A large part of the Internet of Things consists of wireless sensors and actuators that only have one or two simple tasks. For these things range and operational lifespan are more important than data bandwidth. Energy-saving networks with a large range and high density are currently in popular demand. LoRaWAN is just such a system.
Article from Objective 27, 2017
Data traffic requires energy
We are used to 4G and WiFi. We stream our music to our smartphones and watch movies on a tablet. From a park bench, we log onto the company's network with a laptop. These activities all have one thing in common: a lot of digital information goes by air and that requires energy. Data traffic with high bandwidths quickly drains batteries and power packs. Smartphones and laptops require daily charging. Usually, this is not an option for wireless sensors. A smoke detector or a moisture sensor needs to last for months, preferably years. Communication via a mobile or WiFi network requires too much energy, even when the batteries are charged intermediately with solar cells. The much more energy-friendly bluetooth is sadly not an option - too little range. Because the sensor networks generate relatively little data traffic, there is a demand for alternative solutions.
Low Power, Wide Area Network
The answer is networks with a large range, a low energy usage and high density (the capacity to make connections with lots of devices). LoRaWAN is such a Low Power, Wide Area Network (LPWAN). It works with the LoRa radio frequency technology (see frame) and has a so-called star-of-stars topology (see figure page 5). The sensors or actuators (the nodes) are connected to LoRaWAN gateways. These provide the transport of messages between nodes and a LoRaWAN network server that is controlling the network. In theory, one gateway should be able to control thousands of nodes. This number is strongly influenced by the amount of sent data. For pratical applications, the number of nodes per gateway is usually several hundreds.
There are two LoRaWAN providers currently active in the Netherlands that are establishing gateways. One of those, The Things Network (TTN), is a fair-use organization. Technolution is also a member and we have a LoRa gateway on the roof of our office in Gouda. TTN has a lot of faith in LoRaWAN and is working hard to expand its coverage ratio. This organization has succeeded in providing LoRaWAN coverage for the entire city of Amsterdam within six weeks time. The other LoRaWAN provider in the Netherlands is KPN which only offers this service to subscribers. Our country is one of the international forerunners with the coverage ratio of LoRaWAN. The use of the term ‘Wide Area’ is in the case of LoRaWAN certainly not an exaggeration. The gateway on our roof in Gouda was already available for a node in Zoetermeer on the first test. This is a distance of over 15 kilometers.
LoRa radio frequency
LoRaWAN works with the LoRa (Long Range) frequency modulation technology that was developed by Semtech. LoRa is based on the so-called spread-spectrum technique and uses a variation of chirp spread spectrum (CSS). This uses the modulation of broadband FM pulses. The data that is to be sent is encoded by increasing and/or decreasing the frequency during a certain period of time. The CSS technique provides a very high signal sensitivity and a low use of energy. LoRa can demodulate signals that are 19.5 dB below the noise floor, while similar systems require a signal of 8 to 10 dB above the noise floor. The effect is that LoRa signals have a large range. They can penetrate buildings and are almost completely unaffected by reflection. LoRa thus describes the radio technology that is being used in the network topology of LoRaWAN.
Data traffic via LoRaWAN
The low energy usage of LoRaWAN has one drawback. The data rate is modest, namely between the 0.3 and 50 kb/s. This is a determinator for the maximal distance from the node to the gateway; the lower the data rate, the longer the distance can be. The data rate also determines the duration of the transmission and thus the capacity (the number of nodes) per gateway. A LoRaWAN node can send one data package per transmission, preferably with a payload as small as possible (the ‘useful’ load). The actual maximum number of bytes that can be sent depends on the aforementioned factors.
Suitable for sensor networks
The low data rates of LoRaWAN appear to be restricting for developers. However, precisely these restrictions make LoRaWAN suitable for sensor networks. A LoRa node communicates in half-duplex mode: it can send and receive, but not at the same time. A LoRa gateway can receive data from eight nodes at the same time; sending can only be done to one node at a time. A sensor network, however, has a lot more than eight nodes per gateway. That is why it is important to organize the duration and the amount of the transmissions through the nodes properly and to make sure there are enough gateways. When nodes perform small transmissions with a set time period, for example one every five or ten minutes, a gateway can still communicate with hundreds of nodes.
The low data rate is no problem for most sensor networks. The amount of data a sensor wants to sent are usually no larger than a couple of bytes. A consequence of the low data rate is that wireless software updates are currently not possible via LoRaWAN.
A lot of sensor networks working with LoRaWAN do not have security as a high priority because there is no sensitive data being sent through the network. In addition, the sensor data is only available on a local basis for those who can receive the LoRa RF signal. Security between nodes and gateway becomes a more important issue when LoRaWAN is being used to control actuators. It is being used to control processes and devices after all.
LoRaWAN offers a build-in 128 bits AES encryption on two levels: network and application. When a node is activated for the first time, it will automatically perform a 'handshake' with the gateway and reveal its network security encryption to the node. After that, the node is included in the network. This method is called Over The Air Activation (OTAA). When someone is looking to create a network with a lot of sensor nodes, this is the quickest way to do so. A different method is Activation By Personalization (ABP). This way, the security keys of the nodes are made known to the gateway beforehand. As soon as one of the registered nodes is active, the gateway will include it in its network. Unknown nodes are rejected by the gateway. The ABP method is in principle safer than the OTAA method. If it is certain that the node will make contact with the right gateway, the OTAA method is sufficient. There is also a 128 bits AES-security key on application level. This will prevent the network or network operator from gaining access to the application data.
LoRaWAN in practice
The sensor network Sense2Grow is based on LoRaWAN technology. It was developed by Technolution for applications in, among other sectors, the horticultural sector. The system consists of sensor nodes, a WIO node (wireless I/O), LoRaWAN gateways and web applications for data presentation and analysis. It is an open platform: each LoRaWAN sensor can be connected to Sense2Grow, even nodes come from other manufacturers. Sense2Grow is therefore an evolutionary system that will continue to develop into other applications.
Technolution has developed two sensor nodes for Sense2Grow so far: a smoke sensor and a temperature sensor. They are fitted with solar cells that provide enough energy in a normally lit environment for communication between the nodes and the gateways and the charging of the batteries. In the temperature sensor, the superfluous energy of the solar cell is used to power a fan. This prevents the sensor from heating up from direct sunlight on its casing. The expected operational lifespan of the nodes is five years.
We have also developed a WIO node (Wireless I/O). This provides I2C, SPI, RS485 and GPIO interfaces and makes it possible to connect third-party devices to the Sense2Grow system. New sensors, like a CO2 sensor, are currently under development.
Sense2Grow: fire prevention and temperature monitoring in the greenhouse
Greenhouse producers are struggling with high fire risks. The hot grow lights can explode, causing fire. Such a fire usually starts with smoldering materials and the development of smoke. When the Sense2Grow smoke detector detects smoke, it will use the gateway to send a signal to the connected alarm. The horticulturist can then act before the flames get out of hand.
In a greenhouse of several hectares, temperature differences can be expected. But how big can these deviations be? Horticulturists can see the affect of high or low temperature in the growth of their crops. But often they do not have any insight into the scale or the precise location of the temperature differences. By placing an intricate network of temperature nodes in the greenhouse, the Sense2Grow system can generate a heat map of the greenhouse. This often leads to surprising insights: one of the Sense2Grow users discovered that there were temperature differences of over ten degrees in his greenhouse over a distance of hardly a hundred meters!
Other applications with LoRaWAN
It is not difficult to imagine other applications for sensor networks based on LoRaWAN. Situations with slowly changing environmental factors are particularly suitable. We are currently researching the monitoring of the grease levels in the grease injectors of axes and bearings in heavy machinery. Air quality is another environmental factor. The ammoniac level in pigsties or the particulate matter in the air of crowded city centers can be measured using LoRaWAN sensors These are situations that are now being checked manually on a daily basis. With the implementation of a LoRaWAN sensor network, we can save a lot of time and make the process more efficient.
The future of LoRaWAN
LoRaWAN is still developing. The growth of the Internet of Things will only strengthen this trend. Suppliers will provide single chip solutions with built-in LoRaWAN functionality. The technology will become cheaper and more widely available. There will be linked solutions, with sensor nodes, actuators, gateways, applications for visualization and management of data and end users applications. We focus on offering systems that resemble the business logic of our clients, including device management, required electronics and software. This is how we will build on our knowledge of the underlying radio technology and the hardware-software chain.
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What is the Internet of Things?
What is LoRaWAN?