Measurements of GPS Receiver Compatibility with Interplex-Modulated M-code Signals

P. A. Dafesh, R. L. Wong, M. D. Partridge and T. Fan

Abstract:	The modernized IIR and IIF satellites will use Interplex Modulation to transmit the C/A, P(Y) and new military (M)-code signals on the L1 and L2 GPS carriers. Modulation of the M-code signal using the GPS version of the Interplex modulation, or the equivalent Coherent Adaptive Subcarrier Modulation (CASM), produces an intermodulation (IM) signal in addition to the BOC(10,5) M-code signal. The IM signal is the product of the C/A, P(Y) and (10,5) M-code signal and is mathematically equivalent to a 10.23 MHz Manchester code signal (also denoted by BOC(10,10)) that has been previously studied as a candidate M-code signal. The signal is required to provide the constant envelope feature of the Interplex modulation. In the paper, "Compatibility of the Interplex Modulation Method with C/A and P(Y) Code Signals," presented at ION-GPS-2000, theoretical discussions, simulations and hardware measurements of correlation response illustrated that the signals produced by the Interplex modulation do not appear to degrade the performance of C/A and P(Y) code receivers. This paper describes the first measurements of the backward compatibility of a simulated constellation of M and IM signals with commercial C/A code receivers. The simulated signals are spectrally equivalent to what a GPS receiver would detect after a constellation of modernized IIR or IIF satellites are deployed and were generated using an arbitrary waveform generator. The same approach was used in prior M-code backward compatibility measurements with commercial GPS receivers, conducted in the absence of Interplex modulation (i.e., no IM signal). The work is an extension of the above mentioned Interplex modulation compatibility paper to examine the effects of a constellation of Interplex signals on the performance of commercial-off-the-shelf (COTS) GPS receivers. The paper describes the theoretical background, methodology, experimental setup, receiver impacts and conclusions.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	100 - 108
Cite this article:	Dafesh, P. A., Wong, R. L., Partridge, M. D., Fan, T., "Measurements of GPS Receiver Compatibility with Interplex-Modulated M-code Signals," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 100-108.
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