Kenneth Johnston, KTEQ GEOSPACE, Canada

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Abstract:

This paper proposes a low-cost (less than $250 USD) emulation capability of low-power Global Positioning System (GPS) Radio Frequency Interference (RFI) that is representative of modernized GPS jammer waveforms and modulations. The proposed system is consistent with the US FCC and Industry Canada Spectrum Management policy and regulations while meeting the requirements of lab testing GPS RFI and assessing the impact on GPS receivers. During the past several years there has been a proliferation of Personal Privacy Devices (PPDs) that have been well documented in Institute of Navigation (ION) papers and through the STRIKE3 project in Europe. Many of these PPDs are of low quality and have minor impact on actual GPS positioning or timing reliant systems. In Canada, it is illegal to import, purchase, possess or operate a GPS jammer. High performance RF Signal Generators and Waveform Generators that are capable of emulating GPS RFI signals up to at least 10 dBm are typically used in the lab by governments and larger companies. For smaller businesses, academia and some research organizations, often the cost of such equipment exceeds available budgets. These policy and financial constraints present challenges for a segment of the GPS industry to develop and test GPS RFI detection and monitoring capabilities and to assess the impact of new RFI mitigation algorithms and techniques specifically designed to counter GPS RFI. During this research, GPS RFI signals were generated using a combination of low-cost wideband RF synthesizers, specifically RF evaluation boards and modules based on Analog Devices (AD) ADF4351 chip and a low-cost Direct Digital Synthesis FeelTech FY6300 Function/Arbitrary Waveform Generator. The equipment was configured to generate examples of GPS RFI including Continuous Wave (CW), multi-tone, stepped tone, chirp waveforms, pulsed, narrowband and wideband noise waveforms, and Pseudo Random Noise (PRN) waveforms that were tailored to closely match the relevant GPS RF spectrum but could be easily modified for other GNSS systems based on the needs of a user. The generated RFI waveforms were recorded for comparison using a Signal Hound USB SA44B spectrum analyzer and a low-cost Airspy R2 Software Defined Radio. The combination of the ADF4351 and the FY6300 effectively jammed a Ublox NEO-7N GNSS receiver using selected RFI waveforms.