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Blind algorithm for decision feedback equalizer

IEICE TRANSACTIONS ON COMMUNICATIONS 1997年第1期E80B卷 200-204页

作者： Seo, BS Lee, JH Woong, C Department of Electronics Engineering Seoul National University Seoul 151-742 South Korea

In this letter, we propose a blind adaptation method for the decision feedback equalizer (DFE). In the proposed scheme, a DFE is divided into two parts: a front-end linear equalizer (LE), and a prediction error filter (PEF) followed by a feedback part. The coefficients of the filters in each part are updated using constant modulus algorithm and decision feedback prediction algorithm, respectively. The front-end LE removes intersymbol interference ISI, and the PEF with feedback part whitens the noise to reduce noise power enhanced by the LE. Pre-processing by the LE enables the DFE to equalize nonminimum phase channels. Simulation results show that the proposed scheme provides reliable convergence, and the resulting symbol error rate is much less than that of the conventional LE and very close to that of the DFE using a training sequence.

关键词： blind equalization decision feedback equalizer constant modulus algorithm decision feedback prediction algorithm

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Blind Equalization Using Coordinate Mapping for 4-PAM and 16-QAM Signals

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Chinese Journal of Electronics 2014年第1期23卷 124-128页

作者： RAO Wei Nanchang Institute of Technology

It is well known that the famous constant modulus algorithm(CMA) presents a large steady-state Mean square error(MSE) for nonconstant modulus signals. In this paper a coordinate mapping approach for a4-PAM nonconstant modulus signal is described which can change the signal to an Offset QPSK(OQPSK) constant modulus signal. And a new algorithm based on this approach is proposed which is also suitable for a 16-QAM signal. For the 4-PAM and 16-QAM nonconstant modulus signals the proposed algorithm can achieve a zero steadystate MSE in a noiseless environment but CMA *** analysis and simulations results demonstrate the high performance of the proposed algorithm.

关键词： Blind equalization constant modulus algorithm Coordinate mapping

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A Novel constant modulus Array for Multiuser Detection

A Novel Constant Modulus Array for Multiuser Detection

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第七届国际信号处理会议

作者： ZHANG Ji-dong 1 ZHENG Bao-yu 2 Fu Hong-liang2 (1: ShangHai JiaoTong University , Shanghai China 200030 2:NanJing University of Posts and Telecommunications NanJing China 21000

A novel multitarget constant modulus array structure is proposed for CDMA systems in this paper. The new algorithm for the structure is called pre- despreading and wavelet denoising constant modulu

关键词： constant modulus algorithm Wavelet denoising Multiuser detection Communication signal processing

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Optimal Polarization Demultiplexing for Coherent Optical Communications Systems

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2010年第7期28卷 1121-1134页

作者： Roudas, Ioannis Vgenis, Athanasios Petrou, constantinos S. Toumpakaris, Dimitris Hurley, Jason Sauer, Michel Downie, John Mauro, Yihong Raghavan, Srikanth Univ Patras Dept Elect & Comp Engn Rion 26500 Greece Corning Inc Corning NY 14831 USA

Spectrally-efficient optical communications systems employ polarization division multiplexing (PDM) as a practical solution, in order to double the capacity of a fiber link. Polarization demultiplexing can be performed electronically, using polarization-diversity coherent optical receivers. The primary goal of this paper is the optimal design, using the maximum-likelihood criterion, of polarization-diversity coherent optical receivers for polarization-multiplexed optical signals, in the absence of polarization mode dispersion (PMD). It is shown that simultaneous joint estimation of the symbols, over the two received states of polarization, yields optimal performance, in the absence of phase noise and intermediate frequency offset. In contrast, the commonly used zero-forcing polarization demultiplexer, followed by individual demodulation of the polarization-multiplexed tributaries, exhibits inferior performance, and becomes optimal only if the channel transfer matrix is unitary, e. g., in the absence of polarization dependent loss (PDL), and if the noise components at the polarization diversity branches have equal variances. In this special case, the zero-forcing polarization demultiplexer can be implemented by a 2 2 lattice adaptive filter, which is controlled by only two independent real parameters. These parameters can be computed recursively using the constant modulus algorithm (CMA). We evaluate, by simulation, the performance of the aforementioned zero-forcing polarization demultiplexer in coherent optical communication systems using PDM quadrature phase shift keying (QPSK) signals. We show that it is, by far, superior, in terms of convergence accuracy and speed, compared to conventional CMA-based polarization demultiplexers. Finally, we experimentally test the robustness of the proposed constrained CMA polarization demultiplexer to realistic imperfections of polarization-diversity coherent optical receivers. The PMD and PDL tolerance of the proposed demultiple

关键词： Coherent communications polarization demultiplexing constant modulus algorithm

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An improved CMA for dispersion compensation in 100 Gbps DP-QPSK optical signal transmission system

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OPTIK 2017年 136卷 480-486页

作者： Qin, Jiangyi Liu, Chunwu Huang, Zhiping Su, Shaojing Zhang, Yimeng Natl Univ Def Technol Coll Mechatron Engn & Automat Changsha 410073 Hunan Peoples R China

An improved constant modulus algorithm (CMA) for dispersion compensation in 100 Gbps Dual Polarization-Quadrature Phase Shift Keying (DP-QPSK) optical signal transmission system is proposed to achieve better reliability receiving performances. In the receiver, we combine variable step size and Mean-Square Error (MSE) to improve the conventional CMA. Compared to conventional CMA, the proposed algorithm has a better performance in adapting the time varying channel and the strong noise. Meanwhile, the proposed algorithm has a faster convergence rate than the previous one. Simulation results show that the improved CMA can achieve the dispersion and polarization demultiplexing of 100 Gbps DP-QPSK optical signal transmission system efficiently. (C) 2017 Elsevier GmbH. All rights reserved.

关键词： Optical communications constant modulus algorithm Dispersion compensation Variable step size Mean-square error

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The mutual coupling and diffraction effects on the performance of a CMA adaptive array

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 1998年第3期47卷 728-736页

作者： Yuan, H Hirasawa, K Zhang, YM Kyocera DDI Inst Future Telecommun Inc Tokyo 1500001 Japan Univ Tsukuba Inst Informat Sci & Elect Tsukuba Ibaraki 305 Japan Japan Corp Commun Lab Kawasaki Kanagawa 213 Japan

The performance of the constant modulus algorithm (CMA) with the steepest descent method used in an adaptive array of monopole antennas mounted on a rectangular conducting plate was investigated. The mutual coupling (MC) effect among the array elements and the diffraction effect caused by the conducting plate were taken into account in the calculation by a hybrid method of moment method (MRI) and geometrical theory of diffraction (GTD). Simulations showed that the CMA adaptive array performs differently when the MC and the diffraction effects are taken into account. In some cases, the speed of convergence is slower with MC, and in other cases it is faster. Also, in multipath scenarios the array sometimes converges on a weaker delayed ray rather than the direct ray when MC is included. The capture property is explained by the fact that the CMA algorithm is sensitive to initial conditions and the initial array pattern is directional due to MC-not omnidirectional as in the ideal case. The performance of the array on a finite ground plane is different from that on an infinite ground plane due to diffraction effects.

关键词： adaptive array constant modulus algorithm finite conducting plane monopole mutual coupling

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A Robust Maximum Likelihood algorithm for Blind Equalization of Communication Systems Impaired by Impulsive Noise

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CIRCUITS SYSTEMS AND SIGNAL PROCESSING 2019年第5期38卷 2387-2401页

作者： Li, Jin Feng, Da-Zheng Li, Bingbing Nie, Weike Xidian Univ State Key Lab Integrated Serv Networks Xian 710071 Shaanxi Peoples R China Xidian Univ Natl Lab Radar Signal Proc Xian 710071 Shaanxi Peoples R China Northwest Univ Sch Informat Sci & Technol Xian 710027 Shaanxi Peoples R China

To improve the performance of the blind equalizer (BE) in impulsive noise environments, a robust maximum likelihood algorithm (RMLA) is proposed for the communication systems using quadrature amplitude modulation signals. A novel robust maximum likelihood cost function based on the constant modulus algorithm is constructed to effectively suppress the influence of impulsive noise and ensure the computational stability. Theoretical analysis is presented to illustrate the robustness and good computational stability of the proposed algorithm under the impulsive noise ambient. Moreover, it is proved that the weight vector of the proposed BE can converge stably by LaSalle invariance principle. Simulation results are provided to further confirm the robustness and stability of the proposed RMLA.

关键词： alpha-Stable distribution Blind equalization Robust maximum likelihood algorithm Inter-symbol interference constant modulus algorithm

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Polarization Tracking in the Presence of PDL and Fast Temporal Drift

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2022年第19期40卷 6408-6416页

作者： Farsi, Mohammad Hager, Christian Karlsson, Magnus Agrell, Erik Chalmers Univ Technol Dept Elect Engn SE-41296 Gothenburg Sweden Chalmers Univ Technol Dept Microtechnol & Nanosci SE-41296 Gothenburg Sweden

In this paper, we analyze the effectiveness of polarization tracking algorithms in optical transmission systems suffering from fast state of polarization (SOP) rotations and polarization-dependent loss (PDL). While most of the gradient descent (GD)-based algorithms in the literature may require step size adjustment when the channel condition changes, we propose tracking algorithms that can perform similarly or better without parameter tuning. Numerical simulation results show higher robustness of the proposed algorithms to SOP and PDL drift compared to GD-based algorithms, making them promising candidates to be used in aerial fiber links where the SOP can potentially drift rapidly, and therefore becomes challenging to track.

关键词： Signal processing algorithms Channel estimation Symbols Optical fiber dispersion Optical polarization Optical fiber amplifiers Optical fiber couplers constant modulus algorithm hybrid algorithm least square algorithm polarization-dependent loss polarization tracking state of polarization

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An orthogonalized blind algorithm for hybrid of adaptive array and equalizer

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INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS 2014年第2期27卷 201-215页

作者： Leou, Maw-Lin Wu, Chien-Min Liaw, Yi-Ching Su, Hui-Kai NanHua Univ Dept Comp Sci & Informat Engn Chiayi 622 Taiwan Natl Formosa Univ Dept Elect Engn Huwei 632 Yunlin Taiwan

The problems generated by the interference will be more complicated in the future. A combination of adaptive array and equalizer has been employed to solve the problems of interference when an adaptive array alone cannot suppress all the interferences. A constant modules algorithm (CMA) of the combination system was proposed to solve the problems of insufficient degrees of freedom and main-beam multipath interference when no training signal is transmitted. The limitation of the CMA for combination systems is due to its slow rate of convergence. In this paper, an orthogonalized blind algorithm for hybrid of array and equalizer (OBHAE) is proposed to combat the problems of the interference. Because the modified input vector of the adaptive array is orthogonalized by the OBHAE in advance, the convergent rate of the CMA system can be improved by the OBHAE. When the coherent interference presents, the performance of the system will be degraded. In this paper, an orthogonalized spatial smoothing blind (OSSB) algorithm is proposed to further enhance the cancellation of the coherent interference. In the OSSB, we combine the OBHAE with the spatial smoothing method to combat the coherent interference problem. Simulation results are presented to demonstrate the merits of the OBHAE and the OSSB. Copyright (c) 2012 John Wiley & Sons, Ltd.

关键词： adaptive array equalizer constant modulus algorithm degrees of freedom main-beam multipath interference orthogonalized blind algorithm

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Avoiding ill-convergence of finite dimensional blind adaptation schemes excited by discrete symbol sequences

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SIGNAL PROCESSING 1997年第2期62卷 121-162页

作者： Wigren, T Uppsala Univ Dept Technol Syst & Control Grp S-75103 Uppsala Sweden

A general framework for convergence analysis of finite-dimensional blind adaptation algorithms of Bussgang type is presented. The approach allows discrete symbol sets and can be used for analysis of systems with both poles and zeros. The main tool of analysis is an associated differential equation whose stability properties are proved to be tied to the convergence properties of a general blind stochastic approximation algorithm. The recently highlighted ill-convergence problem of for example the constant modulus algorithm (CMA) is then addressed. The problem is partially solved using new blind adaptation algorithms which are not derived by criterion minimization. Instead, the averaged updating directions of the suggested stochastic gradient schemes are designed to guarantee global stability of the associated differential equations. (C) 1997 Elsevier Science B.V.

关键词： averaging blind adaptation blind equalization constant modulus algorithm convergence analysis nonlinear Wiener model

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