GPS World

Tag: resilient receivers

  • The latest tech fights for GNSS resilience

    The latest tech fights for GNSS resilience

    Image: Harxon
    Architecture of the X-Survey antenna. (Image: Harxon)

    Blocking interference

    Interference can be blocked at the data-collection stage, using an advanced antenna.

    Harxon’s X-Survey is a compact high-precision GNSS antenna. It provides superior navigation and communication performance in surveying applications. A frontal band-pass filter setting effectively rejects out-of-band signals before they enter the low-noise amplifier of the antenna for signal augmentation.

    Meanwhile, the filter itself has insertion loss, making a low insertion loss filter a prerequisite for optimal system noise reduction. To avoid this situation, X-Survey employs ceramic filter with low signal loss and in-band flatness to significantly improve system anti-interference capability and ensure reliable signal receiving.

    The mosaic module provides AIM+ mitigation technology. (Image: Septentrio)
    The mosaic module provides AIM+ mitigation technology. (Image: Septentrio)

    See also:

    How resilient PNT protects global networks from attack or failure

    Is internet time good enough for cybersecurity?

    Resilient receivers

    Septentrio began to tackle the interference problem more than 20 years go, designing and manufacturing high-precision GNSS receiver technology with emphasis on reliability and robustness. The result is Advanced Interference Monitoring and Mitigation (AIM+) technology which secures the company’s GNSS receivers against jamming and spoofing interference. AIM+ has recently been upgraded with an extended anti-spoofing functionality.

    Building on its existing spoofing detection, Septentrio has developed a new anti-spoofing algorithm for its commercial receivers. The algorithm leverages Galileo Open Service Navigation Message Authentication (OSNMA) for spoofing resistance. It was developed in the framework of the GSA FANTASTIC project with the goal of improving the security of timing in critical infrastructure.

    Mobile devices and cloud applications increasingly rely on GNSS technology used by telecom companies. Having secure and robust GNSS receivers in telecom infrastructure is key to reliable mobile and positioning services.

    Alternative signals

    Prototype design of the PNT-5500. (Image: Jackson Labs)
    Prototype design of the PNT-5500. (Image: Jackson Labs)

    A new reference receiver, Jackson Labs’ PNT-5500, includes a custom Satelles/Iridium (STL) and GPS receiver, and an optional Edge Grandmaster/PTP1588 capability.

    Using STL signals received directly through a small antenna mounted on the device, the PNT-5500 provides nanosecond timing synchronization in GPS-challenged environments, including deep indoors (no rooftop antenna required). It provides secure timing during GPS jamming and spoofing events. The unit is designed for high-volume, low-cost telecom small-cell synchronization, and is optionally available with holdover oscillators such as DOCXO and CSAC atomic clocks.

    While GPS is vulnerable to jamming and spoofing, the PNT-5500 uses the Iridium infrastructure to provide assured timing that is impervious to spoofing and provides 1,000X higher signal strength compared to GPS, producing jamming resilience and deep-indoor reception. The system is designed to be fully interoperable with legacy equipment, for a low-cost, fully-deployed Assured PNT capability alternative to GNSS today.

    Assessing vulnerability

    Image: Qascom
    Image: Qascom

    Qascom offers several robust PNT services and products, including vulnerability assessment, robust navigation and interference localization.

    Vulnerability assessment is the key proactive measure, using cutting-edge signal generators to design and test tomorrow’s receivers. For example, Qascom’s QA707 GNSS simulator tests receivers against emerging jamming and spoofing threats, allowing OEMs to discover in advance any potential vulnerability that may affect the availability and the integrity of the signal.

    Robust navigation is supported by advanced mitigation algorithms, equipped with pre and post-correlation algorithms, as well as the inclusion of sensor fusion and dead-reckoning features.

    Qascom’s attack detection products include external monitoring networks that support GNSS receivers. These networks provide an accurate perception of the operational environment, allowing threat characterization, classification and forecast. For instance, Qascom’s QB100 enables the simultaneous threat detection and localization by means of a monitoring cluster that delivers 24/7 situational awareness to a set of target receivers within the protection area.

    Reliable timing

    Meinberg provides GNSS timing solutions for nearly every application type. Its reliable systems are based on firmware built from the ground up by an in-house team of expert engineers. All Meinberg firmware is constantly checked and updated to ensure it adapts to evolving industry standards.

    The company’s synchronization systems use a built-in Meinberg GPS receiver or combined GPS/GLONASS clock. They also support a broad range of reference time sources, including 1 PPS, 10 MHz, inter-range instrumentation group time codes (both direct current level shift and amplitude modulated), or network time protocol (NTP) servers. This redundancy in synchronization sources means Meinberg’s systems are protected against a loss of signal. Furthermore, to ensure the correctness of the reference time and date, an intuitive Secure Hybrid System (SHS) feature includes an independent secondary clock for enhanced plausibility checks.

    For superior holdover performance, the Meinberg XHERB (with one or two Rubidium modules from Stanford Research) can be added to the Meinberg Intelligent Modular Synchronization (IMS) time and frequency systems. If the reference clock loses its sync source, the XHE chassis will provide the sync reference for the IMS chassis based on its holdover performance.

  • Expert Advice: Low-End Jam Resilience May Not Be Desirable

    Expert Advice: Low-End Jam Resilience May Not Be Desirable

    Jan Wendel
    Jan Wendel

    By Jan Wendel

    At the European Navigation Conference held in Bordeaux, France, April 7–10, a keynote session and ensuing panel discussion addressed the issue of “GNSS Resilience for Terrestrial and Naval Applications.” During the discussion, two questions from the floor drew these responses from panelist Jan Wendel of Airbus Defence & Space GmbH, a leading European aerospace company.

    Do you believe that receiver manufacturers will be able to deliver resilient receivers in the future?

    JW: In order to achieve resilience, regulatory measures can only provide a mid- to long-term solution. Therefore, resilience needs to be addressed at the receiver level as well.

    Considering spoofing, I am not aware of any confirmed spoofing incident. Iran has been claiming to have spoofed a CIA drone, which became for me at least theoretically feasible when I heard the rumor that this drone was equipped with a GPS C/A code receiver. Also, there has been a wrongly configured repeater at the Hannover airport. Nevertheless, spoofing to me does not seem to be a current threat.

    However, jamming is clearly a reality nowadays. In my opinion, we should first decide which level of resilience we actually want to achieve for which type of user receiver. If the simple receivers like in smartphones become more and more robust against jamming, the simple jammers available on the Internet will react with an increasing jamming power. This will leave less margin for the receivers used in more critical applications, which we really would like to see functioning permanently.

    Therefore, resilience for low-end receivers might not be a good idea; maybe it would be better to see them fail in some scenarios.

    Another aspect in the discussion we have had so far is the spreading-code encryption for authentication purposes. Actually, I see spreading-code encryption more as a means to restrict the access of a GNSS signal to authorized users and as an anti-spoofing measure, but not primarily as a means for authentication. Here, we must be aware that the access is not necessarily as restricted as we would like to think.

    With directive antennas, blind demodulation techniques and a communication link, it is possible with a slight delay to achieve a position, velocity and time solution at a rover, without being an authorized user of the respective service.

    We must understand resilience also in a more global sense, that such a possibility must not be detrimental to the applications assuming a restricted access to specific GNSS services.

    Do standards help?

    JW: In general, standards are a good thing, as they help in the construction of complex systems by assuring interface compatibility and also minimum performances. However, care needs to be taken when the standards are defined. For example, in the NMEA 0183 protocol, essential information is missing that is required for integration of a GNSS receiver with an inertial navigation system, for example, vertical velocity, full variance-covariance matrices of the receiver’s position and velocity, or raw data like pseudorange, delta ranges and ephemeris to name a few. Clearly, the NMEA protocol was not designed for GNSS/INS integration, and for its intended use the NMEA protocol fits perfectly.

    However, for many applications, it is not usable. Being a de-facto standard offered by most receivers, I think it would be beneficial if this protocol would follow more a general-purpose spirit, like most of the proprietary protocols of the different receiver manufacturers do. So with the NMEA protocol lacking relevant information, we are in a situation where for many applications either the receiver manufacturers’ proprietary protocols have to be used — given these protocols offer the required information — or the receiver cannot be used at all. For me, this is an example where a standard is not of great help, also because the process of developing such a standard towards an extended scope takes considerable time, if possible at all.

    Jan Wendel is a system engineer at Airbus DS GmbH in Munich, Germany, where he is involved in activities related to satellite navigation, including tracking, integrity and sensor integration algorithms. He received the Dr.-Ing. degree from the University of Karlsruhe, where he is also a private lecturer.