Joint blind estimation of channel and data symbols in OFDM

In OFDM transmission over an FIR channel, an accepted method for combating the resultant ISI is via addition of a cyclic prefix whose length exceeds the the FIR channel duration, to each transmitted data block. This converts the time-domain linear convolution of the FIR channel to cyclic convolution, or effectively, to a multiplicative channel distortion in the frequency domain. The (frequency-domain) multiplicative channel is easily estimated by use of a training sequence thereby greatly reducing the channel equalization complexity at the cost of reduction in spectral efficiency due to the cyclic prefix. This paper explores OFDM systems without cyclic prefix and training sequence. By adopting virtual carriers and exploiting the finite alphabet property of the input symbols, a blind technique for joint estimation of channel and data symbols is developed. While this restores the spectral efficiency, it is achieved at the expense of increased processing complexity at the receiver.