The two major 2G cellular systems are not compatible with each other. GSM and CDMA networks are both widely used worldwide. For example, in the United States, Verizon Wireless, Sprint PCS, and ALLTEL are CDMA operators, whereas Cingular Wireless, AT & T Wireless (merged with Cingular in 2004), and T-Mobile USA are GSM operators. Another wireless operator, Nextel, uses iDEN, a TDMA technology developed by Motorola. While the Europeans enjoy continent-wide, GSM-dominated wireless services, the world’s largest mobile wireless market, China, with a total number of about 398 million subscribers as of 2005 (Source: Computer Industry Almanac Inc.), is basically shared by two companies: China Telecom, which operates a GSM network, and China Unicom, which operates both GSM and CDMA networks. Most differences between the two types of systems have been extensively discussed in the preceding sections, except speech encoding and power control. CDMA employs variable-rate codec for speech encoding, which is more efficient than GSM’s fixed-rate codec. Power control of CDMA systems requires a closed-loop approach, thus it is faster than GSM’s open-loop approach.

Source of Information :  Elsevier Wireless Networking Complete 2010


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