Blind maximum-likelihood data recovery in OFDM

OFDM modulation combines the advantages of high achievable rates and relatively easy implementation. In this paper, we show how to perform blind maximum-likelihood data recovery in OFDM transmission from the output symbol and cyclic prefix. Our approach relies on decomposing the OFDM channel into two subchannels (cyclic and linear) that share the same input and are characterized by the same channel parameters. This fact enables us to estimate the channel parameters from one subchannel and substitute the estimate into the other, thus obtaining a nonlinear relationship involving the input and output data only. The relationship does not show any channel dependence whatsoever and can be exhaustively searched for the maximum likelihood estimate of the input. This shows that OFDM systems are completely identifiable using output data only, irrespective of the channel zeros, as long as the channel delay spread is less than the length of the cyclic prefix.