Wireless Communication Overview

Generic WCS (Wireless Communication System)

Switch

BaseStation

BaseStation

HandsetHandsetPSTN

(Public SwitchedTelephone Network)

Dimensions• Carrier/Network Operator

– Spectrum, PSTN, Internet, …/ISP, Tele Service Provider

• Protocols/Standards/Systems– GSM, AMPS, DECT, PHS, Satellite, ...

• Network Elements– MSC, BSC, BTS, HLR/VLR, IN Elements, ...

• Services/Applications/Service Platform– Voice call, data call, add-on services, ...

• Handset/Terminals/Smart Phone/Wireless Info Appliance– OS, User-Interface, Protocol suite

• Subscriber Behavior

Essential Functions

• Initialization– Register

• Bursty Data/Signaling Transmission– Paging, channel assignment, control signaling,

signaling data, ...

• Mobility– Handoff, roaming

Wireless Communication Challenges

• Resources– Bandwidth– Channel impairment/fading– Utilization

• Mobility– Handover, Roaming– Location management– User access behavior

• Services– Security, Data, ...

• Terminal Equipment• Energy

Technology Trend

AnalogVoice

DigitalVoice

WirelessMultimedia

Narrow bandNarrow band Wide band

Mobile PhoneMobile Phone Mobile Phone +Wireless Data

Wireless InfoAppliance

High-Tier v.s. Low-Tier Systems

• High-Tier Systems– Serving a highly mobile population by means of

sophisticated high-power radios– Larger cell diameter– Higher transmitter power

• Low-Tier Systems– Serving subscribers moving at walking speeds– Smaller cell diameter– Lower transmitter power

A System View

• High-Tier Systems– GSM, DAMPS, CDMA– Satellite Systems

• Low-Tier Systems– CT-2, DECT, PHS, PACS

Existed System Study (1)GSM

(Global System for Mobile Communications)

Outline

• Overview• Architecture• Numbering & Routing• Essential Functions• Air Interface• Dual Band Network Study

GSM Overview

• GSM – Developed by European Community– Following ISDN– Classified as Tele services and Data services– International roaming– Radio transmission is based on TDMA (Time

Divide Multiple Access)

GSM Air Resource Allocation

• Spectrum– Uplink Band

• 890 - 915 MHz

– Downlink• 935-960 MHz

– Spacing• Duplex spacing: 45 MHz• Channel spacing: 200 KHz• Total channel number: 124• Number of slots per channel

GSM Network Components

• MSC: Mobile Switching Center

• BSC: Base Station Controller

• BTS: Base Transceiver Station

• HLR/VLR: Home Location Register/Visting Location Register

• SIM Card: Subscriber Identity Module Card

• Handset• Service Center

GSM System Architecture

PSTN

Data Terminal

HLR/VLR

MSCBSC

OMC(Operation & Maintenance

Center)

OperationTerminal

BTSHandset

A

X.25

A-bis SS7

Network sub-system PSTNRadiosub-system

Mobilestation

UM

SIM Card

• Subscriber Identity Module– Contains

• phone number (MSISDN)• international mobile subscriber identity (IMSI)• status of SIM• service code• authentication key• PIN (personal identification code)• PUK (personal unlock code)

Numbering

• Mobile Subscriber ISDN Number (MSISDN)– Mapping to Mobile Station Roaming Number (MSRN)

by HLR

• International Mobile Subscriber Identify (IMSI)– Stored in SIM/HLR

• Temporary Mobile Subscriber Identity (TMSI)– Assigned by VLR, Stored in VLR

• International Mobile Equipment Identity (IMEI)– Unique ID to handset, used by air interface

Routing

• Information resident in MS & SIM– IMSI, TMSI, IMEI, and misc. information

• Routing Information used by Network– MSISDN, MSRN

Location Information Hierarchy

• Location Area HierarchyHLRHLR

VLRVLR VLRVLR

MSC1MSC1 MSC2MSC2

LA1LA1

HLR: Home Location RegisterVLR: Visitor Location RegisterMSC: Mobile Switching CenterLA: Location AreaMS: Mobile StationLA2LA2

Location Information• Determines subscriber current location• Inform network when subscriber enters a new cell• Have to trade-off between paging and location

update traffic in system planning• Location info contained in

– Mobile country code, mobile network code, location area code, cell ID

• Location information is the major burden for network

GSM Essential Functions

• Registration/Location Updating• Establishing Communication Link• Handover• Roaming

Registration/Location Updating

• Inform system the new location of a MS when it changes Location Area (LA)

• MS continuously measures signal strength to choose the best radio base station

• The mobile station tunes to a new base station with better signal strength

Establish Communication Link

• Handset request available channel from BTS• BTS forward the request to BSC• BSC chooses an available channel and inform

BTS to activate the channel• Information the BSC channel assignment message

carries – a reference number– information about allocated channel (type, frequency,

time slot, …)– the initial transmission power level to be used by the

handset

Handover

• The process of changing cells during a call is called handover in GSM terminology.

• The measurements to choose the best target cell are performed by MSs and BTSs.

• The measurements from the MS and the BTS are processed in the BSC. This evaluation process is called locating.

Roaming

• A subscriber moves from the service area of his/her home service company(or network) to another operating company(or network)

Wireless Data

Computing & Communication

Wireless Information Devices

LaptopCommunicatorSmartphone

PDAMobilePhone

Communication Computing

Wireless Voice & Data Dominate Wireline

0

1000

2000

3000

4000

5000

Revenuemillions

1993 1994 1995 1996 2000?

Internet data calls

Local fixed voice

Mobile telephony

Typical Internet Service Requirements

• Long (or continuous) sessions• Multiple overlay sessions• High degree of burstiness• Large span in QoS requirements

Fundamentally difference from voice telephony

Challenges

• IP network• Protocols• New data services • Generic service platform• Information appliances (Handhelds, Palm d

evices, Smart phones, In-Car systems)

Lots of bandwidth

Today’s GSM Data Services

• SMS (Short Message Service)

• USSD (Unstructured Supplementary Service Data)

• HSCSD (High Speed Circuit Switched Data )

• GPRS (General Packet Radio Services)

• EDGE (Enhanced Data rates for GSM Evolution)

Convergence GSM/IP Network

• H.323• WAP

H.323 Architecture

HLR

MAP

SS7 Network

Terminalgateway Gatekeeper1

Gatekeeper1

Switch

Home ServiceSystem

PSTN

Visiting MS

WAP (Wireless Application Platform)

Wireless Network

FilterFilter

WebServer

WebServer

Filter

WAP Proxy

WAPProxy

Wireless M

arkup L

anguage

Future GSM

SIM Card

GSMmobile

GSM/UMTSmobile

UMTSmobile

Internet(TCP/IP)

BSC (UMTS)

UMTS(IMT-2000)Base Station

BSC (GSM)

GSMBase Station

Co-sited GSM+UMTS Base

Station Subsystem

GGSNSGSN

GPRS+UMTS

Landline NW(PSTN/ISDN)

Network Subsystem(GSM+UMTS)

MSC/HLR(GSM+UMTS)

HLRMSC

IN servicecontrol point

SIM

GSM Radio Steps to 3rd Generation

Development of Radio Technology

Evolution of GSM Platform

Introduction of 3rd generation radio2001 - 2002New multimedia servicesMass market cost of service (IMT-2000)

2000More capacity when needed (GSM384)

1999Internet-like IP packet services (GPRS)

1998Landline-like circuit services (HSCSD)

1997Basic GSM data at 9.6 kb/s

Air Interface Protocols

• SS7– Between PSTN and PLMN ( Public Land Mobile Netw

ork)• X.25

– BSC and Operation centers• A

– Between BSC and MSC• A-bis

– Between BTS and BSC• Um

– Radio interface between BTS and Handset

Air Interface Messages

• RR: Radio Resource Management Messages

• MM: Mobility Management Messages• CM: Call Management Messages

Trafficchannels

Signalingchannel

Full-rateTCH/F

half-rateTCH/H

Frequency correctionFCCH

SynchronizationSCHBroadcast controlBCCHPagingPCHAccess grantAGCHRandom accessRACH

Stand-alone dedicatedcontrol SDCCHSlow associatedcontrol SACCHFast associatedcontrol FACCH

Two-way

Base-to-mobile

Two-way

Air Interface--Channels

Dual Band Network

GSM 900 DCS 1800

Uplink Band 910.20-914.80MHz

1732.60 -1743.60MHz

Downlink Band 955.20-959.80MHz

1827.60-1838.60 MHz

ChannelSpacing

200 kHz 200 kHz

Total Numberof Channels

24 56

Dual Band Network : GSM 900 & DCS 1800 Air Interface

GSM 900 DCS 1800

Uplink Band 890-915 MHz 1710-1785MHz

Downlink Band 935-960 MHz 1805-1880MHz

Channel Spacing 200 kHz 200 kHz

Total Number ofChannels

124 374

Duplex Spacing 45 MHz 95 MHz

Number ofTimeslots per

Channel

8 8

GSM/DCS Network Differences

• DCS 1800 cells are generally coverage limited

• GSM 900 cells tend to be capacity limited• Implying a need for more DCS 1800 cells

to provide similar coverage to a comparable GSM 900

Integrate GSM and DCS Networks

• Integrating 900 and 1800 networks by linking 900/1800 cells to same BSC: An Integrated dual band network– Sharing BSC, MSC, and HLR

• Benefits– Reuse existing resources

• Reuse spectrum means to enlarge the scalability of network and to improve the utilization of spectrum resource

– Simplify the handoff between networks– Flexible and changeable infrastructure

Integrated Dual Band Network

MSC

BSC

DCSBTS

DCSBTS

DCSBTS

GSMBTS

GSMBTS

GSMBTS