共查询到20条相似文献,搜索用时 31 毫秒
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Seen-Ho Hwang Seong-Lyun Kim Hyun-Seo Oh Chang-Eon Kang Jung-Young Son 《Electronics letters》1997,33(19):1602-1603
Traffic nonuniformity degrades the performance of CDMA cellular systems. The authors present a new algorithm called the variable threshold soft handoff (VTSH) which reduces the performance degradation due to traffic nonuniformity in CDMA cellular systems. Unlike the conventional fixed handoff thresholds, the proposed algorithm allows the handoff thresholds (T ADD and T DROP) to vary dynamically according to the traffic density of each cell. This algorithm has been implemented by means of computer simulation and the results show that VTSH improves the overall CDMA system performance in terms of outage probability. The VTSH algorithm can easily be applied to CDMA cellular systems without any modification 相似文献
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CDMA技术已经在当前第三代通信(3G)标准中得到广泛采用,其中多用户检测技术能明显地改善CDMA通信性能,提高其系统容量。本文充分利用空时二维信息来增强CDMA系统的性能,提出一种基于Tank-Hopfield网络多用户检测算法:利用T-H网络快速计算LS的能力,来求解空时多用户检测问题。分析和仿真实验表明该算法的有效性,相比传统的子空间等方法,该方法具备更好的收敛速度和检测性能。 相似文献
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Hsiao‐Hwa Chen 《International Journal of Communication Systems》1999,12(1):49-64
Most CDMA systems serve only finite number of active users. Therefore, using Gaussian approximation to evaluate its performance is inappropriate. In such finite CDMA systems, the selection of spreading codes is of great importance because its performance is very much spreading‐code‐dependent. In this paper, a new algorithm based on multiple variable Bernoulli process is introduced to evaluate bit error rate due to co‐channel interference and thus the capacity of a CDMA system. The algorithm can also be used for large‐sized CDMA systems. The results show that small Kasami and Gold‐like codes offer higher capacity than the others do. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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The authors address the effect of code division multiple access (CDMA) on the performance of wireless packet-switched networks. Although CDMA can enhance throughput, the delay at small traffic loads suffers from bandspreading. For imperfect signal separation at the receiver, performance benefits from CDMA may be lost. The capacity of the particular stack algorithm addressed for collision resolution can be enhanced from 0.32 to ~0.40 if a 10 dB spreading gain with perfect signal separation is employed 相似文献
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针对于CDMA系统自适应天线阵列,提出了一种新的盲自适应MSINR(Maximum Signal-to-Interference plus noise ratio)波束形成算法.首先,将MSINR准则转化为一种新的无约束损失函数,并且从理论上分析该损失函数的性质.然后,应用自适应拟牛顿方法得到在线迭代波束形成算法.该算法无需训练序,而是利用CDMA信号自身的结构特点,结合空间处理提高了系统性能.最后,给出了仿真结果,表明算法具有较快的收敛速度和良好的动态跟踪能力. 相似文献
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分析了当前RFID系统的防碰撞算法,研究防碰撞机制和相关的算法,结合跳频技术与CDMA提出基于跳频CDMA的RFID防碰撞算法。算法以不同的相互正交的码序列区分标签,在同一个时隙中标签通过跳频来防止碰撞的产生。通过一个2.4GHz有源RFID系统来实现和验证算法。实验表明,跳频CDMA算法能有效防止标签碰撞的产生,在时延方面优于二进制树形搜索算法。 相似文献
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功率控制技术是CDMA系统中减小多址干扰的一项关键技术。针对TDD-CDMA系统的多速率业务,提出了一种功率速率联合控制算法,速率控制保证不同业务的服务质量要求,通过线性优化过程获得最大化流量时的功率速率分配。仿真结果表明这一算法是一种近似的最优化功率速率联合控制方案,能够有效地提高系统的总容量,优化系统性能。 相似文献
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多用户检测技术在实际应用中,难以解决的问题是在减少计算复杂度的同时又提高系统性能。本文针对空时CDMA系统设计了一种多用户检测算法,即附带噪声梯度的最速下降算法。此算法利用变步长迭代的思想实现多用户检测,避免了最小均方误差(MMSE)多用户检测庞大而复杂的求逆运算和固定步长收敛速度较慢的问题。计算机仿真结果表明,在空时CDMA系统中使用本文算法,收敛速度大大增加,同时在保持系统性能的前提下能够容纳较多的用户。 相似文献
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In this paper, we consider multiple‐input multiple‐output (MIMO) multi‐tone code division multiple access (MT‐CDMA) uplink transmission over multipath fading channels. The zero‐forcing vertical Bell Laboratories layered space‐time architecture (ZF V‐BLAST) algorithm and maximum ratio combining scheme are applied at the receiver. The average bit error rate (BER) expression is derived provided that the number of receive antennas is not less than that of transmit antennas. The BER expression is verified by simulations. Numerical results show that the numbers of transmit and receive antennas have significant effects on the BER performance of the considered system. Spatial and path diversity show different capabilities to improve the BER performance. The MIMO MT‐CDMA system based on the ZF V‐BLAST algorithm is capable of achieving a better BER performance and a higher capacity than the conventional MT‐CDMA system. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Ebrahim Karami 《Wireless Personal Communications》2012,65(1):53-65
In this paper, a new detection algorithm is proposed for turbo coded Code Division Multiple Access (CDMA) signals in detect and forward cooperative channels. Use of user cooperation makes much improvement in the performance of CDMA systems. Due to the special structure of CDMA systems, cooperative schemes increase the sum and cutoff capacities of CDMA based wireless systems and improve the quality of user-partner link which enhances the overall performance of the system. In this paper, a new combining scheme is proposed that makes the receiver more robust against the decision errors in the partner link. This structure is simulated for punctured 1/2 rate 4 states turbo code in a channel with first order Markov time variation and different Rice factor variances. Through various simulations, it is shown when the channel estimates are available in the partner and receiver, the cooperation between users provides much diversity gain especially while using the new proposed combining algorithm. 相似文献
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本文提出了一种宽线性共轭梯度算法,分析了算法在均值意义下的收敛性,并给出了算法稳定条件。仿真表明,新算法应用于码分多址系统多址干扰抑制时的性能优于Yin(2003)及Schober(2004)所提出的算法。 相似文献
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非周期扩频的同步CDMA系统下行信道的分数阶间隔信道估计 总被引:1,自引:0,他引:1
使用正交扩频码的同步CDMA系统具有对抗同信道干扰的能力,但是多径传播导致信号失去正交性,互相关值增加。在这些情况下,需要对信道进行估计以提高接收机检测性能。以往的基于子空间的CDMA信道估计算法都是在chip速率采样的基础上得到的,其条件是接收信号满足Nyquist定理且信道是最小相位系统,这些条件在实际情况中是很难满足的。该文提出一种应用于非周期扩频的同步CDMA系统的下行信道的分数阶间隔信道估计的算法。计算机仿真表明了算法是有效的。 相似文献
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提出CDMA(码分多址)定位系统中子相关检测算法。首先介绍了CDMA定位系统的构成和相干相关、非相干相关联合检测算法,接着给出了子相关检测算法和计算机分析结果,分析表明,文中提出的方法可有效地节省硬件资源,显著降低相关检测算法的计算复杂度,提高相关检测算法的效率和实时性。 相似文献