Bench Talk

New Version Offers Improved Device Positioning and Location Services

(Source: Anna/stock.adobe.com; generated with AI)

The Bluetooth Special Interest Group (SIG) continues to diversify the target applications of the once consumer-focused short-range wireless technology. Originally designed to wirelessly connect peripherals to host computers, Bluetooth^® technology has become almost ubiquitous as the go-to solution for power-frugal and reliable wireless connectivity, with almost universal smartphone support for the tech has hardly harmed its adoption either.

Bluetooth technology use has expanded into healthcare, consumer, audio, industrial, and numerous other applications. Despite impressive uptake—Bluetooth SIG forecasts approximately 5.9 billion annual device shipments during 2025—success in some target applications has been underwhelming.^[1] One area of note is device positioning and location services.

New enhancements to the Bluetooth protocol, introduced in version 6.0, are expected to spur engineers to use the tech to develop improved device-positioning and location service products: The Bluetooth SIG forecasts a 22 percent CAGR to reach 563 million location services device shipments by 2028.^[2]

Initial Support for Bluetooth Distance-Ranging

Theoretically, wireless connectivity can be used to locate lost objects. Think of those keys hiding in the depths of the sofa. If the keys are attached to a wireless tag, your smartphone can quickly indicate where to start looking. In an industrial environment, wireless mesh networks can help workers quickly locate goods on warehouse shelves. But in practice, implementing such applications is incredibly tricky. Factors such as multipath fading and interference from other nearby 2.4GHz transceivers spoil the signal integrity and undermine location accuracy.

The Bluetooth SIG has already made several attempts to add distance ranging and device positioning support to its RF protocol. First was an attempt to use the transmit (TX) parameter—which provided a reference power level one meter from the transmitting device—to provide a Received Signal Strength Indicator (RSSI). Because the strength of the RF signal tails off inversely proportional to the distance between the two radio devices, it can be used to provide a crude estimate of distance. This technique is useful for locating objects in reasonable proximity, but indicating the direction of one object relative to another is quite a different matter.   

In 2019, Bluetooth Direction Finding (adopted as part of the ratification of Bluetooth v5.1) enhanced Bluetooth device positioning and distance ranging. The technique enables applications to calculate the direction of a received signal using phase measurements made by the Bluetooth Low Energy controller. Two methods were defined, angle of arrival (AoA) and angle of departure (AoD).

While Bluetooth Direction Finding works well, it requires extensive design experience to implement. Designs are complex and can be expensive. As a result, the technology has been limited to high-end applications such as asset tracking high-value items rather than being widely adopted for more day-to-day applications.

New to Bluetooth 6.0

The recent introduction of Bluetooth 6.0 brought several key improvements to the protocol, including:

• decision-based advertising filtering, a new functionality that enables a scanning device to use the information received from a primary advertising channel to determine whether there’s a reason to look for related packets on the secondary channels;
• monitoring advertisers, which allows the Bluetooth Low Energy controller to filter duplicate advertising packets as instructed by the host component of an observer device;
• enhancement to the Isochronous Adaptation Layer (ISOAL), which enables larger data frames to be transmitted using more compact link layer packets;
• an extended link layer feature set, increasing the number of link layer functions about which devices can exchange information; and
• an update to frame spacing, enabling flexible adjacent connection spacing used with connection event packets or connected isochronous stream events.

The most significant enhancement to Bluetooth 6.0 is the introduction of Bluetooth Channel Sounding, which significantly enhances the precision of all previous Bluetooth distance-measuring techniques. The updated Bluetooth specification defines new features of the radio (PHY), features of the controller, security measures, and procedures needed to collect raw measurement data.

New Techniques Simplify Device Positioning

Channel Sounding brings two simple and reliable solutions for distance-ranging applications: Phase-Based Ranging (PBR) and Round-Trip Timing (RTT). Both are standardized and interoperable and can be supported by very simple devices or as an addition to a more advanced product without extra hardware costs and with minimal software additions.

PBR uses the phase shift of a signal sent by the initiator device and returned by the reflector device across multiple frequencies. The data-to-distance conversion uses dedicated algorithms and is performed at the application level. The RTT technique is based on the time it takes for radio packets to travel back and forth between the initiator and the reflector. RTT acts as a secure distance bounding technique to cross-check PBR, and the algorithms used to calculate the distance are simpler than those used for PBR.

For both PBR and RTT, power consumption is generally as low as regular data transfer over Bluetooth Low Energy. Finally, Channel Sounding supports various hardware and software configuration options for accuracy, latency, security, and power consumption.

Inspiring New Applications

Channel Sounding will make it easier for a new cohort of developers to come up with device positioning and distance-ranging applications, including the following possible examples:

• Asset tracking: Channel Sounding promises to bring greater precision, flexibility, reliability, and convenience to distance ranging and locationing without adding significant design complexity and cost.
• Smart locks: Security will improve because the position of the person wanting to use the lock will be known more accurately. Smart locks will also benefit from robust protection against man-in-the-middle and relay attacks.
• Tracking tags: Contemporary tag solutions work well, but the vibration or sound they emit when activated can be muted by things like sofa cushions or blankets. Channel Sounding will enable precise proximity alerts over long distances to overcome the limitations of sound or vibration alarms.
• Appliances: The physical context information provided by Channel Sounding will be useful when working with multiple devices and will assist safety features that activate control functions only when the user is near the device.

Conclusion

Bluetooth Low Energy continues to diversify into new consumer, healthcare, industrial automation, and smart home applications among many others. After a slow start, the locationing sector promises lucrative returns. The Channel Sounding technology added to Bluetooth 6.0 opens a huge range of possible distance-ranging and locationing applications, including enhanced asset-tracking devices, smart locks, tags, and appliances.

Sources:

[1] https://www.bluetooth.com/2024-market-update//
[2]  https://www.bluetooth.com/2024-market-update/#location-services