A Study on Equalization Techniques for an OFDM System

Abstract

We have studied equalization techniques using pilot carriers for an OFDM system. The signal to interference ratios (SIRs) of the equalizer output signal over a time-invariant multipath channel (D/U =10 dB) are calculated for several interpolation schemes : interpolation using FIR filters with the sinc functional impulse response, constant interpolation, linear interpolation, and simplified linear interpolation (which can be achieved without multipliers). The results show that an SIR of 27 dB (input CNR=30 dB, delay time of interference signal=11 μs) is obtained for simplified linear interpolation which can reduce the hardware complexity compared to other interpolation schemes. Also, we have confirmed that the tap numbers of the FIR filter can be reduced without degradation of the SIR by using a window function. Furthermore, for the FIR filters and the simplified linear interpolations, the SIRs are calculated in case of the timing phase offset for the FFT window position. The results show that the degradation of the SIR is very little even when the offset value becomes up to 20 samples for both cases.