Improving Secure Code Estimation-Replay Attacks and their Detection on GNSS Signals

The secure code estimation and replay (SCER) attack was introduced in [1] as a threat for all the schemes that use cryptographic protection of the GNSS signal. There, three possible attack schemes were considered and a detection technique was proposed that assumes the particular strategy employed by the attacker is known to the receiver. The detection technique is based upon the likelihood ratio test (LRT) principle, but some simplifications were introduced, that reduce its computational burden. In this work, we improve on the results in that seminal work, both on the attack and the defense side, by: 1. generalizing the SCER attacks considered in [1] to a wider class and finding the optimal attack within that class, depending on the system parameters; 2. showing that the actual LRT detection scheme performs significantly better than its modification proposed in [1]; 3. formulating the generalized LRT (GLRT) detection scheme, which does not need knowledge of the attack strategy within this class, and deriving its performance

A Novel Navigation Message Authentication Scheme for GNSS Open Service

This paper focuses on Navigation Message Authentication (NMA) for GNSS, a message-level authentication capability that aims at providing assurance of authenticity and cryptographic integrity of the navigation message. In designing a NMA scheme, there is an inevitable trade-off among security, resources (e.g. bandwidth and computational power), and performance (e.g. time to authentication of navigation message and authentication error rate). Other requirements may come from the channel dissemination performance (especially in harsh environments) and the complexity of key management. In this paper, we propose a novel NMA scheme that attempts to amortize the resources typically required for digital signatures by using a one-way chain of authentication tags of the message itself, rather than a chain of delayed keys as in TESLA based proposals. We show that this new paradigm in chaining implementation can offer significant improvements to NMA in terms of flexibility, security and performance. Indeed, all such metrics will be evaluated, compared with alternative proposals and discussed

Weak GNSS signal navigation in lunar missions

Weak GNSS signals could be exploited in future lunar missions to increase navigation robustness, flexibility and autonomy. In these applications GNSS reception suffers from very low signal levels, partial visibility of the GNSS sources and unfavourable geometry, making use of either secondary lobes or the signals’ spill over around the Earth mask. Objective of a recent ESA study was to evaluate the challenges of such a navigation technique using GPS and future Galileo reception with carrier to signal levels as low as 10 to 15 dBHz. Investigated mission phases included transfer orbit, low lunar orbits, lunar ascent and descent as well as surface operation and navigation at the Lagrangian points. The paper presents the approach pursued during the study and shares its main findings, showing first that GNSS can be actually considered as an available and extremely useful navigation resource in all phases, even if part of the missions, and specifically low lunar orbits and descent, will require a mandatory aiding form other sensors. Moreover, external aiding in terms of the content of the data message has been envisaged in order to adopt a snapshot architecture for the receiver and to overcome limits in tracking loops with extremely low carrier to noise ratio. A proof of concept for the proposed receiver has been built and tested in different simulated scenarios. As a final result, a multi-constellation GNSS receiver software can be considered a suitable option to enable autonomous navigation in lunar missions, allowing for large savings in the expensive – and poorly available – ground-based tracking network

A Proposal for Multi-Constellation Advanced RAIM for Vertical Guidance

The GNSS environment will experience major changes in the coming years. GPS and GLONASS are undergoing modernization phases, while Galileo and Compass are currently in their deployment phase. When all these constellations are in their Full Operational Capability (FOC) state, there will be at least three times as many ranging sources than today. In addition, all of these GNSS core constellations will broadcast signals in the two frequency bands, L1/E1 and L5/E5. These signals will be available for civil aviation, allowing users to cancel the pseudorange errors due to the ionosphere. Many studies suggest that it could be possible to achieve global coverage of vertical guidance using multi-constellation, dual frequency Advanced Receiver Autonomous Integrity Monitoring (ARAIM). The benefits of ARAIM would include a reduced ground infrastructure (which would reduce the maintenance costs compared to current augmentation systems), a reduced dependency on any one GNSS core constellation, and, in general, lessen exposure to single points of failure. However, to achieve vertical guidance using ARAIM, it will not be sufficient to adapt the RAIM algorithms that are used for horizontal navigation. This is due to the increased level of safety required for vertical guidance compared to horizontal guidance. Therefore, ARAIM will require a careful faults and effects analysis. Because the integrity provision will be shared across service providers, it will be necessary to develop a common understanding in at least three domains: the navigation requirements, starting with LPV- 200; the airborne algorithm; and the threat model, comprised of both the nominal performance of the constellations and the fault modes. In this paper, we present a concept for the provision of integrity using multiple constellations with ARAIM and an Integrity Support Message (ISM). We will first propose an interpretation of the LPV-200 requirements in the ARAIM context. We will then propose a typical threat model for GNSS which includes both the nominal performance of the constellations and all the faults that need to be mitigated. These threats include both single satellite faults, multiple satellite faults, and constellation wide faults, one of them being the use or broadcast of erroneous Earth Orientation Parameters. We will show how the threats can be mitigated through the use of ground monitoring and the ISM in addition to the ARAIM subset position and residual test. Finally, we will give examples of multiple constellation configurations and performance providing worldwide coverage of LPV-200

Recent Developments for the estimation of the altimeter bias for the Jason-1&2 satellites using the dedicated calibration site at Gavdos

Summarization: The dedicated calibration site for satellite radar altimeters in Gavdos has been operational as of 2004. The small island of Gavdos is located along a repeating ground track of Jason satellites (crossover point No 109 ascending and No. 18 descending pass and adjacent to Envisat), and where the altimeter and radiometer footprints do not experience significant land intrusion. The purpose of such permanent Cal/Val facility is to calibrate the sea-surface height and ancillary measurements made by the satellite as it passes overhead, by using observations from tide gauges, GPS, DORIS and other sensors directly placed under the satellite ground tracks. The successful launch of Jason-2 satellite (20 June, 2008) initiated its calibration-validation phase. This was achieved having the two satellites flying with less than one minute difference and in the same orbit. Using the Gavdos calibration facility the following have been determined: (1) the absolute altimeter bias of Jason-1 satellite for the cycles 209-259; using GDR-C data; (2) the absolute altimeter bias of Jason-2 satellite for the cycles 2-28 using GDR-A data ; (3) the inter- mission bias for the period July 2008 – January 2009. The expansion of the Gavdos Cal/Val facilities with the deployment of a new site in the south of Crete and along pass No. 109 is also presented in this work.Παρουσιάστηκε στο: SPIE, Remote Sensing of the Ocean, Sea Ice, and Land Water Regions 200

Statistical models and latest results in the determination of the absolute bias for the radar altimeters of jason satellites using the gavdos facility

Summarization: The dedicated calibration site for satellite radar altimeters in Gavdos, Greece, has been operational as of 2004. The island of Gavdos is located along a repeating ground track of Jason satellites, adjacent to Envisat, where the altimeter and radiometer do not experience significant land intrusion. In this article, the models and techniques for calculating the satellite altimeter bias, as well as the software tool called “TUCalibrit,” are presented. In summary, over cycles 209–259 for Jason-1 and cycles 1–40 for Jason-2, the altimeter biases have been estimated as B(J1) = +103.6 mm ± 4.7 mm and B(J2) = +181.9 mm ± 6.7 mm, respectively.Presented on: Marine Geodes