Analog Compression of GPS C/A Signal to Audio Bandwidth

Charles Norman

Abstract:	The C/A code repeats 20 times for every telemetry data bit. This repetition places the signal power in spectral lines spaced 1 kHz apart. The signal can be compressed without any loss of signal by transforming these 20 repetitions to the frequency domain and zeroing the frequency bins that have no signal. The remaining bins can be transformed back to the time domain with the bandwidth reduced by a factor of 20. The compression is the same as the number of repetitions used. if the 50 Hz telemetry data bit transitions are removed then more than 20 repetitions may be used. The factor limiting the number of repetitions that can be used now becomes the users motion. If the user motion is limited to .5 g acceleration then the bandwidth may be reduced by more than a factor of 100 without loss of signal. Two additional methods of bandwidth compression are possible but these will result in signal loss. The first method is to eliminate transmission of some of the spectral lines. Since the signal level in each line varies, it is possible to eliminate the lines with the least power to minimize the signal loss. The second method of bandwidth compression is to overlap the output bands. The portion of the output bands that overlap will have increased noise density, causing a reduction in signal to noise ratio. No loss occurs when each line is band limited such that the noise power in the band around each line doesn’t overlap the next line’s band.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2372 - 2375
Cite this article:	Norman, Charles, "Analog Compression of GPS C/A Signal to Audio Bandwidth," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2372-2375.
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