Totally blind APP channel estimation for mobile OFDM systems

Abstract—A new two-dimensional blind channel estimation scheme for coherent detection of orthogonal frequency-divi-sion multiplexing (OFDM) signals in a mobile environment is presented. The channel estimation is based on the a posteriori probability (APP) calculation algorithm. The time-variant channel transfer function is completely recovered without phase ambiguity with no need for any pilot or reference symbols, thus maximizing the spectral efficiency of the underlying OFDM system. The phase ambiguity problem is solved by using a 4-QAM (quadrature amplitude modulation) scheme with asymmetrical arrangement. The results clearly indicate that totally blind channel estimation is possible for virtually any realistic time-variant mobile channel. Index Terms—Blind channel estimation, iterative decoding, or-thogonal frequency-division multiplexing (OFDM). I