Remote access to multiple sensors with LoRaWAN

Central SUPPORT · ‎2019-04-25

We are running up to 10 temperature sensors which are connected to PC with RS-485 via daisy chain topology. These sensors are placed across the line of sight.

Now I am planning to replace RS-485 connection with wireless one while increasing the operating distance up to 2-3 km between the PC and the last sensor in the chain. The PC should collect results in real time every 1-2 seconds (the sensor's result consists of 3 bytes). Measurement results should be available in real time, i.e. received directly.

Is it possible to use LoRaWAN for this application? Can you help with a starter kit and sample code, e.g. for longest connection: PC < 2-3km distance > sensor node (the last one in a future chain)?

NOTE: This question and answer originated from a customer support case which was handled by us. We regularly review support cases and add any helpful ones here for all to benefit from.

Central SUPPORT · ‎2019-04-25

Yes, I think so. Considering LoRa physical layer based on spread spectrum chirp modulation you can achieve communication range up to 10 km, but the bit rate in this case is low i.e. for spreading factor SF=12 it is about 250 bit/s (including protocol overhead, effective bit rate is 30%-40% lower). It means that latency of communication can exceed your requirements. Of course, you can increase the data rate up to 5kbit/s using lower spreading factor SF=7 but distance of communication drops.

In order to meet your requirement in terms of data rate and latency I think you can use PHY and part of MAC layer of a full LoRaWAN protocol stack only. LoRa gateway, network server and application server would add extra communication latency time.

I think, the best way to find the solution is to test a real sensor network. I attached simple example of point-to-point application which can be easily extend to other network topologies. It is based on I-CUBE-LRWAN v1.1.4 (check for updates on st.com later).

Also attached you find some general info about LoRa and ST’s LoRa implementation and ecosystem (included in LORA_P2P_v114.zip file). More info also on st.com, see here https://www.st.com/en/wireless-transceivers-mcus-and-modules/lorawan-technology.html#products.

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Central SUPPORT · ‎2019-04-25

Yes, I think so. Considering LoRa physical layer based on spread spectrum chirp modulation you can achieve communication range up to 10 km, but the bit rate in this case is low i.e. for spreading factor SF=12 it is about 250 bit/s (including protocol overhead, effective bit rate is 30%-40% lower). It means that latency of communication can exceed your requirements. Of course, you can increase the data rate up to 5kbit/s using lower spreading factor SF=7 but distance of communication drops.

In order to meet your requirement in terms of data rate and latency I think you can use PHY and part of MAC layer of a full LoRaWAN protocol stack only. LoRa gateway, network server and application server would add extra communication latency time.

I think, the best way to find the solution is to test a real sensor network. I attached simple example of point-to-point application which can be easily extend to other network topologies. It is based on I-CUBE-LRWAN v1.1.4 (check for updates on st.com later).

Also attached you find some general info about LoRa and ST’s LoRa implementation and ecosystem (included in LORA_P2P_v114.zip file). More info also on st.com, see here https://www.st.com/en/wireless-transceivers-mcus-and-modules/lorawan-technology.html#products.