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在无线通信系统中,码间干扰(ISI)是影响通信质量的重要因素。盲均衡技术不需要发送导频序列便能自适应调节均衡器抽头系数,能够有效去除ISI。文中介绍了盲均衡技术原理,重点研究了恒模类盲均衡算法,通过对恒模算法(CMA)和改进的CMA算法(包括MMA算法和双模式盲均衡算法)的迭代公式分析,得出了恒模类盲均衡算法的性能。计算机仿真表明恒模类盲均衡算法在无线通信中具有良好的均衡性能。 相似文献
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针对时变信道需进行自适应均衡的要求,介绍了最常用的恒模算法(Constant Modulus Algorithm,CMA),并对该算法进行了改进,提出了一种步长因子μ与误差信号的e(n)之间另一种新的非线性函数,该函数较为简单,且在误差e(n)接近零处具有缓慢变化的特性,克服了CMA在收敛调整过程中的不足。同时给出了改进算法的仿真结果,计算机仿真结果与理论分析相一致,表明该算法提高了恒模算法的收敛速度,同时也保留了恒模算法较为稳定的性能。 相似文献
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针对恒模算法(constant modulus algorithm, CMA)在脉冲噪声环境下性能退化的问题,本文基于最大相关熵准则(maximum correntropy criterion, MCC)对恒模算法中基于最小均方误差(mean square error, MSE)准则的代价函数进行修正,推导出适用于脉冲噪声环境的基于MCC准则的恒模盲均衡算法(MCC_CMA)。该算法利用通信信号的恒模特性,首先得到发送信号与均衡器输出信号模值的误差信号,再通过使模值误差信号的相关熵最大来获得其迭代误差调节项,避免了传统高阶统计量算法在脉冲噪声环境下性能退化的问题。对高斯噪声以及α-稳定分布和混合高斯分布两种脉冲噪声环境下的信道均衡问题的仿真实验表明,相对于经典的自适应恒模盲均衡算法,MCC_CMA算法不依赖噪声的先验知识就能获得较快的收敛速度、较低的剩余码间干扰和误码率,并且在不同脉冲强度的脉冲噪声环境下都能够得到较好的均衡结果,表明MCC_CMA算法具有很好的鲁棒性。 相似文献
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直达波参考信号在传输过程中经常会受到噪声、地杂波和多路径干扰的影响,造成信号失真,从而对非合作双基地雷达的性能产生影响.为了恢复脉冲制非合作双基地雷达中的直达波参考信号,考虑采用盲均衡技术重构直达波参考信号.针对直达波信号脉冲持续期间模值恒定、脉冲间歇期内模值为零的包络特性,讨论了盲均衡算法中的恒模算法(CMA)和多模算法(MMA)的特点及其应用条件,在此基础上提出了改进的CMA+MMA算法,仿真结果表明改进的CMA+MMA算法比CMA算法均衡后的互相关函数尖峰更窄,能进一步提高CMA算法对直达波脉冲的均衡性能. 相似文献
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Zhimin Zhou Lanfen Qi Ying Tan 《Journal of Infrared, Millimeter and Terahertz Waves》2001,22(2):255-263
Based on a new multipath channel model, a spatial-temporal combined CM equalization approach is derived at millimeter waves. Computer simulations are presented to testify the theoretical analysis. It is shown that this method can compensate the signal degradation caused by indoor multipath propagation. The convergence behavior of the spatial-temporal CMA is also analyzed. 相似文献
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《Signal Processing: Image Communication》2001,16(5):413-420
In this paper we present an approach to equalize multipath transmitted video signals without any reference signal. This approach takes advantage of the constant envelope feature of the color burst signal, which is transmitted in the blanking interval of each TV line and can be considered as an angle-modulated signal. The constant modulus algorithm (CMA) after Treichler is modified for our purpose. Special attention is given to the equalization of video signals in PAL systems. By making full use of the genuine phase feature of the color burst signal in PAL systems, the Hilbert transform needed by CMA can be saved for equalizing PAL system video signals. In addition to equalize analog TV signal, this paper can also lead to a joint echo cancellation of analog and digital TV signals transmitted in cable network. 相似文献
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Hebat-Allah M. Mourad 《Wireless Personal Communications》2006,36(3):213-227
Although Constant Modulus Algorithm (CMA) is effective to equalize non-minimum phase channels blindly, it suffers from residual
intersymbol interference (ISI) and large Mean Square Error (MSE) when applied to higher order constellations (QAM). Methods
based on cost function matched to the signal constellation namely alphabet matched algorithm (AMA) were previously reported
and proves its superiority on CMA concerning the MSE. Thus dual mode algorithms between CMA and AMA were introduced. A hybrid
technique combining CMA and AMA using a cosine square function as a constellation matched error (CME) was lately reported.
In this paper two different CME functions are introduced. The MSE of the proposed algorithms are calculated using Matlab simulation
under multipath slow fading channels for different signal to noise ratios (SNR) and different levels of QAM constellations.
A comparison is established among them. Depicted results show the effectiveness of the two proposed CME functions.
Hebat-Allah M. Mourad received her B.Sc., M.Sc. and Ph.D. degrees in electrical communication engineering from Cairo University, Egypt, in 1983,
1987 and 1994 respectively. Since 1983, she has been with the Department of Electronics and Communications, Faculty of Engineering,
Cairo University, and is currently associate professor there. Her research interests include optical fiber communications,
mobile and satellite communications. 相似文献
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Property of the Constant Modulus Algorithm to Capture the Weak Signal~~ 相似文献
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Tai-Kuo Woo 《Wireless Personal Communications》2012,62(2):395-410
The Constant Modulus Algorithm (CMA) adopts the constant modulus (CM) criterion to minimize the deviation of the equalizer
output from a fixed value. However it has two drawbacks: (1) slow rate of convergence (2) the likelihood of getting trapped
in a local minimum. The problem gets even worse when the channel delay spread varies rapidly as the filter length cannot match
the delay spread. If the filter length is significantly longer than the delay spread, the convergence rate can be slow. In
this paper, we improve the performance of the standard CMA by using a dynamically partitioned hierarchical structure to organize
the taps of a filter. The filter length is dynamically partitioned according to the delay spread such that they are tightly
matched. Preferably, the length of a sub-filter is slightly longer than the delay spread of the channel. The performance evaluation
is divided into two parts. In Part I, we do simulation runs for both the cost functions and cost surfaces comparing the standard
CMA, where the filter length is significantly longer than the delay spread, and the dynamically partitioned CMA, where the
filter length matches the delay spread. In Part II, an analysis is provided to show that the proposed partitioned scheme can
speed up the convergence rate and reduce the cost function. 相似文献
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A simple method of alternatively using high-inversion and moderate-inversion erbium-doped fiber amplifiers (EDFA's) in an optical amplifier chain is presented to mitigate the self-filtering effect and equalize both signal power and signal-to-noise ratio (SNR) of multiple wavelength channels in wavelength-division multiplexing (WDM) transmission systems. The performance of the compensated system with alternatively used high- and moderate-inversion amplifiers is compared with the uncompensated ones where only moderate- or high-inversion amplifiers are employed. The result shows that the compensated system has a flatter gain profile, a lesser signal power spread, and SNR degradation 相似文献
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CMA算法盲均衡性能分析 总被引:1,自引:0,他引:1
由于受多径传输和有限带宽的影响,无线信道不可避免地存在码间干扰和信道间干扰.盲均衡技术是一种不需要训练序列就能补偿信道畸变的新兴自适应均衡技术.文中从Bussgang类盲均衡原理出发,讨论了属于Bussgang类的CMA盲均衡算法,并利用Simulink对算法进行了仿真.从仿真结果可看出步长对算法收敛性能和精度的影响,步长越小,收敛速度越慢,但稳态误差越小;反之亦然. 相似文献
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In fast-fading channels, the constant modulus algorithm (CMA) is unable to properly track the time-variations because the magnitude of the received signal changes too rapidly. The Kalman filter (KF), however, works well in time-varying channels but needs a training sequence to operate. Therefore, a combined CMA and KF algorithm is proposed in order to utilise the advantages of both algorithms. The associated step sizes of the CMA and the KF algorithm are also varied in accordance with the magnitude of the output. Simulations are presented to demonstrate the potential of the combination 相似文献
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This paper analyzes the lock/capture behavior of constant modulus approach (CMA) for blind multiuser detection. Conditions under which CMA locks on the desired signal and when it captures the interferer are derived. 相似文献
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1 Introduction Multiple-access interference (MAI) due to many simultaneous users constitutes the main limitation of DS-CDMA systems. Multiuser detection techniques can efficiently suppress MAI and substantially increase the capacity of CDMA systems. Over … 相似文献