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MC-CDMA系统是干扰受限系统,存在多址干扰。本文提出一种基于神经网络和粒子群算法的MC-CDMA多用户检测方法。在粒子位置更新中,随机选择部分粒子作为Hopfield神经网络的神经元组成的个体,进行神经网络的更新;其他粒子仍采用原粒子群算法的位置更新策略,从而能加快粒子群算法的收敛速度以及降低计算复杂度。仿真表明在算法参数相同时,该多用户检测方法在误码率、收敛速度、系统容量、抗远近能力等方面都优于基于粒子群算法的多用户检测和基于神经网络的多用户检测,更加逼近于最佳多用户检测的性能。 相似文献
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CDMA系统粒子群多用户检测算法 总被引:1,自引:0,他引:1
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。 相似文献
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基于NLMS的CDMA盲自适应多用户检测算法研究 总被引:1,自引:0,他引:1
多用户检测是抑制DS-CDMA系统多址干扰最有效的技术之一。由于所需的先验知识仪有期望用户的地址码,盲多用户检测技术的研究尤受重视。最小输出能量(MOE)准则被广泛用于盲线性多用户检测。目前已提出的该类检测器多采用LMS或RLS算法。本文则研究基于NLMS算法的盲自适应检测技术,并进一步提出盲自适应变步长NLMS检测器和参数可变的盲自适应变步长NLMS检测器。它们具备很好的收敛速度和跟踪能力,以及较高的输出信干比,同时计算复杂度仅为O(3N)或O(4N),非常适合硬件实现。 相似文献
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多用户检测技术是第三代移动通信系统的关键技术,具备良好的抗多址干扰和远近效应的性能。从移动通信系统抗干扰的角度出发,本文分析了CDMA系统中多址干扰(MAI)产生的原因,对多用户检测技术的概念系统模型及几种基本的多用户检测算法进行了阐述,分析了它们的原理,并比较了各种多用户检测的优缺点,最后指出了其局限性及研究方向。 相似文献
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该文讨论了采用基于最大信噪比比准则的最优天线阵与多用户检测技术相结合的多址干扰抑制方法,并从理论上证明了该方法在系统误码率性能上比单一的多用户检测方法有较大的提高。 相似文献
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In order to accommodate different types of traffic in future wirelesscommunications, it is necessary to consider a system, which can operatesatisfactorily at multiple transmission rates. Due to its capability to copewith the hostile frequency selective fading, that limits transmission rate,and its suitability to handle multi-rate data, multi-carrier CDMA (MC-CDMA)has recently drawn considerable attention as a suitable candidate forsupporting multimedia services in wireless communications. Multi-rate accessschemes where users are able to transmit at different data rates on MC-CDMAsystems are presented in this paper. Four multi-rate access schemes: uncodedfixed spreading length (UFSL), coded fixed spreading length (CFSL), multi-codefixed spreading length (MFSL) and variable spreading length (VSL) schemes areproposed. With these schemes, different traffic such as voice, video and highrate data can be transmitted seamlessly through one MC-CDMA infrastructure.A chip-level minimum mean square error combining (MMSEC) technique is employedfor joint energy combining and interference cancellation purpose. Theperformance of these schemes with MMSEC is compared by both theoreticalderivations and simulation results under frequency selective Rayleigh fadingchannels. 相似文献
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Multi Carrier Code Division Multiple Access (MC-CDMA) is an appropriate modulation technique for high data rates. In this modulation scheme, employing of combining techniques are unavoidable for restoring orthogonality between different user signals. In this paper, the combining techniques of a MC-CDMA based on wavelet transform are studied. The partial combining of the wavelet based MC-CDMA system is suggested and its performance is compared with the maximum ratio combining (MRC), equal gain combining (EGC), orthogonality restoring combining (ORC) and the minimum mean square error (MMSE) techniques. Orthogonal filter banks of the wavelet transforms provide orthogonality between the wavelets and scaling functions, subcarriers and spreading sequences. Therefore, they provide new dimensions in combatting multipath fading, inter carrier interference (ICI) and narrowband interference in MC-CDMA systems. Furthermore, analysis of partial combining shows that coefficients of this technique can be computed in a simple manner. Simulations results indicate that the bit error rate (BER) performance of the proposed scheme is almost comparable with the MMSE combining scheme and the proposed system has a proper performance in terms of BER versus the signal to noise ratio (SNR) in frequency selective fading channels. 相似文献
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瑞利衰落信道中MC-CDMA系统的载波频率偏移性能 总被引:1,自引:0,他引:1
多载波CDMA(MC-CDMA)技术结合了OFDM和CDMA技术的优点,在无线衰落信道中传输高速数据时具有突出的性能。但由于MC-CDMA采用了多载波技术,载波频率偏移对系统性能的影响非常大。本文对瑞利衰落信道下存在载波频率偏移的MC-CDMA系统性能进行了理论分析并对误码率进行了详细讨论。 相似文献
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Yu Xiangbin Zhang Xiaodong Xu Dazhuan Bi Guangguo 《电子科学学刊(英文版)》2006,23(6):837-841
In this paper, a Complex Wavelet Packet (CWP-MC-CDMA) system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re- ceiver antennas in the uplink, we employ the Space Diversity Combining (SDC) technique to improve the sys- tem pertbrmance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh lading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial lading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate (BER) performance over the Discrete Fourier Transform (DFT) and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system. 相似文献
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在分析多载波CDMA(MC-CDMA)技术原理的基础上,利用优化的多带复小波作为多载波调制以及turbo 编码作为信道编码,提出一种基于优化多带复小波和turbo编码的MC-CDMA系统,研究了其在瑞利衰落信道下的误比特率性能。该系统能克服通常MC-CDMA系统插入循环前缀(CP)所带来频谱效率的降低,并能充分利用turbo 码的良好抗信道衰落能力,进一步提高系统性能。理论分析和仿真结果表明该系统性能要好于通常MC-CDMA系统,具有与采用CP的MC-CDMA系统相比较的优势。同时turbo编码的应用显著增强了系统抗多径衰落和多址干扰的能力。 相似文献
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1 IntroductionTheCDMAsystembasedontransmittingpar allelmulti carrierswasfirstproposedatPIMRC’93byN .Yee,A .Choulyandsoon[1 ] .Thisschemeap pliesOFDMtechniquetoCDMAsystems,whichef fectivelyutilizestheperformanceofanti fading ,an ti interferenceofOFDM ,andcombinest… 相似文献
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该文提出了一种新的多载波码分多址(MC-CDMA)系统。与传统的MC-CDMA系统相比,其主要区别是要发送的数据比特先串并转换为多个并行分支,每一个分支用一组正交子载波进行调制。在每个分支上,使用相同扩频序列的不同码片调制子载波。这种系统能更有效地利用传输带宽,实现频率分集。由于该系统降低了每个子载波上的数据速率,扩频序列更容易同步。最后给出了在瑞利衰落信道下的性能分析。 相似文献
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With the fast growth of Internet services, the demand for wireless high speed and advanced multimedia communications is rapidly increasing. Initial multimedia services have already been offered in the second generation systems (2-G). Currently, the third generation systems (3-G) are being deployed and it will support up to 2 Mbps packet oriented data services. But it is expected that the demand for higher data rate and large variety of high quality services will increase further more. Therefore, it is mandatory for the fourth generation systems (4-G) to take each user's quality of service (QoS) control into account.In this paper, we firstly describe an overview on requirements and technical issues for the 4-G systems, and wireless QoS control issues considering End-to-End QoS control in the IP network. Next, we propose broadband wireless access method for the fourth generation mobile communication systems. The proposed method for downlink is based on MC-CDMA (Multi-Carrier Code Division Multiple Access) with Multi-Timeslot, in which total downlink resources are split into three aggregates according to the QoS classes in time domain. It is considered that one of the typical advantages for the MC-CDMA is the effect of frequency diversity. We evaluated the effect by computer simulation using ray-traced propagation model. Simulation results show that short-term fading can be relaxed. Furthermore, we propose Multi-Level (ML) ARQ as one of the link adaptation methods. Simulation results show that the proposed scheme has a good performance with throughput and average retransmission power. 相似文献