Receiver Processing Software Design of the Rockwell International Dod Standard GPS Receivers

Jeffery C. Rambo

Abstract:	This paper describes the design of the Receiver Processing soft­ware used within all of the Phase III Collins User Equipment. The Receiver Processing software controls the highly digitized RF /IF processing necessary to acquire and maintain lock on the GPS satellite signals. This paper provides a detailed description of the Receiver Processing software which has a high degree of common­ality across the entire baseline of one, two and five channel DoD standard receivers, and provides sample acquisition and tracking loop performance data. The Receiver Processing software performs the satellite signal ac­quisition, centering, and tracking operations necessary to provide navigational capability using GPS satellite signals. These opera­tions use the outputs of the four correlation channels per correlator and require control of the code generator and variable oscillators. Receiver Processing is controlled by the Receiver Manager function which selects the satellites to be tracked and the acquisition parameters to be used. Receiver Manager also evaluates the tracking success using signal power measurements. The acquisition operations determine the code phase and code rate offsets where the locally generated signal correlates with the received satellite signal. These offsets are used to begin the centering operations. Special consideration was given to account for varying signal-to-noise ratios, the presence of reflected and interfering signals, and the time-to-first-fix requirements. The centering operations begin with the code phase and code rate offsets supplied by the acquisition operations and perform the code centering and carrier lock-on steps necessary to reduce the tracking errors to a level where the pseudorange and deltarange measurements can be derived. For Cf A code this may also require a data bit synchronization step which aligns the locally generated 20 ms epochs with the incoming data bit epochs. The tracking operations include performing the code and carrier tracking loops, demodulating the 50 Hz downlink data bits, and forming the measurements necessary to provide navigational capability using GPS satellite signals. The design of the tracking loops allows for tailoring the tracking bandwidths to the particular host vehicle environment in order to maximize the performance. Special consideration was also given in the tracking operations to protect against carrier sideband tracking caused by excessive host vehicle dynamics.
Published in:	Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989) September 27 - 29, 1989 The Broadmoor Hotel Colorado Spring, CO
Pages:	217 - 225
Cite this article:	Rambo, Jeffery C., "Receiver Processing Software Design of the Rockwell International Dod Standard GPS Receivers," Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989), Colorado Spring, CO, September 1989, pp. 217-225.
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