LoRa

Description

LoRa (from "long range", sometimes abbreviated as "LR") is a physical proprietary radio communication technique. It is based on spread spectrum modulation techniques derived from chirp spread spectrum (CSS) technology. It was developed by Cycleo, a company of Grenoble, France, and patented in 2014. In March 2012, Cycleo was acquired by the US company Semtech.

LoRaWAN (long range wide area network) defines the communication protocol and system architecture. LoRaWAN is an official standard of the International Telecommunication Union (ITU), ITU-T Y.4480. The continued development of the LoRaWAN protocol is managed by the open, non-profit LoRa Alliance, of which Semtech is a founding member.

Together, LoRa and LoRaWAN define a low-power, wide-area (LPWA) networking protocol designed to wirelessly connect battery operated devices to the Internet in regional, national or global networks, and targets key Internet of things (IoT) requirements, such as bi-directional communication, end-to-end security, mobility and localization services. The low power, low bit rate, and IoT use distinguish this type of network from a wireless WAN that is designed to connect users or businesses, and carry more data, using more power. The LoRaWAN data rate ranges from 0.3 kbit/s to 50 kbit/s per channel.

Features

LoRa uses license-free sub-gigahertz radio frequency bands:

EU433 (LPD433) or EU868 (863–870/873 MHz) in Europe
AU915/AS923-1 (915–928 MHz) in South America
US915 (902–928 MHz) in North America; IN865 (865–867 MHz) in India
AS923 (915–928 MHz) in Asia

LoRa enables long-range transmissions with low power consumption. The technology covers the physical layer, while other technologies and protocols such as LoRaWAN cover the upper layers. It can achieve data rates between 0.3 kbit/s and 27 kbit/s, depending upon the spreading factor.

LoRa is one of the most popular low-power wireless sensor network technologies for the implementation of the Internet of things, offering long-range communication compared to technologies such as Zigbee or Bluetooth, but with lower data rates.

LoRa devices have geolocation capabilities used for trilaterating positions of devices via timestamps from gateways.

LoRa PHY

LoRa uses a proprietary spread spectrum modulation that is similar to and a derivative of chirp spread spectrum (CSS) modulation. Each symbol is represented by a cyclic shifted chirp over the bandwidth centered around the base frequency. The spreading factor (SF) is a selectable radio parameter from 5 to 12 and represents the number of bits sent per symbol and in addition determines how much the information is spread over time.

There are $M = 2^{S F}$ different initial frequencies of the cyclic shifted chirp across the bandwidth around the center frequency. The symbol rate is determined by $R_{s} = B / M$ . LoRa can tradeoff data rate for sensitivity (assuming a fixed channel bandwidth $B$ by selecting the $S F$ , i.e. the amount of spread used.

A lower $S F$ corresponds to a higher data rate but a worse sensitivity, a higher $S F$ implies a better sensitivity but a lower data rate. Compared to lower $S F$ , sending the same amount of data with higher $S F$ needs more transmission time, known as time-on-air. More time-on-air means that the modem is transmitting for a longer time and consuming more energy. Typical LoRa modems support transmit powers up to +22 dBm. However, the regulations of the respective country may additionally limit the allowed transmit power. Higher transmit power results in higher signal power at the receiver and hence a higher link budget, but at the cost of consuming more energy.

There are measurement studies of LoRa performance with regard to energy consumption, communication distances, and medium access efficiency. According to the LoRa Development Portal, the range provided by LoRa can be up to 3 miles (4.8 km) in urban areas, and up to 10 miles (16 km) or more in rural areas (line of sight).

In addition, LoRa uses forward error correction coding to improve resilience against interference. LoRa's high range is characterized by high wireless link budgets of around 155 dB to 170 dB. Range extenders for LoRa are called LoRaX.

LoRaWAN

Since LoRa defines the lower, physical, layer, the upper networking layers were lacking. The specification consist of two parts. The actual LoRaWAN acts as a cloud controlled MAC layer protocol for managing communication between LPWAN gateways and end-node devices. For communication within the cloud, LoRaWAN specifies data formats for higher layers, while the transport protocol could be any Internet protocol.

LoRaWAN is also responsible for managing the communication frequencies, data rate, and power for all devices.

Devices in the network are asynchronous and transmit when they have data available to send. Data transmitted by an end-node device is received by multiple gateways. Each gateway has a multi-channel receiver, while the end-devices can hop between the channels using a single channel transceiver. Gateways forward the data packets without further processing to a centralized network server. This technology shows high reliability for the moderate load, however, it has some performance issues with sending acknowledgements (2016).

The data is then further forwarded to an associated application server. The cloud back-end interface definition uses JSON as data format. The cloud network specifies secure joining protocols for end-devices and possibilities for roaming between gateways. The application data payload is encrypted between the end-device and the cloud application and the content format is not specified by LoRaWAN.

LoRa Alliance

The LoRa Alliance is an open, non-profit association whose stated mission is to support and promote the global adoption of the LoRaWAN standard for massively scaled IoT deployments, as well as deployments in remote or hard-to-reach locations.

Members collaborate in a vibrant ecosystem of device makers, solution providers, system integrators and network operators, delivering interoperability needed to scale IoT across the globe, using public, private, hybrid, and community networks. Key areas of focus within the Alliance are smart agriculture, smart buildings, smart cities, smart industry, smart logistics, and smart utilities.