Learning Rate Updating Methods Applied to Adaptive Fuzzy Equalizers for Broadband Power Line Communications
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Learning Rate Updating Methods Applied to Adaptive Fuzzy Equalizers for Broadband Power Line Communications ´ V. Ribeiro Moises Department of Communications, State University of Campinas, 13083970 S˜ao Paulo, Brazil Email: [email protected] Received 1 September 2003; Revised 31 May 2004 This paper introduces adaptive fuzzy equalizers with variable step size for broadband power line (PL) communications. Based on delta-bar-delta and local Lipschitz estimation updating rules, feedforward, and decision feedback approaches, we propose singleton and nonsingleton fuzzy equalizers with variable step size to cope with the intersymbol interference (ISI) effects of PL channels and the hardness of the impulse noises generated by appliances and nonlinear loads connected to low-voltage power grids. The computed results show that the convergence rates of the proposed equalizers are higher than the ones attained by the traditional adaptive fuzzy equalizers introduced by J. M. Mendel and his students. Additionally, some interesting BER curves reveal that the proposed techniques are efficient for mitigating the above-mentioned impairments. Keywords and phrases: power line communications, broadband applications, nonlinear equalization, fuzzy systems, learning rate updating, impulse noises.
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INTRODUCTION
In recent years, the increased demand for fast Internet accesses and new multimedia services, the development of new and feasible signal processing techniques associated with faster and low-cost digital signal processors, and the deregulation of the telecommunications market have placed considerable emphasis on the value of investigating hostile media, such as power line (PL) channels [1, 2, 3], for high-rate transmissions. A considerable body of research has given much attention to indoor (last-meter, residential, or intrabuilding) and outdoor (last-miles or local area networks and rural networks) PL environments for broadband applications [2, 3, 4, 5, 6, 7, 8]. For last-miles environments, it has been demonstrated that PL channels are as good as telephone and cable TV channels for the transmission of broadband contents [1, 2, 3, 9, 10]. The capacity of PL channels for last-miles applications can surpass 450 Mbps [9]. Modems with bit rates higher than 10 Mbps are nowadays offered by some companies. Nevertheless, a new generation of power line communications (PLC) modems that exceed 50 Mbps is appearing [10]. Such improvement demands, however, some special schemes or solutions for coping with the following problems in the physical layer: (a) the considerable differences between PL networks; and (b) the hostile properties of
PL channels, such as attenuation proportional to high frequencies and long distances, high-power impulse noise occurrences, and strong intersymbol interference (ISI) effects. Equalization techniques are so far widely employed to cope with ISI effects [11, 12, 13]. Among linear and nonlinear equalization techniques available in the literature, adaptive fuzzy equalizers are pointed out as good candidates to tackle nonl
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