Navigating with Time Difference of Arrival Measurements Obtained from Signals of Opportunity

摘要

The Global Positioning System (GPS) provides accurate navigation in a wide range of environments. However, 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. This paper describes a promising alternative positioning method 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. A new approach to navigation using TDOA from SOP is outlined through a three step process. The first step is deciding which SOP to use. The navigation potential, or the theoretical limit on the ability to use a signal for TDOA navigation, is derived and justified as a useful measurement tool when comparing SOP. This is accomplished by applying the Cramer-Rao lower bound to the TDOA navigation problem. The second step is to use SOP to form TDOA measurements. An optimal method for calculating the TDOA measurement is presented. The final step is to use the TDOA measurements to obtain a navigation solution. A novel adaptation of a current GPS position algorithm is presented which will allow the use of TDOA measurements to determine a position solution.