How to Secure GSM-R Radio Links
What Threatens a GSM-R Radio Link and What Can be Done to Mitigate it?
The GSM-R Communication & Control system naturally requires the highest rate of reliability and availability.
Endless efforts have been invested over the years to bring the reliability of the GSM-R system to the highest figure yet the GSM-R industry has faced serious reliability problems because of EMI induced jamming coming from adjacent cellular networks and other man-made EM noise.
The issue is so pressing that some countries are having second thoughts about the very use of GSM-R.
Such a dramatic decision has been made for example by the Finish government:
“………According to the Ministry of Transport & Communications, the current GSM-R network known as RAILI is due for replacement by the end of 2018. Interference from commercial networks has caused problems in the use of GSM-R telephones, while the GSM-R network weakens mobile reception on trains…….” [ref. 1]
It seems the problem is much more serious than anticipated, as the jamming can be intentional with possible terrorist intensions.
As the EMI from neighboring cellular networks as well as the other man-made EM noise are coming from a definite location, a spatial filter antenna, having a very narrow beam along the tracks only, can be implemented in the GSM-R Radio network to attenuate any signal coming from another direction and mitigate such problematic interferences.
The GSM-R jamming problem has been analyzed and summarized in an excellent White Paper titled "Security of Railways against electromagnetic attacks" published by the SECRET project. [ref. 2]
The report looks at the broad possible causes of intentional and unintentional interferences and brings engineering recommendations to the GSM-R Radio engineers for action items.
One of the most interesting and relatively easiest to implement action item deals with the use of narrow beam antennas along the track.
The following is a quote brought in the document: [ref. 2]
“18.104.22.168 Install narrow beam antennas on BTS”
"The objective is to minimize / avoid the effect of jamming coming from a location different from the train position."
"For a radio link, a narrow beam allows the flexibility of restricting as much as possible the "Communication between two devices, with the advantage that other signals or interferences coming from directions other than the direct line of sight between the two devices are strongly attenuated, because they fall on the edge of the main lobe or on side lobes, usually having small gain.
Generally, squeezing the lobe in one direction has the effect of increasing the gain, thus increasing the performance of the communication link; on the other hand, a narrow beam in the context of railways communications requires a steering functionality, since the BTS must always point to the moving train(s)."
Obviously, switching to narrow beam high gain antennas has other benefits aside from increased security.
Such antennas would reduce the number of necessary base stations while conspicuously increasing the signal, improving C/I ratio, BER and data rate.
Does such an antenna exist?
Comarcom’s patented VEGA CC-12 is available off the shelf.
Thousands VEGA antennas have been hard at work in special situations worldwide since 2004. The VEGA CC-12 and related VEGA models are the most advanced, truly narrow beam, very high gain interference excluding antenna for cellular networks and GSM-R bands available.
VEGA’s Dual Slant polarization enables even higher polarization diversity gain.
Implementing VEGA antennas in GSM-R radio links will, in most cases, reduce the number of BTS needed along the line.
Besides being a low cost, easily implemented solution to security issues, VEGA antennas provide better, more reliable communication between the BTS and fast-moving trains.
Vast experience has been gained by operators in many countries who have used VEGA antennas to solve similar situations on major highways and railways.