A spread spectrum detector employs a Doppler phase correction system that improves
correlation of pseudo-noise (PN) codes to a received spread spectrum signal by
combining phase shifts to correlation values, using a fast fourier transform (FFT),
that compensate for the Doppler shift error that is inherent in the signal and
that is imposed upon the signal by movement between the signal source and receiver.
In architecture, the Doppler phase correction system includes a receiver to receive
a spread spectrum modulated signal having the Doppler shift error. A multiplier
produces a plurality of complex first correlation values based upon the signal
and a code. A phase shifter generates a plurality of complex second correlation
values respectively from the first correlation values using an FFT. The second
correlation values are phase shifted by respective different amounts from corresponding
first correlation values, so that the second correlation values exhibit less of
the Doppler shift error than the first correlation values. A combiner, such as
an integrator, combines, or integrates, the second correlation values to derive
a third correlation value that indicates a degree of correspondence of the a code
with the signal.