Almost everyone who uses a smartphone or computer has already had something to do with Bluetooth®. The wireless standard connects headphones and speakers, keyboards and mice with screen devices. Where cables used to be necessary, a radio signal is now sufficient. The big advantage: Every smartphone masters the technology and can put Bluetooth devices into operation.

This also makes the standard interesting for use in buildings – because no infrastructure, no Wi-Fi and no hubs are required for installation. The smartphone is all that is needed. However, not all Bluetooth is created equal

BLE paved the way for Bluetooth in buildings. Apple, for example, used the technology to control lamps, sockets, thermostats, and even door locks in its HomeKit solution.

The limited radio range turned out to be a disadvantage. It is rarely more than ten meters indoors – enough to switch the ceiling light, but too little to be able to route signals to the other end of a residential or office building. Additional Bluetooth hubs along the way had to increase the BLE range.

Chip manufacturers and building technology providers therefore began to look for another solution to the problem. They developed Bluetooth systems based on the mesh principle. Devices form a common network in which radio signals interlock like the mesh of a fabric. Commands can jump from one node to the next to reach even distant destinations.

There are virtually no limits to the size of this mesh network. It can contain up to 32,000 nodes. The devices are assigned different tasks. The standard distinguishes between four functions:

• Low Power nodes form the end points within the network. They sleep most of the time and require hardly any energy in this idle state. They only wake up briefly for actions and send a signal. Typically, these are battery-powered devices such as motion detectors, temperature sensors or wireless pushbuttons.
• Friend nodes establish a connection to end points. They constantly listen to the network and collect messages for their associated low-power nodes. When one of them wakes up, it radios its friend node and asks what’s new. To perform these tasks, friend nodes are connected to the power grid, for example as a flush-mounted module, light or other 230-volt device.
• Relay nodes have the task of forwarding signals in the mesh network. They constitute the central nervous system of the installation. They can be Friend Nodes with additionally connected low-power devices or pure relay stations. Every powered Bluetooth mesh product may also be a Relay Node at the same time.
• Proxy nodes play the role of intermediary: A device with a proxy function serves as an interface between the mesh network and other devices that do not support Bluetooth Mesh themselves. This can be a smartphone, but also an older sensor that is still based on Bluetooth Low Energy. For example, the BLE sensor can be connected via a mesh-enabled light bulb. The light bulb translates the messages from one standard to the other and enables communication.

The entire network is designed to heal itself if a node fails. Since messages do not follow fixed routes, but are spread across the entire mesh (flood messaging), they reach their destination even if the connection is interrupted at one point.

Security and encryption

When designing Bluetooth Mesh, the Bluetooth SIG placed great emphasis on the security of the network from the outset. All data packets are highly encrypted and obfuscated in such a way that even attackers who might eavesdrop on a packet do not know which device it came from. There are no identifiable values such as source or destination addresses.

Neighboring mesh networks are not a problem because each data packet has an identifier of which network it belongs to. Devices from one Bluetooth mesh can neither decrypt nor authenticate the other’s data and do not forward it. Adding new devices is done under strict security conditions with encrypted signals.