Wi-SUN enables interoperable, secure wireless mesh networks
01 December 2022
Wireless technology is a key enabler for many major current tech trends, including the internet of things (IoT) – and smart cities, homes & meters. With 4.2 billion people worldwide living in cities, there is huge demand for connectivity across many different applications. And there are, of course, many competing wireless standards, which all have distinct advantages & drawbacks for different use cases.
This tutorial was originally featured in EPDT's H2 2022 IoT & Industry 4.0 supplement in the December 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.
Here, smart & connected IoT-focused fabless semiconductor company, Silicon Labs will explore one such example, Wi-SUN, a wireless mesh networking technology, and the benefits it brings to a range of smart/IoT applications. We’ll compare Wi-SUN to other wireless standards – and review how it is being used in several European cities, including London and Paris...
Wi-SUN (Wireless Smart Utility Network) is popular in utility and smart city applications, with around 100 million Wi-SUN-capable devices deployed globally. It enables devices such as smart meters and streetlights to interconnect to a common network. Wi-SUN is an open specification, based on IEEE 802.15.4g, as well as other IEEE 802 and IETF standards.
For large Wi-SUN networks, the term field area network (FAN) is used. Wi-SUN FAN is a mesh network protocol, meaning each device in a network can communicate with neighbouring devices. This topology allows messages to travel long distances by hopping from node to node in the network.
Today’s cities typically have thousands of outdoor nodes, both line-powered and battery-powered – including traffic lights, cameras, energy transfer stations, power lines, sewage systems, and more. Every system or device (aka ‘thing’) that operates for the functionality of a city could potentially be treated as a data node.
The Wi-SUN Alliance, which was established in 2011 and now has 300 members, developed and promotes the specification. The Alliance manages the certification process to ensure that devices from multiple vendors conform to the specification and meet the requirements for interoperability.
Figure 1. Wi-SUN in a smart city
Let’s compare Wi-SUN FAN with some other wireless networking technologies. Unlike indoor personal area mesh networks (PAN), such as ZigBee and Thread, the Wi-SUN FAN was designed for a much greater scale of outdoor endpoints, with hops over far longer distances.
Wi-SUN FAN also has the advantage of using freely available unlicensed spectrum, such as the 2.4-GHz frequency, unlike cellular mobile networks, which are owned by licensed spectrum operators.
Wi-SUN FAN devices can be designed for frequent low-latency communication; for instance, set to run at 10 second intervals. The devices use less than 2µA when resting; 8mA when listening; and less than 14mA (at +10dBm) when sending. The low-latency features of Wi-SUN enable on-demand commands, instead of having to wait for the devices to wake and receive or send messages from the network.
As well as Wi-SUN, two of the most popular technologies for utilities, smart cities and the industrial IoT are LoRaWAN (Long Range Wide Area Networks) and NB-IoT (Narrow-Band-Internet of Things), also known as LTE Cat-NB. Wi-SUN FAN achieves higher throughput than either of these alternatives, as it can provide quicker responsiveness and lower network latency in command-and-control applications.
Combined with lower power consumption in sleep and standby modes, this also makes WI-SUN more energy efficient. LoRaWAN and NB-IoT are better suited for applications which requires less frequent communication.
Figure 2. Comparison of Wi-SUN data rates with competing standards
Wi-SUN uses proven enterprise-grade security to reduce the threat from intruders. A key differentiator is the integration of native public-key infrastructure (PKI), which provides security certification capabilities for every device on the network. This is particularly important for devices intended for long-term deployment in the field.
Unlike rival technologies, Wi-SUN also supports IPv6, with all the associated networking security features – such as intrusion detection, traffic shaping, network analysis and penetration testing. This allows Wi-SUN to better mitigate denial-of-service (DOS) attacks, while maintaining network visibility to the level of individual end-devices.
Mesh network improves reliability
A mesh network, such as Wi-SUN, provides better redundancy than a star network, as used by Wi-Fi or LTE, because it has multiple redundant paths from an end-device to the backhaul network, via a router (border router) which links to the internet. If the normal route back to the gateway fails, an end-device has many other pathways available to choose from. In terms of coverage, this topology improves as the size and density of the network increases.
Since a star topology requires end-nodes to have a direct connection to the network, and because many IoT endpoints are stationary (meaning they cannot be moved to find better signal reception), they are prone to obstructions from objects or buildings. Mitigating this requires further investment in base stations.
A Wi-SUN FAN is self-forming, which makes adding new devices to a network easy, and self-healing, so that if a pathway fails, the network will automatically re-route to the gateways. Wi-SUN FAN is also a flexible technology which can adopt a hybrid approach: using a mesh topology in dense networks, such as smart utility meters in a dense urban area; and a star topology to connect assets further out in the field.
Wi-SUN’s mesh network scales in both capacity and size, with its greater bandwidth making it easy to accommodate more data-intensive applications. Wi-SUN performs well in urban and rural deployments, and many networks deploy battery-powered hardware designed for a 15–20-year lifecycle, allowing customers to operate multiple different generations of devices on these networks.
The scalability, performance and reliability of Wi-SUN FAN make it well-suited for dense, low-power outdoor wireless networks. This means it is ideal for smart utility networks and smart cities, which have many common communications requirements, and can therefore be supported by the same networking architecture.
Smart cities can use the existing wireless communications infrastructure provided by Advanced Metering Infrastructure (AMI) or street lighting networks to enable other applications, such as smart traffic signals, public transit signs, parking spaces and electric vehicle charging stations.
Wi-SUN is also a good fit for smart agriculture. The use of IoT in agriculture (smart agriculture or smart farming) has become increasingly important in recent years, making food production more efficient, while also more environmentally sensitive.
Wi-SUN in the real world
In Europe, Wi-SUN has been deployed in multiple cities, including Copenhagen, Paris, Stockholm, Oslo, Bristol, Glasgow and London. One of the biggest deployments is in Paris, where 280,000 connected streetlights have been retrofitted across the city with a Wi-SUN mesh network.
In another major northern European city, a Wi-SUN network has been used to reduce energy costs, increase road safety and promote cycling as part of a citizen health initiative. Wi-SUN-enabled lights and control nodes were used with cameras and noise sensors, to achieve a 60% energy saving for the city’s street lighting, as well as provide nearly 3,000 data sets that can be used by third party developers in smart city applications.
London has also benefited from Wi-SUN. The City of London, the dense financial district also known as the Square Mile, typically has more than half a million people commuting in for work, plus thousands of tourists. The City wanted to add new technologies as part of a renewal of its street lighting, for applications including traffic and parking monitoring, occupancy sensing, environmental monitoring, asset management and, of course, lighting control.
However, the City’s procurement process and trials discovered that its narrow streets and tall buildings made it difficult to find a suitable wireless system. In the end, it chose a Wi-SUN system, which could provide the in-field performance required. In a two-year project, Wi-SUN was rolled out initially to 12,000 street lights, supported by ten gateways. WI-SUN FAN’s self-forming and self-healing capabilities simplified adding devices to the network.
Silicon Labs Wi-SUN solution
To make it easy to begin development, Silicon Labs’ SLWSTK6007A Wi-SUN Wireless Starter Kit provides all necessary tools for developing Wi-SUN wireless applications. The kit is based around the EFR32FG12 wireless System-on-Chip (SoC), and includes sensors and peripherals.
Figure 3. SLWSTK6007A Wi-SUN Wireless Starter Kit
The EFR32FG12 SoC combines a low-power microcontroller (MCU), based on an ARM-Cortex-M4 core, with a highly integrated radio transceiver supporting sub-GHz and 2.4 GHz proprietary wireless protocols and proprietary modulation schemes. It integrates multiple interfaces, including UART, SPI, I2S and I2C, as well as digital-to-analogue and analogue-to-digital converters.
Silicon Labs has also released a Wi-SUN Border Router, which enables robust, long-range wireless communication based on IPv6 Sub-GHz mesh networking. The router helps to reduce time-to-market by speeding up development, certification and deployment.
The number of Wi-SUN FAN certified products continues to grow, and is 40% up compared to last year. In a recent survey by the Wi-SUN Alliance, 87% of organisations said that they are very likely, or definitely going to deploy IoT initiatives in the next 12 to 18 months. Smart city applications are also increasingly being rolled out around the world.
With deployments of smart cities and the IoT becoming widespread, Wi-SUN has an important role to play over the coming years, to provide robust, low-power wireless connectivity in large-scale outdoor applications.
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