All about LoRa(WAN)

I will try to write everything you need to know about LoRa for the first steps. I wrote a thesis about LoRaWAN and TTN in Greek. In some areas it's already obsolete. Here I try to cover all the aspects of LoRa(WAN). Devices, Gateways, Network (TTN) in a very short time.

This a work in progress. For more current and valid info visit the forum.

My motivation

My motivation is to have a low power tracking device without SIM, because here in Greece the M2M SIM's are expensive and not available to individuals (only to companies). With NB-IoT the situation is better but again only available to companies with 1.24€ per month. After discovering LoRa I found a second problem. SIM devices have very large battery consumption. Even if SIM devices where cheaper, I want to track many devices (bicycles, cars, persons). So even cheap SIM's will become expensive and a battery hassle / nightmare management. Yes there is NB-IoT but it's again expensive for many devices and not so good as LoRa energy-wise (but better for deliver-ability and large data). Also I don't know the coverage. I imagine the coverage will be fine on cities, but not outside the cities.

LoRa is for bytes, not for strings

Don't associate LoRa with strings. Think about bytes. How many bytes? Less than 10bytes! If you need more bytes, forget about LoRa. Less bytes is better otherwise LoRa will not be sucessful on IoT world. In my thesis I managed to send location data (GPS), speed, direction, status (fall), battery level with 7 bytes. If you want more bytes go to NB-IoT. With LoRa you have to be a good citizen. Transmit less, so the LoRa IoT community will have no / less problems. Check the graph I made to undestand the problem if you use many bytes. SF12 for one byte of payload requires 1 second (10^3ms) and for 51 bytes you transmit for 3 seconds! This is a serious problem. Because you create noise, inteference to other devices. Share the air-time, don't use many bytes and high SF's.

It's better to use less bytes. Less than 10.

Consult the Airtime Calculator for more details.

Gateway

Similar to mobile providers, with LoRa you need an 'antenna' (it's called Gateway) to receive the messages. You may came across also the term 'concentrator'. This is a device that demodulates / modulates LoRa messages. Gateway is a server that accepts messages (uplinks - from device) or sends messages (downlinks - to device), concentrator is the wireless network card of the server. The Gateway forwards the uplinks to a network server (example TTN) and also accepts messages to forward (downlinks) from a network server (TTN).

LoRa and LoRaWAN

Long story (awkward) short: LoRa is a (de)modulation technique, LoRaWAN is the protocol that connects devices with gateways.

Limitations

Law limitation: You can transmit (Duty Cycle) only 1%? per time. If you want more (unlimited), go to NB-IoT. Extra limitations from TTN: You can transmit every minutes and 30'' (seconds) per day. Your device can receive 10 messages per day. In case you didn't get it. Forget LoRa for bi-directional communication. Only occasionaly bi-direction communication is allowed. When the device sends data it's a uplink when the gateway sends data to the device it's a downlink.

Network (Coverage)

I think the best operator of LoRaWAN is TTN (thethingsnetwork.org). It's free and open sourced.

Some countries have excellent coverage (currently Holland, Switzerland), some not (Greece). Probably you will need to install some gateways to operate your devices. The cost of the gateway is 300€-700€. Check the coverage of you area on ttnmapper.org and the installed gateways on the TTN map.

Gateway

I suggest to use a Raspi (Raspberry pi) for gateway. For concentrator choose the newest (currently SX1302 [SX1303 for extreme temperatures]). Twice the demodulation power, 10 (ten) times less power consumption, so 20 times more efficient. (85mA vs 800mA)

Demodulation

Even the SX1302 does not have enough demodulation power for LoRa. LoRa in Europe currently uses 8 channels. SX1302 ideally should have 64 demodulators (8 DataRates * 8 channels) but it has 8 for SF7-SF12 and 8 for SF7-SF10. Older SX1308 has only 8 demodulators. Also SX1302 has 2dB better sensitivity.

LoRa Collisions

Since we share the same medium (air), collisions will occur. You need to be a good LoRa citizen with the smallest (fastest) possible SF (Spreading Factor), or even FSK and to use the smallest transmitting power. ADR can help with those two problems. Why?

This is very important. LoRa can demodulate different signals on different SF's but if SF9 is received in GW with more than 7dB stronger then the demodulation of SF7 fails. In other words a SF9 +7dB LoRa signal masks a SF7 signal.

SF7 masks the SF9 LoRa message if its transimitting 12.5dB more than SF9.

Here (p.6) we can see than if we have a collision with the same SF, probably the packet will be lost.

Use cases

LoRaWAN and TTN are very limited, what can I do? The most easy is to read data from sensors (weather, air quality, doors, parking sensors). If you have good coverage or if you can add coverage with your own gateway, you can also have GPS tracking. One more interesting idea if you have permanently power supply is a CLASS C device (always listen). To open a door when you car approaches (for example).