Urban/Suburban UHF Geolocation, 16-9381Printer Friendly Version
Inclusive Dates: 03/05/03 - Current
Background - Radio geolocation is an established process for estimating the position/location of a signal emitter. Typically, the geolocation procedure requires a pool of measurements collected by a network of diversely located and inter-communicating sensors, usually with transmitted waves traveling in a general straight path from the transmitter to the sensor. On the basis of this presumption, the location of the unknown transmitter can be estimated by computing the location that produces best consistency with the observed directions of arrival or with the observed propagation times measured at each sensor. However, in the case of an urban environment transmitter, the direct straight-line path from the transmitter to sensors is typically obscured by various intervening urban structures, so that the only operable propagation paths linking the transmitter to each sensor are indirect, with the transmitted signal arriving at each sensor by way of multiple reflections or diffractions and at different times. Under such circumstances, the angle-of-arrival at each DF sensor can be 90° or more in error, and the propagation distance can be a city block or more in error when compared to the actual direction and actual distance between sensor and transmitter. Such errors lead to correspondingly large errors in estimating and determining the transmitter geolocation.
Approach - In a limited selection of three urban-environment scenarios, a wide-band sounder signal will be transmitted and received by a precise time synchronized acquisition sensor consisting of a typical DF antenna array. The wide-band data will be post-processed to characterize the distribution of propagation times, directions of arrival, and signal strengths associated with the multiple simultaneous paths of propagation between transmitter and sensor. The acquisition sensor will acquire wide-band data at several controlled locations to support a subsequent post-processing task for simulating a geolocation network of sensors and statistically quantifying subsequent geolocation accuracies.
Accomplishments - Phase I concluded with a completed survey of Signals of Interest (SOIs) in the UHF frequency range with client input and compared the SOI transmission frequencies to those available for experimental propagation tests. The aim of future collection efforts will focus on using the public ISM bands between 900 and 2400 MHz. Literature searches have been conducted to determine the expected variations in multipath propagation in typical urban areas and an initial analysis has been conducted involving the variations in propagation delays and expected signal strengths. Based on these reviews, an initial transmitter design has been outlined and this IR effort will be completed and results summarized late summer 2004.