Channel Sounding

From smart door locks and access systems to asset tracking and management, Channel Sounding unlocks the true potential of IoT and creates a seamless web of interconnectedness by enabling the highest accuracy distance measurement for intelligent and context-aware systems.

Benefits of Channel Sounding

Channel Sounding, previously referred to as High Accuracy Distance Measurement (HADM), uses Phase-Based Ranging (PBR), Round Trip Time (RTT), or both to accurately measure the distance between two Bluetooth Low Energy connected devices.

 It enables connection-oriented 2-way ranging.

 Supports up to four antenna paths between devices - minimizes multipath effects and enhances accuracy.

 Offers enhanced built-in security features to mitigate the risks of man-in-the-middle or relay attacks.

How Does Channel Sounding Work?

Channel sounding is a method for estimating distances between two devices, designated as the initiator and the reflector. They exchange information across 72 RF physical channels, with the initiator transmitting first, followed by the reflector's response. This alternating transmission and reception enable precise distance measurements. The technique employs Phase-Based Ranging (PBR) or Round-Trip Time (RTT) or both for accurate coordination across the 2.4 GHz spectrum. It also supports one to four antenna paths to improve measurement accuracy and reliability.

Round Trip Time (RTT)

Round trip time (RTT) in a communication channel refers to the duration a signal takes to travel from the initiator to the reflector and back again. By assessing the Time of Flight (ToF) — the time it takes for a packet to be exchanged between the initiator and the reflector — the distance can be estimated. To achieve this, both devices record the Time of Arrival (ToA) and the Time of Departure (ToD). Analyzing the differences between ToA and ToD for both the initiator and the reflector provides the data necessary for a reliable distance calculation. Additionally, in terms of security, since time cannot be reversed, RTT is considered highly secure.

Phase-Based Ranging (PBR)

Phase-Based Ranging (PBR) utilizes the principle of phase rotation in RF signals to determine distances. In this process, the initiator sends a signal with specific frequency and amplitude information, and the reflector measures the phase of this received signal before sending a response. By comparing the phase differences between the signals from both devices, their relative distance can be determined. PBR offers a significant security advantage, especially compared to methods like RSSI (Received Signal Strength Indicator). The complexity of manipulating phase information makes PBR a more secure technology for distance measurement.

Target Applications for Bluetooth Channel Sounding

Proximity Awareness

To develop Bluetooth Low Energy enabled devices that are used in securely controlling and restricting access to spaces.


Door Locks

Keyless Entry

Locating Solutions

For applications like asset management and personal item tracking. It provides the perfect blend of precision and convenience. 

Warehouse Management

Pet Tracking

Item Tracking


Watch Now: How Channel Sounding Enables Indoor Ranging and Accurate Distance Estimation

Channel Sounding Use Cases

Vehicle Access Entry

One primary use-case for Channel Sounding is remote keyless entry to a vehicle. It is used for zonal detection through ranging to authenticate approaching users and unlock the vehicle. It utilizes Bluetooth Ranging through the established connection between the data channels - in this case, the key fob or phone and the anchor points on the car.

Indoor Ranging

Channel Sounding offers a solution for facilities like hospitals and warehouses, enabling both restricted access and asset tracking. It authenticates and allows entry to authorized individuals at doorways, enhancing security. It can also be used to monitor assets such as medical equipment or other high-value items.

Is Channel Sounding the Right Choice for Me?

With the multitude of positioning solutions available in the market today, selecting the ideal one for your IoT project becomes crucial. Allow Silicon Labs to assist you in finding the perfect match for your requirements. Contact us now.

  RSSI Angle or Arrival/ Angle of Departure Channel Sounding
Localization Metric Resolve distance estimation from transmitter signal strength Resolve relative angle between two points Resolve distance between two points using time of flight and phase-based ranging
Antenna Requirements Single antenna Multi-antenna required by spec Multi-antenna not required, but useful for optimal position resolution
Bluetooth LE Connectivity Connection-oriented and connectionless Connection-oriented and connectionless Connection-oriented
Performance Metrics +/- 5m, high susceptibility to multipath interference +/- 3 degrees accuracy – azimuth
+/- 5 degrees accuracy – elevation
+/- 0.3 m < 5m with PBR ranging
+/- 0.5 m > 5m with PBR ranging
Solution Advantages Ubiquitous support for RSSI measurements in existing Bluetooth Low Energy products Scalable solution for real time position tracking
Supports 5-10 year battery life
Small form factor with flexible antenna design
Feature-add for security by proximity

Silicon Labs Channel Sounding Solutions - Coming Soon

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EFR32xG24 Dev Kit

The xG24 Dev Kit is a compact, feature-packed development platform. It provides the fastest path to develop and prototype products that use Channel Sounding for distance estimation over a Bluetooth LE connection. The development platform overs a dual antenna design, supports up to +10 dBm output power and includes support for an accelerometer.  The platform can be powered through a USB connection or by a coin cell battery. 

BGM241S SiP Module Radio Board

The BGM241S +10 dBm SiP Radio Board is designed work with the WSTK main board to support the development of Bluetooth Low Energy Wireless IoT devices that use Channel Sounding for distance estimation. 

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