Parker Dorris, Staff Product Manager for Bluetooth products at Silicon Labs discusses the latest features added to Bluetooth in version 6.0
Bluetooth has gained many features during the 25 years since the version 1.0 specifications appeared. The additions have opened paths to numerous novel applications and markets. That evolution has continued with the changes made in the latest 6.0 version of the core specification and the latest release of Bluetooth Mesh. In the coming years, these new innovations will lead to a new generation of applications for home, retail, distribution and industrial automation users.
A major example of innovation that will extend the capabilities of Bluetooth to new applications is support for secure fine ranging using the protocol’s new Channel Sounding protocol. This protocol lets two devices in wireless range of each other securely and accurately determine the distance separating them. Channel Sounding adds to the roster of location and positioning features already present in Bluetooth LE.
Most existing Bluetooth devices can perform presence detection by detecting incoming advertisements from other devices, analyse the RF signal strength and convert that to distance, but the accuracy of the ranging is only around ±5m. In addition to basic presence detection, and both coarse and fine distance measurement, the standard also supports direction finding using Angle-of-Arrival and Angle-of-Departure measurement techniques.
Bluetooth Channel Sounding
The new Bluetooth Channel Sounding enables secure fine ranging between Bluetooth 6.0 devices. The new protocol takes advantage of the 80MHz bandwidth and multichannel nature of Bluetooth enabling tone and round-trip-time measurements over the full frequency range. The process begins with the ‘initiator’ device and ‘reflector’ devices opening a Bluetooth connection, agreeing on a configuration for measurement based on capabilities comparison and then executing the ranging procedure.
During a Channel Sounding procedure, an initiator sends tones or packets across designated 2.4 GHz channels, and the reflector responds by sending data back to the initiator. Both round-trip time of packets, and phase differences between transmitted and received tones are used to resolve distance.
Transmission over an encrypted Bluetooth connection, time stamps on packets, and other security features help to prevent other nodes from spoofing replies and providing the initiator with a false distance estimate.
In many real-world environments, fine ranging using channel sounding that includes phase measurements can deliver an accuracy of ±0.3m at a range of less than 5m and ±0.5m over 5m.
There are many applications for Bluetooth Channel Sounding sounding in industrial, home and retail settings – for example for keyless entry, asset tracking and infrastructure positioning. The accuracy of Channel Sounding makes it amenable to geofence-based security strategies, opening the doors to users with the correct authorisation as they approach and raising an alarm if they stay in sensitive areas for too long. Similar principles can be applied to keyless entry for cars and houses, where the system unlocks the doors only as the owner comes into close range.
Bluetooth Mesh extensions
Bluetooth Mesh 1.1 introduces several new features designed to reduce the complexity and costs of network setup and maintenance as well enhance the performance, security, and scalability. The highlights of the new Bluetooth mesh standard are summarised below.
Remote Provisioning enables new devices to be added to the network from a single location which is particularly useful for large-scale deployments. In the previous version of the standard the provisioning needed to be done from within the radio range of the device which meant a person was needed to commission the devices.
Certificate-Based Provisioning enhances security by using digital certificates for device authentication during the provisioning process. It ensures that only authorised devices can join the network, providing an additional layer of security. This is especially useful when combined with remote provisioning as it enables secure bulk commissioning of devices, with minimum user interaction.
Mesh Device Firmware Update (DFU) feature standardises the firmware update procedure in Bluetooth mesh networks and allows for efficient over-the-air (OTA) updates of device firmware within the mesh network. The standard also defines a BLOB (Binary Large Object) protocol that uses both multicast and unicast messaging for an efficient delivery of the firmware to the nodes to be updated. This feature is particularly useful for maintaining large networks, such as those used in commercial building automation.
Subnet Bridging feature maintains the ability to include subnets for area isolation while simplifying network complexity. Subnet bridging both increases the network security as each subnet uses a unique security key, and network efficiency as by default messages are nor relayed between subnets.
Directed Forwarding feature improves message delivery efficiency by allowing relay nodes to create direct paths from the source to the destination. This multi-hop method reduces the number of hops needed, thereby enhancing network performance.
Multiple other minor feature improvements are also included in the new Bluetooth mesh standard improving either performance, usability, or security of the technology
These updates make Bluetooth Mesh 1.1 a more robust and versatile solution for a wide range of applications, from smart homes to large commercial buildings and industrial environments.
Large scale, ultra low-power star networking
Periodic advertising with responses (PAwR) is another feature that improves the communications efficiency of large Bluetooth networks by enabling connectionless two-way communication. PAwR suits situations where most of the nodes are relatively simple, fixed elements such as the electronic shelf label (ESL) display units now used in retail outlets. With standardised Bluetooth ESL Profile and Service PAwR can be setup to support up to 128 PAwR Subevents each addressing up to 255 unique devices. This enables network size of more than 32,000 peripherals.
Though devised for networks where the primary mode of communication is one-to-many, PAwR allows bidirectional communications. But the use of subevents achieves this in an energy-efficient way. That makes PAwR highly suited to ESL devices that have a very limited power budget. When a management node needs to update the ESLs in a group, it sends out a subevent message. Each of the nodes attached to that subevent have a designed slot in which they can reply, perhaps with a message to confirm that a price update has been applied.
Alternatively, it may take the opportunity to send an alarm to let administrators know its battery is running low. Through this time-synchronised mechanism, the ESL can power down its wireless transmitter and other functions outside the time slot when it is expected to be fully awake. For situations such as firmware updates, the nodes can take benefit of Bluetooth connection for higher data throughput. They can return to the energy-saving PAwR mode afterwards.
Though retail represents a key market for PAwR, there are other situations that can benefit from this ESL-oriented design. One example is in asset management, where a central server needs to keep track of assets such as pallets in a warehouse or product carriers in a production-line environment.
To ensure the PAwR protocol will work in real-world scenarios, Silicon Labs performed extensive tests on a device farm with more than 500 PAwR-enabled devices to determine how well the network can recover after a power outage that disrupts synchronisation. The tests also showed the degree to which the protocol can preserve battery life on ESL devices. The tests showed the capability of PAwR to balance between responsivity and ultra-low power consumption by varying the PAwR Interval timing.
These additions to the latest crop of Bluetooth standards demonstrate the vibrant nature of the wireless protocol and the value to OEMs and integrators of embracing the latest silicon when developing hardware for their systems.
Author: Parker Dorris, Staff Product Manager for Bluetooth products at Silicon Labs
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