Research On Transmission System Based On TR-STBC-OFDM

In recent years,wireless communication,as a vital basic application technology,has witnessed a booming development all over the world.In order to meet the demand for diversified communication services,MIMO and OFDM,which are the core technologies of the physical layer of wireless communication,have received widespread attention.Space-time packet coding(STBC)has been widely used in MIMO systems due to its low complexity linear decoding.Time-reversal space-time packet coding(TR-STBC)has a broader application prospect than STBC because it can effectively combat inter-symbol interference(ISI)in frequency-selective fading channels.Compared with conventional CPOFDM,ZP-OFDM,which uses zero-padding(ZP)sequences instead of cyclic prefixes(CP),has the advantages of lower transmit power consumption,potential multipath diversity,and the ability to effectively combat channel zeros.Therefore,in order to combine the advantages of TR-STBC and ZP-OFDM,the TR-STBC-OFDM system is the main object of study in this paper.In the OFDM system,since the modulation of data at the transmitter is performed in the frequency domain,the time domain waveform at the transmitter is unknown to the receiver,so the maximum likelihood signal detection algorithm is no longer applicable to the TR-STBC-OFDM system.To address this problem,this paper combines the timedomain MMSE channel equalization algorithm with the traditional time-domain matched filtering space-time decoding algorithm,which enables effective signal detection for TRSTBC-OFDM systems.However,both of these time-domain algorithms have very high complexity and the system cannot consistently obtain better BER performance than the conventional STBC-OFDM system,which is investigated in depth in this paper.To address the problem of excessive complexity of the above algorithm,this paper proposes a FDD-TR-STBC space-time decoding algorithm based on frequency-domain decoding,which first performs simple pre-processing of the received signal in time domain at the receiver,then transforms the time-domain convolution process of the signal and channel into frequency-domain multiplication,and finally completes the space-time decoding in frequency domain.When the channel order L=N/4(N is the number of subcarriers),the complexity of the FDD-TR-STBC decoding algorithm is reduced from O(N²)to O(Nlog₂N)when compared with the time domain matched filtering algorithm.Then,the frequency-domain decoding algorithm is applied to the FDD-TR-STBC-OFDM system,and the channel characteristics are compensated by a low complexity equalization algorithm based on ZP-OFDM-FAST-MMSE.Simulation results show that the system achieves better BER performance than the conventional STBC-OFDM system for different numbers of receive antennas,but a slight performance loss is incurred at a single receive antenna compared to the above TR-STBC-OFDM system.In order to solve the performance loss problem in the above FDD-TR-STBC-OFDM system,this paper extends its application to the above MIMO-OFDM system using different spacetime coding schemes using the X-transform instead of the Fourier transform in order to analyze the difference of the X-transform on the performance improvement of different systems.The X-transform is a combination of the Discrete Hartley Transform(DHT)and the Inverse Fast Fourier Transform(IFFT),and has the advantage of lower complexity and reduced peak-to-average ratio compared to the Fourier transform.Simulations of STBCOFDM,FDD-TR-STBC-OFDM and TR-STBC-OFDM systems based on the X-transform show that the X-transform improves the performance of the first two uncoded systems to varying degrees,while the performance of the FDD-TR-STBC-OFDM system is most significantly improved with the 1/2Turbo coding.When the number of receive antennas varies,the FDD-TR-STBC-X-OFDM system can obtain a stable BER performance better than the other systems mentioned above.