Design And Implementation Of MIMO Transmission Based On WARP Platform

With the combination of MIMO technology and OFDM technology,wireless communication gradually shows superiority in transmission rate and anti-interference.The MIMO technology improves the transmission rate of the system without increasing the bandwidth and transmitting power,while the OFDM technology enhances the ability to resist frequency selective fading by using the multicarrier orthogonality.According to the physical layer standard of IEEE802.11 n protocol,this paper designs a 2*2MIMO-OFDM baseband transmission system.Firstly,the frame structure,related parameters and training symbols of the physical layer in IEEE802.11 n protocol are deeply analyzed.After that,the principle of OFDM technology and MIMO technology are expounded respectively,and the different algorithms of space time block code(Alamouti)and layered space time code(V-BLAST)in MIMO are simulated by comparing the BER at different SNR.Secondly,considering that most research on MIMO technology and OFDM technology is based on simulation,according to physical layer of IEEE802.11 n protocol,this paper first designs a 2*2 spatial multiplexing MIMO-OFDM image transmission system combined with MIMO and OFDM,based on WARP platform and Matlab development environment.The system implements each module function in M language on the Matlab software platform.The modules implemented by the transmitter include image dimensionality reduction,modulation mapping,IFFT,CSD,CP insertion and encapsulation.The modules implemented by the receiver include symbol synchronization,carrier synchronization,residual phase correction,channel estimation and detection.Using the mature C-MEX software architecture of WARP platform,calling the interface resources on FPGA through M language,controlling WARP read and write data flow,and completing the transmission in the real environment.In the development,a random number of 16 QAM is used to test each module to ensure the correctness of each module,and then a color image is transmitted to test the whole system.At the same time,each module also gives the corresponding test data.The test results conform to the basic requirements.Finally,considering that space multiplexing(V-BLAST)system is based on the maximum transmission rate,but the diversity gain is insufficient and the system reliability is poor,the MIMO-OFDM combination system which combines the V-BLAST and STBC coding is designed.The system model is given first,then the principle of group interference suppression and maximum likelihood decoding is analyzed.At last,the same pair of color images are sent in the same transmission power and indoor environment.According to the received image quality,symbol constellation,EVM&SNR relation diagram,and the false symbol rate curve of the two systems in different SNR.It shows that the LSTBC system can make up the loss of transmission rate by high order modulation,and the improved diversity gain ensures the reliability of the system.