chungnam national university 1 협업 통신에서의 매체액세스제어 cooperative...

Chungnam National University 1

협업 통신에서의 매체액세스제어협업 통신에서의 매체액세스제어Cooperative Communication MACCooperative Communication MAC

2006. 02

Chungnam National University

Byung Chul Kim

[email protected]

Chungnam National University 통신 핵심기술 워크샵 2

Cooperative CommunicationCooperative Communication

Cooperative communicationCooperative communication• Different wireless nodes cooperate to increase their Different wireless nodes cooperate to increase their

robustness by decreasing the bit error rate and outage robustness by decreasing the bit error rate and outage probabilitiesprobabilities

• Use another mobile to relay informationUse another mobile to relay information



Broadcast Wireless ChannelBroadcast Wireless Channel• Omni-directional wireless antennasOmni-directional wireless antennas• Signals transmitted towards the destination can be overheard at the Signals transmitted towards the destination can be overheard at the

relay partnerrelay partner Partner can process this overheard information and re-transmit Partner can process this overheard information and re-transmit

towards the destinationtowards the destination Destination processes signals from both mobilesDestination processes signals from both mobiles BenefitsBenefits

• Spatial DiversitySpatial Diversity• Higher Data rates and throughputHigher Data rates and throughput• Lower DelayLower Delay• Power EfficientPower Efficient• Lower interferenceLower interference• Increased CoverageIncreased Coverage



Spatial diversity gainSpatial diversity gain• Store and forward: Store and forward:

traditional relaytraditional relay

• Amplify and forwardAmplify and forward

• Coded cooperationCoded cooperation

• Multi-hop Multi-hop CommunicationCommunication


Problems of wireless communicationProblems of wireless communication

Problems of multi-rate IEEE 802.11bProblems of multi-rate IEEE 802.11b• 3 different modulation scheme3 different modulation scheme

- 1Mbps: DBPSK, 2Mbps: DQPSK, 5.5 & 11Mbps: CCK1Mbps: DBPSK, 2Mbps: DQPSK, 5.5 & 11Mbps: CCK

• Fairness problem: equal channel access probabilitiesFairness problem: equal channel access probabilities- Performance anomaly: low data rate nodes (say 1Mbps) will occupy the Performance anomaly: low data rate nodes (say 1Mbps) will occupy the

channel for longer duration for the same size framechannel for longer duration for the same size frame

- Reduced overall network throughputReduced overall network throughput

• Shortest path routing: Low data rateShortest path routing: Low data rate

Adaptive Modulation and CodingAdaptive Modulation and Coding• Data rate based on the distance between the AP and STAData rate based on the distance between the AP and STA

• Service quality enhancement method is required at the Service quality enhancement method is required at the boundaryboundary


Cooperative Communication MACCooperative Communication MAC

GoalsGoals• Reduce the channel time for low data rate node by assisting itReduce the channel time for low data rate node by assisting it

s transmissions transmission

• Enhance the robustness of the WLAN operationEnhance the robustness of the WLAN operation

New AlgorithmNew Algorithm• Relay node Selection AlgorithmRelay node Selection Algorithm

• Relay node Relay node 고려한 고려한 new CSMA/CA Algorithmnew CSMA/CA Algorithm

• Backoff and Retransmission AlgorithmBackoff and Retransmission Algorithm



CMAC ProtocolCMAC Protocol• The partner retransmits the MAC frame that it received from The partner retransmits the MAC frame that it received from

the source when the frame is received in error at the destinatithe source when the frame is received in error at the destinationon

• The backoff window size of partner << that of source The backoff window size of partner << that of source prio priority to the relaying datarity to the relaying data

• direct link : 오류 확률 p

• Ndirect = 1/(1-p)

• NCMAC = 1*(1-p)+2*p = 1+p



Shortest path algorithmShortest path algorithm

• (1/11+1/5.5)(1/11+1/5.5)

= 3.7Mbps= 3.7Mbps



Relay node Relay node 선택 선택 - I- I• Physical node tablePhysical node table 에 각 에 각 modulation typemodulation type 에 대한 에 대한 threshold threshold

SNR SNR 존재 존재 수신한 수신한 SNRSNR 에 근거해서 최적의 에 근거해서 최적의 modulation modulation scheme scheme 선택선택

• APAP 와 다른 노드 간 통신 와 다른 노드 간 통신 overhearingoverhearing 해 해 headerheader 내에 있는 내에 있는 relay noderelay node 와 와 APAP 간 전송 속도 계산간 전송 속도 계산

• 수신한 신호 세기로부터 자신과 수신한 신호 세기로부터 자신과 relay relay 간의 간의 path loss path loss 계산계산



Relay node Relay node 선택 선택 - II- II• Sender-receiver channel quality: extract the piggybacked Sender-receiver channel quality: extract the piggybacked

transmission rate in the CTStransmission rate in the CTS

• Sender-relay node, relay node-receiver channel quality: sense Sender-relay node, relay node-receiver channel quality: sense the signal strength of RTS or CTS, respectivelythe signal strength of RTS or CTS, respectively

• Sender-receiver flowSender-receiver flow 가 주어진 경우 가 주어진 경우 MAC layer relayMAC layer relay 를 통해 를 통해 더 빨리 전달 가능한 경우 더 빨리 전달 가능한 경우 willing listwilling list 에 해당 송에 해당 송 , , 수신 노드의 수신 노드의 MAC MAC 주소를 포함주소를 포함

• 각 노드는 주기적으로 자신의 각 노드는 주기적으로 자신의 willing listwilling list 를 를 one-hop one-hop 이웃에게 이웃에게 광고광고



모든 노드는 모든 노드는 helper table helper table 관리관리 Table Table 구성구성

- ID : MAC address of (helper)ID : MAC address of (helper)

- Time : time the last packet from is heard.Time : time the last packet from is heard.

- : Transmission rate between and the destination: Transmission rate between and the destination

- : Transmission rate between the current station and : Transmission rate between the current station and hdR

shR hShS

hShS



• Table UpdateTable Update- : can hear the RTS/CTS exchanged between AP and : can hear the RTS/CTS exchanged between AP and

- : measuring the received power level: measuring the received power level

• Selecting a helperSelecting a helper- Check the helper table and calculates the time needed to transmit via each Check the helper table and calculates the time needed to transmit via each

helperhelper

- two hop transmission via the helper two hop transmission via the helper

hdR

shRhS



Reserving the channelReserving the channel• RTS frameRTS frame 에 새로운 필드 포함에 새로운 필드 포함 ..

- The ID of , and The ID of , and

RTS RTS 수신한 수신한 helperhelper• SIFSSIFS 후 후 helper ready to send (HTS) helper ready to send (HTS) 송신송신 ..

- HTS packetHTS packet 은 은 CTS packetCTS packet 과 같음과 같음 ..

RTS RTS 수신한 수신한 • 에 의해 에 의해 HTSHTS 를 수신할 경우 를 수신할 경우

- CTS CTS 전송 전송 : : 를 경유하여 전송하기 위해 필요한 시간을 예약를 경유하여 전송하기 위해 필요한 시간을 예약• HTSHTS 를 수신하지 못했을 경우를 수신하지 못했을 경우

- CTS CTS 전송 전송 : : 직접 전송할 때 필요한 시간을 예약직접 전송할 때 필요한 시간을 예약

RTSRTS 를 전송하고 를 전송하고 CTS CTS 받은 받은 • Helper tableHelper table 에서 삭제에서 삭제

hS shR hdR

dS

hS

hS

hS

sS



• CTSCTS 를 수신한를 수신한- RTSRTS 후 후 HTSHTS 를 수신했을 경우를 수신했을 경우

– 로 데이터 전송로 데이터 전송– 는 는 CRC CRC 체크 체크 , SIFS, SIFS 후 에게 전송후 에게 전송

- RTSRTS 후 후 HTSHTS 를 수신하지 못했을 경우를 수신하지 못했을 경우– 로 직접 전송로 직접 전송– Helper tableHelper table 에서 삭제에서 삭제

• Data Data 수신한 수신한 - 에 직접 에 직접 ACKACK 을 전송을 전송

sS

dS hS

hS

hS dS

dS

sS



With HelperWith Helper

Without Without HelperHelper



Adaptively changed transmission rateAdaptively changed transmission rate• Sender does not know the transmission rate of the impending Sender does not know the transmission rate of the impending

packet in advancepacket in advance

• SolutionSolution- Sender first calculate the duration of the RTS and CTS transmissions Sender first calculate the duration of the RTS and CTS transmissions

only(basic rate, 2Mbps)only(basic rate, 2Mbps)

- After the sender receives CTS (or RCTS), it calculates the durations of After the sender receives CTS (or RCTS), it calculates the durations of the data packet and the ACKthe data packet and the ACK



Comparison of two carrier sensing mechanismComparison of two carrier sensing mechanism



Different transmission rates Different transmission rates different transmission different transmission rangesranges• When the sender sends data at high rate, some one-hop When the sender sends data at high rate, some one-hop

neighbors may stay within its carrier sensing range but neighbors may stay within its carrier sensing range but cannot extract the information of the durationcannot extract the information of the duration

• SolutionSolution- Reservation-sub-header(RSH)Reservation-sub-header(RSH)

- RSH is inserted preceding the data frameRSH is inserted preceding the data frame

- Sent at the same or lower rate compared to RTSSent at the same or lower rate compared to RTS



Dynamic channel conditionDynamic channel condition• Adaptive decision when to perform relayAdaptive decision when to perform relay

• Credit ranging in [0.0, 1.0]Credit ranging in [0.0, 1.0]- Choose the relay node with the largest creditChoose the relay node with the largest credit

- Successful relaying node increment the credit by 0.1Successful relaying node increment the credit by 0.1

- Fail Fail decrement by 0.1 decrement by 0.1

- Willing list Willing list 수신 수신 increment by 0.5increment by 0.5



Impacts of RelayImpacts of Relay• 망의 망의 Spatial ReuseSpatial Reuse 에 영향을 미침에 영향을 미침



Throughput IncreaseThroughput Increase



Energy EfficiencyEnergy Efficiency


ConclusionsConclusions

Significant improvement enabled by cooperationSignificant improvement enabled by cooperation• Capacity, delay, energy consumption, and interference reductCapacity, delay, energy consumption, and interference reduct

ionion

Enhance the robustness of the WLAN operationEnhance the robustness of the WLAN operation

Heals the anomaly problem of 802.11 multi-rate STAsHeals the anomaly problem of 802.11 multi-rate STAs

Enhance the WiBro STA’s QoS at the boundary of the Enhance the WiBro STA’s QoS at the boundary of the cellcell


ReferencesReferences

A Cooperative MAC Protocol for Wireless Local Area A Cooperative MAC Protocol for Wireless Local Area NetworkNetwork• Pei Liu, Zhifeng Tao, and Shivendra PanwarPei Liu, Zhifeng Tao, and Shivendra Panwar

Cooperative Communication MAC (CMAC) – A New Cooperative Communication MAC (CMAC) – A New MAC Protocol for Next Generation Wireless LANsMAC Protocol for Next Generation Wireless LANs• Sai Shankar, Chun-Ting Chou, and Monisha GhoshSai Shankar, Chun-Ting Chou, and Monisha Ghosh

rDCF: A Relay-enabled Medium Access Control ProtorDCF: A Relay-enabled Medium Access Control Protocol for Wireless Ad Hoc Networkscol for Wireless Ad Hoc Networks• Hao Zhu and Guohong CaoHao Zhu and Guohong Cao

Cooperative Communication in Wireless NetworksCooperative Communication in Wireless Networks• Aria Nosratinia, Todd E. Hunter, and Ahmadreza HedayatAria Nosratinia, Todd E. Hunter, and Ahmadreza Hedayat

chungnam national university 1 협업 통신에서의 매체액세스제어 cooperative...

Documents