Timing offset error extraction method and apparatus

Abstract

A periodic training signal is transmitted over a communications channel from a transmitter to a receiver. At the receiver, a spectrum estimation module is used to measure the spectrum of a set of uncorrected samples of the periodic training signal. The spectrum estimate is available at a discrete frequency spacing of an integer fraction (L>1) of the frequency spacing of the set of samples of the periodic training signal. A timing offset estimation module is then used to measure the ppm offset between the local and remote crystals. The timing offset estimation module runs in parallel with the spectrum estimation module. The spectrum estimate is convolved with the DFT of a periodic ramp function and the result squared to product an error spectrum. The error spectrum represents the error induced by differences between timing in the transmitter and receiver clock. The error spectrum is subtracted from the estimated spectrum to produce a corrected spectrum. The corrected spectrum may be used to generate an SNR spectrum to characterize the communications channel.