Zigbee or Bluetooth Mesh: Which is right for your application?
Mesh networking is a useful technique for extending the range and capability of a network. Wi-Fi relies on a central router with a limited range, which all network traffic funnels through. One can extend a Wi-Fi network using repeaters or access points, but those still must push traffic back through the router before it can reach another device on the network or the outside internet.
A postal comparison
Even if two Internet of Things (IoT) devices are in close physical proximity, they must communicate through the Wi-Fi router. It’s akin to mailing a letter to your next-door neighbor. A postal worker picks up the letter and takes it to a processing facility, just for another postal worker to take it right back where it started.
Mesh networking is like walking next door and handing the letter to the neighbor yourself. Both you and your neighbor are nodes in the network and can communicate with each other without going through a central router. If you're sending a letter to a neighbor down the street, you can hand it to your next-door neighbor, who hands it to their next-door neighbor, and so on.
At some point, such as if the letter must reach the other side of town, this delivery method becomes inefficient. Abandoning the postal analogy, mesh networking is ideal for applications with many nodes. It is trivial to add or remove nodes from the network, so long as no individual node is too far from another. Each node receives the data packets addressed to it and data can reach the internet through a gateway.
Mesh networking options
There are several mesh networking protocols available today, but two of the most popular for IoT applications are Zigbee and Bluetooth Mesh. Both have advantages and disadvantages, but engineers must decide which to use when building a new network. In this article, we will explore some of the factors that can help with that decision.
The Zigbee Alliance released the official IEEE 802.15.4-2003 Zigbee specification in late 2004. Since then, the specification has seen many revisions. There are currently 300 million deployed Zigbee nodes, making it the most popular mesh networking protocol in use today.
Bluetooth Mesh is much newer. The Bluetooth Special Interest Group (SIG) released the standard in 2017. Bluetooth Mesh is based on the well-established Bluetooth Low Energy (BLE) protocol, but the mesh capabilities are still in their infancy.
A technology’s maturity is important for three reasons. The first is that all new technologies have bugs and kinks that take time to work out. The second is that documentation becomes more comprehensive as time goes by. The final reason is that compatible hardware needs time to come to market.
Zigbee’s maturity adheres to the first two of those three, but hardware compatibility is a different story. There are many dedicated Zigbee microcontrollers and SoCs (system on a chip), but Bluetooth Mesh works with the same BLE hardware that is already widespread today.
Frequency, range and mesh network size
This leads us to the first big point scored by Bluetooth Mesh. Both Zigbee and Bluetooth Mesh work license-free in the 2.4GHz spectrum worldwide, but a wide range of devices have BLE, and therefore Bluetooth Mesh, capability. That isn’t true for Zigbee. This means that a Zigbee mesh network needs a gateway to communicate with most other devices, like smartphones.
Zigbee and Bluetooth Mesh networks have similar range limits between nodes — 10 meters to 100 meters, depending on conditions. But Zigbee can support more nodes in a mesh. Bluetooth Mesh has a theoretical limit of 32,000 nodes, while Zigbee has a theoretical limit of 65,000 nodes.
That means that a Zigbee mesh network can, in theory, cover twice as much area. But in practice, it is likely that other practical concerns will limit the size of your network before you get anywhere close to reaching the maximum number of nodes supported by either protocol.
Power consumption and sleep modes
Power consumption is a practical consideration that engineers must consider, particularly when nodes are battery powered. All Zigbee and Bluetooth Mesh nodes acting as routers must be active to move data across the mesh. End devices in both protocols, however, can sleep if they don’t need to participate in the mesh. When active, Bluetooth Mesh nodes require less power than Zigbee nodes.
A more important limitation is the data rate of each network. Here, Bluetooth Mesh wins again — at least at first glance. It has an air data rate of 1Mbps. Zigbee’s air data rate is 250Kbps. But air data rate alone is misleading since data hops between several nodes. The path that data follows through the mesh network determines data transfer efficiency.
Mesh network architecture varies, even when using a single protocol. Both the physical location of the nodes and the logical structure of the network determine the architecture. The latter is configurable. If, for example, end devices need to sleep, a Zigbee mesh network can utilize several router nodes near clusters of end device nodes. If power consumption is not a concern, far fewer router nodes are necessary.
A great hardware choice
While Zigbee and Bluetooth Mesh networks are distinct, they have more similarities than differences. Both are great options, which is why it is fortunate that you don’t have to choose between them. Modern hardware, like STMicroelectronics’ STMWB55 series of SoCs, supports both Bluetooth Mesh and Zigbee mesh networking.