Device localization has become indispensable in many applications. GPS and cellular networks deliver accurate outdoor data but fall short indoors or when it comes to sub-meter requirements. Although precision can be improved with the help of cellular networks, the added costs and energy consumption make such solutions impractical.
A growing number of applications now focus on short-range devices, i.e., tracking objects in local networks over short distances to generate local position intelligence. This is precisely where various standards and proprietary technologies are seeking to establish themselves. At this point, Bluetooth with Channel Sounding comes into play.
Bluetooth is an established technology, integrated into many areas of modern life. For years, Bluetooth Low Energy (BLE) has served as the workhorse of short-range communication, supporting energy-efficient data transmission across billions of devices. Since its introduction, BLE localization solutions have used the Received Signal Strength Indicator (RSSI) to estimate distances between devices. RSSI is adequate for rough proximity detection, such as determining whether a device is nearby. But not for more precise measurements. Environmental variables, interference and multipath reflections render RSSI an unreliable measure of distance. Companies that contributed to Bluetooth Real-Time Location Services (RTLS) recognized this early on, leading to the introduction of the “Direction Finding” (DF) feature in Bluetooth 5.0. Today, it serves as the backbone for many smart, Bluetooth-based RTLS systems.
The limitations of RSSI-based approaches make Bluetooth unsuitable for industrial RTLS applications. Until now, these applications have been dominated by special ultra-wideband (UWB) solutions. Moreover, while UWB systems deliver distance data in the centimeter range, they demand greater RF design development effort and face additional regulatory requirements. For many applications where sub-meter accuracy is sufficient, UWB systems are thus too complex or too expensive. Channel Sounding in Bluetooth 6.0 closes this gap. It provides adequate accuracy for many applications without the extensive integration effort demanded by UWB.
BLE-based Channel Sounding enables reliable and precise ranging with cost-effective and easy-to-develop hardware. While earlier Bluetooth generations used RSSI values to roughly estimate the distance between two devices, Channel Sounding now allows direct characterization of the radio channel.
How does Channel Sounding work?
Basically, Channel Sounding is about time and phase. Phase-based ranging (PBR) and round-trip time (RTT) measurements can be used to determine the exact distances between two devices. With PBR, the devices exchange signals across multiple frequencies and compare the resulting phase shifts. This enables precise distance calculation (Figure 1). RTT works in a similar way to radar: A device sends a packet, the receiving party responds, and the difference in round-trip time provides the distance (Figure 2). By combining both methods, Bluetooth achieves a level of accuracy that was unattainable with RSSI. The decisive factor here is not only accuracy but also that this further development is based on the same BLE technology that has become a cornerstone of the Internet of Things (IoT).
Although PBR and RTT work reliably in most real-world scenarios, they need additional support to mitigate effects like multipath propagation, interference or attacks such as relay attacks. Bluetooth 6.0 therefore incorporates additional security mechanisms to complement Channel Sounding. Signals can be randomized, encrypted and verified to ensure that the distances determined are not manipulated. Furthermore, devices can use multiple antennas to reduce errors caused by reflections through spatial diversity. This combination of time measurement, phase comparison and cryptographic protection makes Channel Sounding a practical tool for real-world applications.
Hardware base for Channel Sounding
One example of implementation is the new PAN-B611 module family from Panasonic. It provides the Channel Sounding functionality in a compact, pre-certified package. It is based on the nRF54L15 from Nordic Semiconductor, one of the first Bluetooth SoCs that supports precise ranging and angle measurements. The chip integrates a radio subsystem for phase and round-trip analyses, a powerful Cortex-M33 processor and cryptographic protection mechanisms. A separate RISC-V co-processor assumes time-critical tasks. Besides ranging, the support for multiple antennas also enables angle-based positioning and thus more detailed detection in both two and three dimensions.
The PAN-B611 routes all pins of the nRF54L15 on a hybrid footprint with castellated edges and LGA pads. Measuring just 10.35 x 9.6 x 1.9 mm, the module is suitable for designs with tight space restrictions. Versions with integrated chip antennas are suitable for compact designs, while models with external antenna connections also allow for multi-antenna setups. All pins of the nRF54L15 are routed out on the PAN-B611-1x modules to ensure that, for example, a PAN-B611-1B can be used for a multi-antenna Channel Sounding setup where an antenna switch is controlled with up to four GPIOs. In many applications, however, use of the integrated antenna in the PAN-B611-1C is sufficient for a rough distance estimate. This eliminates the need for customer-specific antenna adaptations or additional approvals and shortens development cycles.
For memory-intensive applications, Panasonic offers the PAN-B611 module family with an optional and compact 4 MB flash memory chip without changing the form factor. The additional memory allows for measurement data to be stored for further processing, e.g., for cryptographic processes or machine learning algorithms on the edge device. This also helps support the execution of non-time-critical routines directly from the memory (execute-in-place, XiP) as well as the management of larger firmware packages and over-the-air (OTA) updates. Figure 3 shows the PAN-B611 module with an integrated antenna.
The modular approach facilitates integration into existing designs and shortens development times. Developers can focus on the application logic, while certification and RF design are dealt with at module level.
From asset tracking to augmented reality (AR)
Location information creates added value in many areas of life. The possible applications are just as diverse. In healthcare or logistics, cost-effective sub-meter accuracy can significantly help to boost efficiency. Devices can be located immediately, inventories adjusted automatically and processes optimized without human error. In consumer applications, smartphones with Channel Sounding will be able to interact more securely with smart locks or vehicles in the future, as actual physical proximity is verified. In AR and VR systems, precise positioning improves synchronization between the digital and the physical environment. Scenarios based on the exact location data of each family member can also be used in smart homes, for instance the room-specific control of lighting and air conditioning.
One possible example is a smart lock that uses Channel Sounding for distance verification and simultaneously supports a smart home protocol like Matter. This allows for the actual proximity of a Bluetooth key or smartphone to be checked while enabling integration into an interoperable smart home. The optional 4 MB flash memory of the PAN-B611 provides sufficient space for larger firmware packages with protocol stacks, cryptography libraries and OTA functions.
Summary
Channel Sounding is an optional feature of Bluetooth 6.0 but given the growing popularity of new devices is likely to become the standard one. It marks the transition from probabilistic to deterministic ranging and takes Bluetooth to a whole new level: From a simple communication interface to a platform for spatial detection.