Patent ID: 6512720
Filing Date: 2003-01-28
Classification: H04B,H04W,Y10S

Abstract:
A method for Doppler compensation in a phase coherent underwater communications system, comprising the steps of:a) receiving a communications signal from a plurality of underwater communications channels, said signal comprising a sequence of raw data; b) then applying a Doppler estimation to said data, said Doppler estimation performed according to the steps of: i) applying a concurrent sinusoidal signal in a different band than the band of the communications signal; and ii) applying a Fourier transform over a duration larger that a packet length to thereby obtain a Doppler-shift frequency fcd; c) demodulating the raw data using the fcd; d) low pass filtering the demodulated raw data; e) applying resampling and downsampling to the data at a fractional sampling rate, for n samples per symbol, and generating a synchronized, Doppler-phase-corrected output signal, according to the steps of i) determining a fractional sampling time at multiple intervals of 1/(n*fcd); and ii) resampling the data by interpolating between two sample points of the data before and after the said multiple intervals; f) then applying the synchronized, Doppler-phase-corrected fractionally sampled signal to a phase locked loop and equalizer; g) then comparing an estimated symbol with a decision symbol and updating a plurality of tap coefficients; and h) outputting decision symbols.