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CMA-Based Blind Equalization and Phase Recovery in OFDM/OQAM Systems

Abstract : This paper deals with a constant modulus algorithm-(CMA) based blind equalization method for orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) scheme. The authors propose to combine the CMA with a low-pass filter in order to increase the convergence speed of the equalizer, and to avoid the detection of the received symbols with phase mismatch. Simulations results show that the convergence speed is largely increased, and the proposed method achieves bit error rate (BER) performance very close to that of the perfect channel estimation and equalization. Index Terms—Blind equalization, OFDM/OQAM, CMA, Impulse Noise Cancellation. I. INTRODUCTION The blind equalization is an interesting solution for the channel inversion (or deconvolution) since it guarantees the signal a maximum spectral efficiency. Indeed, these techniques do not use pilots, the blind equalizer only takes advantage of a few signal features to perform the channel inversion. In [1], B. Farhang-Boroujeny has adapted the blind equalization using the constant modulus algorithm (CMA) proposed by D. N. Godard in [2] to the cosine modulated filter bank (CMFB) modulation. In [3] the authors proposed to use the second order moment of the received signal, while the CMA is used in [1]. In filter bank multicarrier (FBMC), and in particular in orthgonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM), only few papers deals with blind equalization. Due the convergence delay of the blind methods and the uncertainty on the phase of the recovered symbols, the blind channel equalization remains a pending challenge not much studied by the scientific community, in particular in FBMC. In this paper we propose a constant modulus algorithm-based (CMA) blind equalizer for OFDM/OQAM systems. As in [1], we consider a one-tap per carrier equalization, since it is particularly adapted to the multicarrier systems. As mentioned in [4], this type of technique may lead to local solutions and implies that the symbols are detected with a phase shift of 0 or π. The proposed method consists of filtering the equalizer response in order to smooth the channel frequency response. The principle of the proposed technique is simple, since it is similar to a low-pass filter as used in channel estimation [5]. The addition of a differential phase coding allows to suppress any uncertainty on the phase of the recovered symbols.
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Vincent Savaux, Faouzi Bader, Jacques Palicot. CMA-Based Blind Equalization and Phase Recovery in OFDM/OQAM Systems. 2016 23rd International Conference on Telecommunications (ICT), May 2016, Thessaloniki, Greece. ⟨10.1109/ict.2016.7500466⟩. ⟨hal-01311054⟩



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