madwi� Proje t.• RraaWifiManager - lass implementing RRAA rate ontrol algorithm ini-tially des ribed by S. H. Y. Wong et al. [47℄.• IdealWifiManager - rate ontrol manager implementing an "ideal" rate ontrol algorithm similar to RBAR algorithm [21℄. In this approa h stationmonitors SNR for every re eived pa ket and sends this information to thetransmitter. Transmitter pi ks a transmission mode examining re eivedSNR information and target's Bit Error Rate (BER) hoosing one adequateto transmission mode-spe i� SNR/BER urves.48

Chapter 8Analysis of QoS Provisioning inMulti-rate EDCA WLANsThis part of the thesis presents the simulation analysis of QoS provisioning inwireless BSS and IBSS networks that utilize EDCA fun tion in multi-rate en-vironment. Seven rate ontrol algorithms are evaluated in the ontext of theirin�uen e on transmission hara teristi s su h as throughput, pa ket loss ratio,mean frame delay and others. These rate ontrol algorithms are: ARF, AARF,AARF-CD, CARA, AMRR, Onoe and Minstrel.The Analysis overs IEEE 802.11a, b and g PHYs. Simulations are arried inns-3 simulator framework whi h was des ribed in Chapter 7.8.1 Common Assumptions8.1.1 Channel onditionsConditions of the wireless transmission medium model used in the following s e-narios are des ribed using path-loss propagation model. The re eption power is al ulated with log-distan e model using Formula 8.1.

L = L0 + 10nlog10(d

d0) (8.1)Symbols present in Formula 8.1 as well as their values used in the simula-tions are shown in Table 8.1. Channel model utilized a ross all the simulationexperiments was initially des ribed in [24℄.Propagation delay is onstant due to the onstant propagation speed whi his equal to the speed of light - 3 · 108 m/s .8.1.2 EDCA Parameter SetThe default set of EDCA parameters is employed in the following s enarios. Table5.2 presents these parameters. 49

Table 8.1: Log-distan e propagation model parametersSymbol Value Commentn 3 path loss exponentd0 1.0m referen e distan e [m℄L0 46.6667 path loss at referen e distan e [dB℄L - path loss [dB℄d - distan e [m℄8.2 S enario 1. Mean transmission delay. BSStopology.First experiment examines the transmission delays in the tra� �ows betweenQSTAs that send di�erent types of data. Listed earlier rate ontrol algorithmsare tested to see whi h one of them a ts best in terms of transmission delays inQoS enabled network.AssumptionsThe EDCA system that is going to be evaluated in this s enario onsists of fourQSTAs and one QAP serving as a gateway to the DS. Ea h QSTA that ontendfor hannel a ess in the BSS generates UDP tra� belonging to di�erent AC.Figure 8.1 presents the simulated single-hop network topology.Three PHYs are utilized a ross the experiment - IEEE 802.11a/b/g. QSTAsare named A (voi e tra� , AC_VO), B (video tra� , AC_VI), C (best-e�orttra� , AC_BE) and D (ba kground tra� , AC_BK). Ea h of them generates UDPdata stream at 54 Mbit/s when IEEE 802.11a and g PHYs are evaluated and 11Mbit/s for IEEE 802.11b PHY. A single transmitted pa ket is 600 bytes in size.Aforementioned values were hosen to make the hannel saturated with tra� ,so the in�uen e of the sele tion of the rate ontrol algorithm on the transmissiondelays is learly visible.The values of the mean transmission delay are al ulated using Formula 8.2,where rxPa kets is the total number of re eived pa kets for the �ow and delaySum onsists of the sum of all end-to-end transmission delays for all pa kets of the�ow that were re eived.mean transmission delay = delaySum

rxPackets(8.2)50

Figure 8.1: BSS simulation topology51

Simulation ResultsThe experiment was arried in three di�erent network types - ea h employeddi�erent PHY: IEEE 802.11 a, b and g. The values of mean transmission delay olle ted during the experiment are gathered in Table 8.2.Table 8.2: Mean transmission delays in IEEE 802.11a/b/g BSS networks.PHY AC CARA AARF-CD Minstrel ARF AARF AMRR Onoea AC_VO 157 160 172 215 216 430 626AC_VI 668 521 494 1416 1425 2147 2428AC_BE 980 2010 3222 3498 3093 2970 3341AC_BK 4342 3570 2466 3485 3478 3373 3437b AC_VO 975 866 894 1720 1340 2240 4333AC_VI 2676 2170 2185 4230 3460 5066 8666AC_BE 8985 8110 7893 9567 9807 9468 9760AC_BK 8845 7636 7573 9655 9728 9317 9704g AC_VO 329 255 274 869 833 4053 4020AC_VI 1339 1062 1169 4682 4711 1903 2062AC_BE 3375 3181 3225 3713 2981 3556 3793AC_BK 3227 1170 1769 3680 3451 3758 3719802.11aSimulation shows that in 802.11a network Minstrel and CARA a hieve smallestvalues of transmission delays in data �ow with sensitive tra� of AC_VO (Figure8.2 and 8.3). Mean delay values rea hed by these rate ontrol algorithms arealmost the same for this AC. The result of AARF-CD is 9,6% worse, while originalAARF and ARF performan e is very lose to ea h other and is 36,9% larger when ompared to Minstrel's result. Two rate ontrol s hemes that are situated in thevery end of the tested algorithms are AMRR and Onoe. The former algorithm'sresult is almost three times worst then Minstrel's. The latter, whi h performan ewas the worst, a hieved the value of mean transmission delay whi h is four timesworst.In terms of AC_VI situation is similar. However, AARF-CD swit h pla e withMinstrel. CARA remains se ond, with 5,4% worse result then AARF-CD's, whilethird, Minstrel a hieves 35,2% larger value of mean transmission delay. Also thistime, ARF and adaptative ARF show similar results, whi h are about 2,8 timesworse then AARF-CD out ome. AMRR and Onoe a hieve the worst results - 4,3and 4,9 times larger mean transmission delay values.52

Figure 8.2: Mean transmission delays of the �ows in IEEE 802.11a BSS network.

Figure 8.3: Mean transmission delays of the �ows in IEEE 802.11a BSS network(y axis adjusted). 53

For best e�ort AC, best rate sele tion me hanism is Minstrel. The se ond- CARA - is more then two times worse. Other algorithms a hieve mu h worseresults varying from 3 times worse for AMRR to 3,7 times for AARF. AARF-CD,whi h in previously dis ussed AC was �rst, this time is sixth.Ba kground AC �ow is best handled by AARF-CD. The next �ve rate ontrolme hanisms (AMRR, Onoe, ARF, AARF, CARA) perform about 1,4 times worse.However, Minstrel a hieves this time far mu h worse result - 4342 ms whi h is1,8 times worse then AARF-CD (2466 ms).802.11bIn 802.11b environment, CARA and AARF-CD are best algorithms for AC_VOand AC_VI. AARF-CD a hieves 3,2% worse result then CARA for AC_VO and0,7% for AC_VI. The order of algorithms out omes for these ACs is the same asdepi ted in Figure 8.4 and 8.5. The latter pi ture in ludes the results with y axisadjusted so the di�eren es are learly visible. Third, for both ACs is Minstrel,whi h espe ially in AC_VO �ow, performs similarly to CARA and AARF-CD. Theworst is Onoe - the value of mean transmission delay is 5 times worse thenCARA's for AC_VO and 4 times worse for AC_VI.

Figure 8.4: Mean transmission delays of the �ows in IEEE 802.11b BSS networkThe order of algorithms' results is also the same for AC_BE and AC_BK. The�rst is AARF-CD with CARA the se ond and Minstrel the third. For best e�ort54

Figure 8.5: Mean transmission delays of the �ows in IEEE 802.11b BSS network(y axis adjusted)tra� , the di�eren e between �rst two algorithms is larger then in ba kgroundAC - CARA is 2,7% worse then AARF-CD, while 1,3% for AC_BE.What is more, for AC_BE �ow, the third Minstrel is 13,8% worse when om-pared to the �rst AARF-CD. The rest of algorithms' results vary from 19,9% forAMRR to 24,2% for the worst, ARF. In ba kground AC �ow, Minstrel a hieves16,7% worse result then the �rst algorithm, while last three - AARF, Onoe andARF - perform almost the same.802.11gSimulation arried utilizing 802.11g PHY, shows a signi� ant division amongrate ontrol algorithms in their performan e in AC_VO �ow as shown in Figure8.6 and 8.7 (y axis adjusted). CARA, AARF-CD and Minstrel an be named low-laten y algorithms with lowest mean delay values (AARF-CD 7,5% and Minstrel29,0% worse then the �rst CARA). The se ond group is omposed of ARF andits adaptative version, AARF. Out ome a hieved by this set is more then 3times worse then CARA's. The last group, whi h an be stated as high-laten yalgorithms onsists of Onoe and AMRR - their results are almost 16 times worse.For AC_VI �ow, �rst three algorithms remain the same. The se ond AARF-CDis 10,0% worse then CARA, while Minstrel - 26,1%. The group of des ribed aboveAC_VO low-laten y algorithms this time swit hed pla e with AC_VO high-laten y55

Onoe and AMRR.ARF, whi h performs the worst in video AC �ow shows best mean trans-mission delay results in best-e�ort tra� . The next are CARA and AARF-CD.However, both of them with at least 2 times worst out omes then ARF.In terms of ba kground AC, the order of algorithms' results is the same as inthe voi e AC. CARA performs the best. The se ond, AARF-CD, is 51,1% worse.Other algorithms also do not a t as good as CARA and are from 2,8 (Minstrel)to 3,2 (AMRR) times worse.

Figure 8.6: Mean transmission delays of the �ows in IEEE 802.11g BSS networkDetailed on lusionsSimulation shows that in terms of mean transmission delays CARA and AARF-CD are the best rate ontrol me hanism. Both algorithms an di�erentiatetransmissions failures due to ollisions from those aused by errors introdu edby the transmission hannel with a onditional usage of RTC/CTS transa tions(CARA also uses the additional me hanism of CCA dete tion). This allows fornot de reasing the rate when it is not ne essary whi h is ru ial for low-laten ytra� of AC_VO and AC_VI.In 802.11a based network model, Mistrel algorithm a hieved result that isalmost equal to this of CARA's in AC_VO �ow. It's approa h is very e�e tivesin e it does not produ e any RTS/CTS overhead basing only on the statisti alinformation about probed rates and hoosing a ordingly optimal data rates.56

Figure 8.7: Mean transmission delays of the �ows in IEEE 802.11g BSS network(y axis adjusted)However, the Minstrel's performan e in low-priority tra� �ows is not sowell. This is due the fa t that probing frames whi h are ru ial for Minstrel'soperation and rate adaptation are spending more time in EDCAF queues, thusthe algorithm annot rea t as qui k as it rea ts when it steers the high-priority�ows.The performan e of ARF and AARF is rather poor. The reason for that maybe in their over-aggressive manner of de reasing the rate to the not optimal,lower one be ause of the inability of di�erentiating between ollisions and hannelerrors.8.3 S enario 2. Mean transmission delay. IBSStopology.Se ond s enario evaluates the aforementioned set of rate ontrol algorithms interms of mean transmission delays in IBSS (ad-ho ) network. STAs send datadire tly to their neighbours, without the use of AP.57

AssumptionsThere are four QSTAs (A, B, C and D) in this s enario, ea h generating tra� at 54 Mbit/s making the hannel saturated. QSTA A sends voi e tra� (AC_VO)to station B. Station B sends video (AC_VI) tra� to station C. Station C sendsbest-e�ort (AC_BE) tra� to station D. Finally, station D sends ba kgroundtra� (AC_BK) to station A. Channel model and EDCA parameter set is thesame as in S enario 1. QSTAs use IEEE 802.11a PHY. The simulated IBSStopology utilized a ross this s enario is shown in Figure 8.8.

Figure 8.8: IBSS simulation topology58

Simulation ResultsTable 8.3 and Figure 8.9 show mean transmission delay values a hieved by rate ontrol algorithms.Table 8.3: Mean transmission delays in IEEE 802.11a IBSS network.PHY AC CARA AARF-CD Minstrel ARF AARF AMRR Onoea AC_VO 399 405 430 1290 1353 1377 1432AC_VI 1904 1180 1959 3360 3038 3124 3057AC_BE 2493 1751 3074 2409 1609 2564 2860AC_BK 2741 - - 3081 2949 2937 2899

Figure 8.9: Mean transmission delays of the �ows in IEEE 802.11a IBSS network.In terms of voi e tra� , CARA and AARF-CD a hieve lowest transmissiondelays (CARA - 399, AARF-CD - 405 [ms℄). Third, Minstrel a hieved 7,8% worseresult. Other algorithms perform more then four times worse with results varyingfrom 1290 ms for ARF to 1432 ms for Onoe.AARF-CD performs best in AC_VI �ows. Se ond CARA and third Minstrelare about 63% worse. ARF, AARF, AMRR and Onoe a hieve more then 3 timeslarger mean transmission delay values omparing to AARF-CD.59

AARF is �rst in terms of best-e�ort AC with mean delay value of 1609 [ms℄.Se ond, AARF-CD is 142 ms worse. CARA's result is third - 54,9% worse thenAARF's.Ba kground tra� , whi h is transmitted with lowest priority is transmittedwith lowest laten y using CARA (2741 [ms℄). What is interesting, both AARF-CDand Minstrel ould not deliver frames of this AC, possibly due to the saturationof the hannel. Onoe (2899 [ms℄) and AMRR (2937 [ms℄), that perform poorlyin terms of voi e and video tra� , are this time se ond and third.Detailed on lusionsSimulation shows that tra� marked with voi e AC experien es lowest delays.CARA, AARF-CD and Minstrel are �rst in ase of sensitive tra� of voi e andvideo. However, tests arried in extremely saturated IBSS network showed that interms of ba kground tra� transmission, AARF-CD and Minstrel do not manageto send pa kets from AC_VI queue. This agrees with EDCA poli y (data ofother ACs is more important, thus AC_BK data is not sent when there are notenough resour es to do so), but the bahaviour of di�erent algorithms (f.e CARA)shows that even in the saturated hannel, ba kground tra� an be su essfullytransmitted.The order of the algorithms' AC_VI �ow results is almost the same as in BSSenvironment. However, a hieved mean delay values are more then two timesbigger in IBSS network. What is more, delays in AC_VI �ow a hieved by ARF,AARF, Onoe and AMRR are larger then in best-e�ort and ba kground AC �ows.This means that EDCA poli y is not ful�lled in this ase.Both CARA and AARF-CD employ RTS/CTS transa tions in their theoryof operation to di�erentiate ollisions from hannel errors. This is ru ial foroperating at maximum and most e� ient rate sin e the transmission rate is notunne essarily de reased. However, AARF-CD's ill operation in terms of AC_BKis a serious drawba k. This leads to the on lusion that CARA remains the bestrate ontrol s heme that deals well in both BSS and IBSS network types, ful�llingEDCA poli y and a hieving top mean transmission delay results.Onoe appears to be the worst rate ontrol me hanism. It does not a t wellin BSS as well as IBSS ar hite ture. This may be explained by its onservativebehaviour - Onoe in reases the rate only when its redit value hits appropriatethreshold. Thus, it annot rea t qui kly to hanges of the hannel onditions.60

8.4 S enario 3. Throughput. BSS topology.Se ond s enario tests the throughput - an average rate of su essful frame de-livery of the network tra� �ows between four QSTAs and the QAP. Networktopology utilized a ross this experiment is the same as in S enario 1 and is shownin Figure 8.1.The set of rate ontrol algorithms stated at the beginnning of this hapter isevaluated in three network models, ea h with di�erent PHY (802.11a/b/g), tosee whi h one of them a ts the best in terms of a hieved network throughput.AssumptionsEa h of four QSTAs generates tra� belonging to di�erent AC. QSTAs are gen-erating data at 54 Mbit/s when 802.11a PHY is used, 11 Mbit/s in 802.11b and54 Mbit/s in 802.11g. These values were hosen and tuned to learly demon-strate the di�eren es between operation of di�erent rate ontrol s hemes. Thesize of a single pa ket is 600 bytes.Throughput is al ulated using Formula 8.3.throughput = receivedBytes

simulationT ime(8.3)Simulation ResultsThis se tion presents the results of the experiment that was arried in networkmodels employing three aforementioned PHYs. Throughput values obtained dur-ing the simulation run are presented in Table 8.4.802.11aSimulation shows that in terms of voi e tra� algorithm that rea hes highestthroughput value is Minstrel as shown in Figure 8.10. However, CARA is only1,9% behind and AARF-CD a hieves result whi h is 8,8% worse then Minstrel's.Results of ARF and AARF are almost the same with 27,2% loss to the leadingalgorithm. Performan e of AMRR and Onoe is the worst for this AC - almost 4times smaller then Minstrel's.In terms of AC_VI �ow, Minstrel swit hes pla e with AARF-CD. Minstrel isnow third (26,3% worse). The order of the rest algorithms remains the same.Throughput value of the se ond CARA is 5,1% worse then AARF-CD's. Alsothis time performan e of ARF and its adaptative version is almost the same and61

Table 8.4: Throughput [Mbit/s℄ in IEEE 802.11a/b/g BSS networksPHY AC Minstrel CARA AARF-CD ARF AARF AMRR Onoea AC_VO 11,937 11,708 10,892 8,687 8,707 3,011 2,984AC_VI 2,786 3,587 3,781 1,286 1,293 0,780 0,743AC_BE 0,256 0,218 0,171 0,022 0,018 0,022 0,083AC_BK 0,321 0,295 0,286 0,096 0,082 0,085 0,085b AC_VO 1,902 2,144 2,071 1,374 1,055 0,801 0,403AC_VI 0,674 0,838 0,830 0,513 0,411 0,333 0,186AC_BE 0,176 0,200 0,205 0,121 0,113 0,098 0,052AC_BK 0,182 0,215 0,216 0,134 0,118 0,110 0,061g AC_VO 5,703 7,337 6,832 2188 2,092 0,434 0,436AC_VI 1,374 1,731 1,563 0,324 0,324 0,221 0,216AC_BE 0,146 0,151 0,101 0,008 0,010 0,037 0,036AC_BK 0,165 0,248 0,231 0,030 0,032 0,040 0,040about 2,9 times worse, when ompared with the leader. AMRR and Onoe a hievethe worst throughput values and are pla ed at the very end.ARF and AARF end last when onsidering best-e�ort tra� �ow. Theirresults are very similar to ea h other but are 11,6 times worse then Minstrel'sthat this time leads. CARA is se ond again with 14,8% loss to the �rst algorithmwhile third, AARF-CD a hieves 33,2% worse result. AMRR rea hes slightly betterout ome then �fth Onoe.AC_BK hart in Figure 8.10 presents a division between algorithms. Last four(ARF, AMRR, Onoe, AARF) perform very similarly - about 3,8 times worse then�rst Minstrel. The se ond CARA is 8,1% behind while the third AARF-CD is10,9% worse, when ompared to Minstrel.802.11bFigure 8.11 presents throughput values a hieved by the rate ontrol algorithmsin 802.11b network. In terms of voi e AC, CARA appears to be the best ratesele tion s heme. The se ond is AARF-CD, results of whi h are very similar.Throughput values of the third, Minstrel are 11,3% worse then CARA's. Thenext two are ARF and adaptative ARF. Last but one - AMRR - a hieves result 2,6times worse then leading CARA. Onoe �nishes at the very end - its performan eis 5,3 times worse.Out omes of CARA and AARF-CD are almost the same in the �ow of videoAC tra� (di�eren e of less then 1%). The third, Minstrel a hieves 19,6% worseresult. Performan e of other algorithms is more then 1,6 times worse, omparedwith CARA's result. Also this time Onoe is the last.62

Figure 8.10: Throughput of the �ows in IEEE 802.11a BSS network

Figure 8.11: Throughput of the �ows in IEEE 802.11b BSS network63

For both AC_BE and AC_BK �ows AARF-CD and CARA a hieve highest valuesof throughput. Performan e of CARA is only 2,4% worse in best-e�ort and 0,5%in ba kground tra� . In both ases Minstrel is third with 15,7% loss both forAC_BE and AC_BK. For all ACs, Onoe's results are the worst. What is more,overall throughput a hieved in ba kground tra� �ows is higher then in best-e�ort �ows.802.11gIn 802.11g based network, CARA a hieves best throughput results in all tra� �ows. In AC_VO �ow, the se ond AARF-CD is 6,9% worse while Minstrel, whi his third a hieves 22,2% worse result then the �rst CARA. Performan e of ARFand AARF is very similar and is about 3,4 times worse. Onoe's and AMRR'sout omes are very low - almost 17 times worse then CARA's.In terms of video AC, situation is similar. The order of algorithms is the samewith one ex eption - AMRR swit hes pla e with Onoe. However, di�eren ebetween last two algorithms and fourth ARF and �fth AARF is not so signi� antas in AC_VO �ow. The division between two groups of algorithms is learly visible.AARF-CD, whi h is se ond in this ase, is 9,7% worse then the �rst CARA whileMistrel - 20,6% worse. Other four algorithms perform about 5,3 times worse.

Figure 8.12: Throughput of the �ows in IEEE 802.11g BSS networkThere are two leading algorithms in terms of best-e�ort �ow - CARA and64

Mistrel. Third is AARF-CD, a hieving 2/3 of the throughput result of CARA.AMRR and Onoe perform very similarly to ea h other and are about 4 timesworse then the �rst algorithm. Performan e of AARF and ARF is rather poor -about 15 times worse when ompared to CARA.CARA is also �rst in AC_BK tra� �ow. AARF-CD's result, whi h is se ond is6,8% worse. Third Minstrel is 33,4% worse. The rest algorithms do not performwell - their results are more then six times poorer.Detailed Con lusionsSimulations arried with all PHY models (IEEE 802.11a/b/g) show that thethroughput of the lower priority streams (AC_BE, AC_BK) rea hes smaller valuesthen this of higher priority sensitive tra� (AC_VO, AC_VI) as expe ted.However, the throughput a hieved by ba kground �ows is higher then inbest-e�ort streams. Reason for that behoviour may lay in the 802.11e EDCAparameter set. Although the values of the CWmin and CWmax are for bothACs the same, the value of AIFSN for AC_BK is 2,5 times larger then for AC_BE.The smaller the AIFSN, the higher the han e of winning the ontention for thea ess to the medium. However, more frequent a ess to the hannel, whi h inthe simulation was very saturated, resulted in higher rate of ollisions, thus lesspa kets were orre tly re eived.Experiment showed that best three rate ontrol algorithms, that a hieve high-est throughput values are CARA, AARF-CD and Minstrel. This results lead tothe on lusion that me hanism that are able to dete t the reason for missedACK frame, indi ate whether the loss happened due to frame ollision or hannelerrors (like CARA and AARF-CD) a t the best.However, Minstrel, whi h does not perform su h a he k a hieved �rst pla ein 802.11a based network for all ACs' �ows. What an be on luded from thisis that the Minstrel's approa h of random probing the hannel by sending probepa kets at di�erent rates is very e�e tive. Furthermore, another advantage ofMinstrel is that a ording to [46℄ only around 5% of pa kets is not transmittedwith the optimum rate.8.5 S enario 4. Throughput. IBSS topology.Fourth experiment evaluates throughput that is a hieved by four QSTAs thatsend voi e, video, best-e�ort and ba kground tra� to ea h other. Thus, thereare four �ows, ea h of a di�erent AC.65

AssumptionsThis experiment bases on the previous s enario where BSS network topology wasutilized. Figure 8.8 presents the evaluated IBSS topology while Table 5.2 defaultEDCA parameter set that is employed in this s enario. Tests are arried usingIEEE 802.11a PHY model. As in S enario 3, ea h QSTA generates data at 54Mbit/s and tries to forward it to the neighboring station. Pa kets are 600 bytesin size. Throughput is al ulated using Formula 8.3.Simulation ResultsThe throughput values a hieved by the set of algorithms during the experimentrun are presented in Table 8.5 and shown in Figure 8.13.Table 8.5: Throughput [Mbit/s℄ in IEEE 802.11a IBSS network.PHY AC CARA AARF-CD Minstrel ARF AARF AMRR Onoea AC_VO 4,717 4,605 4,397 1,382 1,312 1,286 1,234AC_VI 1,661 1,662 1,619 0,487 0,544 0,531 0,542AC_BE 0,026 0,025 0,033 0,039 0,022 0,024 0,049AC_BK 0,013 0,000 0,000 0,038 0,035 0,030 0,045Three algorithms: CARA, AARF-CD and Minstrel perform best in terms ofa hieved throughput of AC_VO �ows. Their results vary from 4,717 [Mbit/s℄for CARA to 4,397 [Mbit/s℄ for Minstrel. Other algorithms do not ex eed thethroughput value of 1,4 [Mbit/s℄. The lowest value is a hieved by Onoe - 1,234[Mbit/s℄ whi h is 3,8 times worse then CARA's.In terms of video AC the overall performan e of the algorithms is very similarto that experien ed in AC_VO �ows. The �rst three rate ontrol s hemes (AARF-CD, CARA and Minstrel) perform more then 3 times better then other algorithms.Onoe a hieves highest values of throughput in best-e�ort AC �ows. Se ondARF is 20,4% worse while the third Minstrel 32,6% worse when ompared toOnoe. Onoe is also �rst in terms of ba kground tra� . What is interestingMistrel and AARF-CD do not transmit any frames marked with this AC, favouringother ACs.Detailed on lusionsThe best rate ontrol s heme in terms of throughput in a saturated, IBSS EDCAnetwork would be the algorithm that a hieves the highest throughput values invoi e AC �ows, while the lowest in ba kground AC �ows.66

Figure 8.13: Throughput of the �ows in IEEE 802.11a IBSS network.CARA meets these requirements and a hieves better results then the otherrate ontrol me hanisms. Although the performan e of AARF-CD and Minstrelis very similar to CARA's in AC_VO, AC_VI and AC_BE �ows, aforementioned al-gorithms lower the throughput in AC_BK �ow in the overaggressive manner. Thatresults in frames marked with ba kground AC being dropped and not transmitted.AARF-CD and CARA are very similar in their theory of operations (see Chap-ter 6). Both use RTS/CTS transa tions to di�erentiate transmission failures aused by hannel errors from those introdu ed by ollisions. The reason forAARF-CD's ill behaviour in AC_BK �ows may lay in the sele tion of the rightmoment to perform a RTS/CTS operation. CARA does not perform RTS/CTSpro edure whenever the rate hanges while AARF-CD swit hes it o� on ratede rease and turns it on when the rate is in reased.Furthermore, what an be on luded from the out omes for �rst two ACsis that four algorithms: ARF, AARF, AMRR and Onoe form a group with verysimilar, low throughput values while CARA, AARF and Minstrel a hieve resultsthat are more than three times better.In ase of AC_VO and AC_VI �ows AARF performs almost equally to ARF.The bene�ts of the adaptation add-on of AARF is not visible. What is morethe results in the remaining �ows (AC_BE and AC_BK) show that original ARFa hieves even better throughput values. This behaviour is also visible in theresults obtained in simulated earlier 802.11a BSS network.67

8.6 S enario 5. Pa ket loss per entage. BSStopology.Third s enario evaluates the set of rate ontrol algorithms in terms of pa ketlosses in data �ows of EDCA based network. There are many fa tors that may ause pa ket losses su h as network ongestion, ollisions or bit errors. Thisexperiment does not fo us on the sour es of these losses. The algorithms aretested to see, whi h of them deals best with saturated network environment byguaranteeing low values of lost pa kets per entage of sensitive data �ows.AssumptionsSimulation topology in this experiment is the same as in S enario 1 and 2. Thetopology onsists of a QAP and four QSTAs as shown in Figure 8.1. Three PHYmodels are utilized a ross this s enario (802.11a/b/g). QSTAs are generatingdata belonging to di�erent ACs at 14 Mbit/s in 802.11a, 10 Mbit/s in 802.11gand 3 Mbit/s in 802.11b. These values were hosen so the di�eren es betweenalgorithms out omes an be easily visibile. Size of a single pa ket is 600 bytes.Simulation ResultsPa ket loss ratio values obtained during the simulation run are gathered in Table8.6. The following se tions present simulation results a quired in three simula-tions - ea h utilizing di�erent PHY.Table 8.6: Pa ket loss per entage in IEEE 802.11a/b/g BSS networks.PHY AC Minstrel CARA AARF-CD ARF AARF AMRR Onoea AC_VO 13,0 14,2 19,7 36,6 36,8 76,4 78,2AC_VI 79,5 73,7 72,4 90,6 90,5 92,3 94,7AC_BE 98,1 98,5 98,9 99,9 99,9 99,4 99,5AC_BK 98,0 98,1 98,1 99,4 99,4 99,4 99,4b AC_VO 36,1 27,7 30,6 56,8 63,6 75,7 86,0AC_VI 77,6 71,5 71,6 84,0 86,0 89,9 93,5AC_BE 94,2 92,9 93,0 96,0 96,3 96,9 98,3AC_BK 94,2 92,6 92,5 95,8 95,9 96,6 98,3g AC_VO 37,1 23,9 30,1 77,3 78,3 93,9 95,6AC_VI 84,8 82,5 84,0 96,7 96,7 97,5 97,9AC_BE 98,4 98,7 99,2 99,9 99,9 99,6 99,7AC_BK 98,3 97,9 97,8 99,7 99,8 99,6 99,668

802.11aFigure 8.14 presents the per entages of lost pa kets for all evaluated rate on-trol me hanisms. In terms of the �rst AC, the di�eren es between rate ontrolalgorithms are signi� ant and learly visible. The video AC �ow results show aslight advantage of AARF-CD and CARA. However, ba kground and best-e�ort�ows su�er from heavy pa ket losses. Thus, to di�erentiate between algorithms'results, the y axis has been appropriately adjusted - see Figure 8.15.

Figure 8.14: Pa ket loss per entage of the �ows in IEEE 802.11a BSS network.The lowest values of the pa ket loss ratio in voi e AC are a hieved by Minstrel.Se ond is CARA with 9,2% worse result. AARF-CD also a ts well with 19,7%of lost pa kets. ARF and AARF perform similarly - their results are about 2,8times worse then Minstrel's. AMRR and Onoe �nish at the very end with resultsmore then two times worse then those in ARF group.In terms of AC_VI the best results are a hieved by AARF-CD. CARA is only0.4% worse. Minstrel has 7,0% loss when ompared with AARF-CD. Performan eof the other algorithms is poor (more then 25% worse).Minstrel is �rst in AC_BE �ow. The se ond, CARA, is 0,3% worse this timewhile AARF-CD - 0,8%.Behaviour of the algorithms in ba kground �ow is very interesting. First threealgorithms' results are very lose to ea h other. Also the other four algorithms69

Figure 8.15: Pa ket loss per entage of the �ows in IEEE 802.11a BSS network(y axis adjusted).perform very similarly, almost the same, with about 1,7% worse results thenMinstrel's.802.11bIn 802.11b environment CARA remains unbeaten in three ACs as shown in Figure8.17. However, CARA's behaviour is very similar to AARF-CD in all ases (onlyfor AC_BK AARF-CD is �rst). Minstrel is third for all the ACs. The di�eren esbetween algorithms' results are very small in best-e�ort and ba kground �ows.Figure 8.17 presents the Pa ket loss per entage for di�erent algorithms with yaxis s aled so the di�eren es an be spotted.The order of last �ve algorithms is for this PHY the same in all AC �ows.ARF and AARF are fourth and �fth, AMRR sixth and Onoe last.The di�eren e between leading two (CARA, AARF-CD) and the rest is mostvisible in best-e�ort and ba kground �ows.802.11gFor sensitive voi e and video tra� �ows in 802.11g network the �rst three is thesame (Figure 8.18). AARF-CD leads in both ases. Performan e of the se ondMinstrel is 25,9% worse in AC_VO and 1,9% in AC_VI. Sin e the di�eren es70

Figure 8.16: Pa ket loss per entage of the �ows in IEEE 802.11b BSS network(y axis adjusted).

Figure 8.17: Pa ket loss per entage of the �ows in IEEE 802.11b BSS network71

between the tested algorithms are very small (espe ially for ba kground andbest-e�ort �ows) Figure 8.19 presents the same results but with s aled y axis.In terms of voi e AC, the result of the third CARA is 55,7% worse when om-pared to the �rst AARF-CD. ARF and adaptative ARF perform almost equally.The same an be said about Onoe and AMRR whi h out omes are poorest.

Figure 8.18: Pa ket loss per entage of the �ows in IEEE 802.11g BSS networkThe performan e of last four algorithms in the video AC �ow is very similarand is about 17,2% worse then the �rst AARF-CD's.For best-e�ort tra� AARF-CD swit hes its pla e with CARA. Se ond Min-strel a hieves pa ket loss ratio result whi h is 0,3% worse then CARA's. However,Minstrel is �rst in ba kground tra� �ow.Detailed Con lusionsIn all simulated network models, ea h based on di�erent PHY, �ows of sensitivetra� en ountered the least pa ket losses. As expe ted, in the saturated net-works, AC_BE and AC_BK �ows su�ered from heavy pa ket loss ratio. However,sin e ba kground and best-e�ort tra� an be usually retransmitted (oppositeto voi e and video where retransmitted frames are often useless for the re eiver),this behaviour is desirable, prioritizing low-laten y tra� .72

Figure 8.19: Pa ket loss per entage of the �ows in IEEE 802.11g BSS network(y axis adjusted)Thus, the most signi� ant are the results of Pa ket loss per entage in voi eand video tra� �ows. In 802.11a network, algorithm of �rst hoi e is CARA(2nd in both AC �ows). Good performan e of AARF-CD in this network model(AC_VO - third, AC_VI - �rst) whi h is very similar to CARA in its theory ofoperation shows that algorithms that an di�erentiate ollisions from hannelerrors have an advantage over the rate ontrol s hemes that do not utilize thiste hnique. Furthermore, CARA and AARF-CD o upy �rst two pla es also in802.11b network, in this ase in terms of all AC �ows. What is important, the apability of monitoring the sour e of the pa ket loss is ru ial for the rate sele -tion - it gives the algorithm the information whether the rate de rease is reallyneeded, thus allows for longer transmitting at higher rate. Frames transmittedusing high rate values spent less time on the hannel and are exposed for hannelerrors for less time. This results in lower pa ket loss rate.Mistrel, whi h does not try to monitor the sour e of the pa ket losses,a hieves very good results (1st in 802.11a AC_VO, AC_BE, AC_BK �ows, 3rd in802.11b, 2nd in 802.11g). This shows that statisti al approa h present in Min-strel's theory of operation is very e� ient. What is more, RTS/CTS overheadis not generated, whi h is an advantage over CARA and AARF/CD that use onditional RTS/CTS transa tions. 73

8.7 S enario 6. Pa ket loss per entage. IBSStopology.Sixth s enario measures the pa ket loss ratio in IBSS network using IEEE 802.11aPHY. Figure 8.8 presents the simulated network topology.AssumptionsFour QSTAs ontend for hannel a ess in IBSS ar hite ture. Ea h generatesdata of AC_VO, AC_VO, AC_VO and AC_VO, and sends it to the neighboring station.Tra� is generated at 14 Mbit/s (the same value as in S enario 5). Pa kets are600 bytes in size.Simulation ResultsPa ket loss ratio values a hieved during the experiment run are gathered in Table8.7 and shown in Figure 8.20.All evaluated algorithms experien ed heavy pa ket losses in best-e�ort andba kground AC �ows. Pa ket loss per entage for those ACs was equal to 100%,therefore results for AC_BE and AC_BK are omitted.Table 8.7: Pa ket loss per entage in IEEE 802.11a IBSS networkPHY AC CARA AARF-CD Minstrel ARF AARF AMRR Onoea AC_VO 65,13 66,01 70,44 90,07 90,20 90,40 90,60AC_VI 87,72 87,34 85,88 95,90 95,95 96,03 95,91

Figure 8.20: Pa ket loss per entage of the �ows in IEEE 802.11a IBSS network74

In terms of AC_VO CARA a hieves lowest value of lost pa kets ratio (65,13%).AARF-CD whi h is se ond is only less then one per entage point worse. Traf-� �ow under Minstrel's ontrol su�ered from 70,4% loss of pa kets. Otheralgorithms perform almost equally with loss ratios at level of 90%.Minstrel's result is lowest in video AC �ows (85,88%). Out omes of CARAand AARF-CD are very similar (87,72 and 87,34%). ARF, AARF, AMRR andOnoe a hieve results from 95,90% for ARF to 96,03% for AMRR.Detailed on lusionsAs expe ted pa ket loss ratio is smaller in voi e tra� transmissions. Algorithmsthat a hieve best results in IBSS network are Minstrel, CARA and AARF-CD.This is the same as in BSS environment. However, pa ket losses in AC_VO �oware more signi� ant in IBSS network - pa ket loss ratio is more than three timeslarger for aforementioned algorithms.Former experiment, where throughput was evaluated showed that CARA,Minstrel and AARF-CD a hieve highest throughput values. This fa t orre-sponds with the out omes of this simulation and explains why those algorithmsa hieved good results also this time. Sin e pa kets are transmitted at higherrates ( ompared to other algorithms), they spend less time in the hannel andare exposed to errors and ollisions for a smaller amount of time. In the result,overall per entage of pa ket loss is smaller.Results obtained from AC_VI �ows in BSS and IBSS networks are very similar,although slightly bigger in ase of IBSS.Performan e of Onoe and AMRR is poorest - both algorithms end on lastpla es in voi e and video �ows. What is more ARF and AARF, whi h a hievedbetter results than Onoe and AMRR in BSS network, this time a hieve far mu hworse out omes.8.8 S enario 7. Bit error rate.The set of rate ontrol algorithms that are examined is the same as in previousexperiments. Seven rate ontrol algorithms are evaluated in the ontext of theirin�uen e on transmission hara teristi s su h as throughput, pa ket loss ratio,mean pa ket delay and jitter.This s enario he ks the algorithms' behaviour in the network utilizing a hannel with three di�erent error hara teristi s. Ea h algorithm is simulated inthe network where BER is equal to 10−4, 5 ∗ 10−5, 10−5. This shows how ea hparti ular algorithm operates in a environment with varying error rate. What75

is more, the simulations are arried in saturated and unsaturated networks toexamine the possible di�eren es between rate ontrol s hemes.AssumptionsThe EDCA network that is going to be simulated in this s enario is omposedof six QSTAs. On ea h QSTA four appli ations generate tra� belonging todi�erent AC (voi e, video, best-e�ort and ba kground). A single transmittedpa ket is 700 bytes in size. Figure 8.21 presents the simulated network topology.The distan e between neighbouring QSTAs is 50m.

Figure 8.21: S enario 7 topologyChannel onditionsThere is no propagation loss. Pa kets are re eived with the signal strength theywere transmitted. As in previous s enarios, the default set of EDCA parametersis employed (see Table 5.2). Propagation delay is onstant due to the onstantpropagation speed whi h is equal to the 2/3 of the speed of light.As stated before BER is �xed and is set to three di�erent values (10−4, 5·10−5and 10−5) for ea h simulation y le. IEEE 802.11g serves as a PHY model inthis s enario. 76

SaturationAppli ations on QSTAs generate voi e, video, best-e�ort and ba kground tra� .Ea h appli ation generates UDP data stream at given rate. The simulation isrun two times. First run utilizes the saturated environment. In this ase ea happli ation generates data at 0,86 Mbit/s. This value was hosen to make the hannel saturated with tra� . This means that a single QSTA is generating 3,44Mbit/s at the appli ation layer.Se ond simulation run is performed in the unsaturated environment whereea h appli ation generates data at 0,031 Mbit/s (single QSTA generates 0,124Mbit/s).Simulation ResultsThe experiment was arried with three di�erent BER values (10−4, 5 · 10−5and 10−5) in saturated and unsaturated environment. This se tion presents theresults gathered during the experiment.Throughput in saturated environmentThe values of throughput (per AC) are shown in Table 8.8 and Figures 8.22 and8.23.What an be seen from the results is that ACs of voi e and video tra� takepre eden e over low-priority ba kground and best-e�ort ACs. The throughputvalues of low priority tra� �ows are either very low or even equal to zero whi hmeans that there is no data transmission for those �ow.Table 8.8: Throughput in IEEE 802.11g saturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 41,58 41,58 38,96 40,71 39,24 42,31 40,71AC_VI 12,19 12,19 12,32 12,63 12,32 12,03 12,63AC_BE 0,29 0,29 0,42 0,10 0,20 0,16 0,10AC_BK 0,00 0,00 0,20 0,00 0,10 0,00 0,005 · 10−5

AC_VO 57,01 57,01 59,31 59,23 59,52 59,56 59,23AC_VI 16,78 16,78 17,67 14,86 18,93 17,78 14,86AC_BE 0,00 0,00 0,49 0,23 0,49 0,16 0,23AC_BK 0,00 0,00 0,39 0,00 0,15 0,10 0,0010−5

AC_VO 75,28 75,28 297,94 74,67 580,22 92,5 74,67AC_VI 19,58 19,58 88,52 19,74 179,61 24,42 19,74AC_BE 0,34 0,34 0,72 0,59 3,33 0,61 0,59AC_BK 0,00 0,00 0,16 0,00 0,13 0,10 0,0077

All simulated rate ontrol algorithms perform almost equally when the BERvalue is set to 10−4 and 5 ·10−5. In terms of BER set to 10−4, throughput valuesfor AC_VO varies from 38,96 Kb/s for AARF-CD to 42,31 Kbit/s for Minstrel.When the value of BER is set to 5 · 10−5 the di�eren es are even smaller - from12,03 Kbit/s for Minstrel to 12,63 Kb/s for AMRR and Onoe.Although the throughput a hieved by the simulated algorithms is very similarin saturated environment, two algorithms take the lead when the BER valuede reases to 10−5. CARA in su h a ase a hieves 580,22 Kbit/s for AC_VO and179,61 Kbit/s for AC_VI while AARF-CD 297,94 Kbit/s for AC_VO and 88,52Kbit/s for AC_VI. CARA is able to transmit voi e data almost two times fasterthen the se ond AARF-CD.Throughput of AC_BE and AC_BK �ows for all BER values is very lowand does not ex eed 0,72 Kbit/s (maximal value for AARF-CD and BER set to10−5). ARF, AARF, Onoe and AMRR are the only algorithms that fail to transmitba kground data during the simulations with three di�erent BER values.

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Figure 8.23: Throughput in IEEE 802.11g saturated network with �xed BER (2)

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Throughput in unsaturated environmentThe values of throughput (per AC) are shown in Table 8.9. In this ase, thesimulation was run in the unsaturated environment.Table 8.9: Throughput in IEEE 802.11g unsaturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 32,34 32,43 32,75 32,75 32,28 32,69 32,36AC_VI 32,49 32,05 32,78 32,75 32,11 32,93 32,16AC_BE 1,85 2,11 1,72 2,58 0,42 4,35 2,09AC_BK 0,49 0,28 0,39 0,29 0,47 1,44 0,225 · 10−5

AC_VO 33,86 33,80 33,80 33,77 33,75 33,81 33,85AC_VI 33,88 33,83 33,86 33,81 33,88 33,85 33,83AC_BE 19,74 19,42 24,17 17,60 29,60 33,78 17,52AC_BK 3,81 3,24 5,77 3,01 9,66 33,32 2,7610−5

AC_VO 33,88 33,88 33,88 33,85 33,88 33,88 33,86AC_VI 33,93 33,93 33,93 33,90 33,93 33,93 33,91AC_BE 33,95 33,95 33,95 32,00 33,95 33,95 28,4AC_BK 33,98 33,98 33,98 8,79 33,98 33,98 5,79For 10−4 BER value, the throughput of the AC_BE and AC_BK �ows is verylow while the tra� of voi e and video ACs is sent at highest available throughput.Only Minstrel is able to transmit data of these ACs in su h onditions rea hing4,35 Kbit/s for AC_BE and 1,44 Kbit/s for AC_BK �ow. Other algorithms donot ex eed 0,5 Kbit/s.When the BER de reases, the more of the ba kground and best-e�ort data isable to be transmitted. This is learly shown in Figures 8.24 and 8.25. For BERvalue set to 10−5, almost all of the rate ontrol algorithms are able to send dataat full speed. The only ex eptions are AMRR and Onoe. For those algorithmserror level of 10−5 is still not enough to perform well.Minstrel's behaviour is this time the best. The algorithms rea hes the maxi-mum throughput in the environment with 5 · 10−5 BER value. The se ond andthird are CARA and AARF-CD. However in terms of aforementioned BER value,the se ond CARA transmits the ba kground tra� at 9,66 Kbit/s whi h is morethen 3 times slower then Minstrel's result. Analogi ally, AARF-CD transmitsba kground tra� at 5,77 Kbit/s. Other algorithms in this ase do not ex eed4 Kbit/s.80

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Figure 8.25: Throughput in IEEE 802.11g unsaturated network with �xed BER(2)

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Delays in saturated environmentThe values of mean delay (per AC) are shown in Table 8.10 and Figures 8.26and 8.27.Due to the EDCA poli y, tra� of high-priority ACs should be transmittedwith lower delay values then best-e�ort and ba kground data. However, duringthe simulation run many ex eptions from this rule o urred. Most of the algo-rithms transmitted best-e�ort and ba kground tra� with lower delays then inother ACs.The answer for this behaviour is that in saturated environment the pa ketsof low-priority ACs are in the minority and thus, small number of these pa ketstransmitted with low delay values introdu es a signi� ant hange in the averagedelay �gure for the whole AC.Thus, when talking about delays in saturated environment we should onsideronly the �ows that a hieved non-zero or not insigni� ant throughput. ACs thatful�ll these requirements are AC_VO and AC_VI. The transmission delays ofthese �ows are almost equal for all the simulated algorithms. Only CARA andAARF-CD are able to a hieve smaller delays for voi e transmission. However thiso urs only in the environment with BER value set to 10−5. CARAs result inthis ase is almost two times better then ARRF-CDs.Table 8.10: Delay in IEEE 802.11g saturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 9423 9423 9452 9345 9442 9428 9479AC_VI 9265 9265 9263 9361 9227 9205 9307AC_BE 8459 8459 7209 7781 9958 8160 5757AC_BK - - 6721 - 5952 - -5 · 10−5

AC_VO 9361 9361 9399 9361 9436 9311 9345AC_VI 9304 9304 9319 9271 9362 9307 9361AC_BE - - 8684 7825 9307 7051 7781AC_BK - - 6628 - 6847 223 -10−5

AC_VO 9358 9358 6741 9442 3659 8930 9361AC_VI 9290 9290 9231 9227 8983 9228 9271AC_BE 7182 7182 7891 9958 8496 7313 7825AC_BK - - 8062 5952 4322 9256 -Delays in unsaturated environmentThe values of mean delay (per AC) are shown in Table 8.11 and Figures 8.28and 8.29. 83

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Figure 8.27: Delay in IEEE 802.11g saturated network with �xed BER (2)

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In the unsaturated environment, the transmission takes pla e as expe tedwith EDCA rules ful�lled. For all BER values, AC_VO and AC_VI �ows aretransmitted with small delays. For voi e AC these values vary from 43 ms (Min-strel) to 73 ms (CARA) for 10−4 BER value, 12 ms (Minstrel) to 21 ms (AARF,AMRR, Onoe) for 5 ·10−5, and 1 ms (AMRR, CARA) to 15 ms (Onoe, Minstrel)for 10−5.In terms of video AC, the results are very similar. However, CARAs behaviouris this time the worse. With 941 ms delay (BER 10−4) the algorithm takes thelast pla e.When it omes to the environment with 10−5 BER value, the best algorithmsare: CARA, AARF-CD, ARF and AARF. The delay values a hieved by thesealgorithms in all AC �ows are insigni� ant - 1-3 ms for CARA, 1-10 ms forAARF-CD, 3-33 ms for AARF and 2-65 ms for ARF.Table 8.11: Delay in IEEE 802.11g unsaturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 53 52 51 48 73 43 51AC_VI 180 189 185 141 941 114 188AC_BE 7234 7988 7422 8452 4281 7236 7230AC_BK 8006 8247 7865 8159 7249 7367 52855 · 10−5

AC_VO 20 21 19 21 17 12 21AC_VI 29 31 26 33 22 14 31AC_BE 7144 7301 6549 7899 3857 146 7609AC_BK 8331 7958 8892 8042 8947 389 801010−5

AC_VO 2 3 1 14 1 15 15AC_VI 2 2 1 18 1 20 20AC_BE 7 7 2 2023 1 4031 4031AC_BK 65 33 10 7304 3 7645 7645Pa ket loss in saturated environmentThe values of mean pa ket loss (per AC) are shown in Table 8.12 and Figures8.30 and 8.31.In the saturated environment all transmission �ows su�er from signi� antpa ket losses. The performan e of rate ontrol algorithms in terms of pa ketlosses in environments with BER set to 10−4 and 5 · 10−5 is almost equal.The di�eren es show up when the BER de reases to 10−5. In this aseCARA and AARF-CD are able to send voi e and video tra� with lower losseswhile the other algorithms still a hieve results that are almost the same as in the86

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Figure 8.29: Delay in IEEE 802.11g unsaturated network with �xed BER (2)

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environments with higher BER. CARA's result is 36,49% for AC_VO and 80,33%for AC_VI. The se ond AARF-CD a hieves 67,38% for AC_VO and 90,30% forAC_VI.Table 8.12: Pa ket loss in IEEE 802.11g saturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 95,45 95,45 95,73 93,52 95,7 95,37 95,54AC_VI 98,66 98,66 98,65 98,37 98,65 98,68 98,62AC_BE 99,97 99,97 99,95 99,98 99,98 99,98 99,99AC_BK 100 100 99,98 100 99,99 100 1005 · 10−5

AC_VO 93,76 93,76 93,51 91,83 93,48 93,48 93,52AC_VI 98,16 98,16 98,06 97,84 97,93 98,05 98,37AC_BE 100 100 99,95 99,94 99,95 99,98 99,98AC_BK 100 100 99,96 100 99,98 99,99 10010−5

AC_VO 91,76 91,76 67,38 95,7 36,49 89,87 91,83AC_VI 97,85 97,85 90,3 98,65 80,33 97,33 97,84AC_BE 99,96 99,96 99,92 99,98 99,64 99,93 99,94AC_BK 100 100 99,98 100 99,99 99,99 100Pa ket loss in unsaturated environmentThe values of mean pa ket loss (per AC) are shown in Table 8.13 and Figures8.32 and 8.33.In the unsaturated environment where the BER value is set to 10−4, thealgorithms perform similarly. The losses in high-priority AC �ows are small from3,32% (AMRR) to 4,73% (CARA) to for voi e and from 2,93% (Minstrel) to5,53% (AARF) for video tra� .When the BER de reases, Minstrel is the algorithm that a hieves the bestresults. Minstrel su eeds in signi� ant lowering the losses when other algorithmsare not able to do so. The algorithm is the only one that rea hes 2% level ofpa ket loss for all AC �ows in the environment with BER set to 5 · 10−5.In terms of BER equal to 10−5, �ows ontrolled by ARF, AARF, AARF-CD,CARA and Minstrel do not su�er from pa ket losses. AMRR and Onoe are theonly algorithms that do not perform well in su h a onditions.Jitter in saturated environmentThe values of mean jitter (per AC) are shown in Table 8.14 and Figures 8.34 and8.35. 89

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Figure 8.31: Pa ket loss in IEEE 802.11g saturated network with �xed BER (2)Table 8.13: Pa ket loss in IEEE 802.11g unsaturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 4,53 4,29 3,33 3,32 4,73 3,53 4,48AC_VI 4,24 5,53 3,37 3,47 5,35 2,93 5,21AC_BE 94,56 93,79 94,95 92,41 98,75 87,2 93,84AC_BK 98,56 99,18 98,85 99,14 98,61 95,76 99,365 · 10−5

AC_VO 0,05 0,24 0,24 0,34 0,39 0,19 0,1AC_VI 0,14 0,29 0,19 0,34 0,14 0,24 0,29AC_BE 41,81 42,85 28,8 48,15 12,84 0,48 48,4AC_BK 88,77 90,48 83,04 91,16 71,56 1,93 91,8610−5

AC_VO 0 0 0 0,1 0 0 0,05AC_VI 0 0 0 0,1 0 0 0,05AC_BE 0 0 0 5,75 0 0 16,33AC_BK 0 0 0 74,04 0 0 82,9491

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Figure 8.33: Pa ket loss in IEEE 802.11g unsaturated network with �xed BER(2)93

Jitter was measured only in those �ows where the throughput was not equalto zero (transmission o urred) and a signi� ant amount of tra� was ex hangedso the obtained results are reliable.In the saturated environment, jitter values in �ows ontrolled by ARF and itsadaptative version AARF are almost the same.In terms of 10−4 BER value, AARF-CD was the only algorithm that sentenough ba kground data so the jitter ould be al ulated. All other algorithmsfailed to do so. The situation is similar for 5 · 10−5 and 10−5 BER. In that aseAARF-CD ad CARA were the only algorithms that were ontrolling the rate wellenough to transmit tra� belonging to ba kground AC.When onsidering only the high-priority tra� of voi e and video, Minstreland CARA show a very good behaviour. CARA takes the lead in the environmentwith BER value set to 10−5. In su h a ase the algorithm is 6 time better thenMinstrel in terms of jitter when omparing the AC_VO �ow.Table 8.14: Jitter in IEEE 802.11g saturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe10−4

AC_VO 98 98 111 82 113 92 94,17AC_VI 267 267 279 253 298 279 280AC_BE 266 266 796 1358 86 611 -AC_BK - - 3574 - - - -5 · 10−5

AC_VO 84 84 80 70 83 80 82AC_VI 240 240 209 214,5 220 222 253AC_BE - - 1336 1356 846 1 1358AC_BK - - 5740 - 551 - -10−5

AC_VO 72 72 19 113 9 62 70AC_VI 223 223 60 298 31 184 214AC_BE 3017 3017 1447 86 606 745 1356AC_BK - - 947 - 1762 - -Jitter in unsaturated environmentThe values of mean jitter (per AC) are shown in Table 8.15 and Figures 8.36 and8.37.In the unsaturated environment AARF is the best algorithm that a hieveslowest values of jitter in terms of BER set to 10−4. When the BER is de reasedto 5 · 10−5, Minstrel is the best. For 10−5 error rate both ARFs, AARF-CD,CARA and Minstrel show very low jitter values that vary from 0 ms (AARF-CD)to 9 ms (Onoe and AMRR). 94

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When judging only by high-priority ACs, Minstrel's behaviour is the best.Jitter values in these terms are equal to 40 ms (AC_VO) and 76 ms (AC_VI)for BER set to 10−4, 11 ms (AC_VO) and 14 ms (AC_VI) for BER set to5 · 10−5, and 1 ms (AC_VO, AC_VI) for BER set to 10−5.The worst results are a hieved by Onoe and AMRR.Table 8.15: Jitter in IEEE 802.11g unsaturated network with �xed BER.BER AC ARF AARF AARF-CD AMRR CARA Minstrel Onoe

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AC_VO 16 17 15 17 13 11 17AC_VI 26 28 23 29 19 14 28AC_BE 141 150 132 147 124 57 148AC_BK 449 490 272 439 244 106 52910−5

AC_VO 1 1 0 9 0 1 9AC_VI 1 1 1 13 0 1 15AC_BE 3 5 2 84 1 2 93AC_BK 13 10 5 287 2 2 354Detailed on lusionsSimulation shows that in terms of both saturated and unsaturated hannel envi-ronment, high-priority ACs takes the pre eden e over best-e�ort and ba kgroundACs. That onforms to EDCA rules. The EDCA poli ies are also obeyed in theenvironments with di�erent error rates.Some algorithms perform better then the others. The main purpose of thiss enario was to examine whi h one of them a ts good in a environment wheretransmission �ows are exposed to errors.In terms of throughput and mean transmision delays su h algorithms areCARA and AARF-CD. As stated in the previous s enarios' on lusions both al-gorithms are able to di�erentiate transmission failures aused by ollisions fromwhose that were introdu ed by the transmission hannel. The algorithms employRTS/CTS transa tions to do so. CARA also uses the additional CCA dete tionme hanism.Minstrel approa h is very e�e tive in the unsaturated hannel onditions.It's me hanism bases on the stati al information about probed rates. What is97

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Figure 8.37: Jitter in IEEE 802.11g saturated network with �xed BER (2)

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more, Minstrel does not introdu e any RTC/CTS related overhead. Thus, it ana hieve higher throughput values.In terms of pa ket loss per entage CARA and AARF-CD are the best rate ontrol algorithms. Dealing very well in environments with all tested BER values.Their very good behaviour is ru ial in voi e and video ACs where pa ket lossesare unwanted and the retransmission is in most ases pointless. The same an besaid about jitter, whi h a�e ts mainly voi e and video transmissions. Also thistime CARA and AARF-CD perform very well. In the unsaturated environmentMinstrel also shows very good results, even better then aforementioned CARAand AARF-CD.8.9 Implementation IssuesMain issue that aroused when it ame to introdu ing QoS provisioning in ns-3simulations was the la k of a model of appli ation that allowed for assigning agenerated tra� desired user priority and a ess ategory.In all above presented simulations, the On-O� appli ation model was used.The theory of operation of this model is very simple. The appli ation generatesa Constant Bit Rate (CBR) UDP tra� . Data �ows are generated onstantlywithout breaks, so the data queue of the STA on whi h the appli ation is installedis never empty.However, existing model of the On-O� appli ation did not support QoS pa kettagging. In order to solve this problem, the On-O� appli ation model was ex-tended with this fun tionality, enabling tagging of the pa kets with desired UPtag.Another issue that aroused during the development of the simulation ode wasthe la k of �exible error model for ns-3's WiFi implementation that would allowfor setting a desired BER value. To over ome this limitation, an existing errormodel (YansErrorRateModel) was modi�ed and extended with the fun tionalityof setting a �xed BER value.

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Chapter 9Con lusion9.1 SummaryThis thesis presented an analysis of multi-rate mode of IEEE 802.11 EDCA wire-less networks. IEEE 802.11e QoS support features were thoroughly explained aswell as the ns-3 network simulator and it's apabilities and limitations in termsof simulation of multi-rate EDCA environments.The problem of missing appli ation model that ould generate tra� of thespe i� AC was solved by modifying existing On-O� appli ation. Extended modelof On-O� appli ation allowed for QoS pa ket marking whi h was ru ial in allthe simulation experiments.All tested rate ontrol algorithms were des ribed and their theory of operationwas explain to exhibit their drawba ks and advantages.Evaluation on two types of networks (IBSS and BSS) was arried in ns-3 network simulator. Various simulation experiments were performed. IEEE802.11a, b and g PHY models were utilized.First two experiments examined the mean transmission delay of the �ows arrying tra� belonging to di�erent ACs.The next simulations fo used on throughput a hieved in network where therate is ontrolled by the sele ted algorithms.Next two experiments examined the per entage of lost pa kets in four �ows- ea h ontaining data marked with di�erent AC.Finally, the last s enario evaluated algorithms' behaviour in di�erent envi-ronments - ea h with di�erent error rate - in both saturated and unsaturated onditions.The simulations were arried in BSS and IBSS environments. The results ofthe simulations and their auses were dis ussed.Simulation showed that three algorithms: CARA, AARF-CD and Minstrela hieve best results, regardless of the metri s used. That led to the on lusionthat the algorithms that are apable of distinguishing failures that o urred due ollisions from those aused by hannel errors perform better than those that donot have this apability.Another on lusion was that a ompletely di�erent approa h used by Minstrelresulted in very good results. Minstrel probes the hannel by sending probing101

frames at di�erent transmission rate from the one that is urrently set and he k-ing whether their re eption was su essful.Simulations also showed that the performan e of the very popular ARF rate ontrol algorithm is poor in both saturated and unsaturated network environ-ments.9.2 Future WorkThe modi� ation of the existing On-O� appli ation allowing for tagging pa ketswith desired UP will be proposed as an add-on to the ns-3 and ontributed tothe proje t.The addition to the simulator's WiFi eror model (YansErrorRateModel) thatenables the user to set a �xed Bit Error Rate value will be ontributed as well.Furthermore, the simpli�ed ode of the simulations, after appropriate modi-� ations will be proposed as an addition to already existing example simulationsthat ome with ns-3, sin e the number of QoS related sample s enarios is smalland not su� ient.

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Bibliography[1℄ IEEE Standard for Information Te hnology � Tele ommuni ations and Infor-mation Ex hange between Systems � Lo al and Metropolitan Area Networks� Spe i� Requirements � Part 11: Wireless LAN Medium A ess Control(MAC) and Physi al Layer (PHY) Spe i� ations, Amendment 5: Enhan e-ments for Higher Throughput. IEEE 802.11n-2009.[2℄ IEEE Standard for Information Te hnology � Tele ommuni ations and Infor-mation Ex hange between Systems � Lo al and Metropolitan Area Networks� Spe i� Requirements � Part 11: Wireless LAN Medium A ess Control(MAC) and Physi al Layer (PHY) Spe i� ations. IEEE 802.11-2007.[3℄ Minstrel, algorithm do umentation.Linux Wireless., May 2011. Available athttp://linuxwireless.org.[4℄ Minstrel, algorithm spe i� ation and sour e ode. the MadWi� Proje t, May2011. Available at http://madwi�-proje t.org/.[5℄ ns-3, The Network Simulator, February 2011. Available athttp://www.nsnam.org/.[6℄ Onoe, algorithm spe i� ation and sour e ode. the MadWi� Proje t, May2011. Available at http://madwi�-proje t.org/.[7℄ SampleRate, algorithm spe i� ation and sour e ode. the MadWi� Proje t,May 2011. Available at http://madwi�-proje t.org/.[8℄ A. Ahmad. Wireless and mobile data networks. John Wiley & Sons, In .,2005.[9℄ Wi-Fi Allian e. Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput,Multimedia-Grade Wi-Fi Networks. September, 2009.[10℄ N. Baldo, M. Requena-Esteso, J. Nunez-Martinez, M. Portoles-Comeras,J. Nin-Guerrero, P. Dini, and J. Mangues-Bafalluy. Validation of the IEEE802.11 MAC Model in the ns3 Simulator using the EXTREME Testbed.SIMUTools '10 Pro eedings of the 3rd International ICST Conferen e onSimulation Tools and Te hniques, ICST, Brussels, Belgium, 2010.[11℄ B. Bellalta, C. Canoa, M. Oliver, and M. Meo. Modeling the IEEE 802.11eEDCA for MAC Parameter Optimization. Het-Nets 06, Bradford, UK,September 2006. 103

[12℄ G. Bian hi. Performan e analysis of the IEEE 802.11 distributed oordina-tion fun tion. IEEE Journal on Sele ted Areas in Communi ations, 18(3):535�547, Mar h 2000.[13℄ J. Bi ket. Bit-rate sele tion in wireless networks. Master's thesis. Mas-sa husetts Institute of Te hnology. Dept. of Ele tri al Engineering and Com-puter S ien e, 2005.[14℄ T. Bingmann. A ura y Enhan ements of the 802.11 Model and EDCAQoS Extensions in ns-3. Diploma thesis. University of Karlsruhe. Fa ulty ofComputer S ien e. Institute of Telemati s, 2009.[15℄ B. E. Braswell. Modeling Data Rate Agility in the IEEE 802.11a Wire-less Lo al Area Networking Proto ol. Master's thesis. Naval PostgraduateS hool, Monterey CA, 2001.[16℄ Y. P. Chen, J. Zhang, and A. N. Ngugi. An e� ient rate-adaptive MAC forIEEE 802.11. MSN'07 Pro eedings of the 3rd international onferen e onMobile ad-ho and sensor networks, 2007.[17℄ C. Q. Shen D. He. Simulation study of IEEE 802.11e EDCF. Vehi ularTe hnology Conferen e, 2003. VTC 2003-Spring. The 57th IEEE Semian-nual, Vol. 1, 2003.[18℄ R. Fuller A. Pfund E. Ouellet, R. Padjen. Building a Cis o Wireless LAN.Syngress Publishing, In . p. 67-69, 2002.[19℄ Y. Ge, J.C. Hou, and S. Choi. An Analyti Study of Tuning Systems Pa-rameters in IEEE 802.11e Enhan ed Distributed Channel A ess. ComputerNetworks, vol. 51, no. 8, pp. 1955-1980, 2007.[20℄ T. R. Henderson, S. Roy, S. Floyd, and G. F. Riley. ns-3 Proje t Goals. inWNS2 '06: Pro eeding from the 2006 workshop on ns-2: the IP networksimulator, 2006.[21℄ G. Holland, N. H. Vaidya, and P. Bahl. A rate-adaptive MAC proto ol formulti-hop wireless networks. in Pro . ACM Int. Conf. Mob. Comp. Netw.MobiCom 2001, Rome, Italy, 2008.[22℄ A. Kamerman and L. Monteban. WaveLAN-II: A High-performan e wirelessLAN for the unli ensed band. in Bell Lab Te hni al Journal, pages 118-133,1997.104

[23℄ J. Kim, S. Kim, S. Choi, and D. Qiao. CARA: Collision-Aware Rate Adap-tation for IEEE 802.11 WLANs. 25th IEEE International Conferen e onComputer Communi ations, Pro eedings In INFOCOM, 2006.[24℄ M. La age and T. R. Henderson. Yet Another Network Simulator. in WNS2'06: Pro eedings of the 2006 workshop on ns-2: the IP network simulator,page 12. ACM, 2006.[25℄ M. La age, M. H. Manshaei, and T. Turletti. IEEE 802.11 rate adaptation:a pra ti al approa h. INRIA Res. Rep., no. 5208, 2004.[26℄ B. Gi Lee and S. Choi. Broadband Wireless A ess and Lo al NetworksMobile WiMAX and WiFi. ARTECH HOUSE, INC., p. 399, 406, 458, 459,2008.[27℄ F. Maguolo, M. La age, and T. Turletti. E� ient ollision dete tion forauto rate fallba k algorithm. IEEE Symposium on Computers and Commu-ni ations, ISCC, 2008.[28℄ S. Mangold, S. Choi, P. May, O. Klein, G. Hiertz, and L. Stibor. IEEE802.11e Wireless LAN for Quality of Servi e. in Pro . European Wireless'02,Floren e, Italy, April 2002.[29℄ D. Matthews. Wireless Rate Control Algorithms and Measurement. FinalReport for COMP520-08Y. University of Waikato. Department of ComputerS ien e. Hamilton, New Zealand, 2008.[30℄ R. M. Met alfe and D. R. Boggs. Ethernet: Distributed Pa ket Swit hing forLo al Computer Networks. ACM Communi ations, 19(5):395�404, 1976.[31℄ A. N. Ngugi. E� ient Rate Adaptation in IEEE 802.11. Master's thesis.Memorial University of Newfoundland, 2008.[32℄ Q. Ni. Performan e Analysis and Enhan ements for IEEE 802.11e WirelessNetworks. IEEE Network 19 (4) 21�27, 2005.[33℄ S. Pal, S. R. Kundu, K. Basu, and S. K. Das. IEEE 802.11 Rate ControlAlgorithms: Experimentation and Performan e Evaluation in Infrastru tureMode. PE-WASUN '08 Pro eedings of the 5th ACM symposium on Per-forman e evaluation of wireless ad ho , sensor, and ubiquitous networks,2008.[34℄ Q. Pang, S.C. Liew, and V.C.M. Leung. A Rate Adaptation Algorithmfor IEEE 802.11 WLANs Based on MAC-Layer Loss Di�erentiation. Pro .Se ond IEEE Int'l Conf. Broadband Networks (BroadNets), 2005.105

[35℄ G. Pei and T. Henderson. Validation of ns-3 802.11b PHYmodel. Boeing Resea h and Te hnology of TBC, available athttp://www.nsnam.org/pei/80211b.pdf, 2009.[36℄ D. Qiao, S. Choi, and K.G. Shin. Goodput analysis and link adaptationfor IEEE 802.11a wireless LANs. IEEE Transa tions on Mobile Computing,vol.1 no. 4, pp. 278-292, 2002.[37℄ K. Rama handran, H. Kremo, M. Gruteser, P. Spasojevi, and I. Seskar. S al-ability Analysis of Rate Adaptation Te hniques in Congested IEEE 802.11Networks: An ORBIT Testbed Comparative Study. IEEE International Sym-posium on a World of Wireless, Mobile and Multimedia Networks, 2007.[38℄ T. S. Rappaport. Wireless Communi ations: Prin iples and Pra ti e. Pren-ti e Hall, 1999.[39℄ B. Sadeghi, V. Kanodia, A. Sabharwal, and E. Knightly. Opportunisti media a ess for multirate ad ho networks. in Pro . ACM MobiCom 2002Conf., Atlanta, USA, 2002.[40℄ S. Sehrawat, R. P. Bora, and D. Harihar. Performan e Analysis of QoSsupported by Enhan ed Distributed Channel A ess (EDCA) me hanism inIEEE 802.11e. in IEEE Journal on Sele ted Areas in Communi ations, 2004.[41℄ V. A. Siris and C. Cour oubetis. Resour e Control for the EDCA Me ha-nism in Multi-Rate IEEE 802.11e Networks. WoWMoM, pp. 419-428, 2006International Symposium on a World of Wireless, Mobile and MultimediaNetworks (WoWMoM'06), September 2006.[42℄ Z. Tao and S. S. Panwar. Throughput and delay analysis for the IEEE802.11e enhan ed distributed hannel a ess. IEEE Transa tions on Com-muni ations 54(4): 596-603, 2006.[43℄ I. Tinnirello and S. Choi. E� ien y Analysis of Burst Transmissions withBlo k ACK in Contention-Based 802.11e WLANs. IEEE International Con-feren e on Communi ations, 2005.[44℄ G. A. Wainer. Dis rete-Event Modeling and Simulations: A Pra titioner'sApproa h. Taylor & Fran is Group, LLC, 2009. p. 11.[45℄ B. H. Walke, S. Mangold, and L. Berlemann. IEEE 802 Wireless SystemsProto ols, Multi-hop Mesh/Relaying, Performan e and Spe trum Coexis-ten e. John Wiley & Sons Ltd, pp. 83, 95, 2006.106

[46℄ Y. Wei, K. Bialkowski, J. Indulska, and H. Peizhao. Evaluations of MadWi�MAC layer rate ontrol me hanisms. 18th International Workshop on Qualityof Servi e (IWQoS), 2010.[47℄ S. H. Y. Wong, H. Yang, S. Lu, and V. Bharghavan. Robust rate adaptationfor 802.11 wireless networks. published in ACM Mobi om 06, 2006.[48℄ W. Wu, Z. Zhang, X. Sha, and C. He. Auto rate MAC proto ol based on ongestion dete tion for wireless Ad Ho networks. Inform. Te hnol. J., 8:1205-1212, 2009.[49℄ Y. Xiao. Enhan ed DCF of IEEE 802.11e to support QoS. in. Pro . IEEEWCNC, New Orleans, LA, vol. 2, pp. 1291�1296, 2003.

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