Bluetooth mesh: A new backbone option for smart buildings

Bluetooth mesh: A new backbone option for smart buildings

Technology News |
The evolution of intelligent LED drivers is doing more than just enabling control over lighting systems in commercial buildings. Using embedded intelligence in LED drivers has opened up a new strategy for building management. LED luminaires equipped with sensors can form a building management infrastructure capable of managing systems for an entire building. The challenge is communications – what’s the most effective way to link digital lighting fixtures into a single connected infrastructure?
By Jean-Pierre Joosting

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Many vendors are beginning to standardise on Bluetooth mesh as an open and robust wireless approach that can scale to handle control, monitoring and management in any building.

Intelligent LED drivers have become the enabling technology that forms the backbone for smart buildings. Drivers include microcontrollers so they already have the embedded intelligence to customise lighting. For example, they can be programmed to match installed fixtures from different manufacturers by changing light intensity and hue, or can be programmed for specialty applications such as indicator lights.

LED luminaires are ideal for building management since they are the most prevalent electrical devices in any structure. Lights are everywhere in a facility, and when equipped with sensors can monitor building conditions as well as luminaire performance. Sensors can be configured to detect fire, smoke, CO2, specific sounds, and other hazards, including a programmed response to trigger a fire alarm or alert security services. However, to be effective, luminaires have to be connected into a single infrastructure with two-way communications, all manageable from one dashboard or console. This is where Bluetooth mesh plays a role.


Wireless lighting controls save energy

Buildings already are being retrofitted with LED luminaires to save energy – switching to LEDs can deliver an immediate lighting energy savings of up to 75 percent. LED drivers also can be programmed to manage heat and power output for further savings, but it’s impractical to program lights one at a time. You need some form of network infrastructure to centralize lighting control and optimise energy savings.

If wired infrastructure is desired, DALI has been a standard for many years. Lately, Power over Ethernet (PoE) is gaining acceptance to both power and connect LED luminaires. LED lighting can be connected using Category 5 or 6 cable, and PoE lets you eliminate the LED drivers needed to convert DC to AC. While networking luminaires with Ethernet simplifies creation of a building management infrastructure, PoE is really only applicable for new installations; few would want to rewire an entire building with Ethernet cable as part of an LED retrofit project.

If wired networking solutions are impractical, wireless connectivity is more than viable. LED lighting manufacturers have started to successfully implement Bluetooth mesh to create an interconnected lighting system. SIG-qualified Bluetooth mesh is an open standard so vendor interoperability is assured, it’s scalable, and mesh topology is robust with built-in failover.


Bluetooth mesh for wireless controls

Bluetooth and Bluetooth Low Energy (BLE) each communicate by sending short wireless bursts of data. Bluetooth mesh expands this communications infrastructure to hundreds or thousands of devices or nodes that share connections with other devices in the same vicinity.

Bluetooth was originally developed for point-to-point connectivity, but Bluetooth mesh uses a flood network strategy that provides many-to-many connections, communicating with all the nodes within range all at once. Though there are limits to the number of nodes data will transverse, every incoming packet is broadcast across every outgoing connection. The result is a lattice or mesh capable of sharing data at rates up to 1 Mb/s. And since it is a mesh framework there is no single point of failure; if one node fails the data is automatically rerouted over another path. It also makes it easy to add and remove nodes without disrupting connectivity (see figure 1).

Figure 1: Bluetooth Mesh Topology.

For smart lighting and building controls, Bluetooth mesh has the added advantage of two-way communications, so devices can be commissioned and tuned as well as monitored. Bluetooth sensors are installed in strategically placed smart LED fixtures, they join the network and report data back to the centralised system or dashboard.

Using smart LED drivers as Bluetooth mesh nodes you can create a building-wide infrastructure to monitor and control a facility by area or by circuit by mixing a few smart LED drivers and dumb drivers.


The anatomy of Bluetooth mesh

Security cameras, environmental sensors, and luminaires that require more power can be wired into the central power system and readily incorporated into the Bluetooth mesh infrastructure. And since BLE is low power, some types of nodes can also run off of batteries, which can be useful for hard-to-wire lighting installations or applications.

Bluetooth mesh nodes can be programmed for various complex tasks. There are four common node features:

  1. Low-power feature – Power-constrained nodes, such as those running on batteries can be configured to conserve power by reducing radio broadcast time.
  2. Friend feature – If nodes don’t have power constraints they can be designated friend nodes that store incoming messages, security updates, and other data to be shared with low-power nodes.
  3. Relay feature – Relay nodes are extremely useful for scaling Bluetooth mesh networks, rebroadcasting messages so they can be shared from node to node.
  4. Proxy feature – Proxy nodes transmit and receive packets between Bluetooth Generic Attribute (GATT) and Bluetooth mesh nodes.

Each node has one primary element plus additional elements, each with specific entities that define its function (see figure 2). A LED light, for example, can have one element and multiple functions, on/off, brightness, colour temperatures, etc.

Figure 2: Structure of Bluetooth mesh node.

Bluetooth mesh also communicates via a client/server architecture with three different communications models:

  • The Server Model is composed of one or more states with one or more elements to define their behaviours. For example, there could be an on/off switch state, a sensor state for temperature or ambient light, or a power level state from 1 to 10.
  • The Client Model defines the set of messages used by the client, such as sending a message reflecting on or off or showing power level 1 through 10.
  • The Control Model has multiple functions and applies control logic. For example, to cool a device, a sensor records the operating temperature and the client to the temperature sensor accepts a specific value. If the temperature is above a pre-set threshold, it activates a server request to turn on the cooling system. The control logic defines the rules of operation.

For data communications, Bluetooth mesh can handle data packets up to 384 bytes, but for machine-to-machine (or luminaire-to-luminaire) communications most messages will fit in an 11-byte frame. The packet starts with one byte of opcode for special messages, then includes 2 bytes for standard messages or 3 bytes for vendor-programmed messages. Each Bluetooth packet also includes a source and destination address, as well as sequence numbers to prevent replay attacks.

Bluetooth mesh also uses control messages and access messages. Control messages manage the operation of the network, such as sending heartbeat or friend requests. Access messages are used to allow clients to retrieve state values from the server. The opcode in the packet identifies the operation of the message, such as identifying the state (e.g. on or off), or setting the state parameters (e.g. target value such as on/off, transaction identifier, transaction time, delay, etc.).

Security is strongly addressed in Bluetooth mesh. Every message is encrypted using NetKeys and authenticated with AppKeys. NetKeys function at the network layer (assuming there are no subnets and all communications uses the same NetKey). AppKeys function at the application layer and are therefore associated with different applications. For example, AppKeys could be used for building security, HVAC, or lighting. Relay nodes, such as wall switches or LED lights, would have NetKey access but would not have AppKey access for restricted areas so they could not decrypt the application data.


Applying Bluetooth mesh models and states

As you can see, Bluetooth mesh has a well-defined, secure two-way communications structure that makes it ideal for building and lighting control. Once LED luminaire sensors are in place, Bluetooth mesh can be used to monitor and instruct sensors for a wide range of building operations, such as lighting, HVAC, security systems – any machine-controlled application.

Every Bluetooth mesh node has its basic functionality defined and implemented by models that operate as a subset of the primary element described above. Every element has to have one or more instruction models that define the functionality of the specific node while stating the condition of specific elements. This is where true monitoring and management takes place (see figure 3).

Figure 3: Models function as a subset of nodes.

With our LED light example, the model function could be on/off and brightness with associated states of on or off and 0-10 (similar to dim levels with 0-10v dimming). Bluetooth mesh also supports composite states of two or more values. For example, LED hue may change independent of brightness, which enables more complex sets of instructions. Every model has a unique address consisting of 16 bits (as defined by the Bluetooth SIG), or 32 bits (which include 16 bits for a vendor identifier), therefore each model has a unique address.

With a wireless network of smart LED drivers in place, you have the physical infrastructure capable of managing an entire building. And Bluetooth mesh has the versatility to monitor virtually any device and issuer controls to address most building conditions. The combination of an LED driver ecosystem with Bluetooth mesh-enabled building controls promises to become the endoskeleton of building monitoring and management systems, empowering smart buildings for years to come.

 

About the author:

Russ Sharer is Vice President of Global Marketing and Business Development for Fulham – www.fulham.com

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