Global Navigation Satellite Systems (GNSS) - Attacks and Countermeasures

Increasing numbers of mobile computing devices, user-portable, or embedded in vehicles, cargo containers, or the physical space, need to be aware of their location in order to provide a wide range of commercial services. Most often, mobile devices obtain their own location with the help of global navigation satellite systems (GNSS), integrating, for example, a global positioning system (GPS) receiver. Nonetheless, an adversary can compromise location-aware applications by attacking the GNSS-based positioning: It can forge navigation messages and mislead the receiver into calculating a fake location. In this paper, we analyze this vulnerability and propose and evaluate the effectiveness of countermeasures. First, we consider replay attacks, which can be effective even in the presence of future cryptographic GNSS protection mechanisms. Then, we propose and analyze methods that allow GNSS receivers to detect the reception of signals generated by an adversary, and then reject fake locations calculated because of the attack. We consider three diverse defense mechanisms, all based on knowledge, in particular, own location, time, and Doppler shift, receivers can obtain prior to the onset of an attack. We find that inertial mechanisms that estimate location can be defeated relatively easy. This is equally true for the mechanism that relies on clock readings from off-the-shelf devices; as a result, highly stable clocks could be needed. On the other hand, our Doppler Shift Test can be effective without any specialized hardware, and it can be applied to existing devices.

Advanced Algorithmic and Architecture Designs for Future Satellite Navigation Receivers

Youssef Tawk

The use of global navigation satellite system (GNSS) receivers for navigation still presents many challenges, in particular in urban canyon and indoor environments where satellite availability is reduced and received signals are usually much atten- uated. In addition, the reception of additional signal replicas due to reflections on the surrounding environment, i.e. multipath, introduces biases in the pseudorange measurements, which in turn lead to extra positioning errors. The navigation per- formance of a GNSS receiver depends greatly on the behavior of the phase lock loop (PLL) and the delay lock loop (DLL). To maintain the robustness of these loops in such conditions, several enhancement methods can be implemented to improve upon standard stand-alone mass market receivers. For instance, well-known techniques include the use of multi-constellations to improve the availability of visible satellites, take advantage of the potential multipath mitigation of the new GNSS signals, and an increase of the integration time combined with a decrease of the PLL and DLL filters bandwidths to improve sensitivity. Moreover, external aiding in the form of time, Doppler, position, or almanac that can be provided through coupling with other sensors can also contribute substantially in improving navigation performance in challenging environments. The aim of this dissertation is to address the challenges of satellite based naviga- tion in demanding environments in order to improve the navigation performance of the future GNSS receivers. Within this context, two research directions are adopted in this thesis. The first is to explore the performance and advantages of the upcoming Galileo signals and in particular the E5 Alternate Binary Offset Carrier AltBOC(15,10), and the second is to investigate the potential of low-cost micro-electro-mechanical systems (MEMS) based inertial sensors to complement GNSS receivers. In the first research direction, we present investigations of the processing of Galileo E5ab in a full band or of only one of its components, i.e. either E5a or E5b. More specifically, a new acquisition algorithm is proposed for wiping off the secondary code and thereby increase the coherent integration time while requiring a reasonable implementation complexity as compared to other architectures. Moreover, an archi- tecture for tracking the E5 pilot channel as an AltBOC(15,10) or BPSK(10) modulation is introduced, and the performance of well-known discriminator types is analyzed using analytical derivations and simulations of linearity and stability regions, thermal noise tracking errors, multipath error envelopes and tracking thresholds. Different parameters, such as the front-end filter bandwidth, the early/late chip spacing, un- normalized and normalized discriminators, are taken into consideration. The results we obtain are used to illustrate the main advantages and drawbacks of using the E5 signal in demanding environments as well as to help defining the main tracking loop parameters for an enhanced performance. In the second research direction, we consider the coupling of a global positioning system (GPS) receiver with an inertial navigation system (INS) based on MEMS sen- sors. In the past, one of the main constraints holding back the proliferation of such hybrid systems was the price of the inertial sensors, but with the widespread dissemi- nation of MEMS-based sensors this is no longer the case. Therefore, a GPS/INS Tightly Coupled Assisted PLL (TCAPLL) architecture is proposed in this dissertation, and most of the associated challenges that need to be addressed when dealing with very- low-performance MEMS inertial sensors are presented. The architecture includes a data monitoring system responsible for checking the quality of the measurement flow to maintain robust tracking and accurate navigation. The implementation of the TCAPLL is discussed in detail, and its performance under different scenarios is assessed. Finally the proposed architecture is evaluated through a test campaign using a vehicle that is driven in urban environments, with the purpose of highlighting the pros and cons of combining MEMS inertial sensors with GPS over GPS alone.

EPFL2013

Standalone GPS L1 C/A Receiver for Lunar Missions

Paul David Blunt, Cyril Botteron, Vincenzo Capuano, Pierre-André Farine, Jérôme Leclère, Jia Tian, Yanguang Wang

Global Navigation Satellite Systems (GNSSs) were originally introduced to provide positioning and timing services for terrestrial Earth users. However, space users increasingly rely on GNSS for spacecraft navigation and other science applications at several different altitudes from the Earth surface, in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO), and feasibility studies have proved that GNSS signals can even be tracked at Moon altitude. Despite this, space remains a challenging operational environment, particularly on the way from the Earth to the Moon, characterized by weaker signals with wider gain variability, larger dynamic ranges resulting in higher Doppler and Doppler rates and critically low satellite signal availability. Following our previous studies, this paper describes the proof of concept “WeakHEO” receiver; a GPS L1 C/A receiver we developed in our laboratory specifically for lunar missions. The paper also assesses the performance of the receiver in two representative portions of an Earth Moon Transfer Orbit (MTO). The receiver was connected to our GNSS Spirent simulator in order to collect real-time hardware-in-the-loop observations, and then processed by the navigation module. This demonstrates the feasibility, using current technology, of effectively exploiting GNSS signals for navigation in a MTO.

Mdpi Ag2016

Orbital Filter Aiding of a High Sensitivity GPS Receiver for Lunar Missions

Paul David Blunt, Cyril Botteron, Vincenzo Capuano, Pierre-André Farine

Recent studies have shown that weak Global Navigation Satellites System (GNSS) signals could potentially be used to navigate from the Earth to the Moon. This would increase autonomy, robustness and flexibility of the navigation architectures for future lunar missions. However, the utilization of GNSS signals at very high altitudes close to the Moon can be significantly limited by the very low power levels seen at the receiver’s antenna. This can result in a strongly reduced visibility of the GNSS satellites, which can worsen the already poor relative geometry of the GNSS receiver to the GNSS satellites. Furthermore, during most of a Moon Transfer Orbit (MTO), the very weak GNSS signals are also affected by Doppler shifts and Doppler rates larger than the ones generally experienced on the Earth, due to the much higher relative dynamics between the receiver and the transmitters. As a consequence, commercial GNSS receivers for terrestrial use cannot successfully acquire and track such signals. More advanced architectures and specific implementations are thus required to use GNSS for lunar missions. In this paper we propose the use of an adaptive orbital filter to aid the GNSS acquisition and tracking modules and to strongly increase the achievable navigation accuracy. The paper describes the orbital filter architecture and tests results carried out by processing realistic radio frequency (RF) signals generated by our Spirent GSS 8000 full constellation simulator for a highly elliptical MTO.

Institute Of Navigation2016

Advanced Algorithmic and Architecture Designs for Future Satellite Navigation Receivers

Youssef Tawk

EPFL2013