Pre-Filter Based on Allpass Filter for Blind MIMO-OFDM Equalization Using CMA Algorithm

Masatsune ISHIHARA
Yoshio ITOH

IEICE TRANSACTIONS on Communications   Vol.E100-B    No.4    pp.602-611
Publication Date: 2017/04/01
Publicized: 2016/10/28
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2015EBP3517
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
MIMO-OFDM,  blind equalization,  permutation,  allpass filter,  

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We propose a pre-filtering system for blind equalization in order to separate orthogonal frequency division multiplexing (OFDM) symbols in a multiple-input multiple-output (MIMO) - OFDM system. In a conventional blind MIMO-OFDM equalization without the pre-filtering system, there is a possibility that originally transmitted streams are permutated, resulting in the receiver being unable to retrieve desired signals. We also note that signal permutation is different for each subcarrier. In order to solve this problem, each transmitted stream of the proposed MIMO-OFDM system is pre-filtered by a unique allpass filter. In this paper, the pre-filter is referred to as transmit tagging filter (TT-Filter). At a receiver, an inverse filter of the TT-filter is used to blindly equalize a MIMO channel without permutation problem. Further, in order to overcome the issue of phase ambiguity, this paper introduces blind phase compensation.