Spatial-temporal equalization for IS-136 TDMA systems with rapid dispersive fading and cochannel interference

In this paper, we investigate spatial-temporal equalization for IS-136 time -division multiple-access (TDMA) cellular/PCS systems to suppress intersymb ol interference and cochannel interference and improve communication qualit y. This research emphasizes channels with large Doppler frequency (up to 18 4 Hz), delay dispersion under one symbol duration, and strong cochannel int erference. We first present the structure of the optimum spatial-temporal d ecision-feedback equalizer (DFE) and linear equalizer and derive closed-for m expressions for the equalizer parameters and mean-square error (MSE) for the case of known channel parameters. Since the channel can change within a n IS-136 tine slot, the spatial-temporal equalizer requires parameter track ing techniques. Therefore, we present three parameter tracking algorithms: the diagonal loading minimum MSE algorithm, which uses diagonal loading to improve tracking ability, the two-stage tracking algorithm, which uses diag onal loading in combination with a reduced complexity architecture, and the simplified two-stage tracking algorithm, which further reduces complexity to one M x M and one 3 x 3 matrix inversion for weight calculation with dir antennas. For a four-antenna system, the simplified two-stage tracking alg orithm can attain a 10(-2) bit error rate (BER) when the channel delay spre ad is half of the symbol duration and the signal-to-interference ratio (SIR ) of the system is as low as 5 dB, making it a computationally feasible tec hnique to enhance system performance for IS-136 TDMA systems.