一种粒子滤波的盲多用户检测快速算法

该文在时间观察状态空间模型基础上,针对粒子滤波计算复杂的问题,构造了一种在同步快变平衰落信道下计算复杂度低的粒子滤波的DS-CDMA盲多用户检测快速算法。该算法通过对超过门限数目的粒子分类,以不同类别粒子的概率差值作为粒子滤波所需粒子数目是否足够的判断准则,自动调节不同情况下所需的粒子数目,并对不同类别粒子概率差值下盲多用户检测性能进行分析。仿真结果表明,该文算法可以在保证盲多用户检测性能的前提下有效地降低运算复杂度,且检测性能与概率差值成正比。     

CDMA系统粒子群多用户检测算法

Kennedy和Eberhart提出的粒子群优化算法(PSO),作为一种新的并行优化算法,在解决多维和非线性的复杂问题中,性能优良且算法简单易于实现。本文对二进制粒子群优化算法进行改进,并将其应用于DS-CDMA通信系统的多用户检测中,提出了基于矢量的二进制粒子群多用户检测器(V-BPSO-MUD),同时提出了两种高效实用的多用户检测器:基于矢量的串行二进制多用户检测器(VS-BPSO-MUD)及基于矩阵的二进制多用户检测器(M-BPSO-MUD)。仿真结果表明,PSO多用户检测器充分利用了粒子群优化算法的优良特性,性能明显优于传统的CDMA检测器,接近无多址干扰情况。     

最优多用户检测问题研究

DS-CDMA无线通信中的最优多用户检测属于NP完备组合优化问题,启发式方法是求解这类问题的有效方法,通过分析最优多用户检测问题的适应值曲面特征,研究设计了系列低计算复杂度、接近最优多用户检测性能的启发式算法.仿真结果表明,基于演化策略的多用户检测算法能够在中等规模用户数情况下提供与最优多用户检测相当的性能,而快速迭代局域搜索算法能够以较低的计算复杂度得到比其他局域搜索算法更好的解.     

基于独立分量分析的DS—CDMA多用户检测方法

将独立分量分析应用于DS-CDMA系统的多用户检测中,提出了基于ICA后处理的匹配滤波多用户检测方法.该方法用匹配滤波器的输出初始化独立分量分析的迭代,然后用快速ICA算法改进初始估计.仿真结果表明:文中提出的方法在高信噪比的情况下,误码性能得到了较大改善.     

基于Kalman滤波的盲多用户检测算法

盲多用户检测技术是第三代移动通信的关键技术,本文仿真分析了DS-CDMA通信系统中盲多用户检测的Kalman滤波算法的性能.并且将子空间算法和Kalman滤波算法进行结合,使得盲多用户检测的Kalman滤波算法的计算量大大降低.     

基于粒子群优化算法和多级检测的多用户检测器

提出了一种新颖的基于粒子群优化和多级检测的混合算法的多用户检测器。介绍了最佳多用户检测模型以及粒子群优化算法的基本思想。进行了理论依据和仿真性能分析。仿真结果表明：该检测器在误码率性能上明显优于传统检测器和解相关检测器,在抗“远一近效应”上也优于传统检测器与多级检测器,计算复杂度较低。     

逼近幂迭代子空间跟踪算法在多用户系统中的应用研究

本文将基于逼近幂迭代的子空间跟踪算法应用于多用户系统中.该算法利用适当的补偿矩阵逼近经典幂迭代子空间跟踪方法,在不增加计算复杂度的基础上保证了算法的全局收敛.将该算法应用于波达方向(DOA)估计及盲多用户检测系统中,利用接收的数据矢量估计信号子空间,进而可得到DOA的精确估计及检测器的权向量.仿真验证了算法在多用户系统中的有效性.     

异步DS-CDMA盲多用户检测

该文研究了频率选择性瑞利衰落信道中的异步DS-CDMA系统盲多用户检测。提出一种期望信号矢量估计方法,该方法同时利用了多径传播和接收机同步失调的特性,以利于把盲线性滤波优化技术应用于稳健的干扰抑制。为了抑制多址干扰(MAI),提出一种基于投影的辅助矢量(PAV)算法。该算法计算复杂度低,特别适用于短数据采样时滤波矢量的快速优化,仿真结果表明在低输入信号干扰噪声比(SINR)时能提供有效的干扰抑制,在高输入SINR时具有稳健的性能。     

基于Social Cognition粒子群算法多用户检测

最优多用户检测方法具有最优性能,但复杂度高,利用优化算法求解可以降低实现复杂度。粒子群算法是一种简单有效的新型群智能优化算法,研究了一种Socialcognition模型简化粒子群算法,并应用于大用户量CDMA多用户检测问题,主要考虑降低算法复杂度,提高算法的实现效率。分析及仿真表明该方法在系统用户数量较大时具有较好性能。     

MC-CDMA系统迭代检测中的一种基于EM的信道估计算法

该文将多用户检测和译码相结合的迭代检测技术应用于MC-CDMA系统。多用户检测器由串行干扰消除和其后的MMSE滤波器组成。信道估计器采用一种基于期望最大(EM)信道估计算法,该算法降低了信道估计的复杂度,仿真表明其具有良好的性能。     

Linear multiuser detectors for synchronous code-divisionmultiple-access channels

Under the assumptions of symbol-synchronous transmissions and white Gaussian noise, the authors analyze the detection mechanism at the receiver, comparing different detectors by their bit error rates in the low-background-noise region and by their worst-case behavior in a near-far environment where the received energies of the users are not necessarily similar. Optimum multiuser detection achieves important performance gains over conventional single-user detection at the expense of computational complexity that grows exponentially with the number of users. It is shown that in the synchronous case the performance achieved by linear multiuser detectors is similar to that of optimum multiuser detection. Attention is focused on detectors whose linear memoryless transformation is a generalized inverse of the matrix of signature waveform crosscorrelations, and on the optimum linear detector. It is shown that the generalized inverse detectors exhibit the same degree of near-far resistance as the optimum multiuser detectors. The optimum linear detector is obtained     

Near optimum tree-search detection schemes for bit-synchronousmultiuser CDMA systems over Gaussian and two-path Rayleigh-fadingchannels

Simple reduced tree-search detection schemes of the breadth-first type are applied to suboptimal joint multiuser detection in bit-synchronous code-division multiple access (CDMA) systems over both Gaussian and two-path Rayleigh-fading channels. It is pointed out that in contrast to the case of the optimal multiuser detector, the choice of the receiver filter severely influences the performance of suboptimal multiuser detectors. Simulation results supported by analysis show that breadth-first tree-search algorithms using a decorrelating noise whitening receiver filter perform better than similar receivers, which solely use a matched filter (MF) for virtually all nonsingular spreading code sets studied. Most of the code sets are randomly generated. The M- and T-algorithm detectors based on decorrelating noise whitening filter (WF) outputs can achieve near optimum performance at a very low complexity compared to the optimal detector, although the proposed detectors are more complex than some known suboptimum detectors. Furthermore, the use of combining techniques is considered for a two-path Rayleigh-fading channel, and a semi-synchronous CDMA structure is proposed. It is shown that if maximum ratio combining (MRC) is employed, the decorrelating noise WF still exists. The corresponding suboptimal combining detector with a decorrelating noise WF outperforms a similar noncombining detector     

Multiuser detection for DS-CDMA systems using evolutionary programming

This article introduces a new multiuser detection scheme which uses evolutionary programming (EP) to detect the user bits based on the maximum-likelihood decision rule. The major advantage of the proposed detector is that it has a lower computational complexity compared to other popular evolutionary-algorithm-based detectors. The simulation results show that the EP has always converged to the optimum solution with a small number of generations. The simulated average computational time performance demonstrates that this approach achieves practical ML performance with polynomial complexity in the number of users.     

Multiuser Detection for Out-of-Cell Cochannel Interference Mitigation in the IS–95 Downlink

This paper considers the application of multiuser detection techniques to improve the quality of downlink reception in a multi-cell IS–95 digital cellular communication system. In order to understand the relative performance of suboptimum multiuser detectors including the matched filter detector, optimum multiuser detection in the context of the IS–95 downlink is first considered. A reduced complexity optimum detector that takes advantage of the structural properties of the IS–95 downlink and exhibits exponentially lower complexity than the brute-force optimum detector is developed. The Group Parallel Interference Cancellation (GPIC) detector, a suboptimum, low-complexity multiuser detector that also exploits the structure of the IS–95 downlink is then developed. Simulation evidence is presented that suggests that the performance of the GPIC detector may be near-optimum in several cases. The GPIC detector is also tested on a snapshot of on-air data measured with an omnidirectional antenna in an active IS–95 system and is shown to be effective for extracting weak downlink transmissions from strong out-of-cell cochannel interference. The results of this paper suggest that the GPIC detector offers the most performance gain in scenarios where weak downlink signals are corrupted by strong out-of-cell cochannel interference.     

Suboptimum soft-output detection algorithms for coded multiuser systems

In this paper, we consider coded asynchronous multiuser signals in an additive white Gaussian noise channel. Since optimum joint multiuser detection (MUD) and forward error correction (FEC) decoding is characterized with a very high computational complexity, we consider disjoint MUD and FEC decoding. The optimum disjoint multiuser detector is the soft-output maximum a posteriori detector that provides sequences of a posteriori probabilities to the corresponding FEC decoders. It involves backward and forward recursions resulting in high complexity and processing delay. In this paper, we consider several suboptimum soft output disjoint multiuser detectors that involve only forward recursions and have reduced complexity and delay.     

Genetic algorithm assisted joint multiuser symbol detection andfading channel estimation for synchronous CDMA systems

A novel multiuser code division multiple access (CDMA) receiver based on genetic algorithms is considered, which jointly estimates the transmitted symbols and fading channel coefficients of all the users. Using exhaustive search, the maximum likelihood (ML) receiver in synchronous CDMA systems has a computational complexity that is exponentially increasing with the number of users and, hence, is not a viable detection solution. Genetic algorithms (GAs) are well known for their robustness in solving complex optimization problems. Based on the ML rule, GAs are developed in order to jointly estimate the users' channel impulse response coefficients as well as the differentially encoded transmitted bit sequences on the basis of the statistics provided by a bank of matched filters at the receiver. Using computer simulations, we showed that the proposed receiver can achieve a near-optimum bit-error-rate (BER) performance upon assuming perfect channel estimation at a significantly lower computational complexity than that required by the ML optimum multiuser detector. Furthermore, channel estimation can be performed jointly with symbol detection without incurring any additional computational complexity and without requiring training symbols. Hence, our proposed joint channel estimator and symbol detector is capable of offering a higher throughput and a shorter detection delay than that of explicitly trained CDMA multiuser detectors     

A flexible receiver for CDMA multiuser communications

Code division multiple access (CDMA) capacity is limited by interference amongst users. The effect of this interference on receiver outputs depends on the users' signatures and the actual detector used in the receiver. A matched filter receiver is particularly sensitive to interference, whereas an optimum multiuser receiver is less sensitive but infeasible due to its exponential complexity. We propose a receiver structure that trades detection performance for reduced complexity. It can interpolate between the performances and complexities of these two receivers. Our detector uses a tree structure, and some of its special cases are the decision feedback detector, the decorrelating detector, and the optimal linear detector. We show that at equal complexity levels, a particular implementation of our detector outperforms these detectors. We also show that our approach can be used with a minimum-mean-square-error design criterion and coded CDMA transmission     

Near-far resistance of multiuser detectors in asynchronous channels

Consideration is given to an asynchronous code-division multiple-access environment in which receiver has knowledge of the signature waveforms of all the users. Under the assumption of white Gaussian background noise, the authors compare detectors by their worst case bit error rate in a near-far environment with low background noise, where the received energies of the users are unknown to the receiver and are not necessarily similar. Conventional single-user detection in a multiuser channel is not near-far resistant, and the substantially higher performance of the optimum multiuser detector requires exponential complexity in the number of users. The authors explore suboptimal demodulation schemes which exhibit a low order of complexity while not exhibiting the impairment of the conventional single-user detector. It is shown that there exists a linear detector whose bit-error-rate is independent of the energy of the interfering users. It is also shown that the near-far resistance of optimum multiuser detection can be achieved by a linear detector. The optimum linear detector for worst-case energies is found, along with existence conditions, which are always satisfied in the models of practical interest