Patent ID: 6330291
Filing Date: 2001-12-11
Classification: H04B

Abstract:
A frequency tracking loop for a communication system that uses orthogonal M-ary Walsh modulation to generate communication signals, the loop comprising:rotation means for receiving an input signal and a frequency offset estimate and for producing a frequency shifted input signal, with the amount of frequency shift being controlled by the frequency offset estimate;correlation means for determining a correlation between a predetermined set of Walsh functions and the frequency shifted input signal and for producing a correlation vector;discrimination means for receiving said correlation vector and for producing a frequency error signal proportional to a difference between said tracking loop and communication signal frequencies, wherein said discrimination means comprises:means for finding a first correlation result having a greatest energy value;means for determining a binary representation of a corresponding first index value for the first correlation result; andmeans for inverting at least one bit of said binary representation of said first index value to generate a second index value corresponding to a second correlation result; andfiltering means for accumulating said frequency error signal, and for producing said frequency offset estimate.