Public safety radio systems are the backbone of emergency communication. And like any other element of national critical infrastructure, operators of these networks face the challenge of maintaining tight timing accuracy against a backdrop of increasing cyberattacks.

Welcome to the simulcast problem 

Public safety radio uses a simulcast system. This involves multiple transmitters sending the same signal over the same frequency to ensure broad coverage over a large geographical area. The precise timing of these simultaneous transmissions is crucial to avoid issues like multi-path interference and phase misalignment. To ensure precision, each transmitter in a simulcast system is equipped with a Global Navigation Satellite System (GNSS) receiver, which serves as a reliable and precise timing source capable of maintaining 33 microseconds of phase alignment of remote transmitters. If public safety radio GNSS systems fail to maintain these levels of accuracy, communications can be disrupted. 

So far, so technical. How about a more concrete illustration of why GNSS matters so much to public safety radio systems?

The GNSS network used by a major US public safety radio system was recently seriously compromised by a jamming attack. An unknown rogue operator managed to block a receiver’s timing source, and with no viable backup option in place, timing and synchronization across multiple transmitting towers failed. This left emergency services — the police, the fire service, ambulances — without effective communications. Anyone attempting to speak across the network was met with garbled, unintelligible replies over a sustained period. 

No major events were unfolding at that particular time — no floods, no infernos — but there could have been. And let’s face it, there’s always some emergency happening somewhere. With its public safety radio system rendered ineffective, the lives of citizens, not to mention first responders, were at stake.

At a recent Association of Public-Safety Communications Officials (APCO) national conference in Nashville, I discovered that nearly every public safety radio manufacturer faces challenges with inadequately backed-up GNSS systems. This is especially concerning given the potential chaos and loss of life due to gaps in timing and synchronization defenses.

How to protect GNSS-dependent timing networks

It might surprise you that equipment capable of seriously compromising vital GNSS services is cheap, widely available and accessible to anyone. It’s little wonder then that cyberattacks are increasing globally. But while bad actors may have easy access to jamming and spoofing devices, there is another side to this coin. Public safety radio systems can leverage intelligent, robust and resilient fail-safe solutions that ensure the integrity of emergency communications for prolonged periods of GNSS unavailability. Public safety radio networks also fall under the US Government Exec. Order 13905, which demands resilience in the use of GNSS for synchronization. These public safety radio networks must be hardened against GNSS disruptions.

Establishing a core enhanced primary reference time clock (ePRTC) supported by Precision Time Protocol (PTP) as a backup to local GNSS receivers ensures that even when cyberattackers attempt to block or spoof GNSS signals, timing accuracy throughout the network can still be maintained through an internal atomic clock. PTP provides a network-based time synchronization fallback that offers an extra layer of resilience against GNSS outages. The result? Secure, uninterrupted and clear communications for emergency first responders. Additionally, the use of encrypted timing signals from low-Earth orbit (LEO) satellites such as Satelles’ Satellite Time and Frequency (STL) service can supplement GNSS timing while the ePRTC hardens the network against loss of all RF-sourced timing signals. 

Ensuring uninterrupted emergency communication

While the challenges posed by the simulcast problem in public safety radio are severe, innovative solutions are on the horizon. Our team at Oscilloquartz, a part of Adtran, recognizes that this isn't just a technical dilemma – it's a pressing public safety crisis. In response, we’ve developed two independent or combined solutions for maintaining critical public safety communications during loss of GPS timing signals: 

1. Supplement each site with a LEO satellite receiver with STL service.

a) This approach enhances resilience as STL signals are 1,000 times more powerful than GPS and not impacted by commercial GPS jamming devices, so STL still works during GPS jamming events.
b) Additionally, our 5405-S micro-clock solution features dual GPS/STL receivers in a very small package for comprehensive coverage.

2. Install our ePRTC solution for extended timing assurance. This provides 4+ months of continual timing in the event of a loss of GPS timing signals, distributed to transmitter sites via your Ethernet-based network connections.

Our ePRTC technology leverages the unmatched precision of our Oscilloquartz atomic cesium clocks in conjunction with our grandmaster units, offering an advanced timing solution with superior holdover performance. This combination ensures steadfast synchronization, maintaining critical operations even amidst severe GNSS signal disruptions.

Leveraging GNSS and STL receivers that meet the accuracy and stability requirements of public safety radio networks and/or implementing the ePRTC technology to harden an entire radio network while providing precise network timing when GNSS fails is the only way to address the simulcast problem. Failure to put these systems in place means we risk turning our emergency response systems into unreliable networks prone to failure at the worst possible times. This is a crisis hidden in plain sight that we can no longer afford to overlook.