The path to a LoRaWAN with truely a wide range contains many pitfalls. Since all LPWAN innovations are based on radio technologie a lot of influences can lead to lousy results.
So please do yourself a favour and don’t start like us with a magnificent and superior range of – *drum roll*, please – roughly 400m. Our first test results almost ended up in not continuing exploring this revolutionising new LPWAN technologie at all …
This article (or rather listcle) will help you to avoid the biggest problems that can occure during your LoRaWAN range test.
1. Aim high: Understand the the power of the gateway (antenna) height
In getting big LoRaWAN coverages with as few gateways as possible height can only be hit by height. You might say: “Yeah right, that is quite obvious and really basic since we talk about radio technologie”. Especially in urban (e.g. small/medium city) environments, the height of the antenna has a very big influence. By taking a closer look at the Hata model, a propagation model for predicting the path loss of radio waves, with different antenna heights (4m, 8m, 16m and 32m) to an endpoint of 1m height, you will get a pretty good idea how important height is. What is noticeable is that the covered distance at a fixed RSSI is almost tripled from 4m compared to 32m antenna height. So best is to find a very good and high spot for your antennas.
2. Do not take your test results for granted
Radio performance is subject to many different influences – and many of them can change over time (we cover this in detail somewhere else, currently only available in German). This means that what you measure, or not measure, today can be quite different tomorrow, next month or next year. For example just consider the following scenarios:
- Weather: You measured at a bright day, but a heavy rain or snow could influence your signal quality
- Personal/City Traffic: Your signal of your room sensor was really good, but now a truck is parked right in front of your window
- Attenuation: Imagine having a new construction site or building, park etc. that is new in between your transmitter and receiver
- Radio traffic: You are a LoRaWAN pioneer and your radio signal highway is completely free, but a big boom reaches your city and radio traffic increases – and therefore also collisions of signals.
So these examples can lead to different results during time. If you are not continually testing you can’t take any for granted.
3. Test over a longer period of time
As written above, different influences can cause your results to vary even on a hourly basis. Therefore it is recommended to extend your tests and test your radio quality as long as possible. Especially if you want to test reception on a specific spot to install a sensor. For this purpose it is highly recommended to make a device connectivity test. This will give you a better understanding of the different influences, you can check the upload/downlink or retransmission rate and more and more get a better picture of your receptions and coverage.
4. Know the details about your RSSI values
RSSI is the relative received signal strength in your LoRa-network. The value shown is just an indication of the radio power level being received by the device – gateway or sensor. In general you can say, the higher the RSSI number, the stronger the signal. But – and here it comes, the beloved BUT in those kind of sentences – the number does not linearly correspond to the distance between transmitter and receiver. Since the radio signal is subject to many different influences (from attenuation of objects to reflection/distraction etc.) the RSSI won’t tell you much about the bigger picture, especially if you only measure some spots and for a short period of time. In addition the signal strength (in dBm) is subject to a logarithmic loss dependent on the distance.
See graph the below:
This means you can’t just compare the RSSI values of your range test and indicate the influences of the general attenuation (and especially the distance as one part) – especially if you reach low RSSI values, indicated as the shaded area below -100 RSSI. The lower you get, the less linear correlation you will have between the distance (in free space) and the RSSI value. The lower the value, the less valuable information you get out of the RSSI value alone.
The lower you get, the less information you can get out of the RSSI solely.
To make this a bit more practical, we analyzed >1600 test messages from an Adeunis Field Tester to a Kerlink Wirnet Station 868 Gateway located in 45m height in a small to medium city in Germany. The whole test period was about 2 months.
As you can see, below -100 there is a very big distribution of the RSSI value to the corresponding distances. So a single point RSSI won’t give you much details about the attenuation and the linked distance.
See the following video for more insights about the basics of LoRaWAN and the influences of your signal quality by Thomas Telkamp:
5. Add as much metadata as possible
Any at least semi-serious test will result in a a big amount of data. You won’t end up with just a simple data point telling you what the RSSI value at a specific time was. You most likely will have several data points with RSSI values at different times. Such a dataset will make it difficult to exactly differentiate where the value was recorded and under which circumstances.
If you want to be able to draw a rock solid conclusion that is worth sharing, you will need to do better: You should be testing your network at several locations. If GPS is not available (e.g. if your doing indoor testing) you’ll have to think of a way to record your location along the way.
We recommend to collect at least the following data dimensions:
- Location (lat, lon)
- Height (above/below ground)
- Surrounding (building inside/outside, forest, street etc.)
- Weather conditions
When you follow these 5 simple rules your coverage test will tell you more about your network than you expected. In almost any test scenario there is this exciting sparkling diamond of know how that is waiting to be discovered. – Now get out there and install, test and learn!
If you have any interesting testing guidelines that we might have forgotten, please, contact us right away and share it with us.