Comparing the two most prevalent mobile communication technologies Apr-17 GSM vs. CDMA Comparing the two most prevalent mobile communication technologies

What is …? GSM (Global System for Mobile Communication) Based on TDMA technology Mainly used in Europe, Middle-east and Africa CDMA (Code Division Multiple Access) Based on a spread-spectrum technology Mainly used in North America

Technology: FDMA Transmission over Radio Frequency (800MHz – 1900MHz) Frequency Division Multiple Access An analog system. Each user is given one channel (i.e., one frequency). Bad utilisation. CH 3 CH 4 Frequency Time Power CH 1 CH 2

Technology: TDMA GSM uses TDMA (Time Division Multiple Access) CDMA is a "spread spectrum" technology, allowing many users to occupy the same time and frequency allocations in a given band/space. Each mobile station has a unique digital code. The signals are spread over the entire spectrum of 1.25MHz unlike FDMA/TDMA. Power Time Frequency Channel 1 Channel 2 Channel 3 Channel 4

Spectrum Mobile communication uses Radio Frequency (RF) Apr-17 Spectrum Mobile communication uses Radio Frequency (RF) GSM uses frequencies 824 – 849 MHz (25 MHz band) and 869 – 895 MHz (25 MHz band) The EMSpec.gif is from http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

Cellular Architecture Apr-17 Cellular Architecture HLR BSC A Abis VLR Um PSTN MSC BSC EIR AuC Mobile Station (MS) Subscriber Identity Module (SIM) International Mobile Equipment Identity (IMEI) Base Station subsystem, consisting of: Base Transceiver Station (BTS) Base Station Controller (BSC) Network subsystem, consisting of: Mobile services Switching Centre (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Equipment Identity Register (EIR) Authentication Centre (AuC) BTS Mobile Station Base Station Subsystem Network Subsystem

Cells The coverage area is divided into hexagonal cells Apr-17 Cells The coverage area is divided into hexagonal cells A BTS is situated at three of the vertices of each cell In USA, the spectrum in each cell is divided into two bands: A-band and B-band, each 25 MHz Each 25 MHz band is divided into 832 30 kHz channels Two channels separated by 45 MHz forms a full-duplex channel The number of channels used in a cell varies from as low as 4 to as many as 80 Cell Site

GSM Frames and Burst periods Apr-17 GSM Frames and Burst periods GSM has four types of burst. The above figure shows the normal burst that is used to carry data and most of the signalling. It has 156.25 bits of information. TCH – Traffic Channel SACCH – Assoc. Control Channel BP – Burst Period

Handover/Handoff Internal Handovers (only one BSC involved) Channels in the same cell Cells under the same BSC External Handovers (involved the MSC) Cells under different BSCs under the same MSC Cells under different MSCs (anchor MSC and relay MSC) Techniques used: Minimum acceptable performance: increase power i.s.o. handover Power budget: handover i.s.o. increasing power

Services SMS (Short Message Service) http://www.gsmworld.com/technology/sms/intro.shtml Facsimile (for receiving fax on a mobile station) WAP (Wireless Application Protocol) – a standard to let wireless equipment access the Internet. A Wireless Markup Language (WML) is used to encode the pages instead of HTML. MMS (Multimedia Message Service) EDGE (Enhanced Data rates for GSM evolution) The ever elusive “Killer app”

History and proponents Group Spéciale Mobile Cellular services started in Europe in 1982 13 operators in Europe sign a MoU in 1987 Radiolinja Oy became the first GSM network operator in 1992 cdmaOne (2G) IS-95A (First CDMA cellular standard) First deployed in Sep 1996 by Hutchison IS-95B (2.5G) First deployed in Sep 1999 in Korea CDMA2000 (3G) CDMA2000 1X (Phase 1) Deployed in Korea in 2000 CDMA2000 1x EV-DO CDMA2000 1x EV-DV

Standards and standardization GSM coordinated by 3GPP Release 99 Release 4 (was Release 2000) W-CDMA (Widebad CDMA) coordinated by 3GPP2 B-CDMA (Broadband CDMA) cdmaOne (2G) IS-95A 1.25MHz CDMA channels circuit switched data connections at 14.4kbps IS-95B (2.5G) CDMA2000 (3G) CDMA2000 1X (Phase 1)

Statistics (Geography-wise) Over 1 billion GSM subscribers Over 170 million CDMA subscribers

Statistics (Subscriber growth) Apr-17 Statistics (Subscriber growth) Data from www.gsmworld.com and www.cdg.com. In Feb 2004, GSM announced having reached 1 billion subscribers.

Glossary GPRS – General Packet Radio Service; GPRS represents first implementation of packet switching within GSM, precursor to 3G GGSN – Gateway GPRS Support Node; the gateway between the cellular network and the IP network

References GSM Association website, at http://www.gsmworld.com CDMA Development group, at http://www.cdg.com UMTS World, at http://www.umtsworld.com How Stuff Works: Cell Phones, at http://electronics.howstuffworks.com/cell-phone.htm Cellular Telephone Basics, at http://www.privateline.com/Cellbasics/Cellbasics.html GSM overview, at http://ccnga.uwaterloo.ca/~jscouria/GSM/gsmreport.html