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本文介绍了一种将正交频分复用(OFDM)技术和码分多址(CDMA)技术相结合的多载波CDMA (MC-CDMA)系统,分析了MC-CDMA系统的发射端和接收端的结构,建立了MC-CDMA系统的信号模型,详细分析了MC-CDMA中的多址干扰形式,以及针对MC-CDMA系统的多用户检测原理,提出了一种基于最小误码率准则的多用户检测算法。理想的基于最小误码率准则的多用户检测算法在实际中难于实现,本文采用估计概率密度函数的方法,推导出了一种自适应实现的最小误码率多用户检测算法。仿真结果表明,该算法能够有效抑制多址干扰,降低误码率,同时,该算法还具有比基于最小均方误差准则的多用户检测器更低的误码率的优点。 相似文献
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对多载波码分多址(MC-CDMA)系统的干扰受限问题,提出了利用小波变换良好的时频局部特性和神经网络的良好自学习能力,提高多用户检测性能的原理。同时为解决网络权值和参数修正进化缓慢并且容易陷入最小的问题,采用增加动量项的方法提高网络学习效率。建立了基于小波神经网络的多用户检测器并应用于MC-CDMA系统中。用MATLAB/Simulink软件搭建仿真系统,接收端采用解相关检测(MMSEC)和正交恢复(ORC)检测算法。实验表明,基于小波神经网络的多用户检测技术在误码率(BER)性能上更接近单用户的BER性能。 相似文献
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该文提出一种量子自适应粒子群优化算法,该算法中,粒子位置的编码采用量子比特实现,利用粒子飞行轨迹信息动态更新量子比特的状态,并引入量子非门实现变异操作以避免陷入局部最优。用该算法训练神经网络,实现了径向基函数(RBF)神经网络参数优化,建立了基于量子自适应粒子群优化RBF神经网络算法的网络流量预测模型。对真实网络流量的预测结果表明,该方法的收敛速度和预测精度均要优于传统RBF神经网络法、粒子群-RBF 神经网络法、混合粒子群-RBF 神经网络法和自适应粒子群-RBF 神经网络法,并且预测效果不易受时间尺度变化的影响。 相似文献
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为了最小化多用户OFDM系统的总发射功率,提出利用改进的粒子群算法与遗传算法相结合的联合算法(PSO-GA)来搜索最优的子载波和比特分配。该算法首先利用改进粒子群算法对系统的子载波和比特分配进行优化。算法运行过程中,当更新后的粒子速度大于最大粒子速度或小于最小粒子速度时,取最大粒子速度与最小粒子速度区间中的一个随机值作为更新的粒子速度。待PSO-GA算法的改进粒子群算法收敛后,将收敛后的种群作为遗传算法的初始种群,再利用遗传算法进行系统的子载波和比特优化分配,进而得出最优解。仿真结果表明,利用该算法比利用遗传算法、粒子群算法与Zhang算法的分配方案使系统需要的总发射功率降低2~10 dB。 相似文献
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为了提高多用户检测技术的性能,改善粒子群算法的局部搜索能力,将克隆选择算法(CS)和传统离散粒子群算法(DPSO)相结合,文中提出一种改进的自适应克隆选择粒子群优化算法(ACSPSO),并用于多用户检测。仿真证明,这种基于ACSPSO的检测器在误码率和收敛速度上都比DPSO和CS得到明显改善。 相似文献
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针对STBC-MIMO MC-CDMA多用户检测方法存在计算复杂度高、工程实现困难的问题,提出利用一种混合量子进化算法(HQEA)解决STBC-MIMO MC-CDMA多用户检测问题,该算法不仅具有较低的计算复杂度,而且解决了量子进化算法容易陷入局部最优解、参数个数较多和通过查表来更新量子门的问题。仿真表明,该算法在STBC-MIMO MC-CDMA系统多用户检测问题上,具有比其他智能算法更强的跳出局部最优和寻找全局最优的能力。 相似文献
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Multiuser reception using Hopfield neural network (HNN) for asynchronous multicarrier code-division multiple access (MC-CDMA) in a multipath fading channel is investigated. We have shown that by the appropriate choice of HNN parameters from the channel state information, the HNN can collectively resolve the multipath fading effects and the multiple-access interference in the system 相似文献
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提出一种基于多带复小波和空时编码的多载波CDMA系统,研究了其在瑞利衰落信道下的误比特性能。理论分析和仿真结果表明该系统要明显优于通常MC-CDMA系统,具有与采用循环前缀(CP)的MC-CDMA相比较的优势,而且能够克服通常MC-CDMA系统插入CP所带来能量的减少和频谱效率的降低。同时空时编码技术的应用,显著增强了系统抗多径干扰和多址干扰的能力,进一步提高了系统性能。 相似文献
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LS码是一种具有正交互补性质的多址码,相关性能优良,因此可以用于克服符号间干扰(ISI)和多址干扰(MAI)。它提出了一种克服多载波码分多址(MC-CDMA)系统多址干扰的LS码接入法,并对采用这两种码的MC-CDMA系统进行仿真对比,对比结果表明:相关函数特性好的LS码序列具有较好的正交性更适合于同步的MC-CDMA系统,其克服多址干扰性能较MC-Walsh-CDMA系统强。 相似文献
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Belal A. Al-fuhaidi Hossam Eldin A. Hassan Moataz M. Salah 《Wireless Personal Communications》2014,74(2):439-456
Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement. 相似文献
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Multi-Code Direct-Sequence Code-Division-Multiple-Access (MC-CDMA) has been proposed as a flexible multiple access scheme for wireless packet networks that support a large variety of mobiles with different and even time-varying rates. Using MC-CDMA, traffic streams with significantly different transmission rates can be easily integrated into a unified architecture, with all the transmissions occupying the same bandwidth and having the same spread spectrum processing gain. In this paper, we address medium-access and interference issues in MC-CDMA wireless packet networks. For medium access, we propose and study Multi-Code CDMA (MC-CDMA) with Distributed-Queueing Request Update Multiple Access (DQRUMA) to form a unified bandwidth-on-demand fair-sharing platform for multi-rate wireless services. DQRUMA is an efficient demand-assignment multiple access protocol for wireless access and scheduling. Pseudo-Noise (PN) codes (primary codes) and optimal power levels are allocated to the mobiles on a slot-by-slot basis, and a Maximum Capacity Power Allocation (MCPA) criterion exploits the sub-code concatenation property of the MC-CDMA transmission. Simulation results show that the system provides close to ideal-access performance for multi-rate mobiles, both with homogeneous traffic characteristics and with a mix of heterogeneous traffic characteristics. Finally, we analyze the effects of MC-CDMA intercell interference on the reverse link (i.e., mobile to cell site) and investigate interference reduction by using the Maximum Capacity Power Allocation (MCPA) criterion. Our results show significant reduction in reverse-link MC-CDMA intercell interference is possible using the MCPA criterion. 相似文献
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The reverse link performance of hierarchical wideband multicarrier code-division multiple-access (MC-CDMA) systems is studied. An MC-CDMA system divides the system bandwidth into several equal narrow subbands that are used to transmit multiple signal waveforms in parallel. MC-CDMA systems are known to be robust to multipath fading and narrowband interference. We propose a hierarchical MC-CDMA system where the microcell(s) occupies a fraction of the available subbands. It is shown that such an architecture is a viable way of supporting microcell traffic while protecting the existing macrocell traffic. The effects of microcell Nakagami fading and power control error are also studied. 相似文献
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《Communications, IEEE Transactions on》2005,53(3):545-545
Multiple-Access Interference Suppression for MC-CDMA by Frequency-Domain Oversampling A technique for interference suppression in multicarrier code-division multiple-access (MC-CDMA) systems is proposed which exploits the structural differences in signals that arrive at the receiver with Doppler shifts or carrier offsets. Oversampling the received signal in the frequency domain and properly combining the samples provides the interference suppression. Frequency-domain oversampling is accomplished by using a time extension of the conventional MC-CDMA signal or unconsumed portions of the cyclic prefix. Furthermore, a receiver structure is introduced that despreads and combines groups of samples so that a linear minimum mean-squared error solution for combining the groups is easily found. This combining scheme increases the signal-to-interference ratio experienced by the desired user in the MC-CDMA system. In addition, the receiver performs as well in severe near–far scenarios when there is sufficient frequency separation between the signals of the desired user and an interferer. Numerical results show that the proposed receiver significantly outperforms the conventional MC-CDMA receiver in many channel realizations. 相似文献
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在粒子群优化(Particle Swarm Optimization, PSO)和混合蛙跳算法(Shuffled Frog-Leaping Algorithm, SFLA)的基础上,该文提出了一种新的混合粒子对优化(Shuffled Particle-Pair Optimizer, SPPO)算法,应用于矢量量化的说话人识别。该算法将全局信息交换和局部深度搜索相结合寻求最佳的说话人码本。群体按适应值分为3个粒子对,每个粒子对由两个粒子构成,按先后顺序执行PSO算法中的速度位置更新和LBG算法以实现局部细致搜索,间隔一定的迭代次数通过SFLA混合策略实现粒子对间的信息交换,从而使群体向全局最优解靠近。实验结果表明,本算法始终稳定地取得显著优于LBG,FCM,FRLVQ-FVQ和PSO算法的说话人识别性能,较好地解决了初始码本影响的识别性能的问题,且在计算时间和收敛速度方面有相当的优势。 相似文献