Code Multiplexing via Majority Logic for GPS Modernization

James J. Spilker Jr. and Richard S. Orr

Abstract:	Majority logic has been known for many years as a multiplex technique for binary codes and has been successfully employed in deep-space communications by NASA Jet Propulsion Laboratory. The majority logic combination of an odd number of binary codes has the best cross-correlation with the components codes in the minimax sense, and because it yields a constant envelope signal, is appropriate for transmission via Class C (saturating) amplifiers as opposed to the less efficient Class A (linear) amplifiers. Majority logic thus becomes appropriate to the design of frequency reuse waveforms for GPS Modernization, where both new and backward compatible signals must be multiplexed into the existing GPS spectrum allocations at L1 and L2 in a manner that preserves the integrity of both the military and civilian signals. This paper begins with an overview of the majority logic multiplex technique and some recent extensions, e.g., to accommodate unequal power weighting of the components codes and/or phase-quadrature multiplexing. Application to the design of new military GPS signals is then discussed, including aspects such as: power efficiency and spectral properties of the multiplex, acquisition of the new signals without dependence upon the C/A code, and receiver processing techniques that minimize or eliminate the multiplex loss through use of side information about the component codes and the data they carry.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	265 - 273
Cite this article:	Spilker, James J., Jr., Orr, Richard S., "Code Multiplexing via Majority Logic for GPS Modernization," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 265-273.
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