Bluetooth Channel Sounding: Achieving 10cm Ranging Accuracy

December 7, 2023 -- Packetcraft is collaborating with Imec, a world-renowned semiconductor R&D and innovation pioneer to enhance Bluetooth ranging and location capability. In a co-authored article released by the Bluetooth SIG, both companies discuss a new technique called "channel sounding" for accurate distance measurement between Bluetooth Low Energy (BLE) devices, capable of achieving accuracy within a 10-30 cm range. This technology has significant implications for applications such as real-time location services, secure building access, digital keys, indoor wayfinding, and proximity detection.

A recent market study predicts a significant market growth of Bluetooth® location services in the coming years and it's being driven by increasing interest in things like secure keyless building and digital key vehicle access, indoor positioning, asset tracking, and proximity-based services. Channel sounding, also known as High Accuracy Distance Measurement (HADM), is the most recent of solutions aiming to respond to piqued interest and pain points of a widening market demand and is taking into consideration the innovation challenges, location-finding pain-points and market demands by prioritizing accuracy, standardization, and Bluetooth's pervasiveness in devices and sensors. Below are key highlights, though for the full whitepaper article on channel sounding go HERE.

Applications like indoor positioning and asset tracking benefit from increased Bluetooth accuracy. Source: Getty Images

Current Distance Estimation Techniques

There are currently several existing techniques for Bluetooth distance estimation, including Received Signal Strength Indication (RSSI) and Angle of Arrival (AoA) and Angle of Departure (AoD). These methods have limitations in terms of accuracy and performance, especially in complex environments with obstacles and reflections. Channel Sounding may be used in conjunction with AoA and improves accuracy down to 10cm.

The Tech Behind High-Accuracy is PBR Channel sounding utilizes phase-based ranging (PBR) to accurately measure the distance between devices by analyzing the phase of the radio signal. This method overcomes the limitations of AoA and AoD, which require multiple antennas and can be hindered by multipath environments.

The implementation of channel sounding involves changes to the Bluetooth system's hardware, specifically through a new physical layer with amplitude-shift keying modulation on 72 physical channels. The process is integrated into the link layer of the Bluetooth LE stack, responsible for managing channel sounding procedures, including negotiation, scheduling, and security.

Channel sounding introduces a new physical layer in the Bluetooth architectural system (source)

How it Works

Channel sounding within the Bluetooth architecture operates through a sophisticated process that enhances the accuracy of distance measurement between Bluetooth devices.

1. Phase-Based Ranging (PBR): Channel sounding employs PBR to measure the distance between devices. It analyzes the phase of the radio signal, allowing for precise estimation.

2. Hardware Changes: It introduces a new physical layer in the Bluetooth system with amplitude-shift keying modulation across 72 physical channels. This modification is crucial for the channel sounding process.

3. Link Layer Integration: Most of the channel sounding feature is incorporated into the link layer of the Bluetooth LE stack. This layer handles procedures like advertising, scanning, connection management, and data communication. For channel sounding, it negotiates and sets up the procedure, schedules radio operations, and configures the RF/PHY layer for tone exchanges.

4. Procedure: This consists of channel sounding events where two devices exchange tones for distance estimation and packets containing related data. The procedure is divided into subevents and steps for flexible scheduling and optimal coexistence with other Bluetooth communications.

5. Communication Sequence: The process begins with establishing a Bluetooth LE connection, followed by the exchange of channel sounding capabilities and configuration negotiation. After enabling security, the channel sounding procedure starts. The devices exchange measurement results after each subevent until all physical channels are covered.

6. Distance Estimation Algorithms: The results from the link layer are sent to an application which uses a distance estimation algorithm to calculate the distance between devices. The choice of algorithm can vary based on the application's needs and expected radio environment.

Channel Sounding Offers Flexible Application + Interaction

Channel sounding offers measurement results to be communicated between devices but does not require a specific distance estimation algorithm, allowing flexibility for different use cases. Furthermore, while the new tech offers unprecedented accuracy and security, it may not replace other technologies like ultra-wideband (UWB) impulse radio entirely. Hybrid solutions combining multiple ranging methods may become prevalent in the future based on requirements from the intended application.

The upcoming ratification of Bluetooth channel sounding represents a significant advancement in radio-based distance measurement and positioning. The potential of achieving 10cm accuracy ranging in real-world applications is turning heads as we anticipate new innovation that leverages this capability in emerging products and services.

For more info regarding this tech or other solutions offered by Packetcraft, schedule a 1:1 to discuss.

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