Performance Comparison of Cellular Mobile Communication Systems and their Implementation in Yemen

Abstract

Analog cellular systems are the first generation of cellular systems. These systems use analog frequency modulation (FM) and have a frequency division multiple access (FDMA) based media access control architecture. Second-generation cellular systems primarily use digital modulation and processing techniques and time division multiple access (TDMA). As of 1995, several million TDMA digital cellular subscriber units are operational. These second-generation systems include the GSM (Global System for Mobile Communications), ADC ( American digital cellular IS-54 Standard and JDC, Japanese digital cellular. Third–generation systems using spread-spectrum techniques like code-division multiple access (CDMA), have also been standardized and are now operational in
many countries. System and equipment development in the US led to the adoption of the IS-95 standard for cellular digital communication in the 900 MHz frequency band. In Yemen, mobile communications started by Tele-Yemen company in the 1990s, using FDMA systems. In the year 2000, two other companies, Sabafon and Spacetel started their GSM service, and it is now covering a great part of the country. The government also introduced some isolated mobile services in rural areas. This paper aims to study second- and third-generation cellular systems which are operating or likely to operate in Yemen and to investigate the
performance of these systems. The comparison reveals that CDMA and spread-spectrum systems are superior and suitable for new generations of system applications.

1. INTRODUCTION
The cellular concept began to appear in Bell system proposals during the late 1940s. This idea introduced a new model for mobile radio in which the ‘ broadcast model’ of a high power transmitter, placed at a high elevation, transmitting the signal to a large area was replaced by many lower-power transmitters, each specifically designed to serve only a small area called a cell. The same frequencies (channels) could be reused in different cells with sufficient distance, where the effect of interference between users of the same channel was negligible. The important features of cellular systems are [Feher, 1999 ]:
• Low power transmitters and small coverage zones.
• Frequency reuse.
• Cell splitting to increase capacity.
• Hand-off and central control.
In December 1971, the Bell system submitted a proposal for a new analog cellular FM radio system – The High Capacity Mobile Telephone System (HCMTS). The Federal Communications Commission accepted the proposal, and a spectrum of 40 MHz in the 850-
MHz band was allocated for this system. The US analog standard of the 1980s and 1990s for cellular radio- Advance Mobile Phone Service (AMPS) – evolved from the HCMTS. Several other similar systems were developed in Europe and elsewhere but there was no
worldwide standard for the cellular service at that time. These first generation cellular systems suffer from two drawbacks: capacity limits as the system become more popular and incompatibility which makes it impossible for a person to use the same cellular phone in different countries. These limitations motivated the development of second-generation cellular systems with the goal of achieving higher capacity and improved compatibility.