WIRELESS SYSTEM

AND NETWORKING

References: •Rappaport (Chapter 9 and 10)

•Bernhard (Chapter 3, 4 and 5)

•Garg (Chapter 8 and 9)

•Kaarenen (Chapter 1-5 and 9)

LECTURE 6

Japan Europe Americas

1st Gen TACS NMT/TACS/Other AMPS

2nd Gen PDC GSM TDMA CDMA

3rd Gen (EDGE in Europe and Asia

outside Japan) EDGE cdma2000 W-CDMA/EDGE

WIRELESS EVOLUTION

GSM

• Formerly: Groupe Spéciale Mobile (founded 1982) but now: Global

System for Mobile Communication

• Pan-European standard (ETSI, European Telecommunications

Standardisation Institute)

• Simultaneous introduction of essential services in three phases

(1991, 1994, 1996) by the European telecommunication

administrations - seamless roaming within Europe possible

• Today many providers all over the world use GSM (more than 170

countries in Asia, Africa, Europe, Australia, America)

• More than 500 million subscribers (April 2001)

GSM - Network Architecture

GSM - Protocol Stack

GSM - Logical Channel

GSM - Control Channel

•Control channels fall into three categories: – Broadcast: BCCH, FCCH, SCH

– One way, from base to mobile

– Common Control: RACH, AGCH, PC – One way, some from base to mobile and some from mobile to the base

– Dedicated: SDCCH, SACCG, FACCH – Two-way, stand-alone or embedded in the traffic channels

• All signaling channels share one carrier in a cell – the dedicated control channels may be transmitted on traffic carriers

•Broadcast Channels • Frequency Correction Channel (FCCH)

– Carries information for frequency correction

• Synchronization Channel (SCH) – Carries information for frame synchronization and for

identification of the BTS

• Broadcast Control Channel (BCCH) – Broadcasts general information on the BTS

– Broadcasts cell-specific information, e.g. control channel organization,

frequency hopping sequences, cell identification, etc.

GSM - Control Channel

•Common Control Channels • Paging Channel (PCH) - downlink only downlink only

– for paging purposes

• Random Access Channel (RACH) - uplink only uplink only – used by any MS to request allocation of a signalling channel (SDCCH)

– a slotted Aloha protocol is used, so collisions among MSs may happen

• Access Grant Channel (AGCH) - downlink only

– used to allocate a SDCCH or a TCH

• Notification Channel (NCH) - downlink only – notify MS of voice group and voice broadcast calls (ASCI feature)

• Dedicated Control Channels

• Stand Alone Dedicated Control Channel (SDCCH) – used for call setup (authentication, signaling, traffic channel assignment),

location updates and SMS

• Slow Associated Control Channel (SACCH) – always coupled with a SDCCH or TCH

– for communicating measurement data and control parameters

• Fast Associated Control Channel (FACCH)

– to response to increased signaling demand, e.g. during handover

– bandwidth (bit slots) are stolen from the associated TCH

(traffic data are preempted)

GSM - Traffic Channel • GSM support two types of traffic channels

– full rate (TCH/F): 22.8 kbps

– half rate (TCH/H): 11.4 kbps

• Mapping to physical channel – full rate traffic channel - 1 timeslot

– half rate traffic channel - 1 timeslot in alternating frames

• Full rate channel may carry – 13 kbps speech or data at 2.4, 4.8 or 9.6 kbps

• Half rate channel may carry – 6.5 kbps speech or data at 2.4 or 9.6 kbps

• The carriers in a given cell are separated by Nx200 kHz – N is the frequency reuse cluster size (4 in GSM)

• The traffic carriers have 26-multi-frame structure

• The control carrier has 51- multi-frame structure

• The control carrier has higher energy than traffic carriers

• Reuse the existing GSM infrastructure

• Introduce packet-switched routing functionality

– Better data transfer rates

– Low cost and connectivity-oriented

• Migration Path to 3G Networks

• Share radio resources: users share a pool of channels

– Channels are allocated to users only when packets are to be sent or received

– Users can use several time slots (packet data channels) simultaneously

• Volume-charging: charging is based on traffic volume instead of the duration of a session

• Comparison

– Packet-switched

• High bit rates (up to 170kbit/s)

• Short access times

• Friendly bill (based on volume)

• Robust application support – Frequent transmission of small volumes

– Infrequent transmission of small or medium volumes

GPRS

• New components introduced for GPRS services: SGSN (Serving GPRS Support Node), GGSN (Gateway GPRS Support Node) and IP-based backbone network

• Old components in GSM upgraded for GPRS services: HLR, MSC/VLR and Mobile Station

• SGSN – At the same hierarchical level as the MSC.

– Transfers data packets between mobile stations and GGSNs.

– Keeps track of the individual MSs’ location and performs security functions and access control.

– Participates into routing, as well as mobility management functions.

– Detects and registers new GPRS MSs located in its service area

• GGSN – Provides inter-working between PLMN and external packet-switched

networks.

– Converts the GPRS packets from SGSN into the appropriate packet data protocol format (e.g., IP or X.25) and sends out on the corresponding packet data network.

– Participates into the mobility management.

– Maintains the location information of the mobile stations that are using the data protocols provided by that GGSN.

– Collects charging information for billing purpose.

GPRS ARCHITECTURE

– Circuit-switched

• Low bit rates (maximum 14.4kbit/s)

• Long access times

• Unfriendly bill (based on duration)

• Limited application support

– Large volumes

• Architecture

GPRS

• Backbone network

– Tunnels of data and signaling messages between GPRS support nodes.

– Protocol architecture based on the Internet Protocol (IP).

– GTP (GPRS Tunneling Protocol) used to tunnel user data and signaling between GPRS Support Nodes. All PDP (Packet Data Protocol) PDUs (Protocol Data Units) shall be encapsulated by GTP.

– Two kinds of GPRS backbone Network:

• Intra-PLMN backbone network: The IP network interconnecting GSNs within the same PLMN.

• Inter-PLMN backbone network: The IP network interconnecting GSNs and intra-PLMN backbone networks in different PLMNs.

– Two intra-PLMN backbone networks are connected via the Gp interface using Border Gateways and an inter-PLMN backbone network.

– Border Gateway handles the packet transfer between GPRS PLMNs.

• HLR

– Enhanced with GPRS subscription data and routing information.

– Accessible from the SGSN via the Gr interface and from the GGSN via the Gc interface.

GPRS ARCHITECTURE

Inter-PLMN Backbone

Packet Data Network

Intra-PLMN Backbone Intra-PLMN Backbone

GGSN BG

SGSN SGSN

BG GGSN

SGSN

Gi Gi Gp

GPRS ARCHITECTURE - Backbone

• MSC/VLR

– Not needed for routing of GPRS data.

– Needed for the co-operation between GPRS and the other GSM services. e.g.,

• Paging for circuit-switched calls that can be performed more efficiently via the SGSN

• Combining GPRS and non-GPRS location updates

– Receives location information from SGSN or sends paging requests to SGSN

via the Gs interface. • Mobile Station

– GPRS MS includes two components:

• MT (Mobile Terminal). Typically a handset used to access the radio interface.

• TE (Terminal Equipment). Typically a laptop or a Personal Digital Assistant (PDA).

– Could be one unit combing the functionalities of a MT and a TE.

– Three types of MS:

• Class-A: Could be attached to both GPRS and other GSM services, and the MS supports simultaneous operation of GPRS and other GSM services.

• Class-B: Could be attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time.

• Class-C: Could be exclusively attached to one service type at a given time.

GPRS ARCHITECTURE

GPRS - Protocol Stack

UTRAN - Architecture

UTRAN - Protocol Stack

INTRODUCTION

INTRODUCTION