差分空时编码CDMA系统的多用户接收机设计

利用码分多址和互满正交设计,该文针对多天线系统提出了非相干空时传输方案。它可支持满分集通信,并能有效抑制多用户干扰。基于平坦Rayleigh衰落信道,给出了差分解相关接收机,它不仅隔离了不同用户的检测,而且使不同数据符号的译码彼此独立。     

An improved DOA estimation algorithm for asynchronous multipath CDMA system

This paper proposes an improved Direction Of Arrival（DOA） estimation algorithm for asynchronous multipath Code Division Multiple Access（CDMA） system. The algorithm is based on the correlation matrices of outputs of decorrelator, which is a Multi-User Detection（MUD） approach, one of the key techniques for CDMA system. Through decorrelating processing, the desired user＇s mulipath signals can be resolved and all the other resolved multipath signal interference is eliminated. So the proposed algorithm is expected to perforln much better than algorithm such as that based directly on the Matched Filter（MF） bank outputs. Simulation results confirm this. While the improved algorithm performs better and better as Signal-to-Noise Ratio（SNR） increases, the performance of algorithm based directly on the MF bank outputs can not be improved.     

An improved subspace tracking algorithm for blind adaptive multiuser detection

As the Projection Approximation Subspace Tracking with deflation(PASTd) algorithm is sensitive to impulsive noise, an improved subspace tracking algorithm is proposed and applied to blind adaptive multi-user detection. Simulation results show that the improved PASTd algorithm not only remains the properties of the conventional PASTd algorithm, but also has good Bit Error Rate(BER) performance in impulsive noise environment, thus it can effectively improve the system performance.     

A MATCHED FILTER BANK BASED DOA ESTIMATION FOR ASYNCHRONOUS MULTIPATH CDMA CHANNELS

In this paper, a Direction Of Arrival (DOA) estimation algorithm is proposed for multiuser signals through uplink asynchronous multipath Code Division Multiple Access (CDMA) channels. The algorithm is based directly on the correlation matrices of matched filter bank outputs of desired user‘s multipath signals and it does not require that the elements of base station antenna array outnumber the multipath signals, which is necessary for the conventional sub-space based direction-finding algorithm. Simulation results show that the proposed algorithm estimates the DOA of multipath signals effectively and acceptably. The proposed algorithm has the prominent advantages of low complexity, simpleness and practicality, which make it much more suitable for practical application.     

Influence of Discontinuous Transmission and Power Control on the Average SIR and the Outage Probability of the Uplink of CDMA Systems

In this paper the impact of the voice activity detection process and the powercontrolsystem on the average signal-to-interference ratio (SIR) is investigatedconcerningthe uplink of a single cell code division multiple access (CDMA) based mobilecommunication system. In the literature lower bounds on the average SIR areoftenemployed. Here we show the applicability of such bounds. For this purpose theresultsobtained from these bounds are compared with results obtained fromsimulations.Especially, for a few number of subscribers the differences between the lowerboundand the exact values are significant. Furthermore, the variance of the SIR isinvestigated for different parameters. We found out that significantvariations occurwhich affect the outage probability. But, many authors often employ only theaverageSIR, e.g. for their capacity estimations. However, the variance of the SIR hasto betaken into consideration too.     

Investigation of uplink radio resource management schemes for multi-services in TDD-CDMA systems employing smart antennas

In this paper, a theoretical analysis of Time Division Duplex-Code Division Multiple Access （TDD-CDMA） uplink capacity constraint is presented when employing the smart antenna techniques. The evaluation formulations of capacity and load for multi-services are proposed. In order to maximize the throughput, the objective of optimization is proposed, and an advanced uplink resource management algorithm is developed. The proposed algorithm based on the least interference admission control scheme focuses on the maximum throughput for the circuit switched multi-services. The simulation results show that the proposed strategy has a significant improvement in throughput when the optimum admission control threshold is set.     

A Low-Complexity Multiuser Detector for Asynchronous CDMA QPSK Adaptive Antenna Array Systems

This paper proposes a low complexity joint space-time multiuser detection algorithm for asynchronous DS/CDMA antenna array systems. The proposed multiuser detector is composed of an adaptive antenna array, used as a linear beamformer, and a sliding window decorrelator. A QPSK modulation scheme is used in order to increase bandwidth efficiency. Numerical results are given in terms of Bit Error Rate (BER) under the assumption of a frequency-selective Rayleigh slow fading channel. In particular, the proposed receiver is shown to be near-far resistant, even in worst fading cases, and to exploit completely array introduction while maintaining acceptable computational complexity. The proposed architecture avoids linear filter realization of the decorrelator, which is impractical in the case of a large number of users, and operates with relatively short data frames instead of the complete information sequence. Finally, this receiver is very flexible to changes in timing configuration.     

基于拟生态优化算法的CDMA多用户检测方法

拟生态优化算法是一类模拟自然生态系统运行机制,求解复杂优化问题的智能计算方法,其中的蚁群算法和粒子群算法是较新出现的两种具有不同特点的方法。该文研究基本蚁群算法和离散粒子群算法,并结合CDMA多用户检测问题,改变算法的搜索机制,提出两种CDMA多用户检测的方法。从理论分析以及实验仿真的角度对比两种方法,表明两种方法的计算复杂度低且可以得到较好误码率性能,同时又各有特点。     

The theoretical BER performance analysis of a cooperative diversity scheme in frequency selective fading channel

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.     

Hot spot relief with embedded beam for CDMA systems in haps

This paper proposes a novel micro/macro beam coverage scheme used in High Altitude Platform System （HAPS） Code Division Multiple Access （CDMA） systems. A relief of traffic burden in hot spot areas is achieved by embedding micro-beams into the macro-beams at the hot spot locations, together with appropriate power ratio control and user ratio control. The simulation results show that the hot spot problem can be relieved efficiently with the presented configuration, and a higher and more stable system capacity is expectable despite the variation of user distribution.     

统计/判决电路在CDMA领域中的应用

传统的CDMA技术存在严重的多址干扰现象,使得信道的频谱效率不能达到最佳状态。分析了CDMA通信系统在信道中的性能,并根据香农公式和数字信号最佳接收的知识提出了统计/判决电路,在8分频的前提下,该电路可以在改进CDMA系统通信质量方面起到一定的作用,如改善系统信噪比,降低误码率,提高系统抗干扰性,改善通信质量。