共查询到17条相似文献,搜索用时 78 毫秒
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采用两条支路分集接收的相关瑞利衰落信道容量 总被引:5,自引:0,他引:5
本文研究采用两条支路最大比合并(MRC)或选择合并(SC)分集接收的相关瑞利衰落信道理论容量推导恒定发射功率自适应M进制正交幅度调制(M-QAM)的频谱效率,并将它们与独立同分布瑞利信道理论容量进行比较,其结果对收发信机之间无视距分量路径、接收机上分集天线之间的距离小于半个波长的无线通信系统设计具有指导作用. 相似文献
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多中继协同分集技术在慢衰落无线环境下可以提供巨大的性能增益。该文从接收端平均误符号率的角度,分析了独立的瑞利衰落信道下,采用放大转发的多中继协同最大比合并检测方案和多节点侦听,单中继转发的机会中继方案的性能;并基于矩生成函数推导出两种方案下M-PSK和M-QAM调制信号平均误符号率的闭合表达式。经蒙特卡罗仿真验证,该表达式在中高信噪比下与仿真的实际结果非常吻合。同时也可以看出机会中继的分集增益与协同侦听的节点数成正比,误符号率性能优于使用最大比合并检测的多中继协同方案。 相似文献
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本文分析了快速跳频在部分频带干扰和高斯白噪声信道下的系统误码性能.推导了接收机采用了大数合并的误码率表达式,采用特征函数的办法重新分析了软判决线性合并时的误码率表达式.仿真结果表明,两种合并方法随着分集数的增大误码性能都下降,都不能抗全频带干扰.在干扰比较小时,软判决线性合并整体性能要好于大数合并. 相似文献
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在无线通信中,多径衰落严重影响信号传输的质量。分集接收技术是有效对抗多径衰落、提高信号接收增益、改善通信质量的有效方法之一。瑞利信道、莱斯信道是无线通信信道的主要模型,自身有很多特性。选择合并和等增益合并是常用的合并方式,各自有其优越性能。根据信道特征,将两种合并方式相结合的切换合并,在仿真分析后验证了在接收机应用中的可行性。虽然提高了设备要求,但也加宽了接收机的应用范围。 相似文献
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M-QAM调制技术及在数字MUDS中的应用 总被引:1,自引:0,他引:1
在介绍现有地面无线传输调制技术的基础上,分析了数字MUDS的技术特点及数字MUDS无线传输环境对调制技术的要求,阐述了M-QAM调制技术原理及M-QAM调制技术在数字MUDS中的应用. 相似文献
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Adaptive multilevel QAM (M-QAM) modulation can increase throughput in a wireless packet data network. A technique is discussed for efficiently realising M-QAM modulators on field programmable gate arrays (FPGAs) using 'multiplierless' finite impulse response (FIR) filters with carry-save addition and canonic signed-digit coefficients. An adaptive M-QAM modulator supporting 4, 16, 64 and 256-QAM is presented 相似文献
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We study the effect of imperfect channel estimation (ICE) on the error probability performance of M-level quadrature amplitude modulation ( M-QAM) with maximal-ratio combining and equal-gain combining diversity formats in Nakagami fading channels. We provide a novel formulation of the bit-error rate (BER) of M-QAM with ICE in terms of the signal constellation-dependent effective signal-to-noise ratios (SNRs) or amplitudes, which allows us to derive the general, accurate, and easy-to-evaluate BER formulas for square and rectangular diversity M-QAM with channel estimation errors. Our result shows that the performance loss caused by ICE may be manifested by the signal decision space distortion and a scaling of the effective SNR. Using our analytical result, we evaluate the performance of M-QAM with pilot-symbol assisted modulation and present some insightful findings 相似文献
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The throughput and packet error rate for a selective-repeat ARQ scheme based on a constant-power variable-rate adaptive M-QAM system combined with orthogonal STBC in Nakagami Markovian channels is analysed. The impact of dwell-time on the performance of adaptive M-QAM is considered. 相似文献
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Xiaoyi Tang Alouini M.-S. Goldsmith A.J. 《Communications, IEEE Transactions on》1999,47(12):1856-1864
We determine the bit-error rate (BER) of multilevel quadrature amplitude modulation (M-QAM) in flat Rayleigh fading with imperfect channel estimates, Despite its high spectral efficiency, M-QAM is not commonly used over fading channels because of the channel amplitude and phase variation. Since the decision regions of the demodulator depend on the channel fading, estimation error of the channel variation can severely degrade the demodulator performance. Among the various fading estimation techniques, pilot symbol assisted modulation (PSAM) proves to be an effective choice. We first characterize the distribution of the amplitude and phase estimates using PSAM. We then use this distribution to obtain the BER of M-QAM as a function of the PSAM and channel parameters. By using a change of variables, our exact BER expression has a particularly simple form that involves just a few finite-range integrals. This approach can be used to compute the BER for any value of M. We compute the BER for 16-QAM and 64-QAM numerically and verify our analytical results by computer simulation. We show that for these modulations, amplitude estimation error leads to a 1-dB degradation in average signal-to-noise ratio and combined amplitude-phase estimation error leads to 2.5-dB degradation for the parameters we consider 相似文献
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Bin Xia Jiangzhou Wang 《Communications, IEEE Transactions on》2005,53(3):481-488
This paper studies the effect of channel estimation error and antenna diversity on multilevel quadrature amplitude modulation (M-QAM) systems over Rayleigh fading channels. Based on the characteristic function method, a general closed-form bit-error rate (BER) for M-QAM systems is presented. The effect of the inaccurate channel estimation on the performance for pilot-symbol-assisted modulation M-QAM systems with antenna diversity is investigated. Simulation results for M-QAM (M = 4, 16, 64, 256, etc.) show that the analytical method can accurately estimate the system performance. Moreover, numerical results show that with the antenna-diversity technique, the BER performance improves significantly, especially in perfect channel-estimation cases. It is also found that the channel-estimation error limits the benefit of antenna diversity. By increasing the length of the channel estimator and the amplitude of the pilot symbol, more accurate channel estimation can be achieved, so that the BER performance is improved. 相似文献
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The effect of clipping-induced impulse noise in externally modulated multichannel AM/M-QAM video transmission systems is investigated. It is shown that the bit-error-rate of the M-QAM signals in the symmetric double-clipping events is, to the first order approximation, twice the single clipping events under the same conditions. The results are in good agreement with the experimental data for both 1319-nm and 1550-nm externally modulated laser transmitter-based systems 相似文献
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In this paper, we study the effect of imperfect channel estimation (ICE) on the performance of M-level quadrature amplitude modulation (M-QAM) with maximum ratio combining (MRC) and pilot-symbol assisted modulation (PSAM) in generalized Rician fading channels. By expressing the bit error rate (BER) of MRC diversity M-QAM in terms of the distribution of new decision variables, we derive novel, exact, and easy-to-evaluate BER expressions for diversity M-QAM with channel estimation errors. Our results include versatile system and fading channel parameters (e.g., arbitrary spatial and temporal correlation patterns among the diversity branches), and are valid for arbitrary linear channel estimators and square and rectangular M -QAM with different constellation sizes. In addition, we evaluate the performance of minimum mean-squared error (MMSE)- and sinc-interpolator-based channel estimators with PSAM, and provide some new insights into the performance of M-QAM with PSAM in generalized fading channels 相似文献