Adaptive Array Phase Control using an Integrated Software GPS Signal Processing Architecture

Sai K. Kalyanaraman, Michael S. Braasch

Abstract:	The effect of adaptive array processing on the code and carrier phase of the spread spectrum signal is a function of the signal operating environment and the nature of the adaptive processing mechanism. Spatial adaptive processing (SAP) utilizes its degrees of freedom to form spatial nulls towards interference sources and techniques such as Space- Time Adaptive Processing (STAP) and Space Frequency Adaptive Processing (SFAP) prove effective against both wide and narrow band interferers by forming more precise nulls across space and time/ frequency respectively. GPS antenna arrays employing constrained power minimization to combat interference can preserve the phase and gain of the signal in the desired look direction. However, unconstrained power minimization techniques may cause distortions to the signal of interest. This is of concern when the system requires high precision carrier phase measurements in the absence of additional information regarding the direction of arrival of the desired signal relative to the user platform’s attitude. In addition, in a non stationary signal operating environment, the algorithms used to adapt the weights of the element space or beam space processors are required to have fast convergence properties with minimal sample support. This implies that the weights applied to the GPS signal may vary at a high rate. As a result, the phase of the signals of interest in the desired look direction will vary rapidly. The impact of these phase fluctuations could vary from ranging errors to loss of phase lock due to distortions imposed on the GPS signal. With the advent of software GPS receivers, it is now possible to implement the advanced phase compensation mechanisms in conjunction with null/beam steering baseband modules that are tightly integrated with the GPS receiver processing. This paper will describe the results of such an approach to integrate a software adaptive array with a software GPS receiver. The performance of both code and carrier tracking in the presence of multiple narrow band and wide band interferers will be investigated.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2772 - 2785
Cite this article:	Kalyanaraman, Sai K., Braasch, Michael S., "Adaptive Array Phase Control using an Integrated Software GPS Signal Processing Architecture," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2772-2785.
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