Performance and complexity analysis of wireless communication systems for approaching channel capacity

Abstract

In this dissertation, the performance and complexity of capacity-approaching wireless communication systems are analyzed in many aspects. First, the channel capacity, the maximum allowable throughput over a particular channel, is analyzed. Assuming random selection of codewords, the cut-off rate of MIMO systems is derived as a measure of channel capacity. It is found that the cut-off rate is proportional to the number of transmit antennas at high SNR, while it is proportional to the minimum number of antennas at low SNR. Secondly, the maximum likelihood detection, which is essential to capacity-approaching systems, is analyzed for a variety of situations, specifically, depending on the availability of channel, phase offset and frequency offset at the receiver. Particularly, low-complexity decision-aided detection is proposed for improving the performance of frequency-offset insensitive detection. The performance-complexity analysis shows that the proposed decision-aided detection provides 2 dB gain in performance. Moreover, probabilistic sphere decoding is proposed for improving the performance of conventional sphere decoding with early termination. Specifically, by applying a probabilistic search algorithm to the depth-first sphere decoding, the more promising candidates can be evaluated earlier, resulting in either better performance or lower complexity. The performance-complexity analysis shows that the proposed probabilistic sphere decoding provides up to 9 dB gain in performance or 50% reduction in complexity. Furthermore, since the proposed probabilistic sphere decoding can be implemented by simply adding a few special blocks to conventional sphere decoding, it is broadly applicable to many modifications of sphere decoding. Thirdly, the performance of LDPC-coded MIMO-OFDM systems is evaluated. The union upper-bounds on the error probability are derived analytically, giving useful insights into the system design, for example, the choice of space-t...