Redundancy

Adding redundancy to a system means, that in the case of an interruption there is a back-up option available; which as a design concept is used in many fields of engineering, such as life- and safety-critical systems. Depending on the importance of PNT information, it is recommended to add some redundancy, such as additional hardware, or to enable the use of multiple constellations (Galileo, GPS).  

Having multiple GNSS receivers, multiple antennas (especially at diverse locations), means that if one receiver is jammed or spoofed, the other may be able to take over providing PNT information and maintain the continuity of the system. Modern receivers and antennas are quite advanced, but they have to be configured properly to get all the benefits enabled by the hardware. Some of the things you can configure are what constellations to use (Galileo, GPS, Glonass, Beidou), what corrections to use (to correct for the degradation of the signal caused by environmental factors), what signal band to use (using GNSS signals from multiple frequencies can be used to eliminate ionospheric effects). 

There are also other (relative) positioning sensors and timing sensors available that can be used as backup in case of GNSS outage, think of for example IMUs (inertial measurement units) and high-end clocks. If you have included or want to include alternative sensors in your system it is important to be aware of inter-dependencies between the different sensors: is a sensor initialized or integrated with information obtained from GNSS? And how does a system decide on what sensor information should be in- or excluded in the final output? One of the advantages of GNSS is that it helps you to determine an absolute position solution and it allows you to get a system time that is distributed over the entire world. Alternative sensors can help to for example provide relative positioning information and local time information, for these types of sensors uncertainties build-up over time. It is therefore important to be aware of what uncertainty is still acceptable for you, and determine how long your system can run on information of the alternative sensors before the uncertainty and error limits are exceeded.

Some actions you may take to make sure your system is redundant:

• Diversify in location (receiver and antennas in multiple locations)
• Enable advanced settings in your receiver
• Use multiple constellations, so if one is unavailable there are others to use 
• Use corrections (precise parameters arriving through the internet increasing the precision of your position/timing information) 
• Use multiple frequency bands, so if one is jammed or spoofed there is another band to fall back to
• Purchase back-up hardware
• Integrate alternative PVT sensors.
• Use multiple processing software