1.4. Global System for Mobile and General Packet Radio Service

Although the world of wireless telecommunication experienced remarkable growth in terms of the number of subscribers at the beginning of the 21st century, some mobile wireless operators soon realized that mobile voice service was not enough. The industry has evolved from analog voice to digital voice, and now it is time to leverage high-speed data access provided by 2.5 and 3 G cellular networks for data-centric applications and services. Second-generation cellular systems can be divided into two categories according to the multiplexing access scheme of the radio interface: TDMA or CDMA. The TDMA systems include GSM, D-AMPS (also referred to as IS-136 to supersede IS-54), and packet data cellular (PDC, used in Japan). The CDMA category is fairly straightforward in that the cellular systems utilizing CDMA are also called CDMA systems and they comply with the IS-95 standard. In this section, we first review two second-generation cellular systems, GSM and CDMA (see Table 1.1), then discuss 2.5 G data services and 3 G cellular networks being rolled out worldwide. The introduction to GSM and CDMA focuses on the functional components and key operations.

Table 1.1. 2G Cellular Systems.

2G Cellular System Category	2G Cellular Systems
Time-division multiple access (TDMA)	Global system for mobile (GSM)
	Digitized advanced mobile phone system (D-AMPS) (IS-136)
	Packet data cellular (PDC)
Code-division multiple access (CDMA)	CDMA (IS-95)