Research On Multiuser Detection Based On Beamforming Technology In Multiuser MIMO-OFDM System

The multiuser MIMO-OFDM system with the same subcarrier shared by multipleusers has the characteristics of three dimensions including time, frequency and space,which can effectively improve the transmission efficiency, spectrum efficiency andpower utilization. The spectrum allocation mode with subcarrier shared by multipleusers results in the co-channel interference between users, so it limits the improvementof the system detection performance and the spectrum efficiency. Therefore, this paperhas focus on the multi-user detection problem for MIMO-OFDM system uplink with thesame subcarrier shared by multiple users, aiming at improving the system performancewhile reducing the computation complexity.In order to improve the performance of the multi-user detection algorithm formultiuser MIMO-OFDM system uplink and simultaneously reduce the computationalcomplexity, a low complexity space multi-user detection algorithm for SDMA based onthe BD technique and the SIC technique is proposed. The core of the algorithm is toeliminate the CCI with iteratively successive zero-forcing (ISZF) by only performingpartial interference cancellation and detect the user signals with successive interferencecancellation by selecting the user detection sequence reasonably based on the results ofthe ISZF at the base station. This proposed detection algorithm is defined as iterativelysuccessive zero-forcing and successive interference cancellation (ISZF-SIC). It cangreatly reduce the total number of SVD operations and the dimension of the SVDmatrix by iteratively eliminating interference based on the nullspace orthogonal theorem,resulting in reducing the complexity effectively. In addition, it can increase the diversitygain and further eliminate the residual user interference, so the system performance isimproved simultaneously.The proposed ISZF-SIC algorithm has the advantages of detection performanceand frequency efficiency high and low computation complexity, however, the utilizationof random detection order rather than that of specific order makes system performancedeteriorate in case of tough communication environment. As the solution of errorsstemming from disordering, this article proposes an order iteratively successivezero-forcing and successive interference cancellation (order-ISZF-SIC) algorithm basedon ISZF-SIC algorithm. The key of this algorithm is to decide user detection sequencebased on the sum SNR, where select the user who make the sum SNR max. Because thereasonable user detection sequence is determined with the channel state information, theprobability of error propagation is reduced effectively. As a result, compared to theISZF-SIC algorithm, the system detection performance and spectrum efficiency for theorder-ISZF-SIC algorithm are further improved. However, this order-ISZF-SIC algorithm increases the computation complexity on account of considering the usersequence. Simulation results show that the performance of the order-ISZF-SICalgorithm approximates that of an optimal exhaustion detection algorithm, which innaturally better than the ISZF-SIC algorithm and block diagonalization algorithm. As tothe computation complexity, it is lower than the block diagonalization algorithm buthigher than the ISZF-SIC algorithm.