1. Cellular Networks Part 2
Prof. Abid Yahya

2. Second Generation Cellular
Based on digital transmission
Different approaches in US and Europe
US: divergence
Only one player (AMPS) in 1G
Became several players in 2G due to competition
Survivors
IS-54 and IS-135: backward compatible with AMPS frequency allocation (dual mode - analog and digital)
IS-95: uses spread spectrum
Europe: Convergence
5 incompatible 1G systems (no clear winner)
European PTT development of GSM (uses new frequency and completely digital communication)

4. Advantages of Digital Communications for Wireless
Voice, data and fax can be integrated into a single system
Better compression can lead to better channel utilization
Error correction codes can be used for better quality
Sophisticated encryption can be used

5. Differences Between First and Second Generation Systems
Digital traffic channels – first-generation systems are almost purely analog; second- generation systems are digital
Encryption – all second generation systems provide encryption to prevent eavesdropping
Error detection and correction – second- generation digital traffic allows for detection and correction, giving clear voice reception
Channel access – second-generation systems allow channels to be dynamically shared by a number of users

6. GSM (Global System for Mobile Communications)
Completely designed from scratch (no backward compatability)
Uses 124 channels per cell, each channel can support 8 users through TDM (992 users max)
Some channels used for control signals, etc
Several flavors based on frequency:
GSM (900 MHz)
GSM 1800 (called DCS 1800)
GSM 1900 (called DCS 1900) - used in North America
GSM 1900 phone only works in North America.
In Europe, you can transfer your SIM (Subscriber Identity Module) card to a phone of the correct frequency. This is called SIM- roaming.

10. Mobile Station and Base Station Subsystem (BSS)
Mobile station communicates across Um interface (air interface) with base station transceiver in same cell as mobile unit
Mobile equipment (ME) – physical terminal, such as a telephone or PCS
ME includes radio transceiver, digital signal processors and subscriber identity module (SIM)
GSM subscriber units are generic until SIM is inserted
SIMs roam, not necessarily the subscriber devices
BSS
BSS consists of base station controller and one or more base transceiver stations (BTS)
BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging

11. 2G Technologies cdmaOne (IS-95) GSM, DCS-1900 IS-54/IS-136 PDC
Uplink Frequencies (MHz)
(Cellular)
(US PCS)
MHz (Eurpe) (US PCS)
800 MHz, 1500 Mhz (Japan)
Downlink Frequencies
MHz (US Cellular) MHz (US PCS)
(Europa)
(US PCS)
MHz (Cellular) (US PCS)
800 MHz, 1500 MHz (Japan)
Deplexing
FDD
Multiple Access
CDMA
TDMA
Modulation
BPSK with Quadrature Spreading
GMSK with BT=0.3
p/4 DQPSK
Carrier Seperation
1.25 MHz
200 KHz
30 KHz (IS-136) (25 KHz PDC)
Channel Data Rate
Mchips/sec
Kbps
48.6 Kbps (IS-136) 42 Kbps (PDC)
Voice Channels per carrier 64 8 3
Speech Coding
CELP at 13Kbps EVRC at 8Kbps
RPE-LTP at 13 Kbps
VSELP at 7.95 Kbps

12. Alternatives to 3G Cellular
Major technical undertaking with many organizational and marketing overtones.
Questions about the need for the additional investment for 3G (happy with 2.5G)
Wireless LAN in public places such as shopping malls and airports offer options
Other high-speed wireless-data solutions compete with 3G
Mobitex low data rates (nominally 8 Kbps), it uses a narrowband (2.5KHz) as compared to 30 KHz (GSM) and 5 MHz (3G).
Ricochet: kbps data rates. Bankruptcy
Flash-OFDM: 1.5 Mbps (upto 3 Mbps)

13. Major Mobile Radio Standards USA
Type
Year
Intro
Multiple Access
Frequency Band
(MHz)
Modulation
Channel BW
(KHz)
AMPS
Cellular
1983
FDMA FM 30
USDC
1991
TDMA
DQPSK
CDPD
1993
FH/Packet
GMSK
IS-95
Cellular/PCS
CDMA
QPSK/BPSK
1250
FLEX
Paging
Simplex
Several
4-FSK 15
DCS-1900 (GSM)
PCS
1994
200
PACS
Cordless/PCS
TDMA/FDMA
300

14. Major Mobile Radio Standards - Europe
Type
Year
Intro
Multiple Access
Frequency Band
(MHz)
Modulation
Channel BW
(KHz)
ETACS
Cellular
1985
FDMA
900 FM 25
NMT-900
1986
12.5
GSM
Cellular/PCS
1990
TDMA
GMSK
200KHz
C-450
20-10
ERMES
Paging
1993
FDMA4
Several
4-FSK
CT2
Cordless
1989
GFSK
100
DECT
1728
DCS-1800
Cordless/PCS
200

15. 4G Systems
Wireless networks with cellular data rates of 20 Mbits/second and beyond.
AT&T has began a two-phase upgrade of its wireless network on the way to 4G Access.
Nortel developing developing features for Internet protocol-based 4G networks
Alcatel, Ericsson, Nokia and Siemens found a new Wireless World Research Forum (WWRF) for research on wireless communications beyond 3G.
Many new technologies and techniques (multiplexing, intelligent antennas, digital signal processing)
Industry response is mixed (some very critical)