Synchronization And Adaptive Modulation Algorithms For MIMO/OFDM Systems

The need for wireless data and multimedia services promotes the development and applications of many high-speed wireless communication techniques. Orthogonal Frequency Division Multiplexing (OFDM) techniques and Multiple Input and Multiple Output (MIMO) techniques have gained more and more interest in the last a few years. But there are still many key problems to be solved in OFDM and MIMO, including synchronization, channel estimation and adaptive modulation. These are the research targets in this paper.For OFDM communication systems in multipath environment, we introduce a symbol timing error estimation algorithm based on a new eqivalent system model. It works even in strong multipath environment and its computation cost is relatively small.Exploiting the cyclostationarity of OFDM signals in multipath environment, we further introduce an OFDM coarse frequency error estimator and an OFDM fine synchronizer. The coarse frequency error estimator has a wide estimation range and may be used for initial caption. And the fine estimator can achieve nice performance in multipath environment.We extend the synchronization algorithms for OFDM systems to MIMO-OFDM systems, and introduce a synchronization algorithm for MIMO-OFDM systems based on cyclostationarity. It has nice estimation performance and no pilots are needed.An scattered pilot-aided MIMO-OFDM channel estimation and tracking scheme is introduced. The estimation algorithm nicely achieves the MIMO channel im-pulse responses with small costs. The tracking scheme can track the variance of the MIMO channel and further reduce system cost.Finally, we introduce an MQAM SM-OFDM adaptive power and bits allo-cation scheme. Although it's suboptimal, the scheme is much simpler than the optimal one. The penalty is less than 3dB.