GPS Receiver Block Processing

Gang Feng and Frank van Graas

Abstract:	When a GPS receiver reports a bad measurement, it is often difficult to analyze the anomaly due to a lack of detailed data surrounding the event. A system that samples the GPS radio frequency signal at a rate that preserves all the pertinent signal information allows for off-line processing to determine the cause of the anomaly. The GPS Anomalous Event Monitor (GAEM) is designed to capture GPS data at a rate of 5 mega samples per second for several seconds surrounding an event. New block processing techniques are used on the 12-bit samples to assess the quality of the received GPS signal. Block processing provides estimates of the GPS signal parameters without the use of tracking loops. It not only demodulates the GPS signals, but also analyzes the signal quality. This paper describes block processing algorithms that have been implemented and tested in a software GPS receiver. The sampled data are processed in 1-millisecond blocks. Code-phase, frequency, carrier-phase, and signal-to- noise ratio are estimated for each block of data. Advantages of block processing are discussed and processing results are compared with those for a sequential-processing GPS receiver. By using block processing techniques, the satellite signal quality is analyzed in terms of carrier-to-noise ratio ( 0 / N C ), shape of the correlation function, false acquisition peaks, code-carrier divergence, sudden change in code and/or carrier, and change in the satellite code. Based on the statistical distributions of the detection parameters, thresholds can be calculated to provide a specified probability of a false detection, and to calculate a minimum detectable bias with a specified probability of missed detection. A detection statistic is introduced for the shape of the correlation function.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	307 - 316
Cite this article:	Feng, Gang, van Graas, Frank, "GPS Receiver Block Processing," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 307-316.
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