Cellular Networks Part 2 Prof. Abid Yahya yahyabid@gmail.com www.abidyahya.com

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)

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

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

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.

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

2G Technologies cdmaOne (IS-95) GSM, DCS-1900 IS-54/IS-136 PDC Uplink Frequencies (MHz) 824-849 (Cellular) 1850-1910 (US PCS) 890-915 MHz (Eurpe) 1850-1910 (US PCS) 800 MHz, 1500 Mhz (Japan) Downlink Frequencies 869-894 MHz (US Cellular) 1930-1990 MHz (US PCS) 935-960 (Europa) 1930-1990 (US PCS) 869-894 MHz (Cellular) 1930-1990 (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 1.2288 Mchips/sec 270.833 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

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: 40 -128 kbps data rates. Bankruptcy Flash-OFDM: 1.5 Mbps (upto 3 Mbps)

Major Mobile Radio Standards USA Type Year Intro Multiple Access Frequency Band (MHz) Modulation Channel BW (KHz) AMPS Cellular 1983 FDMA 824-894 FM 30 USDC 1991 TDMA DQPSK CDPD 1993 FH/Packet GMSK IS-95 Cellular/PCS CDMA 1800-2000 QPSK/BPSK 1250 FLEX Paging Simplex Several 4-FSK 15 DCS-1900 (GSM) PCS 1994 1850-1990 200 PACS Cordless/PCS TDMA/FDMA 300

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 890-960 12.5 GSM Cellular/PCS 1990 TDMA GMSK 200KHz C-450 450-465 20-10 ERMES Paging 1993 FDMA4 Several 4-FSK CT2 Cordless 1989 864-868 GFSK 100 DECT 1880-1900 1728 DCS-1800 Cordless/PCS 1710-1880 200

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)