Accurate FFT processing window timing detection based on maximum SIR criterion in OFCDM wireless access

The paper proposes an accurate fast Fourier transform (FFT) window timing detection method based on the maximum signal-to-interference power ratio (SIR) criterion, taking into account the received signal power and intersymbol interference, according to different detected FFT window timings in orthogonal frequency and code division multiplexing (OFCDM) wireless access. The SIR of the received signal after FFT processing is estimated using the desired signal power and the intersymbol interference power calculated using the power delay profile, which is measured by the cross-correlation between the pilot symbol replica and the received signal. Furthermore, since the SIR is calculated only for the received path timing of the first path and those paths exceeding the guard interval duration, which are greater than the noise-threshold value, the computational complexity of the proposed method is low. Computer simulation results show that the proposed scheme reduces the required average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) for achieving the average packet error rate (PER) of 10/sup -2/ by approximately 1.0 dB compared to the conventional method which detects the forward path timing of the power delay profile (16QAM data modulation, six-path Rayleigh fading channel, maximum delay time of 3 microsec, RMS delay spread of 0.86 microsec).