LoRa is low-power wide-area network protocol that can be used to periodically communicate sensor data. LoRa uses a proprietary spread spectrum modulation that is similar to and a derivative of Chip Spread Spectrum (CSS) modulation. This allows for long-range transmission, up to 15 km, with low power consumption. This makes it ideal for battery applications that only need to periodically transmit sensor data.
There are two types of networks that can be built using LoRa modulation. The first is a peer-to-peer or point-to-point network. This is the simplest network that can be created only requiring a minimum of two devices with LoRa radios to develop. In this type of network, each device's radio must set to use the same LoRa settings frequency, coding rate, spreading factor, etc. This type a network is good for small networks with only a few devices that periodically need to transmit data to each other.
The second network type of network described in this article using LoRa modulation is a LoRaWAN network. LoRaWAN is a upper level network protocol, developed by the LoRa Alliance, that uses LoRa modulation for creating a cloud-based network. In LoRaWAN networks end-devices periodically send messages to a gateway, which then forwards to a network server, which forwards it to an application server. Any response is then forwarded back in the reverse order. In order for a device to communicate on a LoRaWAN network it must first join that network, additionally for security purposes the data being sent and received on a LoRaWAN network is encrypted twice. First, the application payload is encrypted with an application key that is only known by the device and application server. Second, the network payload, which includes the application payload, is encrypted with a network key that is only know by the device and the network. This ensures that the data being sent by the end-device to the application is secure.
When developing a LoRaWAN network it requires at least one end-device with a LoRa radio, a gateway, a network server and an application server. However, it is possible to purchase or build a gateway that have the network and application servers built-in to it. Additionally there are several service providers, The Things Network for example, that have public gateways operating in many areas of the world that can be used to receive messages and forward them to your application server. See thethingsnetwork.org for more info about their service. This allows building a LoRaWAN network quickly without investing a lot of time and money in developing and maintaining the network infrastructure. However these services are not required, it is possible to build a private network from the ground up using your own gateways and servers.
Devices that communicate using LoRa modulation requires a LoRa radio, for that purpose Microchip developed the RN2903 module. The RN2903 modules is designed to communicate using LoRa modulation using the US frequency band, additionally the RN2903 module has a built-in stack for connecting to and communicating on a LoRaWAN network.
CCS created a driver for the RN2903 module to assist in development, rn2903.c, for communicating with and controlling the module. The rn2903.c driver is a low level driver that uses serial messages to communicate with and control the RN2903 module. It also has specific functions for controlling RN2903 module's radio, which are used for doing peer-to-peer, point-to-point, communication, and for controlling the RN2903 module's LoRaWAN stack, which is used for connecting to and communicating on a LoRaWAN network. In addition to the rn2903.c driver, CCS also created two additional drivers, lora.c and lorawan.c. The lora.c driver was developed by CCS to use the rn2903.c driver to do peer-to-peer, point-to-point, communication. This is designed so that two or more PIC® MCU devices with RN2903 modules can communicate with each other. The lorawan.c driver was developed by CCS to use the rn2903.c driver to connect a PIC® MCU device with an RN2903 module to a LoRaWAN network. All three of these driver come with the the current version of the CCS C Compiler. CCS will be releasing a LoRa development kit in the near future.
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