Compatibility of the Interplex Modulation Method with C/A and P(Y) code Signals

P.A. Dafesh, L. Cooper and M. Partridge

Abstract:	The existing IIR GPS satellites transmit the P(Y) signal in phase quadrature with the C/A signal. The modernized IIR satellites (IIR-M) are to employ a so called Interplex modulation approach to transmit the new military (M) code signal through a single antenna and RF chain. The Interplex modulation is being employed, as opposed to simply adding the M-code signal on the I or Q phase of the carrier. The approach maintains a constant envelope by introducing a fourth cross-product signal in a controlled manner; it results in significantly greater power efficiency than additive modulation of the M-code signal. In order to ensure that the Interplex modulation method does not degrade the performance of receivers tracking signals from the modernized IIR satellites, it is necessary to quantify whether or not the approach leads to any appreciable GPS ranging performance degradation. This paper presents an independent assessment of the backward compatibility impact of the Interplex modulation method on the performance of current GPS ranging signals. The work describes both simulated and measured performance for GPS signal correlation responses and simulated pseudorange error performance. These results are the first independent verification of the Interplex modulation method that quantifies the impact of the Interplex cross-product signal on new and existing GPS signals.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2122 - 2129
Cite this article:	Dafesh, P.A., Cooper, L., Partridge, M., "Compatibility of the Interplex Modulation Method with C/A and P(Y) code Signals," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2122-2129.
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