Multi-antenna OFDM systems in the presence of phase noise and doubly-selective fading

Graduation date: 2007Orthogonal frequency division multiplexing (OFDM), which has been very attractive for future high rate wireless communications, is very robust to channel multipath fading effect while providing high transmission data rate with high spectral efficiency.\ud Multiple antennas can be combined with OFDM to increase diversity gain and to improve spectral efficiency through spatial multiplexing and space-time coding\ud (STC). This dissertation focuses on performance analysis and detection schemes\ud of multi-antenna OFDM systems in the presence of phase noise and doubly-selective\ud fading where channel is both time-selective and frequency-selective.\ud \ud In space-time coded OFDM (ST-OFDM), channel time variations cause not only intercarrier interference (ICI) among different subcarriers in one OFDM symbol,\ud but also intertransmit-antenna interference (ITAI). We quantify the impact of time-selective fading on the performance of quasi-orthogonal ST-OFDM systems by deriving, via an analytical approach, the expressions of carrier-to-interference ratio (CIR) and signal-to-interference-plus-noise ratio (SINR). We also evaluate the performance of five different detection schemes and show that all these schemes suffer from an irreducible error floor.\ud \ud Multiple-input multiple-output (MIMO) antennas combined with OFDM are very attractive for high-data-rate communications. However, MIMO-OFDM systems\ud are very vulnerable to time-selective fading. We apply frequency-domain correlative coding in MIMO-OFDM systems over doubly-selective fading channels and derive the analytical expression of CIR to demonstrate the effectiveness of correlative coding in mitigating ICI.\ud \ud When applied in fast fading channels, common ST-OFDM receivers usually\ud suffer from an irreducible error floor. We apply frequency-domain correlative coding\ud combined with a modified decision-feedback (DF) detection scheme with low complexity\ud to effectively suppress the error floor of quasi-orthogonal ST-OFDM over fast\ud fading channels.\ud \ud Similar to single-antenna OFDM, MIMO-OFDM suffers from significant performance\ud degradation due to phase noise and time-selective fading. After characterizing\ud the common phase error (CPE) caused by phase noise and ICI caused by phase noise\ud as well as time-selective fading, we derive a minimum mean-squared error (MMSE)-\ud based scheme to mitigate the effect of both phase noise and Doppler frequency shift.\ud We also evaluate and compare the performance of various detection schemes combined with the proposed CPE mitigation scheme.\ud \ud Throughout the dissertation, theoretical performance analysis is always presented\ud along with corroborating simulations