Applies to: Bolt, Dart2, G62, G120
TABLE OF CONTENTS
- TABLE OF CONTENTS
The DM range of hard-wired vehicle trackers support GPS Jamming and GPS interference detection. The available parameters are split into 2 tabs in OEM.
GPS Jamming tab - This sets what constitutes 'jamming' or 'interference'
1 = Interference Parameters
2 = Jamming Parameters
The uBlox EVA M8 GPS module is able to detect and flag 'interference'. Our devices represent this flag with a Digital Input.
Defaults should generally work well, and are best left untouched unless you know what you are doing.
GPS signals are broadcast at specific frequencies, and GPS receivers (our devices) are tuned to pick these up. Generally, they won't be very strong (they are coming from satellites orbiting about 20 000km away after all!). So if the module detects signals in this frequency range that are much stronger, or that make up a large proportion of the total signal, it can consider this interference and report it.
The L1 GPS signal is broadcast at 1575.42MHz, and L2 at 1227.60MHz.
When hard-wired devices are in trip, they will leave their GPS on, getting regular fixes and calculating heading, speed, odometer etc. with this data. So if GPS signal is lost for a long time, there is likely a problem, so we flag jamming.
This is set by the Warning Timeout parameter.
GPS Jamming IOs - these parameters determine what action to take should jamming or interference be detected. By default, all devices will flag interference, and record a log.
The G120 uses inputs 6 and 7 by default. The other devices use inputs 5 and 6.
With these parameters we can set which digital inputs the Interference and Jamming flags are mapped to. 5 and 6 are default.
By default, as soon as jamming/interference is detected, a log is created - this will appear as a Digital Input Changed log.
We can set the device to immediately upload if this is detected - however when in trip, the device will be connected to the network anyway - so even with this not set, if detected in trip this will be uploaded immediately.
Cell Tower Fallback when jammed
NB: Only available on Dart2, G120 - talk to us about support for this feature on other devices.
If GPS Jamming or interference is detected, the device can be set to fall back to Cell ID for location. It will report this in Field 28 in the device data. This data must be sent to a location service such as Google's Geolocation API, to retrieve an estimated lat/long. As of May 2021, this is not integrated in Telematics Guru.
Note that the position accuracy of a cell location using this method is typically within 500-1000m of the actual location. So it is far less accurate than a GPS fix - but it is useful to get some idea of where an asset is if the GPS is being jammed maliciously.
See Cell Tower Fallback for more information.
Jamming/Interference In Telematics Guru
Alerting on GPS Jamming
Devices are already configured to report jamming/interference by default. So we can just set up an alert on TG if we wish to be notified. Simply create an alert and select the input from the list.
Note these inputs may become active a bit more than you think. Other electrical signals may cause interference. So it might not be malicious operators with jammers each time you get an alert.
Display on the Live View
We can edit the I/O mappings to display if interference or jamming is detected right on the live view
Check for evidence of jamming in Telemetry
Maybe we have some mysterious events where trips weren't recorded. We can check if the IOs are active in telemetry.
In telemetry, there are 32 total bits.
However in binary, we start counting from 0, right to left, meaning we have bits 0-31.
So working right to left 0, 1, 2, 3, 4, we can see bits 5 and 6 highlighted below.