Bluetooth Channel Sounding takes positioning to a new level
Location-based services are driving strong growth for indoor positioning systems in multiple sectors. Positioning is used for proximity detection, indoor mapping and asset tracking in logistics, retail and healthcare. This rapidly growing market is fueling innovation in Bluetooth Low Energy (BLE), Wi-Fi and ultra-wideband (UWB), which have all evolved to offer location-based capabilities. As a technology, UWB has already established a lead and a reputation for centimeter-level positioning accuracy, low latency and strong security features. But with its existing strong market adoption, Bluetooth could close the gap by adding channel sounding.
Channel sounding (CS) is a highly accurate, fine-ranging feature offering robust security capabilities and measurement accuracy on a par with UWB. Developers can add CS to build or enhance positioning applications, enabling a wide spectrum of new use cases.
The rapidly developing Bluetooth 6.0 ecosystem supports CS and includes wireless MCUs and toolkits that are available now or coming soon, accelerating development and reducing time to revenue.
Growth forecast for Bluetooth-based location services
Bluetooth 6.0 Channel Sounding: An overview
Bluetooth 6.0 is the latest in a series of releases that have continually enhanced the world’s most widely used short-range wireless communications protocol. Succeeding Bluetooth 5.4, this new release introduces several new, performance-improving features. Here, we focus on the positioning accuracy and security achieved through channel sounding.
Bluetooth CS employs two advanced distance measurement techniques, phase-based ranging (PBR) and round-trip time (RTT), to enable fine ranging between two connected BLE devices. While performance will depend on implementation, expectations are that CS will improve BLE’s distance measurement accuracy from meters to centimeters. In some applications, the system may work collaboratively with existing BLE range finding features, such as RSSI or Direction Finding. They may even use UWB for additional short-range accuracy or the fast exchange of secure information.
Devices implementing CS now use both PBR and RTT in a single, standardized procedure for ranging. Two devices communicate using one of 72 channels within the 2.4 GHz spectrum. The standard supports one to four antennas on both sides of the connection.
PBR calculates the distance between the two devices using the phase difference of the transmitted and received signals. RTT estimates the distance by calculating the time of flight (ToF) of the signal. Together, these techniques allow the connected devices to measure the distance between them up to an expected range of 150 meters.
Bluetooth CS integrates a range of standardized security features to protect against man-in-the-middle attacks and relay attacks, including:
- A distributed random bit generator (DRBG) to randomize channel selection and other aspects of ranging
- Encryption of data used for ranging
- A normalized attack detector metric (NADM) assessing the likelihood of an attack on a communication channel
- Cross-checking the results of both methods (PBR and RTT) to detect inconsistencies in distance estimation
Applications enabled by Bluetooth Channel Sounding
With Bluetooth technology already embedded in all major consumer platform devices, including smartphones, tablets and laptops, Bluetooth CS enables developers to add true distance awareness to connected devices without designing additional radio technology. Target applications for Bluetooth Channel Sounding can be split into two specific categories:
- Localization, or ‘Find My’
Indoor positioning systems enable rapid location of items and people in a mapped area. This includes personal items, assets in warehouses, and specialist equipment and personnel in a medical environment. An increasing number of Bluetooth devices, including but not exclusively cellular handsets, are embedding “find my” capabilities. Channel sounding enables developers to add true distance awareness, making it easier to build services based on locating items and people. - Proximity awareness
Applications such as smart locks and keyless entry systems in vehicles and buildings need robust protection against man-in-the-middle and relay attacks. An unauthorized device can potentially fool a lock into believing the authorized user is within range. These systems use ranging to verify proximity, preventing unauthorized access. Channel sounding would bring new accuracy to this use case.
Understanding the context of presence or distance significantly improves the user experience for a wider range of use cases, including geofencing, human-machine interface (HMI) and interaction with smart home systems, keyboards, laptops and many more.
Developing with Bluetooth Channel Sounding
The Bluetooth 6.0 specification was released in September 2024. Developers have access to a growing ecosystem of hardware, software and development toolkits. Several manufacturers, including Nordic Semiconductor and NXP Semiconductors, are bringing new devices to market that will provide Bluetooth 6.0 channel sounding capabilities.
The ultra-low-power multiprotocol, nRF54L15 series of SoCs from Nordic Semiconductor, for example, are the company’s first to support Bluetooth CS. Nordic also offers Bluetooth-qualified host and controller software through its SDK.
The forthcoming MCX W72 and KW47 wireless MCU families from NXP target industrial IoT and automotive applications, respectively. Both will support Bluetooth CS, enabled through the MCUXpresso Developer Experience toolkit for accelerated embedded system development.
As a standardized Bluetooth feature, developers can be assured of interoperability through the formal Bluetooth qualification program. When choosing the best product for the application, the developer should consider factors such as:
- Bluetooth CS is an optional feature in the Bluetooth 6.0 standard, so not all devices are guaranteed to support it, although as CS becomes more in demand, it is likely to be added as standard in more devices.
- Although the BLE 6.0 specification supports up to four antennas on each device, there is a trade-off between accuracy and power consumption. For certain low-power applications such as asset trackers, a single antenna may suffice, while applications requiring higher accuracy may use more antennas.
- While the Bluetooth standard provides the framework, it does not include distance calculation. It is up to the developer to implement or customize an existing algorithm, according to the specific accuracy and performance requirements of the application, but only one device needs to be running a ranging algorithm. Check for manufacturers offering access to these algorithms and ask Avnet’s technical support specialists about third-party solutions that can be ported to different platforms.
Locks are only the beginning
Bluetooth CS represents an exciting new development, both for the standard and for positioning technology. With major chipset vendors announcing support for channel sounding, the number of IoT devices and smartphones integrating Bluetooth CS is set to increase. Bluetooth device shipments continue to grow, and new devices coming to market will unlock huge opportunities for application developers across all sectors.