Error Probability of Space-Time Block Coded Systems in Multipath Rayleigh Channel: MLSE and suboptimum Decoding

In this paper, we address the error probability performance of space-time block coded system (STBC) in multipath Rayleigh fading channel. We consider STBC with rate one for two transmit antennae and rate half for three transmit antennae, and present an optimal maximum-likelihood-sequence-estimation (MLSE) and a block-by-block suboptimum decoding receiver structures. The proposed receiver schemes are suitable for short-range wireless communication or wireless personal area network (WPAN), where the delay spread is usually smaller than one symbol period. A reduced-state MLSE receiver with new trellis structure is first developed for the multiple-input multiple-output (MIMO) scenario assuming availability of ideal channel state information (CSI). Then a less complex block-by-block suboptimum decoding algorithm is also developed for the unequalized multipath fading channel, as an alternative to the computationally intensive MLSE. The suboptimum receiver symbol timing is optimized in order to obtain minimum error probability for the general multipath power delay profiles. From our simulation results, we show that our proposed MLSE receiver can mitigate the multipath induced intersymbol interference (ISI) effectively and at bit error rate (BER) of 10-3, a two-transmit and two-receive (2, 2) STBC system gains as much as 11.5 dB in SNR over a single-antenna uncoded system. We also verify that the MLSE receiver always outperforms the suboptimum receiver, as expected. Error floors appear in the BER performance curves of the suboptimum receiver because ISI is not equalized, whereas no such floors appear with the MLSE receiver.