Bluetooth® Brings Its Mesh Networking to the Internet of Things

By European Editors

Contributed By Digi-Key's European Editors

Mesh networking is a key architecture for the Internet of Things (IoT). Standards such as IEEE804.15 ZigBee have implemented mesh networking over the last twenty years with success in industrial automation. This means each node of the network can accept and forward data to a neighboring node, allowing a network to scale more easily by just adding new nodes. This is more cost effective and easier to implement than having to use additional gateway devices or access points which often also need more extensive planning to avoid clashing frequencies.

Bluetooth® by comparison has essentially been a point-to-point connection, linking to a terminal such as a smartphone or to an access point such as an iBeacon or Eddystone. As such it has been very successful in wearable technologies, providing a link back to a smartphone and from there to the wider Internet. This has allowed Bluetooth technology to be used in a range of applications that are increasingly connecting directly to the Internet and is driving a demand for mesh networking.

Diagram of nodes linking to the nearest neighbor

Figure 1: Having nodes link to the nearest neighbor allows a mesh network to easily extend the range of Bluetooth devices from room to room.

The latest versions of Bluetooth Smart, from 4.0 onwards, have reduced the power consumption dramatically, as well as the set up time, but also the data rate. This has implications for a mesh network, as the data rate is halved for each additional step in the network.

However, some Bluetooth specialists such as Cambridge Silicon Radio have been working on their own version of mesh networking using Bluetooth. CSRmesh is a software overlay for Bluetooth low energy devices that allows them to not only receive and act upon messages, but also to repeat those messages to surrounding devices. This extends the range of Bluetooth Smart and provides a simple ad-hoc mesh network for the IoT.

One of the first major deployments of CSRmesh is with SK Telecom in Korea, which has developed the world’s first range of smart LED light bulbs, which also function as Bluetooth Smart beacons in a retail environment. This allows an almost unlimited number of smart light bulbs to be simply controlled and networked together in a shop while at the same time location-based special offers can be targeted at smartphone users.

Image of CSR CSRmesh development board

Figure 2: The CSRmesh development board for intelligent lighting control applications.

Current in-store beacon systems require the installation of many wireless sensors around the shop floor, a process, which is often lengthy, expensive, and requires constant maintenance. Using the CSRmesh approach provides a beaconing system without the need to overhaul a building’s infrastructure. With LED smart beacons, a building’s existing lighting fixtures offer complete coverage because they are spread evenly throughout the store. The LED beacon also relies on a permanent mains power supply, meaning the service provider no longer needs to manage hundreds of battery-powered devices.

The system uses LED light bulbs that fit into existing lighting fixtures with each bulb communicating with its neighbor in a mesh. The smart light bulbs are fitted with a pre-certified module based on the CSR1010 chipset and CSRmesh v1.2 protocol layer with beacon capability, and iOS and Android mobile support.

The CSRmesh development board (Figure 2) helps designers implement the mesh protocol on top of standard Bluetooth software. This allows messages to be relayed over multiple Bluetooth Smart devices via a simplified platform for product designers who want to rapidly prototype networking of Bluetooth Smart products and test out the capabilities of a mesh implementation.

To do this, the kit provides a complete set of tools for evaluation and software development, from the development board, the CSR xIDE software development environment, USB programmer and interface cables, example CSRmesh applications for the development board and example host applications, and source code for Android and Apple iOS smartphones.

The development boards are normally powered from two AA batteries, but can also be run from the host USB connection, and additional boards can be easily used to make a larger network.

All this is part of solving the challenge of managing thousands of Bluetooth Smart-enabled beacons in a large space such as a stadium with mesh-based smart lighting beacons.

Another chipmaker, Nordic Semiconductor, has also been working to allow mesh networking on its ultra-low-power Bluetooth Smart devices to provide a low cost, fully developed ULP wireless mesh networking solution to target IoT applications.

Wirepas Pino is a fully automatic, self-optimizing, multi-hop mesh networking protocol stack developed by Wirepas to run on Nordic's nRF51822 Bluetooth chip. It supports high node densities and a theoretically limitless network size (number of nodes) with a network topology that continuously self-optimizes to balance network data traffic between nodes and adapt to changes in their operating environment such as experiencing RF interference.

This can dramatically improve network reliability so that when a node fails, the network will automatically 'heal' by re-routing communications via other nodes around it. This also allows higher network efficiency and lower power for all the nodes as the network can automatically and continuously self-reconfigure to maintain optimal network performance as new nodes are added.

Image of wireless mesh networking connecting Bluetooth throughout large buildings

Figure 3: Finnish startup Wirepas sees wireless mesh networking connecting Bluetooth throughout large buildings.   

As a result of all this interest, The Bluetooth Special Interest Group (SIG) has been incorporating mesh networking into the Bluetooth specification to allow this kind of capability in the standard so that all Bluetooth certified devices can be added to a mesh network. As Bluetooth Smart sensors proliferate in the home, mesh networking will become an integral component to ensure consumers’ Bluetooth-enabled smart locks, lights, HVAC systems, and even appliances work together to deliver a seamless smart home experience.

The Bluetooth Smart Mesh Working Group is building the architecture for standardized mesh networking capability for Bluetooth Smart technology. The move is hugely popular, with over eighty member companies already volunteered to serve on the group, among the highest of any SIG working group.

The group incorporates companies from a broad array of industries, including automotive, mobile phone/mobility, industrial automation, home automation, consumer electronics, and computing. Rather than focusing on one specific use case, the objective of the group is to build a common platform all members can develop to. The group is assessing many user scenarios that would benefit from mesh, including lighting, HVAC control, asset tracking, and security.

One way to easily implement this kind of capability is through a module such as the BLE113 from Silicon Labs. This module is aimed at small and low-power sensors and accessories and integrates all features required for a Bluetooth Smart application, from the radio transceiver, software stack and profiles, to the battery management and monopole chip antenna. This makes it simple to include in an existing design via its flexible hardware interfaces, and will allow these designs to easily access a mesh network. It can be powered directly from a standard 3 V coin cell battery or pair of AAA batteries. In lowest power sleep mode it consumes only 500 nA and will wake up in few hundred microseconds.

Image of BLE113 Bluetooth module from Silicon Labs

Figure 4: The BLE113 Bluetooth module from Silicon Labs.

Part of the advantage of the mesh approach is that it can make Bluetooth almost invisible to the user. With tighter design integration, Bluetooth Smart transceivers such as the DA14580 from Dialog Semiconductor could be embedded into equipment and automatically connect to another nearby node in the mesh. This would bring a very easy way to set up and run smart home and IoT applications. 

The DA14580 provides a fully integrated radio transceiver and baseband processor for Bluetooth Smart 4.1 that can be used as a standalone application processor or as a data pump in hosted systems. The transceiver supports flexible memory architecture for storing Bluetooth profiles and custom application code, which can be updated over the air (OTA) and so at a later date can potentially implement a mesh protocol. The qualified Bluetooth Smart protocol stack is stored in a dedicated ROM and all the software runs on the 16 MHz ARM Cortex-M0 processor via a simple scheduler. The device has been optimized for low power and small size to fit unobtrusively into designs.

The Bluetooth Smart firmware includes the L2CAP service layer protocols, Security Manager (SM), Attribute Protocol (ATT), the Generic Attribute Profile (GATT) and the Generic Access Profile (GAP), as well as custom profiles, which could include the mesh implementation.

The value proposition for Bluetooth technology in the IoT is unmatched, says the SIG, consuming the least amount of power, is the lowest cost, and most widely available wireless solution enabling the IoT today. The key is that bringing mesh networking to the Bluetooth specification will push the technology into entirely new market segments.

The Smart Mesh Working Group expects to have the specification ready for prototype testing later in 2015, and the SIG will look to officially adopt profiles in 2016.

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