Bluetooth 6.0 Channel Sounding

Bluetooth Channel Sounding is a new feature introduced in Bluetooth 6.0 that enhances distance ranging capabilities. It builds upon Bluetooth Low Energy’s (LE) established use in device positioning and location services. Channel Sounding enables secure and precise distance measurement between devices, opening possibilities for innovative applications, especially in mobile phones and battery-powered devices.

The technology behind Channel Sounding relies on two primary techniques: Phase-Based Ranging (PBR) and Round-Trip Timing (RTT). PBR calculates distances by analysing phase differences of signals across multiple frequencies, while RTT measures the time taken for a signal to travel between devices and back. These methods ensure secure and accurate distance measurements, with the algorithms for conversion handled at the application level.

Channel Sounding complements existing Bluetooth features, such as the Find Me Profile, RSSI-based proximity detection and Direction Finding introduced in Bluetooth 5.1, which enabled angle calculations using signal phase measurements.

This feature is expected to enhance numerous applications. For example, it can improve the reliability of beacons by providing accurate proximity alerts, even in challenging conditions. Smart locks will benefit from improved presence detection and enhanced security against relay attacks. Appliances can use the technology for user-centric contextualisation, such as enabling functions only when the user is nearby. Additionally, asset tracking may become more precise and reliable without significant increases in cost or complexity. Bluetooth 6.0’s Channel Sounding feature is designed to achieve distance measurement accuracy within ±10 centimetres. In early test implementations, accuracy levels of ±20 centimetres have been observed.

The adoption of Bluetooth Channel Sounding, like previous advancements such as Mesh, Direction Finding and Angle of Arrival (AoA), is expected to face very long delays in concrete implementation relative to the release of the standard. Also, historically, the adoption of newer Bluetooth LE enhancements has been relatively slow, with limited uptake across the industry. This is due to the requirement for new devices and updated software that leverages new Software Development Kits (SDKs), making the technology complex to develop and deploy. Also, compatibility constraints often mean that new Bluetooth LE features can’t be retrofitted to existing devices.

For those looking to measure distance effectively today, a practical alternative is to use beacons like the iBS03R, which incorporates Time of Flight (TOF) distance sensing as a dedicated hardware sensor. This approach offers immediate, reliable and actually more accurate (25mm rather than 20cm) distance measurement, albeit over a shorter (3m) distance, without waiting for the broader implementation of Channel Sounding in the market.

Bluetooth 6.0

The Bluetooth® Core Specification version 6.0 introduces several key feature enhancements aimed at improving performance, efficiency, and functionality, particularly in Bluetooth Low Energy (LE).

Bluetooth® Channel Sounding: This feature enables secure and accurate distance measurement between two Bluetooth devices, which is essential for applications like digital keys and location tracking.

Decision-Based Advertising Filtering: This enhancement improves scanning efficiency by allowing devices to filter and selectively scan for relevant packets, thereby reducing unnecessary scanning and saving energy.

Monitoring Advertisers: This feature allows observer devices to track when a specific device moves in or out of range, which helps avoid energy waste from scanning for devices that are no longer nearby.

ISOAL Enhancement: Improvements to the Isochronous Adaptation Layer reduce latency in data transmission, making Bluetooth more suitable for time-sensitive applications while also enhancing reliability.

LL Extended Feature Set: The capacity for devices to share information about their supported features has been expanded, accommodating the growing complexity of Bluetooth LE.

Frame Space Update: The previously fixed time interval between packet transmissions is now adjustable, allowing for more flexibility in connection events and isochronous streams, potentially enhancing performance.

But how are future beacons and gateways likely to use the new features introduced in the Bluetooth 6.0?

Specialist sensor beacons are expected to utilise the Channel Sounding feature to estimate distance, potentially offering an alternative to the current beacons that rely on time of flight (TOF) measurements. However, it remains uncertain whether Channel Sounding will outperform existing TOF-based beacons in terms of accuracy and reliability.

Some gateways may adopt Decision-Based Advertising Filtering to improve scanning efficiency. By selectively scanning for relevant packets, these gateways could achieve higher throughput, making them more effective in environments with heavy traffic.

The Monitoring Advertisers feature might find application within smartphones, although this seems unlikely given the lack of a clear use case. While this feature could theoretically help in tracking devices that move in and out of range, the practical benefits for most consumer applications appear limited.

The LL Extended Feature Set is technically interesting but may have limited practical impact. The widespread presence of older beacons and smartphones that do not support this feature could hinder its universal adoption, reducing its overall usefulness in mixed environments.

In summary, while these new features offer exciting possibilities, as with Bluetooth 5.0, their real-world impact will depend on whether and how they are adopted and integrated into future devices, especially considering the existing ecosystem of older Bluetooth devices.