Degradation of digital communication systems in a multipath environment

Conventional wave propagation models for radio networks predict field strength levels only. Wideband wave propagation models however, include algorithms to characterize the radio channel. For digital radio systems the BER of the unprotected radio channel is an important parameter. In the approach presented in this paper, the influence of multipath propagation on different digital modulation schemes is investigated. The calculations are based on a 3D wave propagation model, which yields a field strength-delay spectrum (FDS). The FDS is defined by amplitudes and delays of incident waves, which contribute to intersymbol interference due to multipath propagation. Two algorithms for computation of the BER evaluating the FDS, for both linear and non-linear digital modulation schemes are presented. This paper focuses on GMSK- and PSK-modulation schemes, which are used in digital mobile radio systems (DCS1800, GSM, DECT) as well as in digital audio broadcast systems (DAB). An analysis of the performance of the different modulation schemes in difficult terrain is shown