Precision Geolocation and Co-Channel Interference Mitigation Using Low Bandwidth Communication Links, 16-9221

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Principal Investigators
Don R. Van Rheeden
Carlos A. Garcia

Inclusive Dates: 10/01/01-10/01/02

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. Because 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. The Institute 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 has 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 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 could be achieved on FM-modulated signals without significantly degrading TDOA estimator performance. Geolocation performance of arbitrary TDOA networks was simulated. For example, the illustration below shows geolocation performance of a ten-site TDOA network where the receivers are placed in a random configuration. Expected geolocation accuracy is shown on the bar legend to the right of the plot. SwRI assembled, lab-tested, and field-tested a TDOA data collection and logging system.

This figure shows results from an analysis tool that was developed to predict geolocation accuracy for a network of TDOA receivers

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