te novelty, and that was all. The future of cellular was a car phone future. In just a few years we knew that the market was larger and more based on hand- held phones than our wildest visions. However, even back in 1983, when cellular tele- phone service was just starting, we knew that we had to use radio spectrum more effi- ciently than AMPS, and we were working on a narrowband frequency division multiple access (FDMA) digital channel, a 6-kHz channel for voice. 2 Analog AMPS did give to digital systems, but these were time division multiple access (TDMA) and now CDMA rather than narrowband FDMA. The European GSM standard brought us a dig- 2We also explored higher-order digital constellations for voice privacy and cellular modems (data) within the AMPS channel. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Analog Wireless Telephony (AMPS) Analog Wireless Telephony (AMPS) ital channel more efficient than AMPS, and in the United States, CDMA systems brought a whole new approach to channel reuse with greater efficiency. When a cellular telephone is activated, it is located within the system through radio signal strength measurements and assigned a particular channel for call setup. If the phone moves to another cell, the movement is detected by the change in relative signal strength coming from the phone, and the phone is handed off to a different cell in the middle of a call. The switching of calls while they are in progress was an innovation to telephony engineering required by the cellular network. The important interference to control was cochannel interference from another cell other calls using the same frequency in other parts of the service area. Reuse patterns put the other transmitter far enough away from the serving cell to keep the interfer- ence level under control. Both AMPS (FDMA) and GSM (TDMA) use this method of managing co