13. A digital correlator for correlating a succession of received digital words in a serial bit stream with a reference digital word of bit length L having a reference word period, the correlator comprising: means for providing a set of ramp weights W(k), where k=1 to L/N, where N is a number of word segments comprising said received digital word, each word segment having L/N bits; ramp-weighting summing means for forming a ramp-weighted sum over each of said N word segments, said summing means comprising means for accumulating the respective sums of a product of a reference word bit with a product of a corresponding received bit comprising said segment with a ramp weight W(k) for each bit comprising said word segment; uniformly-weighting summing means for forming a uniformly-weighted sum over each of said N word segments, said summing means comprising means for accumulating the respective sums of a product of a reference word bit with a corresponding received word bit for each bit comprising said word segment; and means for forming a digital correlator output signal at a rate equal to the word segment rate, each output signal comprising a triangular-weighted sum of scaled versions of said ramp-weighted sums and said uniformly-weighted sums over a plurality of preceding word segments covering a predetermined plurality of received words, whereby degradation of said correlator performance caused by Doppler shift modulation on said received signals is reduced.
13. A digital correlator for correlating a succession of received digital words in a serial bit stream with a reference digital word of bit length L having a reference word period, the correlator comprising: means for providing a set of ramp weights W(k), where k=1 to L/N, where N is a number of word segments comprising said received digital word, each word segment having L/N bits; ramp-weighting summing means for forming a ramp-weighted sum over each of said N word segments, said summing means comprising means for accumulating the respective sums of a product of a reference word bit with a product of a corresponding received bit comprising said segment with a ramp weight W(k) for each bit comprising said word segment; uniformly-weighting summing means for forming a uniformly-weighted sum over each of said N word segments, said summing means comprising means for accumulating the respective sums of a product of a reference word bit with a corresponding received word bit for each bit comprising said word segment; and means for forming a digital correlator output signal at a rate equal to the word segment rate, each output signal comprising a triangular-weighted sum of scaled versions of said ramp-weighted sums and said uniformly-weighted sums over a plurality of preceding word segments covering a predetermined plurality of received words, whereby degradation of said correlator performance caused by Doppler shift modulation on said received signals is reduced. 14. The correlator of claim 13 further comprising means for digitally filtering said digital correlator output signals with a Doppler frequency, narrow band filter to enhance signal-to-noise ratio.