An Introduction to Bluetooth Mesh Networking
In this article, you'll get a general understanding of Bluetooth mesh, its topologies, applications, and advantages.
In the context of the Internet of Things (IoT) wireless connectivity, mesh networking capability has been a highly anticipated addition to the Bluetooth standard. Mainly because this feature can extend the coverage range, as well as the use cases, of Bluetooth networks.
The Bluetooth Special Interest Group (SIG) introduced Bluetooth mesh in 2017. Now with the mesh option, Bluetooth looks set to be able to compete with other mesh-capable standards such as ZigBee and Thread.
BLE Mesh Networking
In a previous article, we discussed that mesh networks can provide multiple paths for data packets and make the network more resilient in comparison to a star topology.
Since the nodes in a mesh can act as repeaters, the range of the network can be extended beyond that of a single radio. Due to these advantages, wireless communication protocols that are designed for IoT applications have included mesh networking capability in their standards to enable scaling the network geographically through multi-hop operations.
For example, the networking layer of Zigbee has been designed with an eye on mesh topology requirements from the ground up, though Zigbee also supports star configuration.
BLE (Bluetooth Low Energy), which is now a common option for IoT applications, started to support mesh networking in 2017. A high-level example can be seen in Figure 1.
Figure 1. An example of a BLE mesh network. Image used courtesy of Integra Sources
Unlike Zigbee and Thread, BLE is a latecomer to the mesh networking competition. This should come as no surprise because the original version of Bluetooth was designed as a cable replacement for short-range communications rather than a connectivity solution for sensor-dense environments of IoT applications.
In fact, the original version of Bluetooth, which is now commonly referred to as Bluetooth Classic to distinguish it from BLE, was designed to replace RS-232 cables. Later, it attracted more and more attention due to use cases such as hands-free phone calls with headsets and music streaming applications.
The mesh option extends the coverage range and enables the deployment of BLE in IoT applications such as home automation where communication between devices separated by several walls is commonly required.
Extending BLE Application Range
In addition to extending the coverage range of the network, mesh capability also facilitates the implementation of certain IoT applications by enabling many-to-many communications. A non-mesh version of BLE only supports one-to-one and one-to-many communications as shown in Figure 2.
Figure 2. High-level representation of one-to-one and one-to-many communication
A familiar example of one-to-one communications is wireless audio streaming where two devices are connected to each other. A BLE beacon operates in a one-to-many topology (shown in Figure 3), which we’ll dive into how the communication is established in a later article.
Figure 3. Many-to-many communication facilitates many IoT applications
Generally speaking, beacons are small wireless devices that repeatedly transmit a constant signal that can be received by nearby BLE receivers. Beacons can be used to provide customers with useful information about different products in retail. For example, BLE beacons can be deployed in a shopping mall to advertise discounts to customers. Indoor positioning systems that can locate users inside large buildings are another common application of beacons.
In addition to one-to-one and one-to-many communications, many IoT applications also require many-to-many communications. As an example, consider the home automation use case where several light bulbs need to be controlled using multiple mobile phones. The light bulbs should also respond to commands from a dimmer and/or an occupancy sensor. This requires many-to-many communications, which are inherently provided by a mesh topology.
Mesh capability expands the use cases of BLE and allows it to be employed in applications with completely different forms. Smart homes/offices and industrial control are some of the common applications that need many-to-many communications.
Do We Need a New Mesh Protocol?
One might ask: why do we need a new mesh-capable connectivity solution if protocols such as Zigbee and Thread already support mesh topology?
Many basic features of mesh networking are supported by all of these three protocols. For example, they all include the ability to self-heal, meaning that if a node is disabled or removed, the network reconfigures automatically to repair itself.
However, there are major differences between these protocols. For instance, Bluetooth mesh uses a technique known as managed flooding to route data packets through the network where messages are simply broadcast to all nearby nodes, while Zigbee and Thread use the full routing technique in which. a specific path is chosen for the messages going from node A to node B.
Such differences can have a significant impact on the network performance depending on the application requirements and conditions. Evaluating certain aspects of the Bluetooth mesh technology, such as the network latency, reliability, scalability, etc., might not be straightforward in some cases. Some research papers examine these characteristics and portray a mixed picture of the protocol's performance.
We’ll discuss some of these details in the next article. Below, some of the unique advantages of Bluetooth mesh are discussed.
Note: that the concept of IoT is applied to a wide variety of application scenarios. None of the connectivity solutions can serve all applications well. Depending on the requirements, a particular protocol might be a better fit than the others.
Some Unique Advantages of Bluetooth Mesh
Bluetooth mesh is built on top of the BLE stack (Figure 4 below) and uses the same physical and link layers.
Figure 4. Protocol stack of Bluetooth mesh. Image used courtesy of Aijaz et al
Most smartphones, tablets, and laptops have built-in BLE chips and require only a software update to support Bluetooth mesh. Smartphones with BLE chips can use the mobile applications provided by companies such as Cypress Semiconductor and Silicon Labs to set up Bluetooth mesh networks and control network devices.
Any smartphone with Bluetooth 4.0 or later can monitor and control mesh-connected nodes. Due to this prevalence, the deployment of Bluetooth mesh networks can be more convenient than other similar technologies. For example, most phones and tablets don’t have a ZigBee chip, and hence, you’ll need an additional dongle or gateway between your control device and the Zigbee network.
Another unique feature of Bluetooth mesh is that it supports beacons. Therefore, a Bluetooth mesh network can be used for multiple purposes. For example, a lighting system that uses Bluetooth mesh can also support applications such as asset tracking and indoor positioning, and navigation.
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