| Multiple-Input Multiple-Output(MIMO)system and channel coding technique are the key techniques of the wireless communication system physical layer.MIMO technique significantly improves system capacity and performance at no additional cost of frequency spectrum and plays an important role in modern communication technology.Signal detection technology plays a vital role in the performance of MIMO system,and it is also the focus of current research.Due to its making a good compromise between complexity and performance,the Minimum Mean Square Error-Iterative Soft Decision Interference Cancellation(MMSE-ISDIC)is very suitable for large-scale coded V-BLAST systems.The classical MMSE-ISDIC algorithm achieves the maximum likelihood detection performance at low-order modulation,but the performance loss with high-order modulation system is severe,which severely limits the application of the classical MMSE-ISDIC algorithm in practical systems.Interference Cancellation-Minimum Mean Square Error(IC-MMSE)is a soft-in soft-out iterative soft decision interference cancellation detection algorithm with decoding feedback.Due to its making good use of decoding feedback information,the IC-MMSE can adopt a better convergence performance over the MMSE-ISDIC.When a high-order modulation with non-equal amplitude is adopted,the classical IC-MMSE algorithm suffers from error propagation in dual iteration computation,which leads to a worse convergence performance and severely limits the application of the IC-MMSE algorithm in practical systems.We carry out research on iterative detection algorithms in Turbo coded V-BLAST systems,and Turbo-BLAST systems in which decoding feedback is adopted.The following issue(1)and(2)are for Turbo coded V-BLAST systems,and issue(3)and(4)are aimed at Turbo-BLAST systems.(1)Through the analysis,we find that the likelihood probability information produced by the MMSE-ISDIC sometimes tends to hard decision due to the underestimation of the residual interference and the noise energy,which leads to serious error propagation at high order modulation.In this paper,the residual interference variance to be updated in MMSE-ISDIC algorithm is improved by weighting to slow down the convergence rate of certain symbols,which can reduce the error propagation effect and improve the system performance.(2)For the classical MMSE-ISDIC,we perform a deep statistical studies on the underestimated ratio of MMSE filter output interference-noise energy(interference plus noise energy),and obtain a underestimated ratio matrix of MMSE filtering output interference-noise energy,which is quite robust to different SNR values,and hence arrive at a modified MMSE-ISDIC algorithm.Simulation results show that the modified MMSE-ISDIC algorithm can obtain considerable performance advantage over the classical MMSE-ISDIC algorithm with no complexity increase,and it is suitable for high-order modulation(16-QAM,64-QAM)MIMO systems with different scales.(3)When a high-order modulation with non-equal amplitude is adopted in the Turbo-BLAST systems,the classical IC-MMSE algorithm may encounter the problem of mismatch between the estimated symbol energy and the true value,which results in a reduced convergence performance because the interference cannot be effectively suppressed by MMSE filtering.To solve this problem,we propose a modified IC-MMSE algorithm with symbol energy estimation based on decoding feedback information.Simulation results show that compared with the classical IC-MMSE,the modified IC-MMSE algorithm can improve the performance of the third and fourth iteration with no complexity increase,since the symbolic energy is obtained just by using the decoding feedback information.(4)For the Turbo-BLAST systems,we study the iteration procedure of the IC-MMSE detection module with decoding feedback information.Although the IC-MMSE algorithm adopts dual iterations,it has a defect that some unreliable symbol metrics may increase too fast due to the limited error correction ability of decoding.To reduce the increase rate of the symbol metrics and reduce the error propagation,we propose an enhanced IC-MMSE algorithm.Simulation results show that the proposed enhanced IC-MMSE algorithm effectively reduces error propagation and obtains a faster convergence. |
