Dynamic characteristics of a narrowband land mobile communication channel

Land mobile communication signals are subject to propagation effects that result in variation of the received signal amplitude and phase. The most rapid signal variations are the result of multipath propagation and occur with sufficient severity to make reception difficult. At microwave frequencies, the narrowband (30-kHz) channel is considered nondispersive. It will experience flat amplitude fading and band-limited frequency distortion. An understanding of the dynamic nature of the communication channel is required to design land mobile systems that are tolerant of rapid multipath conditions. A model is presented to characterize the dynamic nature of multipath channels, and a new dynamic measure, fractional power change rate, is introduced. The distribution of the fractional power change rate, power change rate, and phase change rate are predicted by the model and validated by comparison to measured data. The research in this paper is part of an ongoing effort to develop multipath-tolerant demodulation techniques for higher order modulation types. The measures developed are of primary importance for specifying the dynamic requirements for such demodulators.