Time Difference of Arrival Geolocation Using Frequency Translators, 16-R9600

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Principal Investigator
Don R. Van Rheeden

Inclusive Dates:  01/01/06 – Current

Background - A frequency translator is a device that receives a signal in one frequency band and retransmits the signal on another frequency band. The goal of this project is to investigate a time-difference-of-arrival (TDOA) geolocation approach that uses frequency translators as TDOA nodes. Instead of each TDOA site receiving, digitizing, time-stamping, and relaying signal samples over a communications network to a geolocation processor as is commonly done, each frequency translator node would retransmit a signal onto several nonoverlapping frequency bands to a central receiver/digitizer. Such an approach would eliminate the need for a high-speed digitizer, a precision time reference, acquisition computer, and network connection at each node. Because a single central receiver would receive frequency translated signal copies concurrently, no precision timing reference is required. This approach has the potential to significantly reduce node cost, weight, and power requirements.

Approach - The primary objective of this project is to research and develop a frequency translator TDOA geolocation approach. To accomplish this goal, four primary tasks must be completed. First, the cost-benefit tradeoffs of frequency translator hardware components will be studied. Second, different multiplexing schemes on the RF downlink will be investigated. Third, on-air signal testing using commercially available frequency translators will be performed. A geolocation algorithm to process frequency translated copies of a signal and produce transmitter location estimates will be developed. Fourth, a calibration approach to compensate for biases and other error sources inherent in the frequency translator hardware components will be formulated. Group delay characteristics of the frequency translators will be measured.

Accomplishments - We have developed mathematical models to understand the error sources inherent in the frequency translator approach. A result of this development is the discovery of an approach that allows all frequency translated signals to occupy the same downlink frequency band. This approach will reduce the amount of downlink bandwidth required to relay the frequency translated copies of a transmitted signal to a common receiver/digitizer. We have identified a candidate frequency translator hardware architecture that was developed and bread-boarded by SwRI in 2005. Group delay measurements have been taken and showed that this frequency translator design is suitable for this application. The current plan is to perform on-air testing with a set of these translators in the November to December 2006 time period.

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