Hysteretic HNN MAI-Cancellation for CDMA Signals in Multipath Fading Channels

Multiple-access interference cancellation using hysteretic Hopfield neural network receiver for direct sequence code-division multiple access (DS-CDMA) in multipath fading channels is investigated. It has been shown that by applying the phenomenon of “hysteresis” to the Hopfield neural network (HNN) detector, performance of this detector may be enhanced in all near-far situations for different number of multipath rays. Introducing the concept of Hysteresis into HNN has made this suboptimum CDMA detector even closer to the optimum multiuser CDMA detector. As shown by simulation results, the bit-error rate performance achieved by the Hysteretic Hopfield Neural Network detector outperforms the classical HNN detector with a good margin and is promising.     

基于神经网络量子算法的多用户检测器

利用遗传量子算法和Hopfield神经网络，提出了一种融合两种算法优点的神经网络量子算法，并将其应用到CDMA通信系统的多用户检测问题中。所提算法把神经网络嵌入到遗传量子算法的每一代中，可进一步提高量子种群的适应度函数值。通过混合神经网络到GQA中，还可加快GQA的收敛速度进而减少算法的计算复杂度。另外，GQA所提供的良好初值改善了HNN的性能，嵌入的HNN也提高了GQA的性能。仿真结果证明了该方法的抗多址干扰能力和抗远近效应能力都优于传统检测器和一些应用智能算法的多用户检测器。     

Neural Networks for Multiuser Detection of Signals in DS/CDMA Systems

Multiple access interference and near-far effect cause the performance of the conventional single user detector in DS/CDMA systems to degrade. Due to the high complexity of the optimum multiuser detector, suboptimal multiuser detectors with less complexity and reasonable performance have received considerable attention. In this paper, we analyse the performance of the multilayer perceptron backpropagation neural network as a multiuser detector of CDMA signals in AWGN and multipath fading channels. Our results show significant improvement over previous research. We compare neural network performance with the other detectors, and apply different neural networks and criteria, such as decision-based, fuzzy decision, discriminative learning, minimum classification, and cross entropy neural networks, and compare their performance. We propose a modified decision-based network which significantly improves the performance.     

CDMA有限精度序列解相关NP-hard问题的求解方法

该文首先分析了应用有限精度序列为解相关矩阵序列的解相关接收机,将有限精度解相关的多用户检测问题归约为线性约束整数优化问题,同时证明此问题为NP－hard问题。然后给出了用于寻找最优有限精度序列即求解此NP－hard问题的算法。结果说明,最优有限精度解相关器的性能甚至在大的信道占用时较无限精度解相关多用户检测器下降很小。     

A transiently chaotic neural-network implementation of the CDMA multiuser detector

The complex dynamics of the chaotic neural networks makes it possible for them to escape from local minimum of the simple gradient descent neurodynamics. We use a transiently chaotic neural network to detect the CDMA multiuser signals and hence obtain an implementation scheme of the CDMA multiuser detector (TCNN-MD). Computer simulation results show that the proposed detector is clearly superior to Hopfield neural-network-based detector.     

基于贪心算法的CDMA多用户检测

该文从优化计算方法的角度,利用贪心算法对最优解进行分级处理,算法复杂度小等特点,将贪心算法应用于CDMA通信的多用户检测,并结合CDMA通信的实际特点,提出一种基于贪心算法的CDMA多用户检测方法,仿真实验的结果表明,该方法运算复杂度低,可获得接近最优检测的性能。     

凸约束最小误码率线性多用户检测

论文研究了DS-CDMA系统线性多用户检测器的误码率代价函数,证明了最小误码率线性多用户检测器等价于一个约束最优化问题。然后提出了凸约束最小误码率线性多用户检测器,并给出了一个相应的牛顿型迭代算法。仿真结果表明,凸约束最小误码率线性多用户检测器具有良好的性能,而且该算法收敛速度快,稳定性好,易于工程实现。     

城市建筑中移动通信信号的干扰抑制

城市建筑物的结构、高度和密度会对蜂窝移动通信产生影响,在多径扩散信道中产生宽带和窄带干扰。为此,设计一种次优化的盲最小均方误差检测器。在抑制通信系统中宽带干扰(多址干扰和码间干扰)的同时,消除窄带通信系统产生的窄带干扰(包括正弦波信号、自回归信号、多速信号系统中的数字信号等)以及环境噪声,利用子空间分解技术和辅助向量来简化传统检测器。仿真结果证明,当信噪比为10 dB时,该检测器的误码率比传统检测器低约3 dB。     

基于克隆粒子群优化算法的多用户检测器

针对经典离散粒子群优化算法收敛性差的缺点,设计了基于新的运动方程的离散粒子群优化算法。为了解决CDMA系统多用户检测这个NP完全问题,基于免疫克隆选择理论和新的粒子群优化算法,提出了克隆粒子群优化算法,其中,由神经元构成的粒子可以进行随机搜索和经验学习。仿真结果表明,在异步和同步CDMA系统上,该检测器的误码率性能都优于传统方法和其他一些多用户检测器,达到最优检测。     

MC-CDMA系统中的自适应半盲多用户检测算法

研究多载波CDMA(MC-CDMA)上行半盲多用户检测技术，对基于Chebyshev逼近算法实现的最小输出能量(MOE)盲多用户检测进行改进，提出MC-CDMA系统下一种基于子空间跟踪和Chebyshev逼近的自适应半盲多用户检测算法。该算法基于MOE线性检测器原理，充分利用小区内所有用户的扩频码，设计了一种基于MOE准则的半盲检测器，很好地消除了多址干扰。为了减少计算复杂度，将修正的PASTd算法应用于Chebyshev逼近算法估计MOE半盲检测器的最优权向量。该算法计算复杂度低，具有较好的抗多址干扰性能和检测性能。仿真结果验证了该算法的可行性和优越性。     

Multiuser detection based on modified PSO algorithm for synchronous CDMA systems

The computational complexity of the optimum maximum-likelihood detector does not allow its utility for multiuser detection (MUD) in code-division multiple-access (CDMA) systems. In this paper, a novel particle swarm optimization (PSO) algorithm is suggested to carry out MUD for synchronous CDMA systems. This work considers two new aspects, namely an adaptive velocity updating mechanism based on Newton method and a dynamic inertia weight into the standard PSO. These mechanisms can provide more diversity to help avoiding premature convergence and significantly improve the bit error rate performance. Several computer simulation results demonstrate that the proposed modified PSO detector significantly outperforms the decorrelating detector, the linear minimum mean square error detector, and the standard PSO-based detector.     

改进微遗传算法在多用户检测技术中的研究

微遗传算法是一种基于小种群进化的遗传算法,它的应用较大地降低了运算复杂度。从对微遗传算法种群中个体数目的讨论入手,改进了微遗传算法,并将其与多用户检测技术结合,提出了一种新的基于微遗传算法的改进型多用户检测器,进行了理论依据和仿真性能分析。仿真结果表明：该检测器在性能上接近最佳多用户检测器,计算复杂度较低。     

软判决并行干扰消除多用户检测器在未来通信系统中的应用

软判决并行干扰消除器(parallel interfer-ence canceller,PIC)是一种十分接近实用的多用户检测器,文中展示了软判决并行干扰消除多用户检测器在两种主要的第三代移动通信系统候选标准(W—CDMA和CDMA2000)中的应用,并通过仿真验证了其性能改善。     

Optimization of Power Allocation for Interference Cancellation With Particle Swarm Optimization

In code division multiple access (CDMA) systems a significant degradation in detection performance due to multiuser interference can be avoided by the utilization of interference cancellation methods. Further enhancement can be obtained by optimizing the power allocation of the users. The resulting constrained single-objective optimization problem is solved here by means of particle swarm optimization (PSO). It is shown that the maximum number of users for a CDMA system can be increased significantly if an optimized power profile is employed. Furthermore, an extensive study of PSO control parameter settings using three different neighborhood topologies is performed on the basis of the power allocation problem, and two constraint-handling techniques are evaluated. Results from the parameter study are compared with examinations from the literature. It is shown that the von-Neumann neighborhood topology performs consistently better than gbest and lbest. However, strong interaction effects and conflicting recommendations for parameter settings are found that emphasize the need for adaptive approaches.      

Sign-weighted peak minimization problem for feedback systems

This note studies the problem of minimizing a parameterized convex combination of the overshoot and undershoot of a single-input-single-output (SISO) discrete-time system to a fixed input. We provide a simple condition for the solution existence and characterize the structure of optimal solutions. It is shown that a known l_∞ suboptimal scheme also works in our problem. In addition, we make a comparative analysis with the l_∞ problem     

Computational complexity of optimum multiuser detection

Optimum centralized demodulation of the independent data streams transmitted simultaneously by several users through a Code Division Multiple-Access channel is considered. Each user sends an arbitrary assigned signal waveform, which is linearly modulated by symbols drawn from a finite alphabet. If the users are asynchronous, the optimum multiuser detector can be implemented by a Viterbi algorithm whose time-complexity is linear in the number of symbols transmitted by each user and exponential in the number of users. It is shown that the combinatorial problem of selecting the most likely transmitted data stream given the sufficient statistics (sequence of matched filter outputs), and the signal energies and cross-correlations is nondeterministic polynomial-time hard (NP-hard) in the number of users. And it remains so even if the users are restricted to be symbol-synchronous.The performance analysis of optimum multiuser detection in terms of the set of multiuser asymptotic efficiencies is equivalent to the computation of the minimum Euclidean distance between any pair of distinct multiuser signals. This problem is also shown to be NP-hard and a conjecture on a longstanding open problem in single user data communication theory is presented.This work was partially supported by the National Science Foundation under Grant ECS-8504752, and by the US Army Research Office under Contract DAAL03-87-K-0062.     

Multiuser Receiver for DS-CDMA Signals in Multipath Channels: An Enhanced Multisurface Method

This paper deals with the problem of multiuser detection in direct-sequence code-division multiple-access (DS-CDMA) systems in multipath environments. The existing multiuser detectors can be divided into two categories: 1) low-complexity poor-performance linear detectors and 2) high-complexity good-performance nonlinear detectors. In particular, in channels where the orthogonality of the code sequences is destroyed by multipath, detectors with linear complexity perform much worse than the nonlinear detectors. In this paper, we propose an enhanced multisurface method (EMSM) for multiuser detection in multipath channels. EMSM is an intermediate piecewise linear detection scheme with a run-time complexity linear in the number of users. Its bit error rate performance is compared with existing linear detectors, a nonlinear radial basis function detector trained by the new support vector learning algorithm, and Verdu's optimal detector. Simulations in multipath channels, for both synchronous and asynchronous cases, indicate that it always outperforms all other linear detectors, performing nearly as well as nonlinear detectors     

用于长码CDMA系统上行链路的两种多用户检测器

本文介绍了应用于长码CDMA系统上行链路的两种多用户检测器,对所估计的信道向量的统计特性进行了分析和验证,并通过仿真研究了接收机的性能。     

基于改进卡尔曼滤波算法的盲多用户检测器

基于盲检测器的新典范表示形式,提出了一种多径信道下CDMA系统的盲多用户检测器。该检测器使用了一种改进的自适应卡尔曼滤波算法,它在进行状态滤波的同时,在线估计时变的未知噪声统计特性,提高了算法的滤波精度,确保了算法收敛于期望用户。仿真表明,对比原有的随机梯度（LMS）算法,该算法的收敛、跟踪性能更好,且误码率减小了18.7%。     

Minimization of a regulated response to a fixed input

The problem of minimizing a regulated output due to a specific bounded input is solved in the SISO (single-input single-output) discrete-time case. It is shown that, in most situations, the optimal solution will not exist, but given any ϵ>0, it is possible to find a suboptimal solution with performance within ϵ of the optimal performance. The proposed approach is extended to the problem of shaping the error transient response. It is shown how time-domain templates can be used in this problem in the same way that frequency-weighting functions are used in the H^∞ and H² problems