Patent ID: 7340000
Filing Date: 2008-03-04
Classification: H04L

Abstract:
1. In a radio receiver for a wireless packet network, the radio receiver including an analog RF receiver and at least one analog-to-digital converter (ADC) to provide digital received signal samples of a received signal, the radio receiver designed for receiving OFDM signals including a multiplexed plurality of modulated subcarriers, the subcarriers modulated with symbols separated in time by an OFDM symbol period that includes a guard interval, an apparatus to accept the digital samples from the radio receiver and comprising: a subtractor having a first input accepting the received signal samples from the radio receiver and a second input accepting to-be-subtracted equalizing signal, the subtractor having an output generating an equalized signal; a discrete Fourier transformer having an output to provide the modulated subcarriers of the output of the subtractor; a forward processing subsystem having an input coupled to the output of the discrete Fourier transformer to accept the subcarriers, and another input to accept signals that vary as an estimate of the channel response of the subcarriers, the forward processing subsystem including a channel corrector to correct the channel response of subcarriers based on the signals accepted by said another input and that vary as an estimate of the channel responses for the subcarriers, the forward processing subsystem further to carry out pilot correction on the subcarriers, the forward processing subsystem having an output to provide channel corrected modulated subcarrier; a decision subsystem having an input coupled to the output of the forward processing subsystem, the input to accept the channel corrected subcarriers, the decision subsystem having an output to provide a symbol decision for each symbol of the channel corrected subcarriers; a reverse processing subsystem having an input coupled to the output of the decision subsystem, the reverse processing subsystem to apply one or both of the phase error and the timing error that have been corrected in the forward processing subsystem, and the reverse processing subsystem having an output of a post-decision signal that includes an error that approximates one or both of the phase error and the timing error in the subcarriers accepted by the forward processing subsystem, the reverse processing system producing reverse processed post-decision subcarriers; an inverse discrete Fourier transformer having an input coupled to the output of the reverse processing subsystem accepting the reverse processed post-decision subcarriers, the inverse discrete Fourier transformer having an output to provide time-domain post-decision signal samples; and a feedback filter having an input coupled to the output of the inverse discrete Fourier transformer accepting the time-domain post-decision signal samples, the feedback filter outputting a filtered, post-decision sampled signal filtered according to an impulse response approximating a post-guard interval channel impulse response, the filter having an output to provide the to-be-subtracted equalizing signal, the output of the feedback filter coupled to the second input of the subtractor, wherein the impulse response of the feedback filter is directly calculated, and such that the to-be-subtracted equalizing signal includes the effect of a past symbol decision and is used to equalize a present digital sampled symbol from the radio receiver.