How Bluetooth Channel Sounding Redefines Location Accuracy
Illustration: © IoT For All

With its well-known audio streaming and data transfer capacities, Bluetooth technology has become a ubiquitous part of our lives, powering everything from wireless headphones to smart home devices. But did you know that Bluetooth is now leaping towards high-accuracy location services thanks to a groundbreaking technique called Bluetooth channel sounding?

In this article, we’ll explore what Bluetooth channel sounding is, how it works, the benefits it brings to location services, which use cases benefit from high-accuracy distance measurement (HADM), and why it’s such a game-changer in the world of connectivity.

What Is Bluetooth Channel Sounding?

Channel sounding, previously known as high-accuracy distance measurement (HADM), is a new technique to calculate the distance between two Bluetooth devices. It uses phase-based ranging (PBR) on multiple channels to obtain an accurate distance measurement.

Does it sound complex? At its core, the principle of channel sounding is simple.

How Bluetooth Channel Sounding Works?

Look at the picture of the channel sounding procedure and let’s explore the principle in an easy way.

Device A sends a radio signal to Device B, whereupon Device B measures the phase of this signal and transmits it back to Device A with that same phase. Following this, Device A assesses the phase variance between the transmitted and received radio signals to determine the distance traversed by these signals at the time of flight.

This procedure is repeated multiple times over different channel frequencies, thereby the Bluetooth devices can estimate an unambiguous distance in a precise way using phase data.

The upcoming feature brings good news to the increasing number of Bluetooth devices, especially the ones with location services.

What Are the Benefits of Bluetooth Location Services with Channel Sounding?

The benefits of Bluetooth location services with channel sounding are vast and impactful. Here are the key advantages.

High-Accuracy of Up to 10CM

Despite the proven utility of existing Bluetooth ranging technologies, their precision in distance measurements may fall short for more challenging use cases.

The ubiquitous received signal strength indicator (RSSI) technique, available on all smartphones, estimates the distance between two devices based on the decline of the signal’s amplitude. Regrettably, the accuracy of this method is generally limited, often ranging from three to five meters. Besides, RSSI remains vulnerable to interference from external factors, such as absorption and diffraction.

After that, more advanced techniques in distance ranging accuracy are born – Angle of arrival (AoA) and Angle of departure (AoD). Instead of directly estimating distance, AoA and AoD utilize trigonometry to derive distances from the angles of incoming or outgoing radio signals. This methodology can achieve sub-meter accuracy.

Nonetheless, the accuracy may yet fluctuate considerably due to surrounding circumstances. For example, multipath propagation can impede accurate measurements in indoor spaces densely populated with obstacles and reflective surfaces.

This leads us to Bluetooth® channel sounding, the latest wireless technology for high-accuracy location services. The prominent difference between traditional Bluetooth ranging technologies and channel sounding is the measurement method.

With the phase-based ranging, Bluetooth channel sounding leaps towards 10-cm accuracy. Even if the device is in challenging indoor environments, it can get a more precise location than the two previous techniques. Therefore, channel sounding will empower a wide range of applications, eg. asset tracking and indoor navigation.

Enhanced Security Against Signal Manipulation

RSSI has another drawback aside from low accuracy: that is, a security risk. Its signal levels can be tampered with, potentially resulting in breaches in high-security situations.

For example, in security-sensitive use cases such as smart door systems, an attacker could elevate the RSSI level to deceive the system into perceiving someone as closer than they truly are. These vulnerabilities render RSSI inadequate for high-security applications.

For Bluetooth channel sounding, the link layer handles procedures for advertising, scanning, connection management, asynchronous and isochronous data communication, and data encryption. Moreover, its phase-based ranging algorithm can prevent relay attacks. The outstanding ranging technique is fit for car access control systems, digital keys, and high-security applications.

Low-Cost Positioning Solution

Angle of Arrival (AOA) requires multiple Bluetooth antennas (at least three antennas) to get a precise measurement.

Maybe another high-accuracy technology like ultra-wideband (UWB) comes to your mind now. While UWB can reach even sub-centimeter precision, it requires incorporating a new chipset. Additionally, its power consumption, while quickly decreasing, remains notably higher than that of BLE’s. It follows that ultra-wideband (UWB) offers improved accuracy but at the cost of increased budget and complexity.

Aside from the two pros mentioned above, single-antenna Bluetooth LE solutions with channel sounding are more cost-effective than UWB solutions.

Seamless Integration & Interoperability

Bluetooth channel sounding is introduced by existing Bluetooth technology, making it easy to integrate seamlessly into established infrastructure and devices. This means businesses and developers will quickly have easy access to a secure, low-cost, and accurate positioning solution without needing additional chipsets.

The unprecedented accuracy, security, and flexibility of Bluetooth channel sounding break barriers for many applications. Which use cases will probably adopt the tech?

Which Use Cases Prefer High-accuracy Distance Measurement (HADM)?

The applications of high-accuracy distance measurement (HADM) are diverse. Here are some use cases that can benefit significantly from this new technology.

Indoor Navigation: In large shopping malls, the combination of channel sounding with other new Bluetooth technologies like electronic shelf label (ESL) protocols can revolutionize indoor navigation experiences, providing users with precise directions and real-time updates.

Asset Tracking: Bluetooth-based systems have been widely commercialized for asset tracking in industrial and warehouse settings. These systems also leverage existing Bluetooth low-energy technology to meet performance standards. Developers can use channel sounding to improve the positioning accuracy of these systems. This not only helps prevent loss or theft but also improves operational efficiency by streamlining inventory management processes.

Moreover, it provides advanced features to some of the more demanding systems available, like real-time athlete tracking in professional sports.

Vehicle Keyless Entry: Channel-sounding offers several benefits for vehicle keyless entry. This technology provides greater accuracy compared to older systems that rely on Receive Signal Strength Indication (RSSI) for distance estimation. This enables carmakers to meet accuracy standards while reducing the number of Bluetooth antennas on vehicles. Thereby, it decreases the overall cost of a Phone as a Key (PaaK). Additionally, channel sounding security blocks various potential attacks on the keyless entry system.

In short, the high security and accuracy over previous generations of Bluetooth positioning, coupled with its low power profile and low cost, makes Bluetooth channel sounding ideal for applications such as industrial/warehouse/consumer asset tracking, ESL systems, real-time sport/fitness tracking, and automotive digital keys.

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