Bluetooth Low Energy (BLE) technology is a dominant player in the IoT space. Applications such as smart homes, telemedicine, and asset tracking all benefit significantly from BLE’s low power capabilities. However, BLE communication between devices has been limited to one-to-one or one-to-many. In addition, BLE implementation is difficult due to limited communication range, especially in complex environments such as homes where there may be multiple walls between devices. These factors make it impossible to control the entire home environment from a single location.
Many-to-many communication is required when nodes need to receive messages from and send messages to multiple devices.
For example, a group of four light bulbs needs to be controlled by multiple phones.
In addition, they need to receive setup messages from dimmers and/or occupancy sensors.
This requires many-to-many communication.
In order to maximize the effectiveness of BLE in application scenarios such as smart homes, smart buildings and smart cities, developers need to not only achieve many-to-many communication, but also develop advanced technologies that can extend the communication distance and support some devices to run on small batteries.
BLE Mesh (Bluetooth Mesh) can solve these problems.
Bluetooth Mesh is emerging as the technology of choice for home automation because the Bluetooth Mesh network can be accessed directly from a phone or tablet without the need for a gateway.
Interoperability is key to success for any smart home deployment, as a smart home may use products from multiple vendors.
Using standard message formats for a given use case (mode) allows for rapid deployment and ensures interoperability with other BLE Mesh products.
This five-article series discusses the key concepts needed to understand Bluetooth Mesh. We will focus on Bluetooth Mesh's low-power capabilities, privacy and security features, and how to choose devices for your smart home application. The
first article in this series discusses the building blocks of a Bluetooth Mesh network
.
A Bluetooth Mesh network consists of nodes with various types of characteristics.
Figure 1 is an overview of a Bluetooth Mesh network.
From this figure we can see that its nodes have the following types of characteristics:
Figure 1: Bluetooth Mesh Network
Each node can support one or more feature types.
For example, the R+F node in this network supports the relay feature and the friend feature.
Similarly, the R+P node supports the relay feature and the proxy feature.
Relay feature
Allows nodes to pass messages across the advertising bearer. In general, every AC powered node is likely to offer the relay feature, as they have the power to continuously listen for advertising packets and forward them to other nodes. Real use cases for the relay feature include smart lights or AC powered light switches in home automation applications. On the other hand, nodes running on small batteries may not have the relay feature, as the relay feature requires the Rx to be constantly on for the device to hear the advertising packets. This will quickly drain the battery.
Low power node feature
One of the most critical features of Bluetooth Mesh. Unlike relay nodes, low power nodes do not need to continuously listen for broadcast packets. Low power nodes spend most of their time in low power mode, with their friends receiving messages on their behalf. Low power nodes wake up at regular intervals, connect to their friends, and check if there are any pending messages. After communicating with their friends, low power nodes return to low power sleep. This is a very useful feature for battery-powered applications. Applications such as sensor nodes in home automation and price tags in retail stores can benefit from low power features.
Nodes with
the Friend feature
listen to any messages forwarded in the network and can listen on behalf of the associated low-power node. The friend node stores these messages. When the low-power node wakes up and queries the friend node, these messages are passed to the associated low-power node. Because the friend node needs to store messages for one or more low-power nodes, the friend node uses more memory than other types of nodes. The amount of memory required depends on the amount of data/commands that need to be stored in the friend node and passed to the low-power node in the polling operation.
Proxy feature
Allows devices such as smartphones and Wi-Fi Bluetooth Mesh gateways to communicate with the Mesh network. For devices that do not directly support Bluetooth Mesh, nodes with the proxy feature are their entry point into the Mesh network. In a Bluetooth Mesh network, messages are forwarded via the advertising bearer layer. The proxy feature allows nodes to forward messages between the GATT (Generic Attributes) layer and the advertising bearer layer. Multiple nodes in a Bluetooth Mesh network are allowed to support the proxy feature. Any node that supports the proxy feature can be used as an interface for smartphones/PCs to connect via GATT. It is a good idea to have multiple proxy nodes so that if one proxy node fails, the entire network will not be disconnected from the proxy device. This feature makes Bluetooth Mesh more reliable than other Mesh technologies such as ZigBee.
In a Bluetooth Mesh network,
configuration
is the process of adding new nodes to the network.
Configuration requires multiple steps to ensure that unrelated devices are not configured into the network.
Unconfigured devices send beacons at predetermined intervals.
After discovering and selecting an unconfigured device, the configuring device initiates the configuration process.
In the example shown in Figure 1, a smartphone and a tablet act as configuring devices in the network.
According to the Bluetooth specification, not all nodes are mandatory.
In other words, a device can be certified for Bluetooth Mesh even if it does not support all node/feature types.
Typically, chip device manufacturers do not support friendly node and low-power node features certified by the Bluetooth SIG.
This makes it difficult to support battery-powered Bluetooth Mesh applications.
To find out which Bluetooth Mesh nodes/feature types are supported by a Bluetooth Mesh device, visit the Bluetooth SIG website and click “Find a Product”, enter the product you want to find out which nodes/feature types are supported.
For example, if you want to know
the node/feature types supported by the
Cypress Bluetooth Mesh module
CYBT-413034-02
, enter the part number in the product search and the product's Declaration ID, QDID, Company, Product, Specification Name, and Release Date will be displayed.
Click on the Declaration ID, which is D040142 in this case.
The page displays a list of layers supported by the device.
Then click "View ICS Details".
A list of core protocol layers, configurations, and services will be displayed.
You can click on any of these to see the supported features.
If Mesh configuration is supported, it will be listed under Legacy configuration.
Now click on MESH (Mesh Configuration).
This will provide a list of roles and versions, the node role requirements, and whether the feature is supported.
If we look at the description of CYBT-413043-02 in detail, according to the following screenshot obtained from the Bluetooth SIG website, according to the information listed under "Role", the module supports both the node role and the configurator role (see Figure 2).
According to the information listed under "Network Layer Function", it also supports the relay feature (see Figure 3).
According to the information listed under "Upper Transport Layer Function", it supports the friend feature and the low power node feature (see Figure 4).
According to the information listed under "Proxy Function", it supports the proxy feature (see Figure 5).
While the device supports all of these node feature types, it is important to note that most of these node types are optional according to the comments.
For example, the Relay, Friend, and Low Power node features are optional with the prerequisite of supporting the Advertising Bearer layer.
However, for efficient Bluetooth Mesh networking, all of the above feature types are required.
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