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In this paper we evaluate the error performance of wireless communication systems using M-branch maximal ratio combining (MRC) with multiple cochannel interference. Three cochannel interference models are considered: (A) L independent identically distributed (i.i.d.) Nakagami-m cochannel interferers; (B) L independent cochannel interferers consisting of L-N Nakagami-m interferers and N Rayleigh interferers; (C) L independent cochannel interferers in which each interferer follows Nakagami-m distribution for a fraction of time and Rayleigh distribution for the remaining time. In addition, the desired signal assumes Nakagami-m fading. This paper considers that an exponential correlation model is assumed for the desired signals received on each branch, while the interferers are assumed independent. Closed-form expressions are derived for the probability density functions (PDFs) of the instantaneous signal-to-interference power ratio (SIR) at the output of the MRC for the three interference models. Using these SIR PDFs, further closed-form expressions to evaluate the outage probability (OTP) and the average bit error probability (BEP) of differential phase-shift keying (DPSK) are derived. Numerical results showing the impacts of the system parameters on the OTP and the average BEP are then presented. 相似文献
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This paper presents an equalization structure in which antennadiversity, adaptive decision feedback equalization (DFE), interleavingand trellis-coded modulation (TCM) can be effectively combined to combatboth ISI and cochannel interference in cellular mobile radioenvironments. The feedback filter of the DFE can use either tentative orfinal decision symbols of the TCM Viterbi decoding to cancel tail ISIwith the square root Kalman algorithm. A performance bound on theaverage pairwise error probability for TCM under perfect interleavingand equalization is obtained by analysis. Some simulation results whichillustrate the potential of the proposed system will also be given. Inparticular, a performance comparison between the proposed method anduncoded QPSK modulation will be undertaken. 相似文献
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Analysis and simulation results of a DS spread spectrum system in which data detection is based on a matched filter and a median filter are introduced. The results are compared with a simple linear interference cancellation method using a transversal filter. The probability of bit error is calculated in the AWGN channel and with continuous tone jamming when ideal autocorrelation function of the spreading code is assumed. The effect of CW jamming can be eliminated by both methods, so the comparisons are made in the AWGN channel. It is concluded that the median filter causes a loss compared with the transversal filter. The loss is about 1.2 dB when the window length is the minimum. The loss decreases as the window length increases, being, e.g., about 0.35 dB with window length 7 and 0.1 dB with length 19. Therefore, no other cancellation method is needed in data detection when the median filter is already used as an aiding device in the code acquisition process. 相似文献
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匹配滤波器因具有大的时间带宽积而在扩频和CDMA通信中受到极大重视,不仅作为快速捕获和RAKE分集等传统技术的最佳方案,而且在多用户检测、智能天线、多速率甚至是软切换等方面也都能发挥其优势;对匹配滤波器捕获的基本原理进行了研究并着重讨论了其多种FPGA实现结构。 相似文献
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对于双基地声呐而言,回波信号经常会被淹没在强直达波信号的脉冲压缩旁瓣干扰中。提出了一种匹配滤波输出的旁瓣抑制方法。该方法的思想是在匹配滤波输出端设计一个FIR滤波器,使得输出的积分旁瓣电平最小,同时保持主峰输出不变。利用二阶锥凸优化算法获得了旁瓣抑制滤波器的最优解。利用数值仿真,比较了旁瓣抑制方法与常规的汉明加窗方法,结果表明,该方法可在保持输出不变的情况下,提高30 d B的旁瓣抑制性能。利用该方法设计的近中心旁瓣抑制滤波器,局部的抑制性能可达-80 d B。 相似文献
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扩频接收机系统中,载波的捕获是衡量系统性能的重要指标。当系统接入多路叠加并行信号时,若需要在二维对信号进行捕获,所需捕获时间、所耗资源和接收机功耗将成倍增加。文中针对此问题,提出了一种基于差分滤波器的分集接收方案,大幅降低了系统资源的占用,从而减少了功耗、成本和捕获时间。利用伪随机码的双极性和差分滤波结构减少了所用加法器的数量,并结合对伪随机码并行分集的结构,在多路中对滤波结果进行复用。通过对传统快速相关捕获算法、快速捕获算法、频率相关法以及文中基于差分滤波的并行分集结构进行了复杂度对比。其结果显示,基于差分滤波的并行分集结构在节省资源、提高效率上均具有较大优势。 相似文献
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Diversity combining techniques, due to their extreme effectiveness incounteracting fading effects in wireless environment, have been extensivelystudied in recent years. In this paper, we propose an improved switchedcombining scheme using fuzzy adaptive control, namely, fuzzy adaptive switcheddiversity (FASD), which is applicable for implementation at mobile units.Specifically, the fuzzy adaptive control dynamically adjusts the thresholdlevel, at which switching is performed, based on the present varying channelconditions. By incorporating the statistics of mobile fading channels andextensive simulations, we have achieved an effective system design of FASDwhich has a significant improvement in system performance in terms of both thediversity gain and BER (bit error rate), while maintaining reasonablesimplicity in implementation. 相似文献
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在无线通信系统中,不同场景下有不同的传播模型。为了研究发射分集技术对抗多径效应的性能,文中总结了无线通讯系统中室外场景下的传播模型。针对传统的Okumura-Hata传播模型来研究不同环境下发射信号的功率损耗,在接收端计算各信号副本的接收功率,通过与预设的接收功率门限作比较,得出每个信号副本以及各副本等增益合并后的信号可用性,从而研究发射分集对于信号可用性的提升作用。仿真结果表明,分集技术能明显提升接收机接收信号的可用性。 相似文献
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自适应滤波在扩频信号分集接收中的应用研究 总被引:1,自引:0,他引:1
使用自适应滤波器完成对扩频信号的扩频码捕获后,传输信道中由于信号衰落造成的多径信号的幅度就可以从自适应滤波器收敛后的系数权值向量上体现出来.根据分集接收的理论分析,依据多径信号的信号幅度值进行分集接收在理论上是可行的,因此利用自适应滤波器对接收到的多径信号进行隐分集接收是完全可行的.使用自适应滤波器在完成扩频码捕获的同时,在不增加额外硬件支路的情况下就可以实现对多径信号的分集接收功能,从而改善在多径衰落环境下的信道传输性能. 相似文献
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The requirement to suppress narrowband interferences in CDMA communication stems from the overlay concept, i.e., coexistence of different types of signals in the same frequency band. This paper describes the performance analysis of a direct-sequence (DS) CDMA personal communication system sharing a common spectrum with narrowband microwave radio links in the 1.85 to 1.99 GHz band. The coexistence of these two systems within the same frequency band will improve the overall spectrum efficiency, but will also cause interference to both systems. In this paper it is shown that joint spatial and temporal optimum combining provides an efficient means of improving the performance of the DS-CDMA system through cancellation of the narrowband signal and the co-channel interferences. The proposed space-time architecture provides degrees of freedom for both diversity and interference cancellation. It is shown that the joint space-time receiver is robust with respect to the narrowband interference signal bandwidth and its carrier frequency offset from the DS-CDMA carrier frequency. 相似文献
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A Protocol for Multimedia CDMA Personal Communication Networks 总被引:2,自引:0,他引:2
In this paper, a joint CDMA/TDMA protocol has been proposed for integratedvideo-phone/voice/data traffic in personal communication networks (PCN). Thevideophone service is implemented according to H.261 standard. The concept ofdynamic boundary is adopted in both code and time domains to meet thedifferent requirements for videophone, voice and data traffic.Two mathematical analysis methods are adopted to evaluate the systemperformance. One is the traditional Markov analysis (TDMA), which is used tocalculate the average videophone and voice call blocking probabilities. Theother is Transient Fluid Analysis (TFA), which is adopted to evaluate the datadelay and channel utilization performance. Results show that two dynamicboundaries can be adjusted to achieve the optimal system performance, andsuggestions of how to adjust these boundaries are also given. 相似文献