A USRP-based testbed for navigation education, research, and development

Historically, organizations interested in studying navigation signals would typically invest significant resources into specialized radio equipment hardware and/or software simulation. With advances in the computing and analog/digital hardware domains, it is now becoming more viable to conduct this research in a software defined radio environment with equipment that can be quickly and easily reconfigured to receive (or transmit) any of a variety of electronic navigation signals. We fully expect that educational and small business research/development efforts will benefit greatly in the near future from these robust signal capture/analysis systems; they promise to be inexpensive and easy to use, yet can span the manmade RF spectrum. The hardware used for our software defined radio application is the Universal Software Radio Peripheral (USRP), its associated daughter boards to select the frequency band of interest, an appropriate antenna, and a general purpose personal computer (Windows or Linux). By merely installing the relevant daughter board and connecting an antenna, the USRP user is able to view, manipulate, record and transmit RF signals in the range from DC to 5.9 GHz. Closely linked with the USRP are associated software tools for defining and executing a software radio system. These software tools are available in two broad categories; the open source GNU Radio program running under the Linux operating system, and the Simulink/Matlab programs running under a Windows environment. This paper describes the software defined radio platform, with the goal of showcasing its utility to educators and researchers in the navigation community. We begin by providing details on our experience in programming/configuring the USRP using both the GNU Radio and Simulink approach. Then, we demonstrate by example its application to the capture and analysis of several different electronic navigation signals. Four different commonly available navigation signals are considered; going up the RF spectrum these are Loran-C, DGPS, DME, and GPS. For each example, actual captured data is shown; further, some simple processing of the captured data is also demonstrated to show how useful the USRP can be to the educator or researcher. Furthermore, we propose several additional navigation applications that would be well suited to analysis with software radio techniques. While we limit our attention to these four signals, we close by arguing how the real potential of this system lies in its adaptability, allowing for rapid prototyping and verification of new and improved electronic navigation schemes