基于并行混沌遗传混合算法的多用户检测

基于传统遗传算法的多用户检测器易陷入局部最优解且收敛较慢,影响实时性。本文利用混沌优化算法的优势来弥补遗传算法的这一缺陷,使两种算法优势互补,同时采用具有“迁移策略”的并行搜索机制,提出了一种新的次优多用户检测方法———并行混沌遗传混合算法(PCGA),并在同步CDMA系统中对其性能进行了研究。仿真结果表明,我们提出的这种算法能有效克服传统遗传算法易陷入局部极小的问题,计算量小,收敛速度快,在抗干扰与克服“远-近”效应方面均有明显的优势。     

基于并行遗传算法的CDMA优化多用户检测方法

多用户检测技术是第三代移动通信系统CDMA中的一项关键技术。在多用户检测中求解最佳矢量问题可以转化为在遗传算法中求解具有最高适应度函数的问题。本文提出了一种基于并行遗传算法的CDMA多用户检测器,并与最佳多用户检测和传统检测器进行比较,实验结果表明本方法可获得接近最佳检测的性能。由于采用并行遗传算法,这种多用户检测器更易于实时应用和硬件实现。     

基于混沌寻优的CDMA最佳多用户检测方法

混沌运动广泛存在于非线性系统中,它具有遍历性与随机性等优良性质,且在某个域内不可重复的走向每个状态.本文利用混沌的这些优良品质提出了实现码分多址(CDMA)系统上最佳多用户检测的一种混沌寻优方法.计算机模拟表明我们提出的算法具有能克服多址干扰,能寻优到全局极小点,以及能抑制噪声干扰等优点,这为研究CDMA系统上的最佳多用户检测器开辟了一条新的途径.     

基于离散粒子群算法的CDMA多用户检测方法

研究了离散粒子群算法，并将其应用于CDMA多用户检测问题，提出一种基于离散粒子群优化算法的CDMA多用户检测的方法。该方法应用一种新的选择和分区搜索的策略，改进搜索的质量和效率。分析以及实验仿真表明该方法具有计算复杂度低且可以得到较好误码率性能的特点，为寻求新的多用户检测方法提供了思路。     

基于量子遗传算法的CDMA多用户检测技术

多用户检测技术的最优解在常规条件下是个NP难解问题,利用量子态并行计算特性和量子纠缠特性能有效获得多用户检测的最优解,现提出了一种基于量子计算理论和遗传算法理论相结合的量子遗传算法的多用户检测技术.仿真结果表明,此方法在误码率方面具有良好的性能并且其抗多址干扰能力和抗远近效应能力明显优于经典遗传算法多用户检测器和传统检测器.     

一种基于蚁群算法的CDMA多用户检测方法

提出一种基于蚁群优化算法(ant colony optimization algorithm)的CDMA多用户检测(MUD)的方法。该方法在基本蚁群算法的基础上，应用一种新的相遇和搜索分区的策略，来解决最佳多用户检测的组合优化问题，可提高搜索的质量和效率，通过分析以及仿真表明，该方法具有多项式的计算复杂度，并可以得到较好的误码率性能，为寻求新的多用户检测方法提供了思路。     

混合遗传算法在CDMA移动通信多用户检测中的应用研究

研究了将混合遗传算法应用于直接序列码分多址扩频通信的多用户检测,先给出了在异步高斯信道下解调扩频信号的结构框图,然后分析了用混合遗传算法进行多用户检测的理论依据和实际性能。仿真结果表明无论是多址干扰还是抑制远近效应,基于混合遗传算法的检测器都明显优于传统检测器,且其性能非常接近最佳检测器。     

CDMA移动通信系统中的多用户检测技术

本文研究了应用于CDMA移动通信系统中的各种多用户检测技术的原理和优缺点。指出多用户检测技术主要分为线性多用户检测和干扰消除多用户检测两类 ,前者包括解相关检测、最小均方误差检测、子空间斜投影检测和相关矩阵多项式扩展检测 ,后者包括串行、并行干扰消除和判决反馈多用户检测 ,同时对各种多用户检测技术的特点进行了分析比较     

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。     

异步CDMA移动通信系统采用分集接收的多用户检测器

在ＣＤＭＡ移动通信系统中，多址接入干扰可以通过多用户检测技术来消除，而分集接收可以减小信道衰落的影响，本文给出了一类应用解相关检测，天线分集，ＲＡＫＥ多径分集技术的接收机，并对这一类接收机的性能做了分析，结果表明，在上行链路中，应用多用户检测和分集接收能够极大提高接收机的性能。     

Multiuser detection using a genetic algorithm in CDMAcommunications systems

In this study, a hybrid approach that employs a genetic algorithm (GA) and a multistage detector (MSD) for the multiuser detection problem in a code-division multiple-access communications system is proposed. Using this approach: (1) the GA is used as the first stage of the MSD to provide a good initial point for successive stages of the MSD and (2) the MSD is embedded into the GA as a “genetic operator” to improve further the fitness of the population at each generation. Such a hybridization of the GA with the MSD reduces its computational complexity by providing faster convergence. In addition, a better initial data estimate supplied by the GA improves the performance of the MSD, and the embedded MSD improves the performance of the GA. Simulation results for the synchronous and asynchronous cases are provided to show that the approach is promising     

Multiuser detection for overloaded CDMA systems

Multiuser detection for overloaded code-division multiple-access (CDMA) systems, in which the number of users is larger than the dimension of the signal space, is of particular interest when bandwidth is at a premium. In this paper, certain fundamental questions are answered regarding the asymptotic forms and performance of suboptimum multiuser detectors for cases where the desired and/or interfering signal subspaces are of reduced rank and/or have a nontrivial intersection. In the process, two new suboptimum detectors are proposed that are especially well suited to overloaded systems, namely, the group pseudo-decorrelator and the group minimum mean-squared error (MMSE) detector. The former is seen to be the correct extension of the group decorrelator in the sense that it is the limiting form (in the low-noise regime) of the group MMSE detector. Pseudo-decorrelation is also used as a feedforward filter in a new decision feedback scheme. For the particular case of real-valued modulation, it is shown that the proposals of the so-called "improved" linear (also known as "linear-conjugate" or "widely linear") detectors were more simply derived earlier using the idea of minimal sufficiency, which we also apply to the new detectors of this paper.     

Multiuser detection in multipath environments for variablespreading-factor CDMA systems

A way to allow variable data rates in CDMA is by varying the spreading factor in accordance with the data rate requested by the user. A detection scheme suitable for multirate transmission is required in addition to one that combats multiple access interference of other users and intersymbol interference from multipath. In this letter, an energy-add multiuser detection method is combined with a scheme called Cholesky-iterative detection to cope with these challenges. It allows the users to be estimated on a symbol-by-symbol basis, making receiver complexity independent of data package length. Simulation results correspond closely to a single-user lower bound. The results also show that the bit-error probability performances of the various users for the Cholesky-iterative detector are closely clustered, while those of a previously published scheme, decorrelation feedback detection, are more widely spread     

Multiuser detections for optical CDMA networks based on expectation-maximization algorithm

In this paper, we introduce new unblind and blind multiuser detectors for an optical code-division multiple-access system. The detectors have two soft and hard stages. In the soft stage, a soft estimation of the interference is obtained by solving an unconstrained maximum-likelihood problem via the iterative expectation-maximization (EM) algorithm. Then, the hard stage detects the user information bit by solving a one-dimensional Boolean constrained problem conditioned on knowing the interference. Our results reveal that the proposed detectors have very low complexity, and are robust against changes in parameters. Moreover, the numerical results illustrate that despite of their simplicities, our detectors substantially outperform other well-known suboptimum detectors, such as multistage and decorrelating detectors.     

Multiuser detection in asynchronous CDMA frequency-selective fading channels

Multipath fading severely limits the performances of conventional code division multiple-access (CDMA) systems. Since every signal passes through an independent frequency-selective fading channel, even modest cross-correlations among signature sequences may induce severe near-far effects in a central multiuser receiver. This paper presents a systematic approach to the detection problem in CDMA frequency-selective fading channels and proposes a low complexity linear multiuser receiver, which eliminates fading induced near-far problem.We initially analyze an optimal multiuser detector, consisting of a bank of RAKE filters followed by a dynamic programming algorithm and evaluate its performance through error probability bounds. The concepts of error sequence decomposition and asymptotic multiuser efficiency, used to characterize the optimal receiver performance, are extended to multipath fading channels.The complexity of the optimal detector motivates the work on a near-far resistant, low complexity decorrelating multiuser detector, which exploits multipath diversity by using a multipath decorrelating filter followed by maximal-ratio combining. Analytic expressions for error probability and asymptotic multiuser efficiency of the suboptimal receiver are derived that include the effects of multipath fading, multiple-access interference and signature sequences correlation on the receiver's performance.The results indicate that multiuser detectors not only alleviate the near-far problem but approach single-user RAKE performance, while preserving the multipath diversity gain. In interference-limited scenarios multiuser receivers significantly outperform the RAKE receiver.This paper was presented in part at the Twenty-Sixth Annual Conference on Information Sciences and Systems, Princeton, NJ, March 1992 and MILCOM'92, San Diego, CA, October 1992. This work was performed while author was with the Department of Electrical and Computer Engineering, Northeastern University, Boston, USA.     

基于组合混沌遗传算法的最小测试用例集生成

最小测试用例集生成是软件测试的重要研究领域之一.将具有均匀分布特性的Chebyshev和Logistic混沌映射相结合的混沌序列引入遗传算法的选择、交叉和变异操作,并在遗传测试用例选择方法中添加混沌扰动,实现全局最优,以解决遗传算法用于测试用例集约简时局部搜索能力弱、易早熟收敛等问题.在随机生成的测试用例需求对应关系及Siemens测试套件等实例上进行了实验研究,并与现有的经典方法在测试用例集生成规模和算法执行时间上进行了比较,实验结果表明,在保持算法执行时间的基础上,在遗传测试用例方法中引入混沌映射有助于生成规模更小的测试用例集.     

Polygonal approximation based on coarse-grained parallel genetic algorithm

This paper proposes to apply coarse-grained parallel genetic algorithm (CGPGA) to solve polygonal approximation problem. Chromosomes are used to represent digital curves and genes correspond to points of curves. This method divides the whole population into several subpopulations, each of which performs evolutionary process independently. After every migration interval number of generations, these subpopulations exchange their information with each other. Inspired by the designing theory of ensemble learning in machine learning, this paper further improves the basic CGPGA through adopting different but effective genetic algorithms, respectively, in different subpopulations. Both the diversity among different subpopulations and the accuracy in each individual subpopulation are ensured. Experimental results, based on four benchmark curves and four real image curves extracted from the lake maps, show that the basic CGPGA outperforms the used genetic algorithm, and further the improved CGPGA (ICGPGA) is more effective than the basic CGPGA, in terms of the quality of best solutions, the average solutions, and the variance of best solutions. Especially for those larger approximation problems, the ICGPGA is more remarkably superior to some representative genetic algorithms.     

基于共享存储的并行狭义遗传算法

遗传算法具有简单、易算且方便分布并行处理等特点,基于这种优势,遗传算法被广泛应用于众多领域范围内,比如机器学习、工业控制等.为解决高难度的非线性及其相关问题,采用基于共享存储的并行狭义遗传算法,可以有效实现对数据级的并行操作,具有较强的并行度,其只需较少的通讯开销就能获得比原先更高的运行效率,至少提高至50％以上.文中详细阐述了基于共享存储的并行狭义遗传算法,仿真实验验证了其正确性和高效性.     

Multiuser detection of quasisynchronous CDMA signals using lineardecorrelators

A linear decorrelator detector is proposed for a quasisynchronous code-division multiple-access (QS-CDMA) cellular system. It is assumed that each of N users has a Global Positioning System (GPS) generated local clock and attempts to transmit synchronously with the other users in its cell. The base station thus receives N signature waveforms which are approximately synchronized, but with a small timing error due to local oscillator drift, Doppler shifts, and variable distances from the mobiles to the base. The residual timing offset is discretized, and a decorrelator is constructed which attempts to reject the multiuser interference vectors corresponding to the set of possible offsets. A noncoherent version of the decorrelator detector is presented, along with a maximum-likelihood scheme for synchronizing to the desired signal. Bounds and analytical results for the bit-error rate (BER) are obtained for various interferer conditions     

Multiuser receivers for CDMA systems in Rayleigh fading channels

Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection (MLSD) receiver is derived and a general suboptimal receiver to approximate the MLSD is proposed. The performance of the parallel interference cancellation (PIC) and decorrelating receivers is compared. The PIC receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to the channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. The performance of data-aided (DA) and decision-directed (DD) multiuser channel estimation is also compared. DA channel estimation is shown to be more robust than DD channel estimation, which may suffer from BER saturation caused by hangups at high signal-to-noise ratios (SNRs). The impact of channel estimation filter impulse response on the BER is studied by comparing optimal and suboptimal channel estimation filters. The implementation complexity of the decorrelating and PIC receivers is compared in terms of required floating point operations and clock cycles in a practical communication scenario. It is observed that the PIC receiver is only moderately more complex to implement than the conventional matched filter bank receiver, whereas the decorrelating receiver is significantly more complex