Comparison of two FFT structures for fractionally-spaced frequency domain equalizer

A fractionally-spaced frequency domain equalizer (FS-FDE) is needed to transform a received signal into the frequency domain. We consider two fast Fourier transform (FFT) schemes, one with a single 2N-point FFT and one with two N-point FFTs, for the transform of oversampled N symbol data in the FS-FDE receiver. It is shown that the two receiver schemes are equivalent in terms of the characteristics of the FFT output, per-bin SNR after maximum-ratio combining, computational complexity and the residual out-of-band noise rejection property. These properties are verified by computer simulation in additive white Gaussian noise (AWGN) and typical multipath channel.