Novel mitigation techniques for OFDM in a Doppler spread channel

The performance of an orthogonal frequency division multiplexing (OFDM) system degrades in the Doppler spread channel due to intercarrier interference (ICI) resulting from loss of orthogonality. In this paper, multirate sampling theory is applied to a standard OFDM system to reduce ICI. Using the N-point FFT receiver causes circular interference from the periodic extension spectrum of the channel spectrum. The periodic extension spectra due to sampling can be shifted further away from the fundamental spectrum if the sampling rate is increased (upsampling), thus resulting in less ICI for the edge subcarriers. The new detection scheme recovers the data from the outer carriers first. The ICI of the inner carriers is then reduced via a sequential interference cancellation technique, as detection moves from the outer carriers to the inner carriers. Using this method, the error floor is reduced. Upper and lower bounds on probability of error when using BPSK and QPSK modulation schemes, with the upsampling and new detection scheme cases are presented numerically. Also, simulations are done to verify the analytical results.