UBC Theses and Dissertations
Space-time coding for frequency-selective fading channels Chen, Harry Zhi Bing
This thesis studies space-time coded transmissions over frequency-selective channels. For this, the performance of maximum likelihood sequence estimation (MLSE) decoding is analyzed, taking into account channel estimation errors. Furthermore, reduced complexity suboptimum decoding schemes are investigated. To analyze MLSE decoding performance, three lower bounds, namely, the matched filter bound (MFB), the improved MFB (IMFB), and the IMFB I, are derived. The MFB assumes no intersymbol interference (ISI) in the received symbols, while IMFB takes into account the effect of ISI of neighboring symbols, and thus provides a tighter bound. IMFB JL, which is the tightest lower bound for time-reversal and space-time block coding (TR-STBC), in addition, considers the decoupling errors of the symbols from the other transmit antenna. Our numerical results for delay diversity (DD), TR-STBC, and maximum ratio combining (MRC) show that the IMFB, and especially the IMFB JL, match well with simulation results. For reduced complexity decoding, we present three different decision-feedback sequence estimation (DFSE) schemes for TR-STBC and' DD. The first scheme, called unwhitened DFSE (U-DFSE), performs reduced-state sequence estimation based on the output of the spatial-temporal matched filter (MF) typically employed in TR-STBC. The second approach improves upon U-DFSE by subtracting a bias term caused by anti-causal interference from the U-DFSE metric. In the third scheme, the noise component in the output of the spatial-temporal MF is first whitened using a prediction-error filter that can be efficiently computed using the Levinson-Durbin algorithm. Subsequently, whitened DFSE (W-DFSE) is performed. Our results show that for binary modulation, U-DFSE and its improved version can approach the performance of W-DFSE for the full range of delay spreads relevant for the global system of mobile communication (GSM) and enhanced data rates for GSM evolution (EDGE). On the other hand, for high-level modulation, only W-DFSE gives a satisfactory performance.
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