Harmful signal defense
GPS and GNSS systems are used in Positioning, Navigation and Timing (PNT) applications for smart devices, vehicle navigation, fitness tracking, autonomous vehicles, maritime and far more. The total number of active GNSS devices is now numbered in the billions across the globe.
Figure 1. NE555 timer IC — a really good device that, sadly , is used for a bad purpose.
Sadly, there are individuals around the world (including bad actors and cyber threat actors) that want to disrupt the users of GNSS systems for a wide range of malicious purposes. Sometimes this is to cause actual harm to others; in other cases it’s to prevent themselves from being tracked!
In most countries around the world, producing and using a device that interferes with the radio spectrum and disrupts communication services in GNSS — or, indeed, other services that include SATCOM, cellular, broadcast television and radio — is illegal. Authorities such as 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 are typically devices that are quite simple, 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 and that is typically around 1.575 GHz for GPS L1-band. This type of interferer is more of a continuous wave-type and creates a single, strong, in-band interferer.
Figure 2. A typical GNSS layout using RFoF.
Critical Infrastructure includes communications, water, gas and electricity utilities, transportation, data centers and the cloud and, of course, defense establishments. A common requirement for many of these infrastructures is to receive extremely accurate timing signals. A common way to derive these timing signals is to use the time service from GNSS systems. Examples include:
» Phase alignment for AC electricity generation
» Timestamping financial transactions in a data center
» Synchronizing cellular base-stations to enable mobile handover.
Since 1994, ViaLite Communications has been helping critical infrastructure customers design and install GNSS signal routing solutions across fiber optic-based systems. These systems start at the antenna that is located outside.
The RF signal from the antenna is connected to a ViaLite RF over fiber (RFoF) transmitter which is an electrical to optical converter. From the transmitter, a fiber is then extended into the facility and distributed as required to a single or multiple end-point. At each end-point an RFoF receiver converts the optical signal back into electrical RF and is then connected to a device, such as a Time Server. (See figure 2.)
The advantages of using RFoF for GNSS signal extension and distribution include: very low loss connectivity, electrical isolation, optical splitting capability, and (important for cyber security) RFoF by design is also a unidirectional technology. Furthermore, the GNSS signal is not converted into any other modulation or digital data stream and, therefore, becomes difficult to tamper with or for an actor to damage the signal integrity.
How To Protect Critical Infrastructure From GPS Jamming
When a “jamming event” occurs, the critical infrastructure provider must try and prevent the harmful signal from impacting their timing based service and, ideally, they also need to know that the jamming is occurring in order for them to take action or inform the authorities. Avoiding harmful signals can be done in a variety of ways, from specially designed RF antennas through to 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 the company’s offering.
Figure 3. Integrated ViaLite and Focus Telecom jamming
Contained within the Focus Telecom products is a unique and patent-protected interference filtering algorithm that combines the patterns from two omni-directional antennas. This product can and does analyze the direction of the interferer and nullify that invasion 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.
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 such a system, the 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 — there is no need for additional power supplies.
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.
These integrated solutions have already been deployed to users and are now providing them with additional protection against unwanted jamming events. Contact ViaLite to discuss any GPS jamming protection requirements.
Author Richard Jacklin is the Director for ViaLite Communications.