The GAARDIAN project has developed a sensor that can be installed in networks to gather information about the performance of navigation signals, such as GPS and eLoran, over a region.

Project summary

The GAARDIAN project (which stands for GNSS* Availability, Accuracy, Reliability anD Integrity Assessment for timing and Navigation) has developed a sensor that can be set up in local area networks to monitor the signals from navigation satellite and positioning systems, such as GPS and eLoran. Algorithms running both in the sensor and in a central server can detect any anomalies in the signals, or any indications of interference or jamming, and provide real-time alerts to customers who need to assess the reliability of the PNT (positioning, navigation, timing) signal they are using. This information would be particularly useful to the emergency services, communications networks, the military, and the transport network.

Project background

GNSS* signals are becoming very widely used in a broad range of applications from location-based services, to tracking of goods, vehicles and people, to safety-critical tasks such as landing aircraft. However, GNSS signals can experience interference, jamming and multipath effects and it is difficult for users to know whether the signal they are using is fit for purpose at any given time.

The operation of some services requires fast and reliable information about events that might affect a signal's performance – this may be shared warnings of system-wide problems such as satellite failure, or specific information about local interference affecting the service. But no such warning service exists yet.

Users' requirements for information about the reliability of their signal could be met by deploying a network of sensors around a key facility, such as a harbour or airport, or by providing results for a more dispersed, nationwide network of sensors.

Chronos Technology Ltd took the lead on bringing together a group of organisations (see 'Project partners' below) with the necessary expertise to provide a solution which will validate navigation signals.

Once the group was formed, they approached the Technology Strategy Board for project funding, which was granted in 2008. The project started in December 2008 and finished at the end of March 2011.

Project partners

These organisations made the following contributions to the GAARDIAN project:

• GLA – General Lighthouse Authorities
  User Community - Maritime
  eLoran
  
  
• Imperial College London
  User Community - Transport
  Integrity Monitoring Algorithms
  
  
• University of Bath
  GPS and Space Weather
  
  
• BT – Adastral Research Laboratories
  User Community – Telecoms
  
  
• Ordnance Survey
  User Community – Land Geolocation
  
  
• National Physical Laboratory
  Time
  UTC Traceability
  
  
• Chronos Technology Ltd
  Real time Timing measurement to nanosecond granularity
  GPS products, components and system integration
  GAARDIAN Project Leader

Project technical challenges

For GAARDIAN to meet its aims, the partners need to overcome considerable technical challenges.

The project team developed sensors that can continuously log substantial amounts of data about the GNSS signals of interest. The sensors can process some data themselves in real-time, and report any anomalies or interference to users immediately. In addition, the data is reduced to a small number of key parameters that can be fed back to the central server. The server then combines the results from all sensors in the network to determine the geographical extent of any interference or other anomalous behaviour.

The data collected by the sensors must be time-stamped accurately so that the measurements from different sensors can be compared. To ensure this, each sensor has three independent time sources, typically GPS, eLoran and a rubidium oscillator.

NPL's core task within the project was to evaluate eLoran as an accurate and reliable UTC time source and to monitor the long-term performance of the UK eLoran signal. This builds on our expertise in timing and operation of the UTC(NPL) national time scale. We also evaluated the timing performance of the sensor design.

Who benefits from GAARDIAN's results?

The major users of data from networks of GAARDIAN probes are expected to be operators of safety-critical facilities such as ports and airports, telecommunications networks and the emergency services, who need to know immediately if the GNSS signals that they rely on are degraded in any way. Many people will benefit indirectly through the increased confidence in the performance of GNSS signals provided by GAARDIAN networks, as well as the greatly improved response time in detecting and dealing with any sources of interference to the signals.

SENTINEL

A follow-on project from GAARDIAN known as SENTINEL – SErvices Needing Trust In Navigation, Electronics, Location & timing – has been awarded funding by the Technology Strategy Board.

*GNSS in turn stands for Global Navigation Satellite System, such as the USA's GPS or Europe's Galileo.

For more information, please contact John Davis