LoRaWAN is a Low Power Wide Area Network (LPWAN) specification intended for wireless battery-operated things in regional, national or global network. LoRaWAN target key requirements of internet of things include secure bi-directional communication, mobility and localisation services. This standard provides seamless interoperability among smart things without the need of complex local installations and gives back the freedom to the user, developer, businesses enabling the roll-out of the Internet of Things.
LoRaWAN network architecture is typically laid out in a star-of-stars topology in which gateways is a 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 generally bi-directional, but also supports operation such as multicast enabling software upgrade over the air or other mass distribution messages to reduce the on air communication time.
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. To maximise 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.
National-wide networks targeting internet of things such as critical infrastructure, confidential personal data or critical functions for the society has a special need for secure communication. This has been solved by several layers of encryption:
- Unique Network key (EUI64) to ensure security on network level
- Unique Application key (EUI64) to 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:
- 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 synchronised 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.
Sub-GHz Short Range Devices / ISM-Band (169, 433 and 866 MHz)
SRD (Short Range Device) is a term that is applied to a radio device designed to operate over a short range. This also implies that the power levels are low and hence the likelihood of interference to other devices is low. Cost effectiveness is most often an important decision factor to use this technology, because the total cost of ownership is low. Target applications for SRD require less intelligence, range and security and consequently are easier to integrate into end devices.
Typical applications with such kind of requirements are listed below:
- Remote controls (Garage door and gate controls)
- Sensor networking
- Alarms and movement detectors
- Low rate data transmission
Each frequency has a defined maximum output power which limits its range naturally. Factors to consider on the frequency are typically the kind of environment in which the device is used.
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