Y. Li et al., Spatial-temporal equalization for IS-136 TDMA systems with rapid dispersive fading and cochannel interference, IEEE VEH T, 48(4), 1999, pp. 1182-1194
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.