SYNCHRONIZATION FOR MIMO OFDM SYSTEMS

Abstract

Orthogonal frequency division multiplexing (OFDM) systems are vastly preferred for wireless transmission due to their ability to combat multipath and fading wireless channel effects. Multiple input multiple output (MIMO) systems are in demand due to the need for increased data rate and capacity achievable through use of multiple antennas without increasing the bandwidth. A combination of MIMO and OFDM thus combines the robustness against multipath with the increased throughput and capacity, and is therefore an area of modern research. Synchronization errors are a major cause of performance degradation in OFDM systems, so researchers focus on minimizing these errors by proposing improved algorithms. In this thesis, a robust matched filter based timing synchronization scheme for orthogonal frequency division multiplexing (OFDM) systems is presented to achieve improved performance. Training symbol based timing synchronization often exhibits large estimation variance, resulting in performance degradation. The proposed method performs training symbol based timing synchronization at the receiver using matched filter, resulting in remarkable performance improvement in dispersive channels as compared to other methods. The same training symbol is used for channel estimation leading to channel equalization for further improvement in performance. Computer simulations are used to evaluate bit error rate performance for different channels, highlighting the improvement obtained through the proposed method. Furthermore, the proposed scheme is extended for MIMO OFDM systems, utilizing simultaneous transmission and reception of multiple training symbols from the antennas. Based on channel estimates, the received data streams are separated and the individual streams undergo fine timing synchronization to estimate the actual timing point for transmitted data stream. Moreover, estimation of carrier frequency offset and its compensation is incorporated in proposed scheme to ensure its robustness in cases where carrier frequency synchronization is inevitable, in addition to timing synchronization.