Synchronization is a fundamental requirement in all content generation and broadcast; used extensively both in SDI / HDI formats and in IP packet based systems. Synchronization signals are typically generated from equipment including sync pulse generators, master sync references, and for the IP format, Precision Timing Protocol (PTP) grandmaster clock generators. Most sync generators encapsulate a very accurate internal clock which is synchronised to an external reference, which for the vast majority of manufacturers is a GPS & GNSS satellite timing signal. Consequently sync generators are connected to an outside GNSS antenna via coaxial cable or fibre optic cable, like those supplied by ViaLite Communications.
Sadly however there are individuals around the world (including bad actors and cyber threat actors) that want to disrupt the GNSS users, including those in the Broadcast industry, for a wide range of malicious purposes. Security is not just in the domain of IP based internet traffic, preventative and protective measures also need to be taken in the non-IP world including radio, timing and synchronization type signals.
Most timing and sync generators will operate in a “locked” mode to the GNSS signal; when the GNSS signal is lost the generator will move into a “holdover” mode, where the internal clock will maintain an accurate sync for a set period of time. The accuracy of the holdover clock and the time for which it maintains this accuracy is dependent on the technology and quality of the oscillator. For example, a rubidium oscillator will have much greater accuracy and far less drift than a crystal based oscillator. At some point, however, the holdover period will end and the timing sync signal will no longer be in specification or aligned with other timing signals in a larger system.
In most countries around the world, producing and using a device which interferes with the radio spectrum and disrupts communication services in GNSS or indeed other services like satcom, cellular, broadcast television and radio is illegal. Authorities like the FCC in the USA and Ofcom in the United Kingdom, have capabilities to detect GNSS jamming events, locate the perpetrators and potentially prosecute them.
What are GPS Jammers?
GPS jammers are freely available on internet auction sites and typically quite simple devices from an electronics design perspective. Many of them are built from the humble ‘NE555 timer IC’ which is used to drive a Voltage Controller Oscillator (VCO) and antenna. This in turn creates a broadband radio interference. Other crude jammers are produced by filtering the harmonic of a fast rising clock edge oscillator coincident with the GNSS signal band, which is typically around 1.575 GHz for GPS L1 band. This type of interferer is more continuous wave-type and creates a single strong in-band interferer.
Accurate Timing for Broadcast
Since 1994 ViaLite Communications has been helping many broadcast customers design and install GNSS signal routing solutions across fibre optic-based systems. These systems start at the antenna which is located outside. The RF signal from the antenna is connected to a ViaLite RF over fibre (RFoF) transmitter which is an electrical to optical converter. From the transmitter a fibre is then extended into the facility and distributed as required to a single or multiple end-point. At each end-point a ViaLite RF over fibre receiver then converts the optical signal back into electrical RF, and is then connected to a device such as a PTP Time Server or Sync Pulse Generator (SPG).
The advantages of using RFoF for GNSS signal extension and distribution include: very low loss connectivity, electrical isolation, optical splitting capability, and (very important for cyber security) RFoF by design is a unidirectional technology. Furthermore, the GNSS signal is not converted into any other modulation or digital data stream and so very difficult to tamper with or damage the signal integrity.
How to protect Broadcast sync systems from GPS Jamming?
When a “jamming event” occurs, the broadcaster needs to try and prevent the harmful signal impacting their timing based service and ideally, they also need to know it’s happening so they can take action or inform the authorities. Avoiding harmful signals can be done in a variety of ways from specially designed RF antennas through to very sophisticated signal processor based firewalls.
ViaLite has teamed up with the GPS and timing experts at Focus Telecom Ltd to distribute and integrate their family of GPS Resilient and OtoSphere™ jamming protection products into ViaLite’s offering. Contained within the Focus Telecom products is a unique and patent protected interference filtering algorithm which combines the patterns from two omni-directional antennas. It can analyze the direction of the interferer and nullify it from the wanted signal. In addition, Focus Telecom can provide a cloud-based service for providing data and analytics around jamming attacks, when used in conjunction with the company’s GPS Sensor device.
ViaLite and Focus Telecom Integrated GPS Jamming Protection Solutions
The Focus Telecom GPS Resilient Kit and OtoSphere products can be integrated with all of the ViaLiteHD GPS RFoF product range. In a system, the GPS Resilient and GPS OtoSphere products are placed between the antenna and RFoF transmitter. They are powered from the ViaLiteHD transmitter through a DC feed on the RF antenna port, so there is no need for additional power supplies and the Focus Telecom solutions have DC pass-through to the antenna. If customers want additional RF signal gain, the OtoSphere can be used in combination with an additional external in-line amplifier.
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