Timing synchronization and ICI mitigation for pilot-aided OFDM mobile systems

Robust high date rate mobile communications have several challenges. Transmission of high rate information typically experiences higher delay spread in mobile environments. Furthermore, high mobility introduces time-variations which can make the link less reliable.; Orthogonal Frequency Division Multiplexing (OFDM) is suitable for high delay spread applications. However, performance of OFDM systems, is affected by channel estimation, timing synchronization and mobility. Timing synchronization becomes challenging in high mobility applications as power delay profile of the channel can change rapidly due to the sporadic birth and death of the paths. Furthermore, timing synchronization errors introduce Inter-Carrier-Interference (ICI) in OFDM systems. Due to the expansion of symbol length, OFDM systems are very sensitive to ICI. Furthermore, for mobile applications time-variations in one OFDM symbol introduce ICI as well which further degrades the performance. This becomes more severe as mobile speed, carrier frequency or OFDM symbol duration increases. Therefore to have an acceptable reception quality for the applications that experience high delay and Doppler spread, design of robust timing synchronizer, channel estimator and ICI mitigator is essential. This thesis takes an overall look at these issues. While each of them has been looked at separately by other researchers, an overall look allows for better understanding and design of more robust algorithms. Based on mathematical analysis of the overall performance, a new cross-block design is proposed and implemented that uses channel estimation information to improve timing synchronization.; After robust timing synchronization is achieved, two mitigation methods are proposed and analyzed to remove the effect of ICI introduced by high mobility. All the algorithms are tested against high delay and Doppler spread channels. Results of simulation and analysis show considerable performance improvement without a need to increase the training overhead.