Example LoRaWAN application for Mbed-OS

This is an example application based on Mbed-OS LoRaWAN protocol APIs. The Mbed-OS LoRaWAN stack implementation is compliant with LoRaWAN v1.0.2 specification. See this link for information on support for other LoRaWAN spec versions. This application can work with any Network Server if you have correct credentials for the said Network Server.

Getting Started

Supported Hardware

Mbed Enabled board with an Arduino form factor and one of the following:

• SX126X shield
• SX1276 shield
• SX1272 shield

OR

Mbed Enabled LoRa MCU:

• STM32WL : NUCLEO_WL55JC

OR

Mbed Enabled LoRa Module

Mbed OS build tools

Mbed CLI 2

Starting with version 6.5, Mbed OS uses Mbed CLI 2. It uses Ninja as a build system, and CMake to generate the build environment and manage the build process in a compiler-independent manner. If you are working with Mbed OS version prior to 6.5 then check the section Mbed CLI 1.

1. Install Mbed CLI 2.
2. From the command-line, import the example: mbed-tools import mbed-os-example-lorawan
3. Change the current directory to where the project was imported.

Mbed CLI 1

1. Install Mbed CLI 1.
2. From the command-line, import the example: mbed import mbed-os-example-lorawan
3. Change the current directory to where the project was imported.

Configuration and radio selection

For LoRa modules supported by Mbed-OS, the pin set is already provided in the target-overrides field of the mbed_app.json file. For more information on supported modules, please refer to the module support section.

Add network credentials

Open the file mbed_app.json in the root directory of your application. This file contains all the user specific configurations your application and the Mbed OS LoRaWAN stack need. Network credentials are typically provided by LoRa network provider.

For OTAA

Please add Device EUI, Application EUI and Application Key needed for Over-the-air-activation(OTAA). For example:

"lora.device-eui": "{ YOUR_DEVICE_EUI }",
"lora.application-eui": "{ YOUR_APPLICATION_EUI }",
"lora.application-key": "{ YOUR_APPLICATION_KEY }"

For ABP

For Activation-By-Personalization (ABP) connection method, modify the mbed_app.json to enable ABP. You can do it by simply turning off OTAA. For example:

"lora.over-the-air-activation": false,

In addition to that, you need to provide Application Session Key, Network Session Key and Device Address. For example:

"lora.appskey": "{ YOUR_APPLICATION_SESSION_KEY }",
"lora.nwkskey": "{ YOUR_NETWORK_SESSION_KEY }",
"lora.device-address": " YOUR_DEVICE_ADDRESS_IN_HEX  " 

Configuring the application

The Mbed OS LoRaWAN stack provides a lot of configuration controls to the application through the Mbed OS configuration system. The previous section discusses some of these controls. This section highlights some useful features that you can configure.

Selecting a PHY

The LoRaWAN protocol is subject to various country specific regulations concerning radio emissions. That's why the Mbed OS LoRaWAN stack provides a LoRaPHY class that you can use to implement any region specific PHY layer. Currently, the Mbed OS LoRaWAN stack provides 10 different country specific implementations of LoRaPHY class. Selection of a specific PHY layer happens at compile time. By default, the Mbed OS LoRaWAN stack uses EU 868 MHz PHY. An example of selecting a PHY can be:

        "phy": {
            "help": "LoRa PHY region. 0 = EU868 (default), 1 = AS923, 2 = AU915, 3 = CN470, 4 = CN779, 5 = EU433, 6 = IN865, 7 = KR920, 8 = US915, 9 = US915_HYBRID",
            "value": "0"
        },

Duty cycling

LoRaWAN v1.0.2 specifcation is exclusively duty cycle based. This application comes with duty cycle enabled by default. In other words, the Mbed OS LoRaWAN stack enforces duty cycle. The stack keeps track of transmissions on the channels in use and schedules transmissions on channels that become available in the shortest time possible. We recommend you keep duty cycle on for compliance with your country specific regulations.

However, you can define a timer value in the application, which you can use to perform a periodic uplink when the duty cycle is turned off. Such a setup should be used only for testing or with a large enough timer value. For example:

"target_overrides": {
    "*": {
        "lora.duty-cycle-on": false
    }
}

Module support

Here is a nonexhaustive list of boards and modules that we have tested with the Mbed OS LoRaWAN stack:

• MultiTech mDot (SX1272)
• MultiTech xDot (SX1272)
• LTEK_FF1705 (SX1272)
• Advantech Wise 1510 (SX1276)
• ST B-L072Z-LRWAN1 LoRa®Discovery kit with Murata CMWX1ZZABZ-091 module (SX1276)
• ST NUCLEO-WL55JC with sub-GHz SoC (STM32WL)

Here is a list of boards and modules that have been tested by the community:

• IMST iM880B (SX1272)
• Embedded Planet Agora (SX1276)

Building and running

1. Connect a USB cable between the USB port on the target and the host computer.

2. Run the following command to build the example project and program the microcontroller flash memory:

   • Mbed CLI 2

   $ mbed-tools compile -m <TARGET> -t <TOOLCHAIN> --flash --sterm --baudrate 115200

   • Mbed CLI 1

   $ mbed compile -m <TARGET> -t <TOOLCHAIN> --flash --sterm --baudrate 115200

Your PC may take a few minutes to compile your code.

The binary is located at:

• Mbed CLI 2 - ./cmake_build/<TARGET>/develop/<TOOLCHAIN>/mbed-os-example-lorawan.bin

• Mbed CLI 1 - ./BUILD/<TARGET>/<TOOLCHAIN>/mbed-os-example-lorawan.bin.

You can manually copy the binary to the target, which gets mounted on the host computer through USB, rather than using the --flash option.

You can also open a serial terminal separately, rather than using the --sterm --baudrate 115200 option, with the following command:

• Mbed CLI 2

  $ mbed-tools sterm --baudrate 115200

• Mbed CLI 1

  $ mbed sterm --baudrate 115200

Expected output

The serial terminal shows an output similar to:

Mbed LoRaWANStack initialized 

 CONFIRMED message retries : 3 

 Adaptive data  rate (ADR) - Enabled 

 Connection - In Progress ...

 Connection - Successful 

 Dummy Sensor Value = 2.1 

 25 bytes scheduled for transmission 
 
 Message Sent to Network Server

[Optional] Adding trace library

To enable Mbed trace, add to your mbed_app.json the following fields:

    "target_overrides": {
        "*": {
            "mbed-trace.enable": true
        }
     }

The trace is disabled by default to save RAM and reduce main stack usage (see chapter Memory optimization).

Please note that some targets with small RAM size (e.g. DISCO_L072CZ_LRWAN1 and MTB_MURATA_ABZ) mbed traces cannot be enabled without increasing the default "main_stack_size": 1024.

[Optional] Memory optimization

Using Arm CC compiler instead of GCC reduces 3K of RAM. Currently the application takes about 15K of static RAM with Arm CC, which spills over for the platforms with 20K of RAM because you need to leave space, about 5K, for dynamic allocation. So if you reduce the application stack size, you can barely fit into the 20K platforms.

For example, add the following into config section in your mbed_app.json:

"main_stack_size": {
    "value": 2048
}

Essentially you can make the whole application with Mbed LoRaWAN stack in 6K if you drop the RTOS from Mbed OS and use a smaller standard C/C++ library like new-lib-nano. Please find instructions here.

For more information, please follow this blog post.

License and contributions

The software is provided under Apache-2.0 license. Contributions to this project are accepted under the same license. Please see contributing.md for more info.

This project contains code from other projects. The original license text is included in those source files. They must comply with our license guide.