When the reception of GPS signals becomes unreliable, an alternative is to explore signals of opportunity (SOOP) for positioning. Broadcast digital radio transmissions (e.g., digital TV signals) contain field and segment sync codes, which can be used for ranging even though it was not originally designed for so. Another example is the wireless local area network (WLAN) signals. However, there are two major difficulties. Although the location of SOOP sources is known, the number of independent SOOP sources and their geometric distribution may not be favorable for precise positioning. Besides, the clocks of SOOP transmitters are not synchronized, each subject to a different bias and drift. To respond to the 2009 NAECON Grand Challenge, we set forth a cooperative position location approach. The proposed concept makes use of differential ranges between cooperative devices to a common SOOP source, the relative ranges between the cooperative devices, and displacement measurements by the cooperative devices. The cooperation among networked location devices not only allows them to choose the most appropriate positioning mechanism but also provides them with additional measurements to reduce the number of SOOP otherwise required. In addition to data exchange, the radio link between two cooperative devices also allows for estimation of their clock offset. This leads to a joint position location solution via fixedpoint smoothing. In this paper, we present the proposed system concept, its subsystems, and their operations and also analyze preliminary simulation results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.