The LoRa [Long Range Radio] is a sub-GHz wireless RF technology. LoRa is the physical (PHY) layer or the wireless modulation at the hardware level, used to create long-range wireless communication links. The LoRa technology uses chirp spread spectrum modulation to enable long range, robust communication, and low-power consumption.
LoRaWAN is a Wide Area Network (WAN) communication protocol specification built on top of the LoRa technology. The LoRaWAN protocol is a media access control (MAC) layer, which extends the LoRa physical communication layer onto internet networks. The LoRaWAN defines communication protocol and system architecture for the network. Figure 1 shows the different layers of a LoRa network. The LoRaWAN protocol and network architecture have the most influence in determining battery lifetime of a node, security, network capacity, quality of service, and the variety of applications served by the network.
The LoRaWAN network architecture is typically laid out in a star-of-stars topology. Figure 2 shows block diagram view of a star topology. Hence, the LoRaWAN network does not enable device-to-device communications. Data packets can only be transmitted from an end-device to the network server or vice versa.
The LoRa network operates in the license-free 433 MHz, 868 MHz, and 915 MHz Industrial, Scientific, and Medical (ISM) bands, with data rates of 0.3 kbps to 50 kbps for a 125 kHz bandwidth. The LoRaWAN network protocol provides a media access control mechanism, enabling many end-devices to communicate with a gateway using the LoRa modulation.
- End Devices
- Central Gateway
- Network Server
End-devices are the low-power sensor nodes which usually sense data in the field. These nodes are often placed remotely. A LoRa network can have multiple gateways, and the same data packet can be received (and forwarded) by more than one gateway.
The network server is an intelligent and core element in a LoRa network. It manages the network, perform security checks, filters redundant received packets, decoding the packets, schedule acknowledgments through the gateway, and also performs adaptive data rate. If the packet is intended for an application server, the network server sends the packet to the specific application server. Using application server, the user receives data from end-devices through a network server for further analysis. Additionally, the application server determines end-device actions. Figure 3 shows the typical LoRa network topology.
The end-devices use the single-hop LoRa communication to communicate with the central gateway. The gateway is connected to the network server via standard IP connections (for example: Ethernet, Wi-Fi®, 3G).
The end-point communication is bi-directional. Communication between end-devices and gateway is spread out on different frequency channels and data rates. The selection of data rate is a trade-off between communication range and message duration. Due to the spread spectrum technology, communications with different data rates do not interfere with each other and create a set of virtual channels increasing the capacity of the gateway. To maximize both battery life of the end-devices and overall network capacity, the LoRaWAN network server is managing the data rate and RF output for each end-device individually by means of an adaptive data rate (ADR) scheme.