MCMA equalization without signal permutation for MIMO-OFDM systems using M-QAM

We propose a blind equalization system using an all-pass filter for de-mixing orthogonal frequency division multiplexing (OFDM) symbols in multiple-input multiple-output (MIMO) - OFDM system. In a conventional blind MIMO equalization, there is a possibility that originally transmitted streams are permutated, resulting in being unable to retrieve desired signals at the receiver. In order to solve the problem, each transmitted stream of the proposed MIMO-OFDM system is pre-filtered by a unique all-pass filter. The filter is referred to as Transmit tagging filter (TT-Filter) in this paper. At a receiver, an inverse filter of the TT-filter is used to blindly equalize a MIMO channel without any permutation. The system was originally designed for constant modulus symbol such as PSK signal. This paper evaluates the performance of a QAM Transmission which is non-constant.