Mesh Networking, the Critical Open Sesame for Smart Lighting Success

Owners of homes and small buildings are receptive to the benefits of smart technologies like automatic light activation and dimming, which offer improved comfort and convenience as well as utility bills. The home automation market is tipped to exceed $16 billion by 2019. Easy upgrading with minimal disruption or costly rewiring, ideally feasible as a DIY project or using a local installer who does not need specialist IT or smart-building knowledge, will be critical for widespread adoption. Standards bodies have recognized the importance of simplifying processes such as setting up networks and adding new devices, and are introducing standards that minimize the technical expertise required for commissioning and maintenance.

The ZigBee® Alliance, as one example, introduced the ZigBee Light Link (ZLL) profile to provide a standard that focuses more sharply on entry-level smart lighting opportunities and is easier to setup and use than other profiles such as ZigBee Home Automation (ZHA). ZLL implements coordinator-less commissioning that simplifies initial network setup and addition of extra nodes. Common lighting devices and controllers are supported, such as dimmable lights, color lights, and color or scene controllers, while extensions to the ZigBee Cluster Library enhance support for actions such as setting up scenes and controlling color. In the absence of a trusted coordinating device, nodes remain secure by exchanging a network key encrypted with a ZLL master key.

Like the Home Automation profile, ZLL runs on top of the ZigBee PRO wireless network protocol, which has important strengths for home automation and smart lighting. These include low power consumption, as well as support for peer-to-peer mesh connectivity that enables robust fault-tolerant wireless communication throughout networks that extend over large distances.

While low power consumption and the robustness and extended range inherent in mesh networking deliver obvious advantages for smart lighting in homes or offices, another feature that is increasingly expected is the ability to adjust settings using a mobile phone either from within the premises or from a remote location via the Internet. This is not only convenient for users, who tend to carry a smartphone easily to hand, but can also save product vendors the additional overhead of having to build and ship a dedicated controller.

To use a smartphone for controlling devices such as light switches or drivers that are connected to a ZigBee network currently requires the user’s instruction to be routed through the Internet and into a gateway to the ZigBee network. This can introduce a delay in the system response that may not be noticeable when changing a setting such as a thermostat set point but can be unacceptable when trying to turn on lights upon arrival in a darkened room or optimize dimming in time for a favorite television show.

Bluetooth® Low Energy, or Bluetooth Smart, has a number of strengths that could allow it to provide a suitable alternative. A Bluetooth-enabled mobile can be connected to Bluetooth Smart devices in the building without going via a gateway. Since Bluetooth is already supported on more than 90% of smartphones in the field, a large potential user base already exists. This could grow even further, as ABI Research has predicted there will be 10 billion Bluetooth devices in the market by 2018. On the other hand, Bluetooth’s limited range and conventional master-slave communication model are too restrictive to allow a user to control any device from any location within a building. The limited range could be particularly challenging in large buildings such as offices or industrial sites.

Multi-hop communications provide one way of extending the effective wireless range, and this has been achieved with the introduction of Scatternet support in Bluetooth Low Energy since version 4.1. Scatternet allows a device to act as a master in one domain while simultaneously acting as a slave in others. It can thus receive a message from its master and relay the message to its own connected slaves. Although this can allow networks to extend over a longer range, message propagation remains relatively formal and cumbersome.

Some technologies have emerged that enable mesh-type networks to be established using Bluetooth technology. By allowing devices within the network to relay messages between each other, mesh networks are able to extend over areas that are much larger than the maximum point-to-point range of the chosen wireless technology. Among these, CSRmesh™ by Cambridge Silicon Radio enables devices to interact on a peer-to-peer basis avoiding many of the overheads associated with master-slave communication.

Adding Mesh to Bluetooth

A mesh network can operate according to a number of principles. Messages may be routed from one device to another following a specific path to reach the desired destination. However, although Bluetooth Smart was conceived to be the lowest power radio on the market, the memory and processing required to manage this routing can drive up power consumption. This is undesirable in smart lighting, and IoT applications in general, which usually require nodes to operate for periods of months or even years from a small battery without needing maintenance. 

CSRmesh avoids the overheads associated with routing by using a flooding approach. In this case every message is sent to every device within range. These devices, in turn, relay the message to other devices in range. Unlike the case of a network with routing nodes that must be listening and receiving most of the time, the sensors of a flood mesh only wake when they have data to send. Although devices need to wake periodically to scan, a network that contains many nodes that are capable of repeating messages can tolerate a lower scan rate to minimize power consumption. In addition, some devices can exist as passive members of the mesh. This can give network planners extra flexibility to maximize the battery life of nodes such as light switches by configuring these devices to act only as originators and never to listen for messages. They will not be able to forward or relay messages for other nodes, but can operate for many years on a coin cell.

Since there is no concept of routing or coordinating devices in a CSRmesh network, each node is built using a Bluetooth Smart SoC such as a CSR1010 wireless transceiver or other CSR101x family device. This puts enough intelligence in the node to provide additional functionality at no extra cost in terms of the price or power of additional devices such as dedicated sensors. Direct connectivity with the user’s smartphone, for example, makes it possible for devices to be activated by proximity without requiring additional sensors. This could be used in a domestic setting, for example to turn on a porch light as the homeowner approaches the front door, or in a commercial building to activate lights or door locks as a recognized user moves along a corridor.

Because the mesh network can operate without a gateway or Internet connection, there is no single point of failure between the smartphone and the network. Moreover, CSRmesh features lightweight addressing that relieves the burden of running more complex firmware. If the controller is required to operate the lights remotely, a gateway is needed as with any other Internet-based control strategy.

Since originally launching the protocol for lighting applications, CSR has recently introduced CSRmesh Home Automation with extra sensor and actuator models that allow developers to create solutions that can control heating, ventilation, air conditioning, door locks and window sensors in addition to lighting. Home Automation also allows developers to tune the scan rate of nodes in the mesh network, to further extend battery life. Security precautions including an encrypted network key prevent interference and attacks.

Figure 1: The CSRmesh board helps create smart lighting and other home-automation products.

A CSRmesh development board containing an RGB LED and dimmer pushbuttons (Figure 1) allows a quick start for developing CSRmesh applications such as lighting, home automation or sensor networks. Three of these boards are included in the CSRmesh Development Kit, which also provides a software development environment, example applications for the development board, and example host smartphone apps with Android and iOS® source code. Details of a support package created by CSR partner Avi-on provides further insight into developing home-automation products using CSRmesh. The package includes plug and play firmware, a home-automation smartphone app (Figure 2) that can be downloaded from the Apple App Store or Google Play, and a pre-certified module based on the CSR1010.

Figure 2: The Avi-on app is one of the first to control home automation directly via CSRmesh technology.

CEL (California Eastern Laboratories) is using the CSR1010 transceiver at the heart of its B1010SP0 MeshConnect™ mini modules that support the CSRmesh protocol and provide a low-risk Bluetooth Smart solution suitable for use in mesh networks. The modules are footprint-compatible with ZigBee and Thread-based Modules by CEL, and can be used with CEL’s Cortet™ IoT software and mobile app. The modules simplify hardware design by integrating key components as shown in Figure 3. Development can take advantage of the µEnergy Starter Development Kit, which contains CSR’s µEnergy Platform software and CEL’s hardware components and documentation that enable a fast design start.

Figure 3: CEL’s MeshConnect modules simplify development based on CSRmesh and the CSR1010 transceiver.

Standardization in progress

A logical next step for Bluetooth mesh networking is for the Bluetooth SIG to standardize a protocol. This should help to promote the use of Bluetooth in smart-building applications. The SIG has been working towards this objective since 2015, when it appointed the Bluetooth Smart Mesh Working Group. A number of proposals have been under consideration, including CSRmesh, and the SIG should be ready to adopt profiles soon.

Perhaps anticipating a favorable industry response to the standardization of Bluetooth Mesh, ON World has projected that Bluetooth will surge from 7% of residential unit sales in 2014 to become the second largest smart lighting technology by the end of 2019.