Research On Precoding Technology Of Hybrid Space-time Codes In Wireless MIMO Communication System

Hybrid space-time codes technology combines space-time block codes with bell labs layered space-time codes,which can simultaneously provide spatial diversity gain of space-time block codes and multiplexing gain of layered space-time codes,and obtain compromise performance.However,the hybrid space-time codes system has a problem that the detection complexity of the receiver is high and the bit error rate?BER?performance is limited.In response to these problems,it is considered to combine the precoding technique with the hybrid space-time codes system when the channel state information at the transmitter?CSIT?is known.Specifically,this paper studies the corresponding precoding schemes for the hybrid space-time codes system,which is known to have ideal CSIT and non-ideal CSIT.Therefore,the main research contents of this paper are summarized as follows:?1?When the ideal CSIT is known,in order to eliminate the noise's influence of the THP algorithm based QR decomposition under the Zero forcing?ZF?criterion on the hybrid space-time codes system,a scheme combining the QR-THP algorithm under the Minimum Mean Square Error?MMSE?criterion with the hybrid space-time codes system is proposed,and improving BER performance of the system.In order to eliminate the influence of poor subchannels generated by the QR decomposition of the equivalent channel matrix on the reachability of the system,the equivalent channel matrix is proposed as geometric mean decomposition?GMD?,and the nonlinear precoding scheme of GMD-THP is combined with hybrid space-time codes,and derive its precoding scheme under the ZF and MMSE criteria.At the same time,the influence of the transmit antenna correlation coefficient of the Rayleigh fading channel model on BER performance of the system is also explored.The simulation results show that the proposed fusion scheme can achieve better BER performance than the nonlinear precoding scheme of hybrid space-time codes based on ZF-QR-THP,which can improve the system's anti-fading capability.In addition,it was found that the correlation coefficient between the transmitting antennas is inversely related to the system BER performance.?2?Hybrid space-time codes system is difficult to obtain the ideal CSIT in some scenarios,especially,when the duplex mode is frequency division duplex?FDD?,the CSIT needs to be acquired by means of a limited feedback channel.At this time,in order to improve the BER performance of the system,a scheme combining the finite feedback precoding technology of the low complexity discrete fractional sine transform?DFRST?codebook with the hybrid space-time codes system is proposed.Each Alamouti coding unit at the transmitter will determine the corresponding precoding matrix in the DFRST codebook by the received index number of the corresponding optimal codeword matrix.It is verified by simulation that when the BER reaches 10^-3,the proposed scheme can obtain at least 2dB gain compared to the unprecoded hybrid space-time coding system.