The Design Of Optimal Pilots For MIMO-OFDM Channel Estimation Based On MMSE

Multiple-input-multiple-output (MIMO) antenna architecture has the ability toincrease capacity and reliability of a wireless communication system. Withoutincreasing the transmit power and bandwidth. Orthogonal frequency divisionmultiplexing (OFDM) has attracted the attention of scholars for efficient highspeed transmission and robustness to frequency selective channels. Hence, theintegration of the two technologies has the potential to meet the ever growingdemands of future communication systems.In practice for coherent detection, however, accurate channel state informationin terms is critical to guarantee the diversity gains and the projected increase indata rate. In order to track the fast time-varying channels and estimate the channelcharacteristics, we usually use the pilot-based channel estimation methods forMIMO-OFDM system. There are three main issues for pilot-based MIMO-OFDMchannel estimation: the first one is the design of interval and location for pilots, thesecond one is the design estimator with low complexity and well channel trackingcapability and the last one is the optimal training sequence.Many existing optimal training signals are designed for some special cases.The algorithm combine with space-time code can be effectively used only when thenumber of antenna is even and less than eight. This paper presents the generaldesigning for optimal training signals of frequency-selective channels inMIMO-OFDM. And the optimal training sequences proposed in this paper havestrong flexibility in parameter designing, which not only be used at pilot point butalso be used at data point. The nature of discrete DFT cyclically-shift intime-frequency domain is used to simplify the optimality conditions, and under thesimple conditions the pilot structure can be designed well. Then the optimaltraining signals, which minimize the channel estimation mean square error, avoidthe matrix inversion process of channel estimation and reduce the complexity of theLS algorithm. The simulation results indicate that the new pilot scheme isapplicable to multi-antenna system with many OFDM symbols and has a goodestimation performance.