Application of POCET Method to Combine GNSS Signals at Different Carrier Frequencies

P.A. Dafesh, C.R. Cahn

Abstract:	In a previous paper by P. A. Dafesh and C. R. Cahn titled "Phase-Optimized Constant-Envelope Transmission (POCET) Modulation Method for GNSS Signals," presented at ION GNSS 2009, the POCET technique was described as a method to combine a multiplicity of random binary signals into a constant-envelope carrier while maintaining specified constraints on correlations and phase relations. This paper extends that technique to enable combining signals at different carrier frequencies into a constant-envelope carrier and describes potential applications to GNSS. The significant advantage of this combining technique is that it reduces the number of different amplifiers that must be multiplexed in the satellite. The key capability of POCET as a combining technique for this application is that the phase shifts between pairs of correlations can be specified as constraints; in this case, the phase shift is rotating with time due to the frequency difference between the carriers. A sufficiently high sampling rate is required to minimize losses due to the phase rotation. By quantizing the phase shift between the carriers, a reasonably small number of different phase tables needs to be stored in the satellite. One proposed application is to combine a possible new GLONASS CDMA signal at L1 with a GLONASS FDMA signal into a single carrier. Another proposed application is to combine the L2 signals (L2C, P(Y), and M) with the L5 I and Q signals into a single carrier. In this application, due to signal symmetry, only one phase table has to be stored. The power loss due to the combining of the carriers at different frequencies is relatively low, on the order of 1 dB. Furthermore, it is found that the power loss can be reduced through a further enhancement of the POCET method.
Published in:	Proceedings of the 2011 International Technical Meeting of The Institute of Navigation January 24 - 26, 2011 Catamaran Resort Hotel San Diego, CA
Pages:	1201 - 1206
Cite this article:	Dafesh, P.A., Cahn, C.R., "Application of POCET Method to Combine GNSS Signals at Different Carrier Frequencies," Proceedings of the 2011 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2011, pp. 1201-1206.
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