A Family of Split Spectrum GPS Civil Signals

J. J. Spilker Jr, E.H. Martin, B. W. Parkinson

Abstract:	There is a strong need for the next generation of GPS satellites to provide at least one new civil signal in addition to the present C/A signal at the L1 frequency. One candidate for this signal is a signal that we have termed the Split Spectrum C/A signal1. Although this signal is based on the C/A signal and can be treated as a single wide bandwidth signal, most of its power spectral density is concentrated in a pair of frequency zones or sidebands symmetrically offset from the carrier center frequency. The Split Spectrum signal has the following desirable properties: · Redundancy against interference or multipath fading. Each of the two symmetrical sidebands can be tracked individually as separate C/A signals thus providing a substantial degree of redundancy against unwanted interference and frequency diversity against selective multipath fading. If an interfering signal is present at the lower sideband, the receiver can delete the contribution of that sideband and track and demodulate only the upper sideband. Likewise in a multipath fading environment the receiver can optimally diversity combine the tracking parameters of the two sidebands. Quasi-optimal delay lock or narrow correlator type loops can be used to mitigate multipath effects. · Improved tracking accuracy against thermal noise. This signal can either be used as a single wideband signal with its high tracking accuracy or as a pair of redundant C/A signals offset in frequency. If the signal is tracked as a single wideband signal its tracking accuracy is improved relative to thermal noise by its increase in RMS or Gabor bandwidth by a factor of approximately 10-20 depending on the frequency offset employed. The signal can also be tracked by a modified delay lock tracking loop which can operate on either the upper sideband, the lower sideband or a optimal diversity combined combination of the two. In addition the offset carrier phase can be tracked as well to obtain high accuracy tracking. Improved carrier phase ambiguity removal. In addition to the “wide-laning” provided by the simple use of the L1-L2 frequency, the split spectrum signal offers an “ultra-wide-laning” capability by means of the frequency difference between the upper and lower sidebands. This frequency separation for the signals discussed here ranges from 20.46 MHz to 60 x 1.023MHz. · Simple all-digital signal generation. The signal is easily generated using all-digital logic in the satellite to generate a constant envelope signal thereby permitting the use of class C power amplifiers. Unwanted odd harmonic sideband energy is removed by filtering resulting in a loss of only 0.912 dB
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1905 - 1914
Cite this article:	Jr, J. J. Spilker, Martin, E.H., Parkinson, B. W., "A Family of Split Spectrum GPS Civil Signals," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 1905-1914.
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