A high speed data modem for digital cellular radio

This paper describes an adaptive rate modem ideally suited for fading mobile radio channels. The modem adapts its information rate to the time-varying channel conditions by changing the code rate of a special trellis code. The modem exploits the unused capacity in the cellular radio channel and can quadruple the mean data rate of wireless modems. Because trellis coded modulation is used, the bandwidth and symbol rate are constant. A novel estimator and rate changing hardware ensure the modem can track and adjust to rapid multipath fading. The modem can be made backward compatible with existing TDMA digital cellular standards like IS-136 and GSM.