Passive Emitter Localization with Selective TDOA-based Bearing Measurements

Abstract

In recent years, there has been a growing interest in passive surveillance system (PSS) that is capable of precise localization of an emitter at a distance covertly because most of platforms such as aircraft are equipped with electronic warfare systems. The PSS typically consists of four sensors in known spatially-separated positions and performs passive emitter localization with time difference of arrival (TDOA) measurements by the differences in ranges between the emitter and the sensors. However, when TDOA-based bearing measurements are used in passive triangulation, the accuracy of localization depends on the geometric relationship between the emitter and the sensors. In particular, the localization accuracy varies with the geometric conditions in TDOA-based direction finding (DF) for bearing measurement and lines of bearing (LOBs) crossing for triangulation. Therefore, this thesis presents a novel method to select TDOA-based bearing measurements to obtain an accurate estimate in passive triangulation by considering geometric dilution of precision (GDOP) between the emitter and the sensors. Firstly, we introduce passive emitter localization methods which are based on time of arrival (TOA), received signal strength (RSS), bearing, TDOA and frequency difference of arrival (FDOA) measurements in a location system. To give better understanding for emitter localization we explain the localization accuracy definitions and GDOP for describing the effect of geometry on the relationship between measurement error and position determination error. In addition, we explain a basic principle of TDOA-based DF in the PSS and introduce some considerations that affect the bearing measurement error of TDOA-based DF in a real environment such as TDOA-based DF regardless of whether the sensor pair is perpendicular to the true north, mirror image ambiguity resolving and the virtual sensor concept. Finally, we propose a novel method of selecting adequate TDOA-based bearing measurements to enhance the localization accuracy by passive triangulation in the case where four sensors are considered. To obtain an accurate estimate in passive triangulation using TDOA-based bearing measurements, we shall use these bearings selectively by considering GDOP between the emitter and the sensors. To achieve this goal, we first define two GDOPs related to TDOA-based DF and LOBs crossing geometries, and then propose a new hybrid GDOP by combining these GDOPs for a better selection of bearings. Subsequently, two bearings with the lowest hybrid GDOP condition are chosen as the inputs to a triangulation localization algorithm. In simulation results, we show that the use of the virtual sensor concept is suitable for reducing the TDOA-based bearing measurement error in a real environment, the baseline length between the sensors should be selected by considering the system operating conditions to ensure the TDOA-based DF performance from near to far distance, and the sensor deployment configuration has greater effect on GDOP characteristics with respect to the emitter and the sensors rather than the baseline length. Also, we show that the performance of the proposed method exceeds those of the cases in which all TDOA-based bearings and two bearings selected by each GDOP are used as the inputs to a triangulation localization algorithm.