Navigation Potential of Signals Modeled with Multipath Effects and Noise

Kenneth A. Fisher and John F. Raquet

Abstract:	The Global Positioning System (GPS) provides accurate navigation in a wide range of environments. GPS is a line-of-sight (LOS) system, requiring the satellites to be in ”view” of the receiver antenna. It is highly desirable to have the ability to navigate in environments where GPS is not available, such as in urban canyons or indoors. A promising alternative positioning method is using time difference of arrival (TDOA) measurements obtained from signals of opportunity (SOP). SOP are signals that are transmitted for a purpose other than navigation_ however, SOP may also provide navigation ability if properly exploited. SOP are abundant in some areas (e.g. radio stations, television stations) allowing many measurements_ however, the question arises, ”If limited resources prevent the user from exploiting all available SOP, which SOP should be chosen for exploitation?” This paper addresses signal selection with the development of navigation potential, or the theoretical limit on the ability to use a signal for TDOA navigation. One such limit is the Cramer Rao lower bound, which can be considered the most optimistic navigation potential. Prior research has found the navigation potential of a received signal assuming the received signal is the transmitted signal in noise. In this paper, the received signal is modeled as the transmitted signal in noise in addition to multiple delayed and attenuated replicas of the transmitted signal. The multipath model introduced here is a generalization of previous research that may better represent the real world than the transmitted signal in noise alone_ consequently, navigation potential based upon a model that includes multipath effects is more indicative of real world performance. This multipath model is not used for multipath mitigation or to estimate the multipath parameters_ rather, this paper characterizes the ability to estimate the navigation parameters of interest (such as TDOA) when the received signal includes multipath effects.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	320 - 331
Cite this article:	Fisher, Kenneth A., Raquet, John F., "Navigation Potential of Signals Modeled with Multipath Effects and Noise," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 320-331.
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