We evaluate the detection performance of several commercial interference detectors and of a detector that uses the automatic gain control (AGC) level as a test statistic. The evaluations are based on actual measurements of GPS signals and different types of jamming signals, and were performed at the Vidsel test range in northern Sweden.The AGC detector and the Chronos CTL-3500 were shown to work well for all types of jamming signals. The J-alert was able to detect a wideband (20 MHz) signal but not the narrow band (<2 MHz) signals. By contrast, the jamming indicator on a Ublox 6H receiver was only able to detect a slowly varying modulated CW signal, but not signals with larger bandwidth (>2 MHz). We confirmed that C/N0-based Android application detectors could work well in static scenarios but are not suitable in dynamic scenarios, since they cannot distinguish between decreased GPS signal strength and increased interference

It is well known that terrestrial GPS/Global Navigation Satellite Systems (GNSS) receivers are vulnerable and have suffered from intentional and unintentional interference sources. Unfortunately, space-based GPS/GNSS receivers are not exempt from radio frequency interference originating from the Earth. This paper explores data recorded by the GNSS Receiver for Atmospheric Sounding (GRAS) instrument onboard MetOp-A in September 2007, which is assumed to be representative of the typical environment for GPS/GNSS instrumentation in LEO orbit. Within these data it is possible to detect both pulsed interference and variations in the background noise. One plausible source of the pulsed interference is identified. We also show that neither the pulsed interference nor the variations in the background noise degrades the performance of the higher level products from GRAS.

In this work, we evaluate the detection performance of a number of commercial interference detectors and, in addition, of a detector that uses the automatic gain control (AGC) levels as test statistic. The AGC detector has been implemented on a Novatel GPS receiver and on a Universal Software Radio Peripheral (USRP). The evaluations are based on actual measurements of GPS signals and different types of jamming signals, which have been performed at the Vidsel test range in northern Sweden. The AGC detector was shown to work well for all types of jamming signals, in particular the one implemented on the USRP. The Chronos CTL-3500 was also shown to perform quite well for all kinds of signals, although not as good as the USRP with an AGC detector. Quite surprisingly, the J-alert was only able to detect the wideband (20 MHz) signal but not the narrow band (<2MHz) signals. By contrast, the jamming indicator on the Ublox 6 receiver was only able to detect a slowly varying modulated CW (MCW) signal, but not the signals with larger bandwidth (2 and 20 MHz). We confirmed that C/N0-based detectors could work well in a static scenario, but are not suitable in a dynamic scenario, since they cannot distinguish between decreased GPS signal strength (e.g. indoors) and an increased interference level.

GNSS reflectrometry offers a low cost alternative for Earth remote sensing and is used to measure, for example, ocean altimetry, wind speed, wind direction and modeling of the ocean surface state. A bistatic configuration, using one right-handed circular polarized and one left-handed circular polarized antenna, was built for this experiment in order to measure direct and reflected L1 and L5 signals. The direct and reflected signals were compared and the path difference between them calculated, leading to altitude measurements with both L1 and L5 signals. Compared to publicly available signals on L1, the higher code rate of L5 will provide higher measurement sensitivity

A component of most GPS receiver front-ends, the automatic gain control (AGC) can flag potential jamming and spoofing attacks. The detection method is simple to implement and accessible to most GPS receivers. It may be used alone or as a complement other anti-spoofing architectures. This article presents results from a baseline AGC characterization, develos a simple spoofing detection method, and demonstrate the results of that method on receiver data gathered in the presence of a live spoofing attack.

How does the GPS Ll spectrum look like at a commercial airport? How frequently do radio frequency interference (RFI) incidents occur? To answer this, the GPS Ll/Galileo El band was monitored at two different airports for an extended period of time. The monitor stations continuously recorded the noise level using the automatic gain control (AGC) in the frontend. Also, the raw intermediate frequency (IF) signal was recorded at regular intervals as well as when the AGC level dropped below a certain threshold. In this paper the analysis of long-term measurements of the spectrum and AGC level at Luleå Airport outside Luleå, Sweden, and Kaohsiung International Airport in Kaohsiung City, Taiwan, is presented. The results shows that RFI incidents did occur at both airports, although more frequent at Kaohsiung International Airport. The measurements also show that the AGC level is useful in systems monitoring the RFI environment. Importantly, the measured data could be utilized for analyses toward the future introduction of GBAS for civil aviation authorities.

How does the GPS L1 spectrum look like at a commercial airport? How frequently do radio frequency interference (RFI) incidents occur? To answer this, the GPS L1/Galileo E1 band was monitored at two different airports for an extended period of time. The monitor stations continuously recorded the noise level using the automatic gain control (AGC) in the frontend. Also, the raw intermediate frequency (IF) signal was recorded at regular intervals as well as when the AGC level dropped below a certain threshold. In this paper the analysis of long-term measurements of the spectrum and AGC level at Luleå Airport outside Lueå Sweden, and Kaohsiung International Airport in Kaohsiung City, Taiwan, is presented. The results shows that RFI incidents did occur at both airports, although more frequent at Kaohsiung International Airport. The measurements also show that the AGC level is useful in systems monitoring the RFI environment. Importantly, the measured data could be utilized for analyses toward the future introduction of GBAS for civil aviation authorities.

Although GNSS RF signal simulators have long possessed the capability to generate scenarios they are, for example, not yet able to model a realistic scenario with complex multipath. Software defined receivers bridge the gap between simulated and real data to the extent that they may offer a replay capability, where a data set is first recorded to disk and later can be processed several times. Unfortunately, the recorded data generally can not be used by other GNSS receivers, making receiver to receiver comparisons difficult and time consuming.This paper describes a system capable of replaying recorded IF data into any narrow bandwidth L1 GNSS receiver, including an evaluation of the difference (position, timing and SNR) between live and replayed data using a high sensitivity, consumer grade receiver. The performance of the replayed data set was found to match that of the live data.

There have already been a number of well documented cases where the GNSS signals have been interfered by different sources. A number of different methods has been developed to counteract this. One problem with doing experiments to validate the accuracy of interference detection system is that the GPS L1 band is protected, therefore it is difficult to get permission to deliberately broadcast on those frequencies. In this paper we present a novel way to test such a system. The proposed method will be validated by deploying a number of low cost nodes and then an attempt to localize the interference will be made.

Researchers at the university of Colorado have successfully used radio frequency record-and-playback systems (RPS) have gathered importance commercially because it offers the best way to test hardware receivers. RPS constitutes a stark contrast to more traditional signal simulators that use pre-defined trajectories and mathematical models to determine appropriate RF output. Positioning performance of a satellite navigation receiver under test (RUT) is coupled with its RF front-end system and local oscillator quality. The required equipment and connections are minimal when performing RPS drive testing, as no RUTs are included. It overcomes the fidelity limits of simulator-based testing, especially when considering the difficult-to-model urban environment. During receiver development, it requires only a single drive test for each location, as sampled RF data can be replayed from disk.

The GNSS signals are very weak and therefore sensitive to interference. Since the usage of GNSS based services continues to increase, there is a need to develop a cost effective method to detect and localize interference sources. In this paper one such system will be presented. The system uses independent front ends that collects raw IF data. After the collection is done, the files are synchronized in time and frequency so that they can be cross correlated and the time difference of arrival of the interference signal is estimated. This paper will present the initial results from a test in May 2009 where the four stations were deployed and exposed to interference. It will be shown that the system is capable of both detection and localization of wide band interference.