GO-MC-CDMA System Simulation And Research On Multi-user Detection Algorithm

GO-MC-CDMA(group orthogonal multi-carrier code division multiple access)is an important part of 4G+ system.Combining MC-CDMA with OFDM(orthogonal frequency division multiplexing),GO-MC-CDMA has many advantages,such as well orthogonality,robust to multi-path interference and high capacity.Multi-user interference would cause the decrease of system capacity and communication quality.As a key technique in GO-MC-CDMA,multi-user detection can effectively reduce the multi-user interference.In this work,the basic principle of GO-MC-CDMA is analyzed,and the key technologies including multi-user detection,diversity and combining ratio are introduced firstly.By used of the Matlab/Simulink simulation tool,simulation platform of GO-MC-CDMA is constructed,and the influence of different spread spectrum code on the performance of GO-MC-CDMA is analyzed.The results show that the performance of this system which utilizes the Walsh code is superior.Then,the popular multi-user detections based on hard decision are analyzed and compared.With respect to the defect that Zero-Force multi-user detection in GO-MC-CDMA system could amplify the system noise when it tries to suppress user interference,the improvement schemecombining subcarrier-index modulation with zero forced detection is proposed.It can achieve the lower bit error rate,and improve the signal-to-noise gain together with the system performance in spite of the low ratio of the signal-to-noise.The simulation analysis show that the improved zero forced multi-user detection algorithm not only get lower bit error rate,but also suppress the decrease of performance caused by amplifying noise sample.Finally,the structure and the principle of the decoder based on soft decision,MAP(maximum a posteriori)and Log-Map(logarithmic maximum a posteriori)decoding algorithm are briefly introduced respectively.The iterative multi-user detection technology based on turbo principle is analyzed.Aiming at the problem of the high computational complexity of MAP iterative multi-user detection algorithm in the realization process,the multi-user detection algorithm based on sensitive bits algorithm aided logarithmic maximum posteriori iterative is proposed.In this algorithm,the minimum bit square error detection algorithm is used to obtain the initial value of the signal,and the sensitive bit algorithm is used to reduce the searching range of error bits.In addition,the Log-Map iterative decoding is used to exchange the soft information for improving the accuracy of the received signal.The simulation results show that the proposed detecting algorithm can reduce the computational complexity using the Log-Map algorithm which converts the operation from multiplication to addition.Meanwhile,it uses the sensitive bits algorithm to further reduce the computational complexity of calculating method.Moreover,the improved algorithm could effectively reduce the error bit rate and improve the system performance.