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Session B4: Application/Impact of GPS Technologies in the Homeland Critical Infrastructure

Low-Cost GPS Beamforming with $20 Software Defined Radios
Wilbur L. Myrick, Daniel T. Goff, and Robert B. Alwood, ENSCO, Inc.
Location: Room 305
Alternate Number 2

We present a low-cost four-element GPS beamformer leveraging $20 software defined radios (SDRs) combined with a NVIDIA Jetson Tegra K1 System on a Chip (SoC) embedded platform. The objective is to explore the GPS beamforming capability of an experimental low-cost commercial-of-the-shelf (COTS) system that supports both stand alone and distributed GPS monitoring for supporting national critical infrastructure. We show that carrier phase extraction from each SDR operating with a limited processing bandwidth of 2.4 MHz provides enough information to support asynchronous GPS beamforming.
Distributed array beamforming has been a topic of interest due to its added advantage of sensor placement and processing gain for leveraging transmit/receive beamforming configurations. However, having independent local oscillators at each sensor presents a synchronization challenge for a distributed array. We explore leveraging GPS to support both distributed sensor synchronization and beamforming when an external synchronization hardware interface is unavailable for inexpensive COTS SDRs like the RTL-SDRs. The concept of “software” sensor synchronization is presented to support post-processing scenarios involving low cost SDRs leveraged as auxiliary GPS monitoring sensors for national critical infrastructure.
We show the feasibility of GPS beamforming with an inexpensive mobile GPS collection system for exploring GPS monitoring with SDRs lacking an external hardware interface. In particular, the GPS collection system consists of 1) four $20 RTL-SDRs, 2) a Jetson Tegra K1 System, and 3) four COTS GPS active antennas. A description of the collection system will be discussed as well as the process of extracting carrier phase measurements for both SDR clock drift information as well as carrier phase differences to support GPS beamforming.



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