BICM-OFDM Systems over Time-Varying Channels: ICI Cancellation and Diversity Order Analysis

In high mobility scenarios, orthogonal frequency division multiplexing (OFDM) systems experience temporal channel variations within one symbol time to a degree resulting in that the orthogonality among subcarriers is destroyed by inter-carrier interference (ICI) and significant performance degradation may follow, if ICI is left untreated. This dissertation is concerned with the challenging problems caused by high mobility to advanced mobile communication systems that adopt orthogonal frequency-division multiple access (OFDMA) technologies where standard specifications and concerns about complexity demand low-cost methods with deployment readiness and decent performance. In this dissertation, comprehensive frameworks are provided to develop effective approaches for dealing with time-varying channels. To fully understand the problems that fast channel variations may cause to OFDMA systems, fundamental properties and modeling issues of doubly selective fading channels are studied. A simple ICI indicator is devised to show the relative severity of ICI on subcarriers in OFDMA symbols, paving the way for efficient ICI cancellation strategies. Furthermore, a thorough analysis of the ICI indicator is provided to reveal the reasons why it works. It is shown that its probability density function (PDF) is determined by the moving speed meanwhile is insensitive to other factors such as channel power delay profiles and Doppler power spectra. As a result, the applicability of it to indicate channel variations is quite wide-range. Some possible applications of the ICI indicator are also discussed; in particular, its PDF provides valuable information, such as the maximum Doppler spread or the channel fading rate. Equipped with the understanding of mechanism of ICI generation, two approaches to deal with the ICI issue are developed. In the first approach, with the help of