The Wireless Communication System

The Wireless Communication The Wireless Communication SystemSystem

Xihan Lu

Wireless CommunicationWireless Communication

Cellular phone systemCordless telephone systemBluetoothInfrared communicationMicrowave communicationIEEE Wireless LANs (Wi-Fi)Satellite communication

Why “Cellular”?Why “Cellular”?

Three GenerationsThree Generations

AMPSNMTTACS

HCMTS

GSMGPRS

WCDMACDMA2000TD SCDMA

2G 3G1G

1G1G

Start early 80’s Analogue technique AMPT (Advanced Mobile Phone System): North

America NMT (Nordic Mobile Telephony): North Europe TACS (Total Access Communication Service): Europe,

China

HCMTS (High Capacity Mobile Telephone System):

Japan

FDMAFDMA

Frequency Division Multiple Access Different carrier frequencies are assigned to

different traffic channels(speech)One carrier frequency can only carry one

single speech channel at one time

FDMAFDMA

ShortageShortage

Voice information onlyUnsafe （ eavesdropping ）Waste of frequency resource

2G2G

Start early 90’sDigital techniqueGSM : Global System of Mobilephone GPRS : General Packet Radio Service

D-AMPS : Digital AMPS

GSM GSM

TD/FDMA: A mix of FDMA and TDMA The whole useable spectrum was divided to many

200k Hz carrier frequencies —FD Each carrier was divided into 8 timeslots (burst) —TD Each burst is assigned to a user(a logical traffic

channel) One carrier frequency can carry up to 8 logical traffic

channels (voice or data) at the same time The maximum data communication rate is 14.4 kbps

FD / TDMAFD / TDMA

Network StructureNetwork Structure

BTS,BSC and MSCBTS,BSC and MSC

BTS & BSC: Base Transceiver System and

Base Station Controller. Radio signal transceiver, a connection between handset and MSC

MSC: Mobile services Switching Center, switching center of the GSM network, and connect to other networks

DatabasesDatabases HLR : Home Location Register, contains static

information of subscribers and location update data VLR : Visitor Location Register, embedded in MSC

to avoid delay, contains current location information of handsets

AUC : Authentication Center, stores secret keys for authentication and encryption of the radio channel

EIR : Equipment Identity Register, contains a list of all valid mobile equipment in the network, by its International Mobile Equipment Identity (IMEI)

GPRSGPRS

Upgrade of existed GSM networkImproves the data communication ability

GPRSGPRS

Network nodesNetwork nodes

GGSN: Gateway GSM Support Node,Protocol transferring, data encapsulation, a

connection to external networksSGSN: Service GSM Support Node,Communicate with HLR and mobile

handsets, authorization and admission control, charging, mobility management

Data communicationsData communications

In GSM, one user occupies one traffic channel to exchange voice/data information

In GPRS, up to 8 traffic channels(a whole carrier) can be dynamically combined together for one data communication application

The theoretically maximum data transmission rate: 14.4k bps * 8 = 115.2k bps

Advantages of GPRSAdvantages of GPRS

Higher data rateSeamless connection to internetPacket switching rather than circuit switch,

bandwidth is only used when the data is actually used, even though it is always connected

A primary step to 3G

shortageshortage

Not fast enough for the multimedia serviceThe data rate falls when the network is busyUpgrade of handset

3G3G

3G-Standards3G-Standards

Three CDMA standards approved by ITU:Direct Spread CDMA(WCDMA) : Europe,

JapanMulti-Carrier CDMA(CDMA 2000) : North

AmericaTD-Synchronous CDMA(CDMA TDD) :

Europe, China

3G-CDMA3G-CDMA

Code Division Multi AddressSpread spectrum technologyEach single traffic channel occupies the

whole spectrum, but distinguished by a unique digital code

Walsh code: an orthogonal 64 bit pattern, unique in the network

CDMACDMA

FeaturesFeatures

Better voice qualityUp to 2 Mbps data communication rateIncrease battery lifeSoft hand-offExcellent data safetyMore effective spectrum usage than 2G

ConclusionConclusion

ConclusionConclusion

1G 2G 3G

Voice Quality OK OK Good

Data communication

N/A ~115K ~2M

Spectrum usage X 5~6X 10~20X

Communication safety

Weak OK Good

ReferencesReferences

www.gsmworld.com/technology/gprs/index.html www.3gsmamericas.com/pdfs/EOF_Cannes_2003/

Nortel_David_Smith.pdf http://www.fcc.gov/Bureaus/Wireless/Reports/fcc98091.pdf www.rogers.com http://www.itu.int/ITU-D/ict/publications/wtdr_99/material/glossary.ht

ml www.itu.int/home/imt.html http://www.boeschatt.at/Mobil/mobilfunk_html.php?gsm_netzarchitek

tur.php http://www.pt.com/products/gsmintro.html