Digital Signal Processing 17 (2007) 1071–1088 www.elsevier.com/locate/dsp A configurable fractionally-spaced blind adaptive equalizer for QAM demodulators ✩ Kevin Banovi´ c, Mohammed A.S. Khalid ∗ , Esam Abdel-Raheem Department of Electrical and Computer Engineering, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada Available online 27 November 2006 Abstract This paper discusses the design and field programmable gate array (FPGA) implementation of a configurable 18-tap fractionally- spaced blind adaptive equalizer intellectual property (IP) core for quadrature amplitude modulation (QAM) signals. The design can be configured to implement the constant modulus algorithm (CMA), multimodulus algorithm (MMA), radius-adjusted modified- multimodulus algorithm (RMMA), and radius-adjusted multimodulus decision-directed algorithm (RMDA), while it can achieve channel equalization for square QAM signals up to 256-QAM. The input samples to the equalizer tapped delay line are sampled at twice the symbol rate, while the equalizer output and tap coefficients are updated at the symbol rate. This is exploited by the equalizer tap and update modules of the design, which utilize the same hardware to implement two consecutive equalizer taps per module. The IP core is implemented for the Altera Stratix II EP2S130F780C4 FPGA and targets cable demodulators. The implementation operates at a maximum symbol frequency of 8.055 MBaud, which is comparable to recent QAM equalizer designs for cable modems.  2006 Elsevier Inc. All rights reserved. Keywords: Adaptive filtering; Blind equalization algorithms; FPGAs 1. Introduction Adaptive equalizers compensate for signal distortion attributed to intersymbol interference (ISI) which is caused by multipath within time-dispersive channels. They are typically employed in high-speed communication systems, which do not use differential modulation schemes or frequency division multiplexing. There are several methods or modes in which equalizers can achieve adaptation of their tap coefficients. These include the transmission of a known training sequence, known symbol statistics, and decision-directed adaptation. When the methods applied to achieve channel equalization do not include the transmission of a training sequence, it is referred to as blind equalization. There exist many excellent tutorials on the subject of both trained [1,2] and blind equalization [3,4]. The first blind equalization algorithm was published by Sato in 1975 for equalization of pulsewidth amplitude modulation (PAM) signals [5], which was generalized for the complex symbol case by Godard and Thirion [6]. The breakthrough algorithm for blind equalization was the constant modulus algorithm (CMA), which was discovered ✩ This work was supported by Natural Science and Engineering Research Council of Canada (NSERC) and the University of Windsor. * Corresponding author. Fax: +1 519 971 3695. E-mail address: mkhalid@uwindsor.ca (M.A.S. Khalid). 1051-2004/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.dsp.2006.10.009