LoRaWAN range test: a real Line of Sight Long Range test of LoRa communications
In the last months I’ve often talk about Internet of Things communication protocols like Bluetooth, Wi-Fi, Narrow Band IoT and, of course, LoRaWAN, explaining and analysing how they works and which are they strengths and disadvantages, as detailed in the following article. Among them, one of the most interesting one is, of course, LoRaWAN, which allows Low Power Long Range communications for monitoring and sensing Internet of Things applications in a remote area. HERE you can learn how this protocol work, which are its limits and possible use cases, while HERE you can see my review of a LoRaWAN battery powered end node, which I used for many experiment and applications
Now the question is: how far can LoRaWAN and thus LoRa-based communications travel? Which is the LoRaWAN Line-of-Sight operating range? In this article I show a very simple but effective test that answer to this question, in particular for all these applications with direct visibility between the LoRa devices (for example with a gateway placed on a hill or over the roof of a tall building and nodes placed in the surrounding countryside).
Which is the LoRaWAN (and LoRa) Line-of-Sight operating range?
Since I live in a sub-urban area without nearby hills, in order to evaluate the maximum possible Line-of-Sight (so without obstacles in the middle) LoRaWAN range test I decided to install a LoRa-enabled development board (a TTGO T-Beam) on my quadcopter (a DJI Phantom 4 Professional) thus enabling a powerful testbed which rely on my drone (which is the LoRaWAN transmitting end node) and the existing LoRaWAN open network, in particular The Things Network (known as TTN).
The key idea behind the test is the following: keep the drone flying at about 100 meters height and observe how far the LoraWAN messages transmitted by the on-board TTGO T-Beam can travel, by observing the gateways location which can hear the messages. In order to do this, I set the TTGO T-Beam development board to send a message every ten seconds containing GPS latitude, longitude, altitude, number of satellites and HDOP, which is a parameter to determine the GPS accuracy. You can find the source code of this TTGO T-Beam implementation on the author’s GitHub HERE.
Then, the data retrieved by the different LoRaWAN gateways together with TTN Mapper tool allow to determine the Line-of-Sight distance between each gateway and the flying drone, thus providing the LoRaWAN range test results. Finally, all the received packets and the relative distance from the quadcopter are plotted over the TTN Mapper map, as visible in the following paragraphs.
LoRaWAN range test: the setup
In detail, I used as aforementioned a DJI Phantom 4 Professional with a TTGO T-Beam LoRaWAN board installed under the frame, in particular in the back of the drone, keeping attention to avoid the contact between the antenna and the propellers. I decide to use the TTGO T-Beam board because it is a cheap and compact solution, based on a Semtech SX1276 LoRa modem (suitable for EU 868MHz LoRa channels frequency) together with a U-blox NEO-6M GPS module, an ESP32 Wi-Fi and Bluetooth Low Energy (BLE) System-on-Chip (SoC) and the full support to The Things Network. Also, the board is powered by a standard 3.7V 3500 mAh MR18650 Li-Ion battery, which keep the weight of the whole system under 100 grams, board and antenna included.
The test has been performed in a semi-urban environment with multiple low buildings, in the absence of mountains or hills. Then, the flight has been done during a cloudy day with almost no wind, an air humidity of about 80% and a temperature around 3°C. During the flight, the drone position has been almost fixed to the lift-off position, performing an ascending, hovering, and descending flight in the same place. The drone has reached a maximum altitude of about 109 meters, in order to respect the aviation regulators rules. The total flight lasted about 12 minutes and, during the hovering phase, the drone has been slowly rotate itself on the yaw axis.
On the communication side, as already discussed in the LoRaWAN detailed article, in order to fulfil LoRaWAN usage policy the LoRa-enabled board has been set to automatically send a LoRaWAN message every ten seconds with Spreading Factor set to seven, containing the updated GPS data (longitude, latitude, altitude, and HDOP). Finally, the endpoint application attached to the TTN’s application server has been integrated with the TTN Mapper component, in order to decode the received messages’ payload and plot the data over a map showing the LoRaWAN range test results.
LoRaWAN range test: the results
During the 12 minutes flight, 72 LoRaWAN messages have been sent from the TTGO T-Beam board mounted on the drone. Looking at the results on TTN Mapper, the messages have been received by 14 LoRaWAN gateways registered on TTN, therefore allowing to estimate the distances between them and the drone, together with the number of packets successfully received by each gateway and the percentage of correct packets reception. A map with the plotted results is visible as follows, where messages received by TTN gateways are plotted on top of a TTN Mapper’s map.
A more detailed results report instead, is available in the following table, where the number of packets correctly received, the distance and the relative average Received Signal Strength Index (RSSI) are also reported, allowing to better evaluate the possible LoRaWAN operating range achieved during this range test
Analysing the results, it is possible to say that LoRaWAN can achieve an operating range of several tens of kilometres in Line-of-Sight applications, since most of the gateways in this test were located between within a circular range with radius between 30 km and 60 km, with also a gateway located at 75 km over a hill. Despite the not-statistically meaningful results achieved, due to the very low amount of messages sent from the quadcopter and the unknown number of GWs active in the area, this preliminary evaluation shown the potential LoRaWAN operating range in a Line-of-Sight application.
Note: as you can see, there is a LoRaWAN gateway located at 3.9 kilometres which is performing like many others gateways located at 50 and more kilometres. Here is why: this nearby gateway is based on a Raspberry Pi plus a cheap LoRaWAN eight channel dev board which acts as LoRaWAN gateway, but unfortunately is located inside of a building at the fifth floor, that’s why the RSSI is similar to others far away gateways. Poor RSSI is also due to the low antenna quality of this home-made gateway, which can’t be compared to the high quality one installed on the other nearby outdoor gateways.
Since the test has been done with the LoRa modem set to a Spreading Factor equal to seven, there should be more room for higher Spreading Factors, which allow signals to further travel, given the higher airtime and improved receiver sensitivity, as already detailed HERE. Even the average RSSI of some gateways suggest that the system could easily reach a greater distance, maybe also adopting an improved LoRa antenna on the TTGO T-beam transmitter board to gain some link budget in terms of dBm.
What a range! With this simple test it has been possible to show some interesting LoRaWAN operating range in a Line-of-Sight application, illustrating also the potential of LoRaWAN and thus all LoRa-based communications. Of course, in real use case scenario, like in a city or ground application, these range are difficult to reach. But, if you plan to install a gateway on a hill or on a tower, you should reach some interesting results, nothing like these ones but of course with several kilometres behind the two LoRa devices.