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What’s New: An article by Microchip’s Jim Olsen discussing several non-GNSS timing sources.
Why It’s Important: Of PN&T, the “T” is the most important. It is used to operate systems and enable applications, as well as being essential data. A lot of position and navigation systems derive solutions from time signals.
What Else to Know:
- Jim’s list is not all inclusive. There are other broadcast and fiber-based ways of transferring time.
- Full disclosure – Microchip is a corporate member/supporter of the RNT Foundation.
Timing alternatives for critical applications in GNSS-denied environments
May 29, 2024
Critical infrastructure and government entities are in various stages on how to navigate GNSS vulnerabilities and how to provide timing services in GNSS-denied environments. In geographical areas where geopolitical tensions are high, users of GNSS timing are already operating in GNSS-denied environments due to the high levels of GNSS jamming and spoofing activities. In other geographical areas where tensions are lower, GNSS jamming, or interference could be unintentional, but concerns related to what happens if GNSS signals are no longer available for extended periods of time are real.
There are two categories of vulnerabilities to consider including local-area GNSS outages that affect single independent locations and wide-area GNSS outages that affect multiple locations simultaneously. This wide area GNSS outage scenario is the motivating factor for the introduction of timing technology alternatives to GNSS timing receivers, as a backup timing service, and an alternative timing service.
There are some levels of protection for GNSS timing receivers from jamming and spoofing that can be implemented today. GNSS timing receivers are now multi-constellation. This technology allows for tracking of the various GNSS constellations, GPS, BeiDou, Galileo and Glonass with the same receiver. GNS timing receivers and antennas can support multi-band reception. These technologies provide additional resiliency as there are additional frequency bands utilized providing for more immunity from interference. However, these options do not support operation in GNSS-denied environments for extended periods of wide-area outages.
GNSS Alternatives and Approaches
There are multiple technologies and approaches for GNSS backup or alternate timing solutions with various attributes that attempt to satisfy key requirements. The key requirements fall into two categories:
- where they might fit in the various architectures that they are deployed
- the accuracy, reliability and ease of implementation
Timing based solutions can be classified in two categories:
- receiver technologies that can reconstruct absolute UTC traceable time are alternate signals of opportunity
- network-based timing services and time transfer technologies designed to deliver high accuracy reconstruction of absolute UTC traceable time
