The symbol error probability (SEP) of a digital signal processor implemented /spl pi//M M-ary differentially coherent phase-shift keying (MDPSK) modem, using quasi-analytical (QA) simulation techniques, is the subject of this investigation. We study M values of 4, 8, 16, 32, and 64 for use in a fast adaptive data rate mobile radio communication system. The proposed modulation scheme /spl pi//M-MDPSK, is a generalization of /spl pi//4 differentially coherent quadrature phase-shift keying, which is used in the North American time-division multiple-access wireless standard. A QA simulation approach is developed so that real system impairments can be studied without having to resort to lengthy Monte Carlo simulation. In particular, it is found that implementation losses, most notable at M=32 and 64, which result from practical transmit and receive filtering, and symbol timing error, can be largely overcome by using a fixed equalization filter and increased accuracy of symbol timing recovery. We focus on an additive white Gaussian noise channel since, in a fast adaptive rate system, the Doppler spread mobile channel is approximately Gaussian on short time intervals. However, the quasi-analytic technique developed here is directly extendable to a fast Rayleigh fading channel. Specifically, we find that for M=64, the inclusion of a fixed seven-tap zero forcing equalizer at the matched filter output, decreases the SEP degradation at P/sub e/=10/sup -4/ from 7.5 dB down to 0.24 dB. The symbol timing error using a finite-precision interpolator is held to within 1/64 symbol period.

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.

A digital cellular radio code-division multiple-access (CDMA) system can only support a finite number of users before the interference plus noise power density, I/sub 0/, received at the cellular base station causes an unacceptable frame-error rate. Once the maximum interference level is reached, new arrivals should be blocked. In a power-controlled CDMA system, the base station can direct mobiles to reduce their power and data rate to reduce interference and allow more users on the system. This approach is employed in TIA IS-95 with respect to the time-varying voice activity on cellular voice channels. We investigate an alternative technique where we adjust the power and data rate of mobile data users to the time-varying interference level to allow more users on a congested system. This scheme was simulated for various proportions of voice and data users and offered traffic levels. Blocking probabilities are reduced in some cases by two orders of magnitude. Message wait time, now a random variable, may exceed the wait time for a constant rate system at high traffic levels. If the cellular carrier has a maximum blocking requirement, an adaptive rate/power system can increase the capacity. For example, a base station that normally supports 26.4 Erlangs offered traffic with 2% blocking can support 33.5 Erlangs with the same blocking probability if adaptive rates and power control are used. Thus, the adaptive rate system can increase the capacity by 27%.