s in the same band as the current U.S. analog cellular band (AMPS) in which full-duplex operation is achieved by using frequency division duplexing (FDD) with 25 MHz in each direction, with an uplink of 869-894 MHz mobile-to-cell band and a downlink of 824-849 MHz cell-to-mobile band. For AMPS, each analog cellular signal occupies 30 kHz in each direction in a standard FDMA sys- tem. In IS-95, the 25 MHz in each direction is divided into 20 FDMA bands. In each 1.25-MHz band (each direction), direct-sequence spread- spectrum signals are used in a CDMA system. The implementation strat- egy is to introduce this higher-capacity IS-95 system one CDMA system (1.25-MHz band) at a time, using the dual-mode (AMPS and CDMA) mobile units. Among the modulation and coding features of this system are the fol- lowing: Direct-sequence spreading with quadrature phase-shift-keying (QPSK) modulation Nominal data rate of 9600 bps Chip rate of 1.25 MHz Filtered bandwidth of 1.25 MHz The Digital Cellular CDMA Standard Convolutional coding with Viterbi decoding Interleaving with 20-msec span Details for the modulation and coding differ for the uplink and down- link channels. Pilot signals transmitted by each cell site aid the mobile radios in acquiring and tracking the cell site downlink signals. The strong coding enables these radios to operate effectively at Eb/No in the 5-dB to 7-dB range. To minimize mutual interference, this CDMA system uses power control and voice activation circuits. Voice activation occurs in the form of a vari- able-rate vocoder that operates from a high of 8 kbps down to 4 kbps, 2 kbps, and a minimum of 1 kbps, depending on the level of voice activation. With the decreased data rate, the power control circuits can reduce the transmitter power for the lower data rates to achieve the same bit error rate performance. Tight power control, along with voice activation circuits, is crit- ical for avoiding excessive transmitter signal power, which contributes to the overall interference level in this interference-lim