Space-time coding for high data-rate wireless communications over space and frequency selective fading channels

Most current wireless communication systems are designed for low data rates and low mobility support. However, rapidly growing demands for high data rates, high quality, and high mobility services will dominate future wireless communication systems. In order to cope with these diverse challenges, advanced technical innovations are required. Recently, space-time (ST) coding has been proposed as one of the most attractive techniques for high data-rate transmissions in wireless communications. In this thesis, we propose effective ST coding solutions for high data-rate wireless communications over space and frequency selective fading channels. At first, a concatenated ST coding scheme is proposed for flat fading links, followed by the performance analysis, which leads to establishing the design criteria of optimal trellis codes. Based on these design criteria, optimal trellis codes are constructed. Simulation results demonstrate that the proposed concatenated ST codes outperform ST trellis codes under the same spectral efficiency, trellis complexity, and signal constellation. Performance evaluation of ST coding has mainly been done over flat Rayleigh fading channels. By studying the effects of time delay spread, we derive performance criteria of ST codes over unequalized frequency selective fading channels. It is shown that the diversity order is retained in the presence of multipath, but the coding gain is reduced due to the destructive effects of multipath fading. In order to support high-speed ST coded transmissions, the detrimental influence of frequency selective fading must be mitigated. An efficient space-frequency (SF) coded orthogonal frequency division multiplexing (OFDM) system is proposed as a solution. The design criteria of trellis codes used in such SF OFDM system are derived and discussed. It is shown that the proposed SF codes with low trellis complexity can easily exploit the full diversity order provided by the fading channel. This is in contrast to the traditional SF coded OFDM systems where we have to design complicated ST trellis codes to achieve the same goal. The capacity properties of SF coded OFDM over frequency selective fading channels are also addressed. Decoding of ST codes requires channel information at the receiver. By using an orthogonal training pattern, we develop a low rank Wiener filter based channel estimator with significant complexity reduction for SF coded OFDM systems. A simplified approach with further rank reduction is also proposed to further reduce the complexity while attaining good performance