Fractionally spaced non-linear equalization of faster than Nyquist signals

Faster than Nyquist transmissions provide the opportunity of increasing data rate at the expenses of additional inter-symbol interference. The optimum receiver requires a maximum likelihood sequence detector, whose complexity grows exponentially with the number of filter taps and with the number of bits per symbol. In this paper we consider two suboptimal approaches based on non-linear equalization of the received signal. In order to further reduce the receiver complexity we consider an implementation of equalization filters in the frequency domain. The contributions of the paper are a) a receiver architecture for fractionally spaced non-linear equalizers, and b) efficient design methods of the equalization filters in the frequency domain. In particular, the derived optimal (in the mean square error sense) filters overcome approaches proposed in the literature.