Types of Cellular Systems

Unlike in most other countries, the United States has several different and incompatible types of digital cellular phone systems in operation. Each offers different advantages and disadvantages for both voice and data connections. Table 12.1 shows how, as time progresses, the maximum data capabilities will grow increasingly fast, from 14.4Kbps to 384Kbps.

Table 12.1. The Evolution of U.S. Cellular Phone Data Capabilities

Second-Generation (2G) Cellular Technology	"2.5G" Cellular Technology	Third-Generation (3G) Cellular Technology
CDMA	1XRTT	3XRTT (CDMA2000)
GSM	GPRS, EDGE	WCDMA
TDMA	EDGE	WCDMA

The various digital cellular systems you might encounter include the following:

• CDPD Cellular Digital Packet Data was one of the first techniques used to carry digital information over cellular voice networks. This system worked by implanting small packets of digital data into the unused intervals of traditional analog cellular voice channels. This technology is employed mainly by corporations and public service organizations to send small amounts of textual information. Note that its maximum data-transfer rate is only 19.2Kbps. Both AT&T Wireless and Verizon Wireless offer this service in the United States.

• CDMA Code Division Multiple Access is currently the most popular digital cellular technology in the U.S. It is used in both the traditional cellular frequency band of 800MHz and the PCS band of 1900MHz. With the exception of Europe, CDMA is also the digital network technology of choice outside the U.S. For data transfers, CDMA technology has been limited to a maximum speed of only 14.4Kbps. Gradually, CDMA networks are being upgraded to offer packet-switched speeds of 64384Kbps. The major cell phone companies that use CDMA wireless networks include Verizon Wireless and Sprint PCS.

• CDMA2000 A trade name for 3xRTT cellular networks.

• 1XRTT An intermediate evolutionary step for CDMA cellular networks. The 1XRTT networks support data-transfer rates of 153Kbps. Eventually, 1XRTT systems will evolve into 3XRTT systems (also called CDMA2000).

• 3XRTT A third-generation cellular system designed as an evolutionary step for CDMA cellular systems. The 3xRTT systems can transport data at a rate of 307Kbps. This technology is also known by the trade name CDMA2000.

• TDMA Time Division Multiple Access is perhaps the oldest digital cellular technology in the U.S. The data-transfer rate for traditional TDMA systems is a mere 9.6Kbps. Future TDMA networks will offer faster packet data communications, up to 384Kbps. AT&T has been a prime backer of TDMA technologies.

• GSM The Global System for Mobile Communications is the cellular phone standard in Europe and several other parts of the world. In the U.S., its market share is growing. The original data throughput was a measly 9.6Kbps. New 3G systems based on EDGE or GPRS will eventually bump the speed up to 384Kbps. T-Mobile is the primary user of GSM technology in the United States.

• GPRS The General Packet Radio System is an intermediate upgrade from GSM cellular technology. A typical GPRS device, such as the Sierra Wireless AirCard 750, is claimed to have a theoretical maximum data rate of 83Kbps, but actual user throughput will likely be 3056Kbps. The next step for these cellular systems is EDGE.

• EDGE Enhanced Data for GSM Efficiency (or Enhanced Data-rates for Global Evolution) is an upgrade for GPRS and TDMA cellular systems. It provides a peak data-transfer rate of 384Kbps. The next step for these cellular systems is WCDMA.

• WCDMA Wideband CDMA is the latest and fastest level of evolution for today's GSM and TDMA cellular networks. It is said to have a sustained data rate of 384Kbps.