From Nordic Semiconductor: The promise of wireless mesh
Understanding how to deliver successful products that take advantage of the latest technology is particularly challenging when that technology is as complex as wireless mesh networking. These networks are finding favor in situations where many devices need to be monitored and controlled, and where universal accessibility is preferred over dedicated user interfaces. Typical applications include home automation, industrial wireless sensor networks, and building management.
One way to get to grips with mesh networks’ complexity is to imagine that, unlike, for example, a star topology where individual nodes communicate solely with a central hub, every node in a mesh network is directly or indirectly connected to every other node. In most practical implementations, nodes send data to each other via other nodes that provide simpler routing. Typically, there’s more than one way for each node to send data to another; automatically building in redundancy. Redundancy improves network reliability.
Smart home applications benefit from mesh networks. For example, smart lights connected in a mesh network allow a consumer to connect to any light in the network via a smartphone, hub, or remote control, and send commands to control the status, intensity, and color of any other light in the network while receiving status information back.
When such technology becomes commonplace, wired wall switches would go the same way as landline wall sockets.
Ultra low power wireless protocols such as ANT or Bluetooth low energy are among the technologies upon which mesh networks are based. Wireless connectivity solutions such as Nordic Semiconductor’s nRF51422 or multiprotocol nRF52832 Systems-on-Chip (SoCs) allow developers to embed either protocol (or a proprietary 2.4GHz protocol if preferred) into their smart home products.
And if required, ANT or Bluetooth low energy connectivity to a Wi-Fi hub device enables Internet connectivity allowing the consumer to control their system while away from home.
Building in reliability
To ensure long-term network reliability and ease of operation, designers need to consider adding self-forming and -healing capabilities to the mesh network. Self-forming refers to the ability of each new node (for example, an additional smart light) to detect nearby nodes and either join the existing mesh network, or initiate the formation of a new network without requiring input from the user. In the above example, this would mean that the user could install one or dozens of smart lights in their home, and then sit back and relax while the smart lights search for and discover each other, and form connections automatically. Self-forming networks simplify installation and eliminate the need for a user to understand how the lights communicate.
Self-healing refers to the ability of the network to continue to operate while one or more nodes are inoperable, and/or while certain wireless links are blocked. For example, a self- healing network would respond to a broken light by sending messages via another smart light instead. Similarly, if one smart light lost its connection to another (perhaps due to interference, or an obstruction), a self-healing network would reroute to send messages between these two lights via other smart lights.
A bonus is that the user could immediately be informed about failed nodes, something which could be particularly useful if the node was, for example, intended as an external security illumination.
Home security could be improved by networking lights in a neighboring building so that they switched on to illuminate an area left dark by the failure of the nearest light. Additional layers of control would be needed for such a system as nobody wants a neighbor accidentally dimming lights which don’t belong to them.
Simple but complex
Well-designed mesh networks are simple for users to control but delivering this simplicity is not easy, and requires a detailed analysis of how, when, and where communication within the network will occur. Allowing the user to connect to the network at any point, possibly at the same time as other users, complicates firmware design. For example, in a mesh network messages travelling in a certain direction can’t be prioritized as there is no built-in hierarchy.
As multiple users need to be able to control the lights in a typical home, conflicting commands could be simultaneously issued leading to unpredictable results - depending on the path each command takes through the network. The lack of constraints inherent to mesh networks creates “edge cases” that need to be handled, and the difficulty of predicting these extends the time required to test mesh network designs.
At the most fundamental level, designers need solutions that ensure important messages reach their destination(s) within the network. This requires defining an addressing scheme to identify each node; using acknowledged messages and retries as needed; and handling command prioritizations and timings to achieve synchronized responses when appropriate.
There are several commercial technologies available for mesh networking, some based on proprietary technologies, others based on standards such as IEEE 802.15.4. Engineers can even select turnkey solutions such as SecuRemote Smart, by Delphian Systems, which facilitates the building of Nordic nRF51422 ANT SoC-based mesh networks of up to 250 devices.
The Bluetooth Special Interest Group (SIG) has announced plans to launch Bluetooth mesh—a standards-based mesh networking technology—soon after the release of Bluetooth 5, the next version of the technology slated for imminent release. Bluetooth mesh will make it much easier to build networks with Bluetooth technology. Smart lighting company Gooee has already introduced an Internet of Things (IoT) sensor platform based on its interpretation of a Bluetooth mesh (ahead of the formal release of the technology).
Until Bluetooth mesh is formally introduced, ANT has the edge on Bluetooth technology. ANT provides the most flexible capabilities per node, allows developers to configure each node as both a master and a slave, and optionally runs a background scan at the same time. IEEE 802.15.4-based technologies such as ZigBee and Thread, were purpose-built for forming mesh networks, but can require significantly more power than Bluetooth low energy and ANT (depending on the configuration).
ANT has well-developed reference designs to simplify implementation of mesh-like topologies including auto- shared channels that can be controlled by multiple remotes. This topology includes a defined hub, which acts as the relay between controllers and sensors. Connecting several networks together via the hubs results in a close approximation of a mesh network as perceived by the user.
Using ultra low power wireless protocols to implement mesh networks allows for products that need not rely on continuously available Wi-Fi connections. It also allows for minimal power usage to operate the network, which in turn can allow for reasonable operating windows when relying on battery power, and allowing nodes to be completely wireless.
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