Broadband GPS Data Capture for Signal and Interference Analysis

There is growing concern regarding the ability of GPS receivers to operate in the presence of in-band or nearband interference. In-band interference can occur deliberately from GPS jammers or naturally from spurious harmonics from nearby electronics that generate signal products that land in the GPS signal band. To support development and testing of GPS receivers in an interference environment, NAVSYS has developed a broadband GPS signal simulator product which includes the capability to either record live satellite signals during testing or generate simulated signals using the NAVSYS GPS Signal Architect software, and play these files back to generate simulated GPS RF signals for receivers under test. This product allows for broadband capture of the full GPS spectrum and also recording of interference environments. In this paper, we describe how this GPS signal simulator product will also allow during playback for a user to insert interference signals into recorded or simulated GPS signals in a non-jammed environment for testing of a GPS receiver in a simulated interference environment. INTRODUCTION Near-band interference can occur from other close-by transmissions that are higher in power than the GPS received satellite signals. One example of this is the wireless network that was proposed to be deployed by LightSquared. As a result of extensive testing with LightSquared broadcasts by the National Space-Based PNT System Engineering Forum (NPEF), the National Telecommunications and Information Administration (NTIA) and the Federal Aviation Administration (FAA), it was determined that these transmissions would, in fact, effect many existing GPS receivers. To show interference between LightSquared and GPS required testing to be conducted using a wide variety of different GPS receiver types at a number of different special purpose facilities provided by the Department of Defense (DoD) and federal labs. These facilities were selected as they had sophisticated signal simulation capabilities to generate both the GPS and the LightSquared signals and also had anechoic chambers to allow broadcasting these signals to receivers under test (see Figure 1). Live testing was also conducted in New Mexico and Nevada (Figure 2 and Figure 3) to evaluate the effect of interference on first responders’ use of GPS. Figure 1 NAVAIR Anechoic Chamber