Indoor source localization via direction finding technique

Official URL: http://risc01.sabanciuniv.edu/record=b1120027 (Table of Contents)

The location of an indoor transmitter such as a mobile phone in a building can be determined by measuring power or relative timing of the transmitted signal from simultaneous receivers located in the vicinity of the transmitter. A radio location finding system, consisting of two or more equivalent direction finders (DF), is placed outside of the building to pinpoint a transmitter located inside the building. Once the bearing angle is obtained from each DF system, the position of the transmitter is simply the intersection of the bearings from the direction finders. In our experiments, we mostly concentrated on the performance of suggested DF system for both indoor and outdoor applications. We implemented a one-coordinate direction finder to determine only the azimuthal angle of arrival (AOA) of the transmitted signal. Each DF system is composed of two dipole antenna array, receivers, and a laptop computer. A 4-channel sampling oscilloscope with a maximum sampling frequency of 4 Gs/s is used to receive and digitize the received signals. The digitized signals are then transferred to a laptop computer over a General Purpose Interface Board (GPIB) interface for further analysis to extract AOA information. Extraction of AOA information is based on time delay measurement technique. An electromagnetic wave impinging on two antennas separated by a distance of d experiences a time delay. The time difference of arrival between the received signals at the antenna terminals can easily be found by cross-correlating the signals. The delay is estimated as the time lag value where the peak of the cross correlation of two antenna signals occurs. Many experiments are realized in different environments such as anechoic chamber, an indoor RF laboratory and open air sites to measure the performance of direction finder. Using the data we have collected, we modeled a location finding system consisting of three equivalent DF systems located around a building. The simulation results show that the proposed simple DF system will work reasonably well for the location of a tranmitter inside a building. The proposed DF system is a trade-off between a highly sophisticated, but not easily deployable system such as a phased array DF and a simple amplitude comparison DF system. Accuracy of the system will be higher compared to that of an amplitude only system, and also will have an ease of implementation compared to that of a phased array system.