Development of a Prototype Texas Ionospheric Ground Receiver (TIGR)

J. York, D. Munton, M. Mayo, T. Sump

Abstract:	We describe the development and status of the Texas Ionospheric Ground Receiver (TIGR), a flexible soft- ware receiver, operating over a broad range of frequencies that is designed to make ionospheric measurements from satellite signals. Historically, the basis of this work has origins in the TRANSIT satellite system, which for many years served as the US Department of Defense positioning and navigation sys- tem [1]. The dual frequency signals of the TRANSIT system were designed to provide a means for eliminating ionospheric effects, but proved useful in the scientific community for extracting ionospheric measurements. Similar systems were later developed by other countries, for example the Soviet Union developed the Parus/Tsikada system. This type of low Earth orbiting dual frequency beacon satellite later proved useful for ionospheric tomography, as first suggested by Austen, et al. [2]. In the late 1990s, Applied Research Laboratories, The University of Texas at Austin developed the Coherent Ionospheric Doppler Receivers (CIDRs) [3] as a modern receiver capable of tracking the Navy Ionospheric Monitoring System (the renamed TRANSIT system), and generating total electron content measurements (TEC). The TIGR is a replacement for the CIDR which expands on the CIDR capabilities. Notably, the TIGR is designed to be substantially transmitter- independent, such that with a suitable antenna attached, the TIGR is capable of tracking any signal between 100 and 2500 MHz. In this manner, many signals of opportunity might be exploited to yield ionospheric information. We describe the development of the TIGR prototype, which relies in design on modifications of instruments already developed the GNSS Digital Front End (DFE) [4] and the High Rate Tracking Receiver [5]. The DFE is an FPGA-based direct sample receiver that operates over the L-band. For the TIGR we have extended the design of the DFE to operate over the frequency range 100 - 2500 MHz. The RF data is directly sampled via a 2 Gigasample/s ADC and passed to an FPGA, where it is digitally filtered, and down-sampled into three tunable bands, each with a bandwidth of 20 MHz. A reduced digital data stream is passed to a second FPGA, where the individual channels are filtered into multiple narrow signal bands of programmable width, typically 1 kHz, centered on the frequency of the satellite signal as adjusted to compensate for the predicted Doppler shift. Estimation of the phase and amplitude of the signal in this data is accomplished by the use of on-board software running on a general purpose CPU. This process avoids the use of traditional tracking loops and provides improvements in interference identification and filtering. We will describe the design and operation of both the digital processing and the on-board processing software. Finally, we will pro- vide results from initial testing of the TIGR, focusing on the extraction of a total electron content measurement. We discuss the advantage of this design in helping reduce the problem of Radio Frequency Interference (RFI) in measurements.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1526 - 1556
Cite this article:	York, J., Munton, D., Mayo, M., Sump, T., "Development of a Prototype Texas Ionospheric Ground Receiver (TIGR)," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 1526-1556.
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