In 2000, the Global Positioning System (GPS), owned by the US government and operated by the US Air Force, has been open to the civil world without selective availability. M2M players started to propose GPS trackers to enable wireless and long-range positioning solutions for industries such as supply chain and logistics. In manufacturing and retail, some RTLS (Real-Time Locating System) solutions, such as RFID, emerged to provide information about assets located in confined and indoor areas.
The emergence of LPWAN technologies as well as the usage of WiFi infrastructure to geolocate assets has drastically increase the market potential for asset tracking and management applications requiring both indoor and outdoor geolocation.
Globally, 5 main types of technologies are used for IoT solutions:
- GNSS (Global Navigation Satellite System), the American GPS being the most well-known
- WiFi Positioning
- Cell-ID Positioning (not represented in the graphic below)
- RTLS (Real Time Location Systems), which regroups RFID, BLE, UWB, etc
- LPWAN geolocation
Let’s have look at the 3 following technologies: GPS, WiFi Positioning and Sigfox Network location.
The most common way to geolocate an asset is through the GPS method. By adding a GPS module to your device, you will know the position of your assets very easily… when it is located outdoors.
How does it work?
- The GPS module listens to the satellites in sight,
- Once done, the coordinates are sent to your platform through the Sigfox network. The GPS coordinates are usually stored on 6 bytes, so you can send 2 GPS positions within a single Sigfox message (12 bytes),
- The data received by your own server and can be located on a map.
GPS has multiple advantages:
- Highly precise (down to 15 meters / 49 feet),
- Widely used,
- Works almost everywhere on the planet.
It has also its disadvantages:
- Not very efficient indoors,
- High battery consumption,
- Expensive hardware.
You can find an example tutorial of Sigfox + GPS here.
One quite new method to find the position of a device is to listen to WiFi signals around it.
Using WiFi Positioning allows the customer to benefit from a good accuracy (thanks to the maximum range of WiFi access points: 200 meters / 650 feet) without setting-up an ad hoc infrastructure (such as a Real-Time Location System), on a global scale.
How does it work?
- The device (equipped with a WiFi module) "listens" to the different signals around it and recognizes the two strongest ones.
- The device sends the Media Access Control Address (or MAC@) of those WiFi signals to your platform through the Sigfox network. A WiFi MAC@ is 6 bytes, so two MAC@s are perfect for a Sigfox message (12 bytes).
- Once received on your platform, the MAC@s are sent to a WiFi hotspot database for matching.
- The hotspot database server answers with an approximate position (25 to 50 meters, 82 to 158 feet), depending on the number of MAC@s sniffed by the device.
This method has many advantages:
- Works both indoors and outdoors, with high density in urban areas,
- Energy consumption is average (and lower than GPS),
- Accuracy: down to 25 to 50 meters (82 to 158 feet).
It also some has its disadvantages:
- Only works if WiFi networks are available nearby,
- Wi-Fi infrastructure is, by nature, evolving,
- Access to a WiFi hotspots database is rarely free.
You can see a quick implementation example here on GitHub.
Sigfox Network Location is based on a proprietary probabilistic calculation of the most probable location of the device. This is done thanks to the Received Signal Strength Indicator (RSSI) coming from the messages sent by a device and received by the Sigfox infrastructure. It doesn't rely on Time Difference Of Arrival (TDOA) or on the signal's Doppler shift.
The location computation is based on the data obtained from the Sigfox infrastructure. This data comes from several replicas of the same messages sent by a device and received by different base stations.
How does it work?
- The device sends a regular message, where the RSSI information is part of the message's metadata.
- Several Sigfox base stations receive the message. The more stations receiving it, the more precise the location computation can be done.
- With the identifiers of the base stations, the Sigfox infrastructure can assert the location. Thanks to this information, probable locations are computed: the one with the highest probability is selected.
As this method is calculated using regular Sigfox messages, it has three main advantages:
- No extra hardware required,
- Very cost-efficient,
- Message payload can be empty (less battery use) or used for regular data handling.
Moreover, it benefits from advantages of the Sigfox network:
- Low energy for a longer battery life,
- Very long range and global (more than 60 territories covered or in progress) with the capacity to automatically switch from a radio configuration (RC) to another thanks to the Monarch feature,
- Resilient to interference, with the capacity to resist jamming.
It does have limitations:
- The computation method (using RSSI and the location of receiving base stations) allows to have an accuracy in the range of 1 to 10 km precision (0.6 to 6 mi) for more than 80% of the messages, depending on the environment and the base station density in the considered territory.
- Access to the service strongly depends on the Sigfox network coverage in the dedicated territory.
- The Sigfox Network location is perfect for large use cases (high volume of device), where a high level of accuracy is not critical and where battery life is key.
Go this page for more info about Atlas, the geolocation line of services by Sigfox. And below the link to download the Technical Paper about Atlas and the Sigfox Network location.