Bluetooth 6

What Is Bluetooth 6?

Bluetooth^® 6 is the latest major revision to Bluetooth, which enables electronic devices at short range to wirelessly exchange data. Bluetooth 6 was announced in September 2024 by the Bluetooth Special Interest Group (SIG). Some salient features in Bluetooth 6 are:

• Channel sounding, for accurate distance measurements
• Decision-based advertising filtering, for more efficient channel scanning
• Monitoring advertisers, for improved energy efficiency when devices come into and go out of range
• Interframe space updates, for both higher throughput and better coexistence management

According to the SIG, Bluetooth Channel Sounding enables more accurate distance awareness, 10 cm ranging accuracy, and enhanced security. 

Ranging with Bluetooth Channel Sounding

Before Bluetooth 6, a received signal strength indicator (RSSI) measurement was used to infer the distance between two Bluetooth devices, assuming a free space path loss on the link. But if the signal suffered more loss from multipath or shadowing, the distance would be overestimated.

Bluetooth 6 introduces two ways to accurately measure distance:

• Round-trip time (RTT) measurement
• Phase-based ranging (PBR) measurement

RTT

The RTT measurement method in Bluetooth 6 uses the fact that the signal time of flight (TOF) between two devices is half the RTT. It can then accurately compute the distance d as

\(d=(\tfrac{RTT}{2})*c\)

where c is the speed of light. This method requires accurate measurements of the time of departure (TOD) of the outbound signal from device 1 (the initiator), time of arrival (TOA) of the outbound signal to device 2 (the reflector), TOD of the return signal from device 2, and TOA of the return signal to device 1. The diagram below shows the signal paths and the times. The time t_I is the RTT of the initiator, and the time t_R is the time from reception at the reflector to its subsequent transmission.

PBR

The PBR method in Bluetooth 6 uses two signals of different frequencies to measure distance. These signals are simply tones—sine waves. The distance can be calculated as a function of the phase difference between the two received tones. Because a given phase difference value can hold true for an infinite number of distance values, the device supporting Bluetooth 6 selects the shortest distance that satisfies the phase difference condition. The expected range of PBR is about 150 m. Also, if three or more locator Bluetooth 6 nodes participate in RTT or PBR ranging, they can use trilateration to find the location of a device being tracked.

Bluetooth 6 outlines RTT and PBR distance measurement methods, but channel sounding does not mandate a specific algorithm for calculating distance estimates. This flexibility allows device manufacturers to tailor solutions to various use cases, balancing computational complexity with required accuracy and adapting to different radio environments.

Enhanced Security Measures in Bluetooth 6

Bluetooth 6 devices using channel sounding enjoy security from distance spoofing and man-in-the-middle attacks, for the following reasons:

• Bit patterns are randomized with a standard-specified deterministic random bit generator.
• Transmit power can be varied to reduce the received signal-to-noise ratio for attackers.
• Devices can deploy an attack detector system.
• RTT and PBR can be combined to provide redundant distance measurements and more easily detect spoofed results.

Other Bluetooth 6 security enhancements include:

• Use of the Advanced Encryption Standard (AES)
• Decision-based advertising filtering, which reduces unnecessary data transmissions and reduces exposure to unwanted listeners
• Use of Elliptic Curve Diffie-Hellman for secure key generation when pairing two devices

Bluetooth 6 Use Cases and Applications

Bluetooth 6 Channel Sounding can be used for:

• Keyless vehicle entry, performed by communication between a key fob or phone and the car’s anchor points
• Smart locks, to permit access only when an authorized device is within a designated proximity to the locks
• Geofencing, to limit access to designated areas
• Warehouse management, to monitor inventory and manage logistics
• Asset tracking for virtually any object of interest

These use cases can support applications for smart home devices, medical devices, supply chain management, and logistics.

Bluetooth 6 with MATLAB

Channel Sounding

With MATLAB^® and Bluetooth Toolbox, you can model ranging scenarios and estimate distances using the RTT and PBR methods of ranging specified in Bluetooth 6. You can specify any number of Bluetooth locator nodes and perform localization in 2D or 3D, using either RTT or PBR. 

Interframe Spacing

You can also examine the effect of variable interframe spacing in Bluetooth 6 on throughput and latency in an asynchronous connection-oriented logical (ACL) connection. Additionally, you can configure the IFS in a connected isochronous stream (CIS).