With deployment of IoT is spreading across various domains and applications, the requirements of the underlying communication mechanism varies. There is no one-size-fill-all solution as the needs are different in case of throughput, range, power consumption etc. There are many wireless communication technologies, such as Short-range wireless, Cellular, LPWAN etc.
LPWAN stands for Low Power Wide Area Network, designed for sending small data packages over long distances. While short range technologies like Bluetooth, Wi-Fi, Zigbee are cheap, it is limited by distance, cellular technologies like 3G, 4G and 5G have more transmission rate and range but are more costly and high power consuming. LPWAN has overcome the cons of existing wireless technology by compromising on the data rate and featuring the long-range data transmission, low power consumption and being economical. Some of the technologies that comes under LPWAN includes Narrowband IoT (NB-IoT), Sigfox, LoRa and others.
Of these LPWAN, LoRa has a significant market share and finds application across use cases.
Following are key features of LoRa Technology,
- It has very wide coverage range about 5 km in urban areas and 15 km in suburban areas
- Battery lifetime up to 15 years
- One LoRa gateway takes care of thousands of nodes.
- Easy to deploy and low cost.
- Enhanced the secure data transmission by embedded end-to-end AES128 encryption
In this blog, we will cover the underlying technology behind LoRa and its network topology.
LoRa is a long range, low power, inexpensive technology for Internet of Things (IoT) developed by a company called Cycleo, France in 2009, later acquired by Semtech in 2012. The LoRa radio and modulation part is patented and its source is closed. Semtech has licensed its LoRa intellectual property to other chip manufacturers. The LoRa Alliance, an open, non-profit association has been formed to promote the adoption of this technology and has grown to more than 500 members since its inception in March 2015.
The most important aspect of the LoRa is that it uses license-free sub-gigahertz radio frequency ISM bands in the deployed region such as 868 MHz in Europe and 915MHz in North America. Thus, there is no need for a separate licensing for using LoRa in any country.
Usually in digital communication, there are three types of basic modulation techniques such as
Amplitude Shift Keying, Frequency Shift Keying and Phase Shift Keying, in which either amplitude or frequency or phase of the carrier varies according to the digital signal changes. The short coming with these approaches is that since the bandwidth is quiet limited the signal is quiet prone to interference and could be easily jammed. To over come this, spread spectrum techniques are being used where by the signal is modulated such that it is spread across the entire bandwidth. There are many spread spectrum techniques such as DSSS, FHSS, THSS, CSS etc.
Chirp Spread Spectrum
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 is a sinusoidal signal whose frequency increases(up chirp) or decreases(down chirp) over time across the entire bandwidth. This signal is used as the carrier and is modulated according to the data to be transmitted.
LoRa uses three bandwidths: 125kHz, 250kHz and 500kHz. The chirp uses the entire bandwidth and the spreading factors are – in short – the duration of the chirp. LoRa operates with spread factors from 7 to 12. This delivers orthogonal transmissions at different data rates. Moreover it provides processing gain and hence transmitter output power can be reduced with same RF link budget and will increase battery life.
While LoRa is the underlying physical part, LoRaWAN is the network on which that LoRa operates. It is a media access control (MAC) in the data link layer that is maintained by the LoRa Alliance. LoRaWAN defines a set of rules and software that ensures data arrives with an acknowledgement and does not have duplicate packets. It is a network architecture that is deployed in a star topology and so the communication between the end node and gateway is bidirectional.
LoRaWAN defines role of end points and gateway. End points or End nodes are the remote nodes typically housing the sensors/actuators. Gateways or Concentrators forms the heart of the star topology, to which the end points communicate to.
Lora WAN Network Architecture
When an end node transmits data to the gateway, it is called an uplink. When the gateway transmits data to the end node, it is called a downlink. The gateways forward this packet to the network server. The network server collects the messages from all gateways and filters out the duplicate data and determines the gateway that has the best reception. The network server forwards the packet to the correct application server where the end user can process the sensor data. Optionally the application server can send a response back to the end node. When a response is sent, the network server receives the response and determines which gateway to use to broadcast the response back to the end node.
The LoRaWAN protocol defines the Adaptive Data Rate (ADR) scheme to control the uplink transmission parameters of LoRa devices. Whether the ADR functionality will be used is requested by the end nodes by setting the ADR flag in the uplink message. If the ADR flag is set, the network server can control the end node’s transmission parameters. ADR should only be used in stable Radio Frequency (RF) situations where end nodes do not move. Mobile end nodes which are stationary for longer times can enable ADR during those times.
This blog introduced the basics behind LoRa technology including the underlying communication techniques and network topology. In the next blog, we will cover the communication model in more detail including the classes, bands and also the typical configuration available in a gateway.
About Embien: Embien Technologies is a proven enabler in adoption of IoT. We have been working with different communication technologies such as ZigBee, BLE, SigFox, LoRa, NB-IoT and have designed gateways to inter-operate between them. Our services include end device development, gateways design, cloud application development and analytics.