Research On Transmission System Based On Time-reversal Space-time Codes

With the rapid development of mobile communications,higher requirements for signal transmission quality and data rate are needed.Therefore,for a complex transmission environment,how to increase the system capacity and improve the reliability of data transmission under the limited spectrum resources has become an urgent problem to be solved.Multiple Input Multiple Output(MIMO)and Orthogonal Frequency Division Multiplexing(OFDM)technologies can greatly improve system performance and increase system capacity.Space-time coding is an important technology in MIMO.By using space-time coding,the capacity of the wireless system can reach or approach the rational channel capacity.The Space-Time Block Coding(STBC)scheme has been widely used because of its simple coding rules in both transmitter and receiver.However,the traditional STBC scheme is more suitable for frequency-flat fading channels,and Intersymbol Interference(ISI)is easily caused in frequency-selective channels.The Time-Reversal Space-Time Block Coding(TRSTBC)scheme can overcome this problem well.Therefore,this thesis selects the TR-STBC scheme for space-time coding at transmitter.By combining STBC with OFDM,TR-STBCOFDM system is established.The TR-STBC-OFDM system combines the advantages of both,which can effectively improve transmission quality and spectrum utilization of the system,and greatly reduce the computational complexity at the receiver.Synchronization and channel estimation techniques are critical to any wireless communication system.Therefore,this thesis also studies the synchronization and channel estimation of TR-STBC-OFDM systems.Firstly,this thesis introduces the STBC scheme and the related technical principles of MIMOOFDM system.Then by combining the traditional STBC and OFDM technology,the STBCOFDM system is established.Then the system model is given,and its performance is simulated and analyzed.Secondly,the coding and decoding process of TR-STBC is introduced in detail and the TR-STBC-OFDM system is established.Then the data frame structure of the system is designed,and the corresponding synchronization scheme and channel estimation scheme are proposed.In the synchronization algorithm,the Frank sequence with ideal periodic autocorrelation and good cross-correlation is used,and obtains good synchronization performance.The length of the Frank sequence does not become larger as the number of antennas increases,and it has higher bandwidth utilization.In the channel estimation algorithm,the orthogonal training sequences are transmitted on different transmitting antennas,and the LS channel estimation algorithm is used in the frequency domain so that the receiver does not perform the matrix inversion operation,so that the computational complexity is greatly reduced.Finally,the TR-STBC-OFDM system is compared with the STBC-OFDM system.The simulation results show that the performance of the TR-STBC-OFDM system is better than that of the STBC-OFDM system.