Performance of Space-Time Modulation for a General Time-Varying Rician Channel Model

We analyze the performance of trained and differential space-time modulation for channels with a constant specular component and time-varying diffuse fading. We examine the case where the channel varies from sample to sample within a symbol according to a first-order Gauss-innovations model. We show that the effect of the time-varying diffuse channel can be described by an effective SNR that decreases with time. We derive pairwise probability of error expressions based on these effective SNR values that accurately describe performance. We quantify the significant advantage that differential modulation provides at high SNR (where the effect of the timevarying channel dominates). At low SNR (where additive noise dominates), we note that trained modulation with a “perfect” channel estimate provides a 3 dB advantage over differential modulation, but decoding based on an ML channel estimate yields worse performance than differential modulation at all SNR values. Simulation results are provided to support our analysis. Index Terms Time-varying channels, fading channels, space-time modulation, differential modulation, non-coherent coding, multiple antennas, wireless communications. This work was supported by the National Science Foundation under Wireless Initiative Grant CCR-9979452 and Information Technology Grant CCR-0081476. 1