What is LoRa and how does it work?
LoRaWAN is a Low Power Wide Area Network (LPWAN) specification created for wireless, battery-operated devices. LoRa is already deployed in millions of sensors, according to the LoRa-Alliance. Some of the main components that serve as the foundation for the specification are bi-directional communication, mobility and localization services.
The LoRa-Alliance, a nonprofit group and creators of LoRaWAN, is a collaboration of members from around the world tasked to share knowledge and experiences in order to guarantee interoperability between LoRa network operators in one open global standard. While LoRaWAN defines the communication protocol and system architecture for the network, the LoRa architecture enables the long-range communication link. These two elements combine to help determine the battery lifetime of a node, the network capacity, the quality of service, the security and other applications served by the network.
One area where LoRaWAN differs from other network specs is that it uses a star architecture, with a central node to which all other nodes are connected and gateways serve as the transparent bridge relaying messages between end-devices and a central network server in the backend. Gateways are connected to the network server via standard IP connections while end-devices use single-hop wireless communication to one or many gateways. All end-point communication is bi-directional, and supports multicast, enabling software upgrades over the air. According to the LoRa-Alliance, the non-profit organization who created LoRaWAN specifications, this helps preserve battery life and achieve long-range connection.
LoRa is also based on chirp spread spectrum modulation which the alliance claims maintains low-power characteristics and significantly increases communication range. Chirp spread spectrum has been used in military and space communication for decades, but LoRa is the first low-cost implementation for commercial usage. Communication between end-devices and gateways is spread out on different frequency channels and data rates. The selection of the 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. LoRaWAN data rates range from 0.3 kbps to 50 kbps.
A single LoRa-enabled gateway or base station can cover entire cities or hundreds of square kilometers. Of course, range depends on the environment of a given location, but LoRa and LoRaWAN claims to have a link budget, the primary factor in determining communication range, greater than any other standardized communication technology.
The LoRa wireless system makes use of the unlicensed frequencies. These include:
- 868 MHz for Europe
- 915 MHz for North America
Using lower frequencies than 2.4 or 5.8 GHz ISM bands enables better coverage, especially when the nodes are within buildings, according to the LoRa-Alliance.
The security of LPWAN networks will be incredibly important for the future success of IIoT. The LoRa-Alliance has assigned several layers of encryption to its network specification:
- Unique Network key (EUI64) and ensure security on network level
- Unique Application key (EUI64) ensure end to end security on application level
- Device specific key (EUI128)
LoRaWAN has several different classes of end-point devices to address the different needs reflected in the wide range of applications. According to its website, these include:
- Bi-directional end-devices (Class A): End-devices of Class A allow for bi-directional communications whereby each end-device’s uplink transmission is followed by two short downlink receive windows. The transmission slot scheduled by the end-device is based on its own communication needs with a small variation based on a random time basis (ALOHA-type of protocol). This Class A operation is the lowest power end-device system for applications that only require downlink communication from the server shortly after the end-device has sent an uplink transmission. Downlink communications from the server at any other time will have to wait until the next scheduled uplink.
- Bi-directional end-devices with scheduled receive slots (Class B): In addition to the Class A random receive windows, Class B devices open extra receive windows at scheduled times. In order for the End-device to open its receive window at the scheduled time it receives a time synchronized Beacon from the gateway. This allows the server to know when the end-device is listening.
- Bi-directional end-devices with maximal receive slots (Class C): End-devices of Class C have nearly continuously open receive windows, only closed when transmitting.