0. LoRaWAN Basics
Introduction
As IoT becomes more popular, telecommunication companies have begun to offer new connectivity packages. These connectivity packages are specially designed Wide Area Networks (WAN) for IoT, intended for long range communication at low cost.
Sigfox, NB-IoT and LoRa are some of these Low Power Wide Area Networks (LPWAN). The figure below shows the comparison between the available LPWAN in the market.
LoRa
LoRa which is also known as long range wireless modulation, is very similar to our Wi-Fi and Bluetooth communication devices we are all aware of.
It is a specially designed technology created by Semtech, intended for long range, low power and low data rate transmission (that is enough to read sensors).
LoRa actually refers to the proprietary physical layer of the technology as seen below. This physical layer enables long range communication link based on Chirp Spread Spectrum (CSS) modulation.
Its typical range is 2 to 5 km in dense urban areas and 15 to 22 km in suburban areas.
LoRa uses licensed Free Sub GHz radio frequency ISM bands that differs depending on the regional location.
For example:
- USA (902 to 928 MHz)
- EU (863 to 870 MHz)
- China (779 to 787 MHz)
- Asia (923 MHz)
LoRaWAN
LoRa and LoRaWAN are not the same thing. LoRa is used to create the Wide Area Network (WAN) whereas LoRaWAN is the communication protocol and system architecture for network.
Thus, LoRaWAN here refers to the upper layers of the network that handles the networking and communication protocols. This typically makes use of end nodes, gateways and network servers.
LoRaWAN also known as Long Range Wide Area Network, uses non cellular wireless technology and low power wide area modulation technique to enable long range transmissions with low power consumption.
The great thing about LoRa is that end nodes and gateways can be connected wirelessly using unlicensed ISM bands, reducing the cost.
Murata 1SJ LoRa module
The 1SJ Murata module seen below is the one of the world's smallest LoRa module. It is available on a development board for users to develop new user applications.
The figure below showcases the block diagram of the development board architecture. It is packaged together with Semtech's SX1262 transceiver, Murata's 1SJ LoRa module and STM's STM32L072 MCU which is a low power MCU intended to meet the demands of LoRAWAN applications.
*Note: More information can be found directly from the Murata webpage.
LoRaWAN Network Protocol
The LoRaWAN-based network is made up of end devices, gateways, a network server, and application servers as seen below. For example, the end devices are like our Murata 1SJ LoRa device and the Network Server can be from Telkom-Everynet for the Indonesia region.
These end devices send data (collected from various sensors connected to the end node device) to gateways (uplinks), and the gateways transmit these data by forwarding data packets to the centralized LoRa Network Server (LNS) which, in turn, passes it on to the application server as necessary.
Additionally, the network server can send messages (for device settings management) through the gateways to the end devices (downlinks).
End devices in a LoRaWAN network come in three classes: Class A, Class B and Class C. While end devices can always send uplinks at will, the device’s class determines when it can receive downlinks. The class also determines a device’s energy efficiency. The more energy efficient a device, the longer the battery life.
- Class A
Class A end devices spend most of their time in sleep mode. If there is an uplink, a Class A end device opens a short receive window (Rx1) and, if no downlink is received during that period, it opens a second receive window (Rx2). The start time of Rx1 begins after a fixed amount of time following the end of the uplink transmission. Rx2 typically begins two seconds after the end of the uplink transmission, though this duration is configurable. The following diagram illustrates the different receive window state possibilities.
- Class B
Class B end devices extends Class A by adding scheduled receive windows for downlink messages from server using time synced beacons transmitted by gateways. Time for devices to receive downlinks is also known as a ping slot.
- Class C
Finally, Class C (“Continuous”) end devices never go to sleep. They constantly listen for downlink messages from the network, except when transmitting data in response to a sensor event. These devices are more energy-intensive, and usually require a constant power source, rather than relying on a battery.
