Alternatives to GPS: location tracking with GSM and WiFi
LBS (Location-based services) technology allows determining the location of an object without using standard services such as GPS, GLONASS, Galileo or Beidou.
LBS tracking is a wide term that encompasses a variety of different methods. Here we will only look at GSM and Wi-Fi based positioning, show its working principle and reveal how it can be leveraged in mobile apps.
GPS vs LBS tracking
In terms of accuracy, GSM and Wi-Fi based positioning methods are usually less precise than GPS. However, these systems can boast a great advantage — the ability to work in non-ideal conditions. For example, in areas lacking “clear sky”. This means, a GSM signal will be more difficult to block and easier to catch, even if the device is inside a building or underground. To get even more accurate tracking inside buildings, it’s possible to determine locations by Wi-Fi hotspots.
Using LBS allows you to trade data accuracy for longer battery life. This means the method will come in handy when location accuracy is less important than the actual presence of an object in a certain place.
For instance, in long-haul freight transportation, LBS will provide the vehicle’s approximate location and directions throughout the entire journey. It can also be used as a backup option when the GPS antenna or module breaks, still allowing you to find out where the object is.
How LBS tracking works
GSM based tracking
Most GPS trackers and mobile devices use a GSM network for data transmission. In this case, a device’s location can be determined based on a service provider’s network infrastructure.
This tracking method operates on a principle that any powered GMS module communicates wirelessly with one of the closest GSM base stations, switching between them as the device moves. If a device is capable of transmitting data (Cell ID, MCC, MNC, LAC), this data can be looked up in external databases to obtain the location of a cell tower.
This method is called Cell of Origin.
It is the most cost-effective and user-friendly method as it requires no modification of the hardware deployed.
Still, it should be noted that Cell of Origin provides the location of the cell tower, not of the device itself.
This means that 2 devices connected to the same cell tower will show the same coordinates, even if they are away from each other.
The precision of location depends on the density of base station population. In cities’ concrete jungles and developed areas, location accuracy can be down to 50–100 meters, while in rural areas — the error span may reach multiple kilometers.
Also, there are advanced systems used to calculate the distance between the GSM module and the cell tower. These systems typically require modification of the installed infrastructure and are quite high-priced. A common search method is called E-OTD (Enhanced Observed Time Difference).
The method is based on measuring and comparing the transit time intervals of signals coming from several cell towers to the subscriber’s mobile phone. The transit times and locations of cell towers can be used to triangulate the position of a GSM module. For this method to work, base stations receiving a signal must be equipped with an LMU (Location Measurement Unit).
The OTD method provides an accuracy of ~ 125 meters.
Wi-Fi positioning system (WPS)
WPS uses wireless access points to determine locations. It is commonly deployed on mobile phones and is frequently used to provide a better solution for indoor tracking purposes. We can single out several methods of determining the location with WPS.
Received Signal Strength Indicator
The first one is based on the Received Signal Strength Index (RSSI). A receiving device calculates the signal strength from multiple access points. Then the obtained data is processed to create a wave propagation model and calculate the distance to each point.
Calculations can be performed by the device itself or transferred for processing to third-party services.
Fingerprinting
The second method is called Fingerprinting and is based on the first one. Fingerprinting works by recording signal strength (RSSI) from several access points and storing this information in a database along with the known coordinates. That said, in case of visiting the same location, the object should provide the same fingerprint, enabling the system to localize it when there is no connection available.
The precision of this method can be reasonably high (~1.3–2 meters), however, deploying it is challenging as it requires the storage of data and is very sensitive to environment changes — adding or removing furniture or buildings affects the signal strength and changes “fingerprint”.
Time of Flight
The third method is called Time of Flight. ToF uses timestamps recorded by both wireless interfaces to estimate the object’s position and relative distance to access points. This method has an accuracy of 2–4 meters and is typically used for indoor tracking.
The time measurements taken at the wireless interfaces are based on the fact that RF waves travel close to the speed of light, which remains nearly constant in most propagation media in indoor environments. Therefore, the time of flight is not affected as much by the environment (furniture, buildings, etc) as RSSI measurements are.
The working principle is similar to RADAR systems, except regular data and acknowledgment packets are used to measure ToF.
The diagram shows an access point sending a DATA frame to a client device and waiting until receiving the acknowledgment packet (ACK).
As you can see, WPS works well for indoor purposes but it’s not always as easily deployable as GSM tracking.
Data availability for LBS tracking systems
Wi-Fi network data can be hard to obtain as major database providers do not allow free database downloads.
However, base tower locations can be downloaded and there is a variety of open source databases to choose from. One of the best-known services are Mozilla Location Services and OpenCell ID, which together contain data on over 50 million of base stations.
LBS support in hardware devices
LBS features can be implemented differently, depending on the device manufacturer. There are some devices that allow continuous reporting of GSM data (MCC, MNC, LAC, CID), while the others only allow reporting on request once an SMS or GPRS command has been received.
If you are not sure whether your devices support LBS on Navixy — please check integration descriptions on our website.
GSM and Wi-Fi based tracking in X-GPS apps
Navixy provides our own Mobile tracking solution with LBS support included.
Unlike hardware trackers, Navixy mobile apps transmit already processed LBS data. Apps rely on native OS services like Apple Core Location or Google Fused Location depending on which OS is used.
Setting LBS detection radius
LBS detection radius depends on the area where the device is located and the number of base stations or Wi-Fi points. If the device is in a rural area and cannot locate, it is recommended to increase the LBS radius so that remote base stations also contribute to the device’s location.
In a city with a dense cell tower population, the LBS range has to be kept short, as nearby base stations will be sufficient for location and accuracy will be high.
Summing up, LBS tracking is a great positioning tool and a valid alternative to GPS tracking when the latter is not available. We hope you found the article useful and learned something new.
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