Being able to track objects (geolocation) is one of the most important applications of today M2M and more recently IoT networks. As described in the previous article there are several types of network used for IoT. However we are talking about GPS-free geolocation which is one of the “killer apps” for LoRaWAN. SigFox doesn’t support geolocation. Cellular technologies like LTE-CatM and NbIoT should support “native” geolocation (without the GPS) from 3GPP Release 14.
Outdoor geolocation using GPS and/or LoRa
The traditional way of tracking the outdoor location of the device is to install the GPS receiver inside your device which is a common solution for cellular (2G/3G/4G) trackers. GPS receiver is locking on the signal from several satellites which have a very precise atomic clocks and which know their position. Since the distance to each satellite can be easily calculated by multiplying the speed of light with the time delay of each satellite, then by using trilateration from four or more satellites it is possible to get its own longitude, latitude and altitude with the precision of around 15 meters. Better precision can be obtained by using other GNSS (GPS is the first and the most widely used but there are European, Russian and Chinese versions as well) or by using Differential GPS (DGPS). However, for tracking applications the 15-meter precision is more than satisfactory. It’s also important to note that typical cellular solution uses assisted GPS (A-GPS) that is using both GPS and with help of near base stations it can get a much better startup performance.
For LPWAN networks, GPS is not a good solution since LPWAN solutions are designed to consume very little energy and work by using batteries for 5 to 10 years. Since GPS receiver consume much more energy they can decrease the life of the tracked device for up to 50 times, which in most cases isn’t acceptable and the solution is to use LoRa. Similar to the GPS, LoRa gateways use very accurate clocks that record the time in nanoseconds when the packets from devices are received. By calculating the delay to at least three LoRa gateways it’s possible to calculate distance and the position of the device/sensor. This TDOA functionality is built into every LoRa chip (produced by Semtech) so there are no requirements for specific software of firmware. However, it is required that the gateways are running on V2.x firmware revisions. The actual way of finding the location of the device is depicted below since the TDOA method is used:
One of the most important factors of location tracking is of course the location accuracy. Several trials have been made and the average accuracy whne using only LoRa is found to be around 100 meters although it can vary from 50m to 200m or even more. It really depends upon the number of gateways, the type of terrain (rural or urban) and also is the device indoor, bwloe ground in some basement or outdoor. The accuracy of the location is always better in suburban or rural areas than in the urban areas with lots of reflecting signals. LoRa will never have the accuracy of GPS but for many applications that are battery powered this is still fine.
There is another restraint of LoRa and that is the latency i.e. the time to react to change of location or to send a command to the tracked device. If the batteries are used as a power source the upstream messages are sent only a few times within the hour so if you have some fast moving object that might not work well or a bigger battery is needed. For slow moving objects or for static objects however, LoRa geolocation is still fine. Although working commercial LoRa geolocation solutions are rare I managed to find a ready to use solution from french company Kerlink: https://www.kerlink.com/iot-solutions-services/geolocation-solution/
If precise tracking of moving objects is still needed, and you still need to run on batteries, the best approach is to use both LoRa and GPS. This can be used in two ways, one being for GPS to determine location and LoRa to send the location to tracking application. The other way being to determine the location roughly by LoRa and in case there is a need for a higher precision to turn on the GPS receiver. One of the ready to buy devices that I have managed to find the trackers from Abeeway: https://www.abeeway.com/products/
Indoor vs outdoor
Although LoRa signal can penetrate buildings it is even less precise for the indoor since it’s impossible to know where in the building the device is. However, the location could be locked to one or two buildings. Actually, for indoor tracking, local area networking (LPLAN) technologies are used and the examples are: Bluetooth/BLE, WiFi, ZigBee and Z-Wave. However, this approach has problems because of the short range (many access points are needed) and the devices are (with the exception of Bluetooth) more power hungry than LoRa.
So it’s obvious that one area currently not covered in the market are use cases where you need both indoor and outdoor location. I assume that these would be solved by dual radio solutions using LoRa and Bluetooh/WiFi or even three radio solutions using GPS, LoRa and Bluetooth/WiFi.
The most obvious use case for LoRa geolocation is “asset tracking” of devices that needs to be battery powered. Basically it’s possible to pretty much track anything from your dog, cow, bicycle, pallets, containers, airport or harbor assets, cars, delivery items or any other stuff that seams important to you. As long as you don’t need to have a very precise whereabouts of your things, LoRa geolocation is a good way to go.
Some companies even want to locate static assets so in case you have a warehouse with a big amount of valuable merchandise you can use LoRa to monitor and maintain an accurate inventory list. The advantage when compared to RFID is obvious and that would be a much bigger range.
Another application is geofencing i.e. when the tracked device exits the imagined “fence” and an alarm is raised.
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