First thoughts on LoRaWAN in urban areas

After deploying our The Things Network gateway in the German city of Bonn, we had the chance to measure RSSI/SNR right away on our walk back to the central station and compare the results of the very same gateway + antenna mounted outdoors in about the same height (10m) between the sub-urban and urban deployment.

In comparison to our sub-urban deployment of the gateway, we noticed a significant amount of blind spots and/or packet loss next to the massive blocks of big buildings built right next to each other (in Bonn, typically five or six-storied). These are very challenging conditions to something that uses 25mW (14 dBm) of RF-power or less on a very crowded band. You may notice the blind spots in the following screenshot:

Image 1: Screenshot of TTN-Mapper in action (our gateway of interest is the eastern one)

The gateway and its coverage can be found on ttnmapper.org. Note that this time we contributed the data to the public dataset right away which has no display mode to show single measurements. Again, our node was locked to SF12 to achieve 

One thing we’re not sure about: we would have expected to eventually find RSSI below -124dBm at some place. However, we haven’t seen something like that. We’ve seen SNR up to -14.5 (20 is considered to be the ultimate limit with current hardware), but RSSI was still about -121dB, way above what the specs claim to be the lower limit in sensitivity of the chips.

Our furthest successful measurement was about 2,500 meters away from the gateway, crossing basically half of the city. Sometimes we noticed that e.g. crossing the street or changing location slightly allows for packets to be received by the gateway where this wasn’t possible seconds before. We also noted packet loss, where 2-3 attempts to be received from the same location would eventually succeed. We estimate that coverage on ground level was about 70-80% in a range of 500-2,000 meters around the gateway, with some packet loss.

Conclusions:
LoRaWAN remains to be a disruptive technology in terms of coverage for IoT-devices. Small sensors can be deployed over a massive area that can be basically covered with one gateway even in urban space. As we think coverage depends a lot on reflexions and to some extend also diffraction taking place, one would like to see 2-3 outdoor gateways inside a range of maybe 2,000 – 3,000m to achieve maximum outdoor coverage. More, if indoor coverage is desired. All applications should be designed to be tolerant to temporary packet loss right from the start.

How you can help us
We would like to create a detailed map of the coverage of this gateway within the next months. Do you live near Bonn? Please feel free to grab your nodes and fire up TTN Mapper whenever you are around!

Credits
Thanks to everybody involved in funding this gateway.
Thanks to @jpmeijers for mapping service (ttnmapper.org)
Gateway deployed and tested by Janek Thomaschewski, Ramdan Hamdan and Manuel Schmidt on 16.09.2017 in Bonn (Germany)

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