Features of LoRa
LoRa uses license-free sub-gigahertz radio frequency bands
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;
2.4 GHz worldwide.
LoRaWAN has official regional specifications, called Regional Parameters, that you can download from the LoRa Alliance website. The regional parameters include physical layer parameters such as frequency plans (channel plans), mandatory channel frequencies and data rates for join-request messages. The Regional Parameters also include LoRaWAN layer parameters such as maximum payload size.
LoRa is a proprietary spread spectrum modulation scheme that is based on Chirp Spread Spectrum modulation (CSS). Chirp Spread Spectrum is a spread spectrum technique that uses wideband linear frequency modulated chirp pulses to encode information. A chirp pulse is a sweep in frequency on the corresponding bandwidth (125kHz, 250kHz…) defined earlier. Spread spectrum techniques are methods by which a signal is deliberately spread in the frequency domain. For example a signal is transmitted in short bursts, “hopping” between frequencies in a pseudo random sequence.
Adaptive Data Rate
Adaptive Data Rate (ADR) is a mechanism for optimizing data rates, airtime and energy consumption in the network. The ADR mechanism controls the following transmission parameters of an end device.
ADR can optimize device power consumption while ensuring that messages are still received at gateways. When ADR is in use, the network server will indicate to the end device that it should reduce transmission power or increase data rate. End devices which are close to gateways should use a lower spreading factor and higher data rate, while devices further away should use a high spreading factor because they need a higher link budget.
Influence of Spreading factor
LoRa is based on Chirp Spread Spectrum (CSS) technology, where chirps (also known as symbols) are the carrier of data. Lower spreading factors mean faster chirps and therefore a higher data transmission rate.
LoRa modulation has a total of 6 spreading factors from SF7 to SF12. Spreading factors influence following things:
lower spreading factor provides a higher bit rate for a fixed bandwidth and coding rate. Doubling the bandwidth also doubles the bit rate for a fixed spreading factor and coding rate.
Distance Larger spreading factors mean larger processing gain, and so a signal modulated with a larger spreading factor can be received with less errors compared to a signal with a lower spreading factor, and therefore travel a longer distance. For example, a signal modulated with the SF12 can travel a longer distance than a signal modulated with the SF7.
sending a fixed amount of data (payload) with a higher Spreading Factor and a fixed bandwidth needs longer time-on-air. Receiver Sensitivity
Higher spreading factors provide higher receiver sensitivity.
Based on LoRa MAC layer operation there are three classes of end devices in LoRa network. The classes are defined as Class A, Class B and Class C. All device classes support bi-directional communication (uplink and downlink).
Each device uplink to the gateway and is followed by two short downlink receive windows. A device can send an uplink message at any time. After uplink transmission, device will wait for the response from gateway. The end node will open two receive slots at t1 and t2 seconds after uplink transmission. Gateway can respond with first receive slot and second receive slot but not for both.
In addition to class A receive slots, class B devices open extra receive slots at scheduled times. The end node receives time synchronized beacon from gateway, allowing gateway to know when the node is listening.The device periodically opens receive window.
In addition to class A receive slots, class C will listen continuously for responses from the gateway. This allows for low-latency communication but is many times more energy consuming than Class A devices.
Long Transmission Distance With respect to range, a single LoRa-based gateway can receive and transmit signals over a distance of more than 10 miles (15 kilometers) in rural areas. Even in dense urban environments, messages are able to travel up to three miles (five kilometers), depending on how deep indoors the end devices (end nodes) are located.
Low working energy consumption As far as battery life goes, the energy required to transmit a data packet is quite minimal given that the data packets are very small and only transmitted a few times a day. Furthermore, when the end devices are asleep, the power consumption is measured in milliwatts (mW), allowing a device’s battery to last for many, many years.
Capacity The number of messages supported in any given deployment depends upon the number of gateways that are installed. A single eight-channel gateway can support a few hundred thousand messages over the course of a 24-hour period. If more capacity is required, all that is needed is to add additional gateways to the network.
Cost Only a few gateways - configured in a star network are required to serve a multitude of end nodes.
With these advantages, LoRaWAN takes a step forward ahead of existing technologies and continues to be used in more areas and projects!!!