Bluetooth 6: What's New In The Latest Bluetooth Release?

Bluetooth technology is continuously expanding to serve its existing use cases well, as well as to introduce previously impossible applications by improving performance and feature sets to perform new tasks. On September 3, 2024, the Bluetooth Special Interest Group (SIG) released the next iteration of the Bluetooth Core Specification: Bluetooth 6.0

In this article, we’ll aim to provide in-depth technical explanations of the feature included in the Bluetooth 6 specification, their background, benefits, implementation details, and everything else you need to know about what’s available to developers in Bluetooth 6.

What’s New In Bluetooth 6?

Bluetooth 6 introduces several new features that address common concerns in wireless communication. Below are the standout features:

1. Bluetooth Channel Sounding
2. Decision-Based Advertising Filtering
3. Monitoring Advertisers
4. ISOAL Enhancement
5. LL Extended Feature Set
6. Frame Space Update

In the following sections, we’ll break down each of these Bluetooth 6 features and review how each of them aim to further improve wireless connectivity.

Bluetooth Channel Sounding

One of the most significant features of Bluetooth Core Specification version 6.0 is a powerful innovation called Bluetooth Channel Sounding. This feature enables secure fine ranging between two Bluetooth devices, providing a standards-based approach to meet the challenging accuracy & security requirements of applications like digital key solutions and asset tracking.

Bluetooth Channel Sounding achieves its range measurement with new techniques that increase its measurement accuracy. While previous methods were able to achieve accuracy of at best a half meter, Channel Sounding’s techniques improve that accuracy to the sub-10cm level.

Bluetooth Channel Sounding consists of two distinct distance measurement methods, Phase-Based Ranging (PBR) and Round-Trip Timing (RTT), and these methods can be used independently or in combination to achieve highly accurate distance measurements.

Phase-Based Ranging (PBR)

PBR exploits the fundamental properties of radio signals, specifically the relationship between phase, frequency, and wavelength. The PBR process involves:

1. The Initiator transmits a signal at frequency f1 to the Reflector.
2. The Reflector echoes the signal back.
3. The Initiator measures the phase (P1) of the received signal.
4. The process is repeated with a different frequency f2, resulting in a new phase measurement (P2).
5. Distance is calculated using a formula involving the frequency difference (f1 - f2), phase difference (P1 - P2), and the speed of light.

PBR can provide very accurate measurements but is subject to distance ambiguity due to the cyclic nature of phase rotations. This ambiguity occurs around 150 meters when using a 1 MHz frequency separation.

Round-Trip Timing (RTT)

RTT involves measuring the time it takes for a signal to travel from the Initiator to the Reflector and back. The RTT process includes:

1. The Initiator records a timestamp (Time of Departure or ToD) when transmitting a packet.
2. The Reflector receives and echoes the packet back after a pre-negotiated delay..
3. The Initiator records a second timestamp (Time of Arrival or ToA) upon receiving the reply.
4. Distance is calculated using the time difference, accounting for the negotiated processing delay at the Reflector.

RTT can provide unambiguous distance measurements over longer ranges but requires precise timing mechanisms for accuracy.

Security Features of Bluetooth Channel Sounding

Bluetooth Channel Sounding incorporates several security features to protect against attacks such as distance spoofing and man-in-the-middle (MITM) attempts:

●     Randomization: Using a Deterministic Random Bit Generator (DRBG) to create random bit patterns in transmissions.

●     Signal manipulation defense: Employing the LE 2M 2BT PHY with shorter symbol spans and optional SNR control.

●     RF signal analysis: Implementing an attack detector system with a standardized Normalized Attack Detector Metric (NADM).

●     Combined PBR and RTT: Cross-checking results from both methods to detect inconsistencies.

By providing a standardized, secure, and highly accurate ranging solution, Bluetooth Channel Sounding opens up new possibilities for proximity-based applications while addressing the security concerns inherent in wireless distance measurement systems.

Decision-Based Advertising Filtering (DBAF)

Another prominent feature of Bluetooth 6.0 is Decision-Based Advertising Filtering (DBAF), which aims to improve the efficiency of scanning devices when dealing with extended advertising.

DBAF introduces a new type of extended advertising PDU called ADV_DECISION_IND, informally referred to as a decision PDU. This PDU is designed to replace ADV_EXT_IND extended advertising PDUs and is transmitted on primary channels.

Decision PDUs contain application-specified data that allows scanners to make more informed decisions about whether associated AUX_ADV_IND auxiliary packets are of interest.

Advertising & Configuring Decision PDUs

Decision PDUs (ADV_DECISION_IND) are transmitted on either LE 1M or LE Coded PHY. They contain several key fields, including AdvMode, Extended Header, Decision Type Flags, and Decision Data fields. Among these, AuxPtr is the only mandatory extended header field.

Decision PDUs can be configured using HCI commands such as LE Set Decision Data and LE Set Extended Advertising Parameters. Additionally, the Advertising Event Properties parameter is updated to include bits specifically for decision PDU usage.

Scanning & Decision Instructions

There are several decision scanning filter policy modes:

●     No decisions mode: Decision PDUs are ignored.

●     All-PDUs mode: All advertising PDU types are selected, with decision PDUs undergoing specified checks.

●     Decisions-only mode: Only decision PDUs are selected and evaluated.

Decision instructions are configured using the LE Set Decision Instructions command. This specifies the tests to be applied to decision PDUs and employs arrays like Test_Flags[], Test_Field[], and Test_Parameters[].

Test Groups

Tests can be organized into groups to create more complex filtering logic. Internally, groups use logical AND, while different groups are connected using logical OR.

Relevant Fields for Testing & Initiating

Fields that are relevant for testing include Resolvable Tag, AdvMode, RSSI, Path loss, AdvA (advertising device's address), Arbitrary Data, and Vendor-specific data.

The initiating filter policy can be configured to work with decision PDUs, applying similar processing logic as used in the scanning state.

Security Considerations

Resolvable Tags in decision PDUs provide a simple way to label PDUs as relevant to specific applications and devices. The key value used for hash generation and checking must be shared between appropriate devices, with the mechanism to be defined in future GATT attributes and profile specifications.

DBAF offers a powerful and flexible filtering mechanism that allows applications to significantly reduce distractions and improve scanning efficiency in Bluetooth LE environments, particularly those with high numbers of advertising devices using extended advertising.

Monitoring Advertisers in Bluetooth 6.0

The third core feature of Bluetooth 6.0, Monitoring Advertisers, addresses issues related to device discovery and connection establishment in Bluetooth Low Energy (LE) environments.

Prior to this feature, the host component of an observer device could instruct the Bluetooth LE controller to filter duplicate advertising packets. While this improved efficiency, it had a significant drawback: the host had no way of knowing whether a device was still within range when it needed to attempt a connection, leading to wasted energy performing high duty cycle scanning for a previously discovered device that was no longer in range.

To address this issue, this new feature uses Host Controller Interface (HCI) events to inform the host whenever a device of interest moves in and out of range. Key aspects of this process include:

1. New HCI Command: LE Set Advertising Report Enable - Allows the host to enable or disable the generation of advertising reports for specific advertising sets.
2. New HCI Event: LE Advertising Report State - Informs the host about the state of an advertising set (in range or out of range).
3. Configuration Options:
1. Minimum and maximum advertising intervals
2. Number of advertising events that must be missed before considering a device out of range
3. RSSI threshold for determining if a device is in range

Monitoring Advertisers reduces power consumption by preventing unnecessary high duty cycle scanning, which is often performed for devices no longer within range. This feature also improves the user experience by providing more accurate and timely information about device availability, ensuring that connections are attempted only when appropriate. Additionally, it enables a more efficient connection establishment process by allowing the host to react dynamically as devices move in and out of range.

The feature works with both legacy and extended advertising, and it operates alongside existing duplicate filtering mechanisms. Additionally, monitoring parameters can be configured for individual advertising sets or set to default values.

This feature greatly enhances the efficiency of Bluetooth LE devices, particularly in scenarios where multiple devices may frequently move in and out of range.

ISOAL Enhancement in Bluetooth 6.0

The ISOAL Enhancement feature in Bluetooth Core Specification version 6.0 introduces improvements to the Isochronous Adaptation Layer (ISOAL), which is responsible for enabling larger data frames to be transmitted in smaller link layer packets while preserving crucial timing information for correct processing by receivers. 

Prior to this enhancement, ISOAL could produce either framed or unframed PDUs. When framed PDUs were produced, it could lead to increased latency, which was problematic for certain use cases, particularly those sensitive to timing issues. The new ISOAL Enhancement addresses this problem by introducing a new framing mode that significantly reduces latency for time-sensitive applications.

The enhancement also improves segmentation, allowing for more efficient use of available PDU space. This means that a given amount of data can be transmitted using fewer PDUs, leading to improved overall efficiency in data transmission. The new framing mode allows for more flexible segmentation of Service Data Units (SDUs) into PDUs, introducing a new field in the ISOAL header to indicate the framing mode being used.

One of the key benefits of this enhancement is its impact on applications that require low-latency isochronous data transmission, such as high-quality audio streaming or time-sensitive control systems. By reducing latency and improving reliability, the ISOAL Enhancement enables these applications to function more effectively within the Bluetooth LE ecosystem.

Importantly, the ISOAL Enhancement is designed to be backwards compatible with existing ISOAL implementations. This means that devices implementing the new enhancement can still communicate effectively with older devices that do not support it, ensuring continuity and interoperability across different generations of Bluetooth devices.

These improvements collectively address issues with latency and efficiency in isochronous data transmission, which is particularly beneficial for applications like audio streaming or real-time control systems that require low-latency, reliable data transfer.

LL Extended Feature Set

Background

Bluetooth devices exchange information about their supported link layer features to ensure interoperability and optimal use of available capabilities.

The Problem

As Bluetooth LE has grown in sophistication and versatility, the number of supported features has increased, outgrowing the existing feature exchange mechanism.

The Solution: LL Extended Feature Set

This feature enhances the capability to exchange information about supported link layer features:

1. Expanded Feature Set: Supports a larger number of features and allows for future expansion as new features are added to the Bluetooth specification.
2. New HCI Commands and Events: LE Read Extended Features: Allows the host to query the controller for supported features. LE Extended Features Changed: Notifies the host when the feature set changes.
3. Backwards Compatibility: Maintains compatibility with existing feature exchange mechanisms.

Key Benefits

1. Future-Proofing: Accommodates the growing number of Bluetooth LE features.
2. Improved Interoperability: Devices can more accurately determine each other's capabilities.
3. Enhanced Flexibility: Allows for dynamic feature updates and more granular feature support information.

Technical Details

●       The feature set is represented as a bit field, with each bit corresponding to a specific feature.

●       The extended feature set allows for a significantly larger number of features to be represented.

●       Devices can query specific pages of features, allowing for efficient exchange of relevant information.

This enhancement ensures that as Bluetooth LE continues to evolve, devices will be able to effectively communicate their capabilities, leading to better interoperability and more efficient use of advanced features.

Frame Space Update

In Bluetooth LE, the time separating adjacent transmissions of packets in a connection event or connected isochronous stream (CIS) subevent is known as the Inter-Frame Space (IFS).

Prior versions of the Bluetooth Core Specification defined a constant value for IFS, designated T_IFS, with a fixed value of 150 μs. This fixed value limited flexibility in certain scenarios.

To address this issue, Bluetooth Core Specification version 6.0 introduces negotiable frame spacing:

1. Negotiable IFS: Frame spacing used in connections or with connected isochronous streams can now be shorter or longer than 150 μs.
2. New Link Layer Feature Bit: Indicates support for the Frame Space Update feature.
3. New Link Layer Control Procedure: Allows devices to negotiate and agree on an IFS value to use.

Key Benefits

1. Improved Efficiency: Shorter IFS values can lead to improved throughput in certain scenarios.
2. Enhanced Flexibility: Longer IFS values can accommodate devices with slower processing capabilities.
3. Better Coexistence: Adjustable IFS can help in scenarios where Bluetooth needs to coexist with other wireless technologies.

Technical Details

• The negotiable IFS range is from 50 μs to 1000 μs.
• The feature is optional and backwards compatible with devices that don't support it.
• IFS negotiation occurs during connection establishment or update procedures.

Use Cases

1. High-Throughput Scenarios: Shorter IFS can improve data transfer rates.
2. Low-Power Devices: Longer IFS can accommodate devices with limited processing power.
3. Complex RF Environments: Adjustable IFS can help manage interference in crowded RF spaces.

This feature provides more flexibility in how Bluetooth LE devices communicate, allowing for optimizations based on device capabilities and environmental conditions.

Final Thoughts on Bluetooth 6

As with previous updates to the Bluetooth Core Specification, it may take some time before silicon vendors begin integrating support for the new features. After that, module manufacturers will need additional time to implement this support and make it available to developers. However, the foundation has now been set to deliver the most precise distance measurement Bluetooth SIG has ever supported. Developers can dive into the core specification for detailed insights and operational theory. Exciting times ahead!

At Ezurio, we’re always ahead of the curve when it comes to connectivity. Our involvement with organizations like Bluetooth SIG, Wi-Fi Alliance, and LoRa Alliance ensures that we keep our customers at the forefront of innovation, helping them seamlessly integrate the latest technologies into their unique designs.

Our cutting-edge Bluetooth modules, such as the BL54 series, incorporate Nordic silicon with support for the nRF54H20 and nRF54L15 SoCs, boasting dual ARM Cortex-M33 processors and RISC-V co-processors tailored for Bluetooth LE 5.4 applications. Meanwhile, our Lyra 24 Series harnesses Silicon Labs’ powerful EFR32BG24 SoC to combine our wireless expertise with SiLabs’ Bluetooth 5.4 LE tools, offering options in SIP, SMT Module, or USB form factor. Additionally, our Vela IF820 combines Bluetooth Classic and Bluetooth LE via Infineon’s AIROC CYYW20820, available in SIP, SMT Module, and USB formats.

Discover more about our Bluetooth offerings on our website:
https://www.ezurio.com/wireless-modules/bluetooth-modules

For further information on Bluetooth Core Specification v6, visit Bluetooth SIG here:
https://www.bluetooth.com/blog/now-available-new-version-of-the-bluetooth-core-specification/

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