scope:

Introduction

This Report compares the strengths and weaknesses of time-difference-of-arrival (TDOA) versus angle-of-arrival (AOA) methods of signal geolocation. While this Report focuses on TDOA, it should be noted that other geolocation techniques exist¹. The AOA method determines the angle of arrival of a wave at a measurement point. AOA methods have been commonly used in many direction-finding applications, and have some advantages but also some disadvantages related to antenna requirements, for example. TDOA methods, on the other hand, compute the time difference of arrival of a wave at multiple measurement points, and calculate the source point based on timing and wave comparisons. TDOA methods have not been widely used in spectrum monitoring, but have become increasingly useful due to the availability of inexpensive and compact computing power, more advanced radio receiver technology, ready availability of data links, and accurate distributed timing signal availability. The paper will provide a short overview of TDOA technology and some comparison of the strengths and weaknesses of the TDOA method compared to more traditional AOA methods.

¹ Received signal strength (RSS) uses the measured power ratio of a signal at multiple measurement points to compute the source point. RSS is often used for indoor geolocation. Frequency-difference-of-arrival (FDOA) uses the frequency Doppler shift of a moving source (and/or multiple receivers) to calculate the source point. FDOA is often used in conjunction with TDOA for airborne applications.