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Introduction to Bluetooth 5

The latest version of the Bluetooth standard introduces a number of improvements that will be of value to many applications but will perhaps be most important for the Internet of Things (IoT).

The main changes, which will be discussed in this article, are higher speed, increased range, mesh networking, and improved support for advertising and beacons. Bluetooth 5 remains backwards compatible with earlier versions and also provides better coexistence with other wireless networks. The increased range and faster data rates do not require any more power but cannot be used at the same time. In other words, Bluetooth 5 gives the designer choices for how to optimize between data rate, range and energy use.

Devices supporting Bluetooth 5 are becoming available, such as the Nordic Semiconductors nRF52840.Although Bluetooth 5 compliance can be achieved just by supporting the errata (in other words fixing what was wrong or missing in Bluetooth 4.2) it is important to look for devices that provide support for the new features of Bluetooth 5.

Higher speed

Bluetooth 5’s enhanced data rate (EDR) supports higher transmission speeds of up to 2Mbps without increasing output power. This means less energy is used to send the same amount of data that, for battery powered devices, can equate to either a longer lifetime or a physically smaller product.

Most devices will be flash-based, enabling them to take advantage of this increased speed to perform firmware updates. This is important for security and feature updates, particularly for IoT nodes; there are always people searching for new vulnerabilities to exploit.

The higher data rate will also be valuable for applications where rapid response times are required, such as controlling robotic system or machines on the factory floor. It also makes it more practical for nodes to collect data to be uploaded when required.

Increased range

Bluetooth 5 has a theoretical range of up to 400 meters for line of sight connections, which probably means about 120 meters in a more realistic environment. This is about four times the range of the previous version at the same power consumption. However, this can only be achieved at lower data rates, so there is a choice between high speed or greater range. For many low-energy applications, the 500 kbps or 125k bps modes will provide sufficient bandwidth.

At these lower data rates, forward error correction (FEC) is used to improve the recovery of data from background noise. The effective sensitivity is improved by about 12dB, which corresponds to a four-fold increase in range. Importantly, this does not require more output power so the greater range can be achieved without increasing energy use.

Mesh networking

Bluetooth was originally defined as a star network where all nodes connect via a central hub. This limits the size and range of the network. A large network would require multiple hubs with some other, possibly wired, communication between them, which adds to the cost and complexity. Bluetooth 5 introduces support for mesh networking where all nodes can communicate directly with one another, see Figure 1. Messages can be passed through intermediate nodes. This extends the network beyond simple point-to-point wireless connectivity and provides almost unlimited range throughout and even between buildings.

Figure 1: Star (a) and mesh (b) networks.

Mesh networking is already supported by other wireless systems such as Zigbee and has been implemented by some manufacturers of Bluetooth devices using proprietary extensions to the standard. These companies and others worked with the Bluetooth SIG to define the mesh standard.

Bluetooth 5 uses a “flooding” mesh. This means that every packet received by a node is copied to all the other connected nodes until it reaches the destination. This uses the existing scanning and advertising functions to broadcast the packet. This is a simple but effective way of spreading information across the mesh network. Every packet will have multiple paths to the destination, which increases reliability. Battery-powered nodes do not need to relay messages and so being part of a mesh network will not shorten their battery life.

Control can be distributed throughout the mesh using what the Bluetooth SIG calls a “scene” where one user action can trigger a cascade of others. For example, when an owner comes home and opens the front door using a smart lock, other nodes can be informed in order to turn on the lights, turn up the heating, and so on.

Mesh networks will be especially useful in Industrial IoT where there may be a large number of nodes distributed throughout an enterprise. For example, this can be used to manage heating, air conditioning, lighting, security, machine-to-machine communications, system health monitoring, energy use, tracking components through warehouse and factory floor, and many other applications in retail and manufacturing environments.

The mesh network standard is not specific to Bluetooth 5 and can be added to Bluetooth 4.2 implementations.

Improvements to beacons and advertising

Bluetooth 5 provides better support for “connectionless” applications that use beacons, which function without needing to pair with another device.

The improved range is useful for beacon applications. The speed increase isn’t as relevant because it is usually the discovery/connection time, rather than the raw data rate, that is important. In addition, there are advertising extensions which allow more data to be transmitted and also reduce the risk of advertising channel congestion.

The basic broadcast packet size is increased to 255 bytes and packets can be chained to create extended advertising data payloads. This means the beacon can transmit more useful amounts of data and new types of data.

However, Bluetooth has only three advertising channels and these could soon become congested with advertising packets if they all had large data payloads. The advertising extensions address this by using the same three channels for advertising, and then using an alternative (non-advertising) channel to transmit data.

There is a new periodic advertisement mode which allows for more synchronized broadcasting of data between devices.

Improved coexistence

There are multiple wireless connectivity solutions all operating in the 2.4 GHz band including cordless phones, baby monitors, Wi-Fi, Zigbee and LTE cellular networks. Bluetooth 5 improves the ability to coexist with these. As well as avoiding channels already in use by Wi-Fi it adds “slot availability masks” that avoid interference with cellular networks. Bluetooth 5 also has an improved channel-sequencing algorithm (CSA #2) to improve the pseudo-randomness of next hop channel sequencing. This will improve operation in the presence of Wi-Fi and other Bluetooth devices.

To enable products that can work flexibly in this environment, silicon manufacturers are producing devices that support multiple protocols such as ANT, LPWAN (802.15.4m), Zigbee and others within a single SoC.

The improvements in Bluetooth 5 will enable a new range of applications for beacons. For example retail outlets and exhibitions can use beacons to automatically register people’s presence and deliver information about the items the visitor is looking at, including a link with more details or special offers. They can provide navigation information and suggestions of what else to see. The beacons can also gather feedback by tracking people to see where go, where they stop, what they look at or buy and so on.

Bluetooth 5 will also be able to compete in IoT applications, such as smart lighting, which are already dominated by alternatives such as Zigbee. Bluetooth has the advantage that it is already ubiquitous in devices that could be used for control and monitoring these applications.

Author
Mark Patrick, Mouser Electronics

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