Precision Geolocation and
Co-Channel Interference Mitigation Using
Inclusive Dates: 10/01/00 - 10/01/01
Background - A common technical approach used to locate a transmitter is to compute time differences of arrival (TDOA) between multiple fixed receiver sites, and then find a common intersection of hyperbolic curves of position. The most widely used technique to estimate time differences is generalized cross correlation. Since generalized cross correlation requires each fixed site to transmit a large number of signal samples to a central processing station, high bandwidth communication links are typically required. SwRI has developed a signal compression technique that can greatly reduce the amount of data transmitted between sites. A second problem encountered in TDOA systems is obtaining accurate TDOA estimates when receiving narrowband signals. SwRI is investigating techniques to improve TDOA performance on narrowband signals.
Approach - The primary objectives of this program were threefold: develop a lossy compression algorithm to compress TDOA receiver site signal samples with minimal degradation of TDOA estimator performance; improve TDOA performance on narrowband signals; and design and assemble TDOA data collection and logging systems to test performance on live signals.
Accomplishments - SwRI has developed a software simulation that quantifies TDOA timing accuracy as a function of compression ratio for a variety of analog and digital signal types. Simulation studies showed that compression ratios of 10:1 can be achieved on FM modulated signals without significant degrading TDOA estimator performance. The research team has simulated geolocation performance of arbitrary TDOA networks. For example, the figure below shows geolocation performance of a five-site TDOA network where the receivers are placed in a circular configuration. SwRI has assembled and lab tested a TDOA data collection and logging system.