GPS Tracker Technologies
When a tracker has signal issues, it can impact precision, reliability and general functionality and performance of a GPS tracker. A GPS tracker requires at least two types of signals that requires separate modems and antennas to receive: GNSS and a Mobile data network.
The less obvious one is the data network, which is necessary to deliver coordinates and receive instructions. A GPS tracker without mobile data network capability is usually referred to as a GPS logger or Bluetooth Tracker/Finder.
GPS / GNSS
The Global Positioning System was developed during the 60's and 70's by the US Department of Defense research unit (DARPA), inspired by the Sovjet satellite Sputnik and the Doppler effect. The first satellites were launched in 1978 and was fully operational in 1993 where a 24 satellite system was fully operational. In 2016 the European Space Agency's Galileo GNSS system was also operational.
GPS was developed for outdoor use and the signals are sent from satellites 20.000 kilometers in space, on a relatively high frequency. So the signal is weak and on a frequency that has a low degree of penetration. This makes indoor tracking unreliable and tracking in urban areas somewhat inaccurate.
In an open field with no buildings around it, most modern GPS receivers are accurate down to +/-5 meters. But in urban areas with buildings around, precision can be more like +/-30 meters. GPS can be augmented to improve accuracy, but this typically requires a fixed power supply and expensive hardware.
Here is a list of some of the issues that can impact GPS (GNSS) performance and accuracy:
- Indoor or underground
- Signals reflected off walls (multipath/bounce issues)
- Metal surfaces and objects
- Dense materials such as eternit, concrete, steel, metallic paint, duct tape and even chicken wire
- Mountains / valleys
- Water and wet surfaces
- Bad weather (rainclouds, fog and storms)
- Atmospheric disturbances (solar storms etc.)
- Satellite maintenance or slightly incorrect clocks and timings
- Jamming & Spoofing (illegal and extremely rare)
When a tracker fails to find its position within 3 minutes (5 minutes with the Emergency profile active) a less accurate position is provided by an alternate location service (if available). This shows up as a “Bad signal” in the app with 2 bars of service. This can lead to a perception of poor accuracy, but we believe it is better than no position estimate at all. An opaque circle around the trackers estimates position is shown to further illustrate precision issues, which are usually caused by the tracker being indoors or mounted sub optimally.
Mobile network coverage is widespread in the world today, especially in Europe, and most operators will claim complete coverage in most countries. But in practice, even the most widespread network (2G/GSM/GPRS) only has partial coverage, especially indoors. The coverage map below shows 2G signal strength as measured by the European Commissions Joint Research Center. Areas outside the coloured squares may have network coverage, but the signals will be relatively weak as compared to more populated areas.
Coverage is best in and around cities and sometimes weak in rural areas, along coastlines and in mountainous areas.
Countries like Denmark have very good coverage, even in rural areas, but GPRS has an outage ratio of 8% indoors in areas with a house address according to at least one study(1). In a basement, the outage ratio can be as high as 60%.
If the location is in a rural area, the signal strength will typically be weak to start with. If a tracker is mounted in a vehicle, there will be some lost of signal strength, and if that vehicle is indoors, the signal loss is compounded. By indoor we mean surrounded by walls and/or covered by a roof.
Radiosignals have issues penetrating dense materials such as metal and concrete.. They can move around and even along conductive metals like copper, but depending on the frequency the signals will have difficulties getting around metals to a receiver/antenna.
Most battery types discharge current at a relatively high rate compared to the batteries we use. Especially rechargeable batteries discharge quickly even if they are not being used, and their capacity and voltage is quite a lot lower. Most rechargeable trackers need recharging every few weeks due to the battery type used.
The batteries we use have high voltage and low current which results in a high capacity and long battery life. Low voltage and high current results in a higher discharge rate which means lower capacity and shorter battery life.
To ensure that there is enough power available at all times, our battery pack includes a super-capacitor. Without this, the network connection would be less reliable - especially in cold weather, which would also otherwise impact battery life.
1. Lauridsen, M., Nguyen, H. C., Vejlgaard, B., Kovacs, I., Mogensen, P. E., & Sørensen, M. (2017). Coverage comparison of GPRS, NB-IoT, LoRa, and SigFox in a 7800 km2 area. In 2017 IEEE 85th Vehicular Technology Conference (VTC Spring) IEEE. I E E E V T S Vehicular Technology Conference. Proceedings https://doi.org/10.1109/VTCSpring.2017.8108182