Introduction

I’ve been thinking about building a mesh network that uses LoRa to provide text-message sized communications. The initial implementation will use development hardware consisting of an Adafruit Feather equipped with an RFM95 radio, an RTC, and an EEPROM. There’s a list of things that need to be figured out under Open Questions.

There are similar technologies, so it’s useful to consider why they’re not being used:

• Ham radio doesn’t permit encrypted communications, but it’s the closest desirable RF tech.
• LTE requires expensive infrastructure for any communications.
• Bluetooth is very short ranged.
• 802.11 can be used in an adhoc mode, but it’s power hungry and range limited.
• XBee / Zigbee is a complicated protocol that also has limited range.

There’s the option of using LoRaWAN gateways to communicate over longer distances (requiring the use of public infrastructure), but it isn’t required. Nodes can always communicate locally with each other and use the public infrastructure for inter-mesh communications (and it might be possible in the future to look at different technology for this). There’s also opportunity for multiple physical layers: bluetooth to connect to a phone or computer wirelessly (or maybe to transmit larger data), 802.11-enabled gateways, and so on.

There are limitations to using LoRa: images can’t really be transmitted, and messages will be severely limited in size. The theoretic maximum message size is also constrained by the data rate, ranging from 480 bytes at 9600 bps to 1920 bytes at 38400 bps. This doesn’t account for any protocol overhead.