Phil Ward

Peer Reviewed

Abstract: The operation of a NAVSTAR GPS multiplex receiver is defined in this paper as processor-controlled time-sharing of a single channel of receiver hardware in a manner that permits continuous (in a sampled data sense) digital phase-locked loop tracking of four GPS transmitters while simultaneously reading the 50-Hz navigation message data from the same four transmitters. The operational and performance characteristics are described for a proven advanced NAVSTAR GPS digital multiplex receiver front-end design that time-shares one code generator and one carrier synthesizer in accordance with this definition. Multiplexing has been demonstrated with this advanced single-channel receiver front-end in a manner that creates up to eight pseudochannels. The receiver can also be operated at a reduced number of pseudochannels in binary multiples of 4, 2, or 1. The eight pseudochannels provide simultaneous tracking of four GPS transmitters in P-code of both the L, and L, signals. In addition, the space vehicle (SV) 50-Hz navigation message data are read continuously from all four GPS transmitters. The eight pseudochannels emulate a multichannel set that is virtually free of interchannel bias and interchannel phase drift error since all GPS signals of the same frequency travel the same hardware path. Sixteen observables are continuously available: four L, code phases, four LZ code phases, four L, carrier doppler phases, and four L, carrier doppler phases. These measurements are captured directly as a by-product of the nearly instantaneous phase presetting and the digital synthesis of the numerically controlled code and carrier tracking loops. From these raw measurements, the usual GPS receiver pseudoranges, delta pseudoranges, and their LJL, differences can be derived. Quantization noise is negligible since the raw measurements are of such ultrahigh resolution (2 I6 P-chip code phase and 2 I6 cycle carrier doppler phase). The receiver error characteristics are described and actual tracking error plots for 16 simultaneous observables from four real GPS satellites are shown.
Published in: NAVIGATION, Journal of the Institute of Navigation, Volume 30, Number 1
Pages: 34 - 50
Cite this article: Ward, Phil, "AN ADVANCED SINGLE-CHANNEL NAVSTAR GPS MULTIPLEX RECEIVER WITH UP TO EIGHT PSEUDOCHANNELS", NAVIGATION, Journal of The Institute of Navigation, Vol. 30, No. 1, Spring 1983, pp. 34-50.
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