Determination of Early-Late Discriminator Errors on Filtered BPSK Waveforms

B. Fonville, E. Powers, D. Matsakis

Abstract:	GPS receivers commonly use Early-Late discriminators to estimate the position and rate of the internal Prompt codes with respect to the received waveforms. For ideal (non-filtered) input waveforms, the Early-Late discriminator steers the Prompt codes into perfect alignment. However, when tracking filtered BPSK waveforms, a misalignment of the Prompt code occurs, as a function of correlator spacing for a given filter transfer function. The misalignments will cause errors in the final pseudorange measurements, as discussed in previous publications authored by USNO and MITRE Corporation, and may introduce time biases between the different GPS code families, even when they are on a common carrier frequency. The receiver’s pseudorange measurement errors are dependent on the degree of front-end filtering and on the tracking technique that is implemented. In this paper we will focus on the pseudorange errors for BPSK signals. We will show how filtering and correlator spacing affects the pseudorange measurement, and we will show a way to measure and compute the resulting errors so that they could be corrected in receiver software.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3600 - 3606
Cite this article:	Fonville, B., Powers, E., Matsakis, D., "Determination of Early-Late Discriminator Errors on Filtered BPSK Waveforms," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3600-3606.
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