The Wireless Communication System
Wireless Communication
• Cellular phone system
• Cordless telephone system
• Bluetooth
• Infrared communication
• Microwave communication
• IEEE Wireless LANs (Wi-Fi)
• Satellite communication
Why “Cellular”?
Three Generations
AMPS
WCDMA
NMT GSM
CDMA2000
TACS GPRS
TD SCDMA
HCMTS
1G 2G 3G
1G
• 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
FDMA
• 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
FDMA
Shortage
• Voice information only
• Unsafe （ eavesdropping ）
• Waste of frequency resource
2G
• Start early 90’s
• Digital technique
• GSM : Global System of Mobilephone
• GPRS : General Packet Radio Service
• D-AMPS : Digital AMPS
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 / TDMA
Network Structure
BTS,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
Databases
• 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)
GPRS
• Upgrade of existed GSM network
• Improves the data communication ability
GPRS
Network nodes
• GGSN: Gateway GSM Support Node,
• Protocol transferring, data encapsulation, a connection to external
networks
• SGSN: Service GSM Support Node,
• Communicate with HLR and mobile handsets,
authorization and admission
control, charging, mobility management
Data 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 GPRS
• Higher data rate
• Seamless connection to internet
• Packet 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
shortage
• Not fast enough for the multimedia service
• The data rate falls when the network is busy
• Upgrade of handset
3G
3G-Standards
• Three CDMA standards approved by ITU:
• Direct Spread CDMA(WCDMA) : Europe, Japan
• Multi-Carrier CDMA(CDMA 2000) : North America
• TD-Synchronous CDMA(CDMA TDD) : Europe, China
3G-CDMA
• Code Division Multi Address
• Spread spectrum technology
• Each 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
CDMA
Features
• Better voice quality
• Up to 2 Mbps data communication rate
• Increase battery life
• Soft hand-off
• Excellent data safety
• More effective spectrum usage than 2G
Conclusion
Conclusion
1G 2G 3G
Voice Quality OK OK Good
Data N/A ~115K ~2M
communication
Spectrum usage X 5~6X 10~20X
Communication Weak OK Good
safety
References
• 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.html
• www.itu.int/home/imt.html
• http://www.boeschatt.at/Mobil/mobilfunk_html.php?
gsm_netzarchitektur.php
• http://www.pt.com/products/gsmintro.html
