CHANNEL ESTIMATION IN OFDM RECEIVERS
An OFDM receiver includes a fast Fourier transform processor that receives signal samples and outputs frequency domain samples corresponding to a received symbol. A delay element receives sets of frequency domain samples outputs each of the sets of frequency domain samples following a predetermined delay interval. A frequency domain channel estimator receives frequency domain samples and derives channel estimates from each of the sets of frequency domain samples. A channel estimate queue stores a sequence of channel estimates provided by the channel estimator and provides the sequence to a weighted averaging element that outputs an averaged channel estimate. A frequency equalizer outputs an equalized set of frequency domain samples responsive to the delayed set of frequency domain samples and to the averaged channel estimate.
1 . An OFDM receiver, comprising:
a Fast Fourier Transform processor adapted to receive signal samples corresponding to signals received from a channel, the Fast Fourier Transform processor outputting sets of frequency domain samples, each set of frequency domain samples corresponding to a received symbol;
a delay element coupled to receive sets of frequency domain samples and to output each of the sets of frequency domain samples following a predetermined delay interval from the output of the set by the Fast Fourier Transform processor;
a frequency domain channel estimator coupled to receive the sets of frequency domain samples and to derive corresponding channel estimates from each of the sets of frequency domain samples, the frequency domain channel estimator outputting a sequence of channel estimates corresponding to a sequence of the sets of frequency domain samples;
a channel estimate queue storing the sequence of channel estimates;
a weighted averaging element coupled to the channel estimate queue to receive the sequence of channel estimates and to output an averaged channel estimate; and
a frequency equalizer coupled to the delay element to receive a delayed set of frequency domain samples, the frequency equalizer coupled to the weighted averaging element to receive the averaged channel estimate, the frequency equalizer outputting an equalized set of frequency domain samples responsive to the delayed set of frequency domain samples and to the averaged channel estimate.
2 . The receiver of claim 1 , wherein the predetermined delay is sufficient to cause the averaged channel estimate and the delayed set of frequency domain samples to correspond to a same received symbol.
3 . The receiver of claim 1 , wherein the weighted averaging element applies equal weights for averaging channel estimates for a stationary receiver.
4 . The receiver of claim 1 , wherein the frequency domain channel estimator includes an interpolator that receives channel estimates at a first interval and generates channel estimates at a second interval, and wherein the weighted averaging element is coupled to receive the channel estimates at the second interval.
5 . The receiver of claim 4 , wherein the first interval corresponds to positions of pilot signals within an OFDM signal.
6 . The receiver of claim 1 , wherein the weighted averaging element applies center-weighted weights for averaging channel estimates.