Low-Power Wide-Area Networks (LPWANs)
LPWANs are networks connecting resource-constrained (low-power) devices over a wide area (with links up to several km long) with low-bandwidth connectivity, and for relatively low traffic rates. Large wireless sensor networks at urban or metropolitan scale or long-term monitoring deployments are examples of LPWANs — these are thus the natural framework for the Internet of Things. Since LPWANs involve features and constraints that are not typically addressed in classic wireless networking technologies (e.g. Wi-fi, cellular), new technologies are being proposed and developed to support IoT deployments, some examples being LoRa or SigFox.
What is LoRa
LoRa (an abbreviation for… Long-Range) is a wireless infrastructure technology for the IoT, targeting deployments where:
- end-devices are typically battery powered,
- end-devices do not need to transmit more than a few bytes at a time, and
- data traffic can be initiated either by the end-device (such as when the end-device is a sensor), or by an external entity wishing to communicate with the end-device (such as when the end-device is an actuator).
The long-range and low-power nature of LoRa makes it an interesting candidate for smart sensing technology in civil infrastructures (such as health monitoring, smart metering, environment monitoring, etc.) as well as in industrial applications.
LoRa can commonly refer to two distinct layers:
- the physical layer using Chirp Spread Spectrum (CSS) radio modulation technique, and
- a MAC layer protocol (LoRaWAN) — although the LoRa communications system also implies a specific access network architecture.
LoRa architecture and characteristics
A typical LoRa network (see below) consists of a set of end-devices communicating with gateways using LoRa with LoRaWAN. Gateways forward raw LoRaWAN frames from devices to a network server over a backhaul interface with a higher throughput, typically Ethernet or 3G. In this setup, gateways are only bidirectional relays, or protocol converters, with the network server being responsible for decoding the packets sent by the devices and generating the packets that should be sent back to the devices.
LoRa is advertised as one of the key technologies to enable the “Internet of Things” – indeed, is often advertised as “being to the IoT as WiFi was to home networking” – by providing:
- A “star-of-stars” network topology
- Long range, up to 15 km
- Long battery life, over 10 years
- Operation on unlicensed spectrum (433-, 868- or 915-MHz ISM bands)
- High link budget, up to 157 dB
- Low infrastructure cost and low end-device cost
Our research on LPWAN and LoRa
Literature is sparse with anything other than marketing material, and very little independent research has been published on LoRa. Being the “skeptic academics”, our current goals for our work with LoRa include:
- Understanding LoRa operation and main features.
- Quantifying LoRa technology by way of experimental measurements, in particular focusing on its transmission range, throughput/capacity, power consumption, MAC protocol performance, etc.
- Based on the measurements and observations obtained, proposing and evaluating new mechanisms to improve the performance of LoRa and adapt its operation to new IoT applications.