What Is Bluetooth Channel Sounding?

Bluetooth Channel Sounding is a safe, advanced technology for measuring the distance between two Bluetooth Low Energy devices. One device serves as the initiator and another acts as the reflector.

They send signals over different radio frequencies to take readings that are transformed into distance by the using of a ranging algorithm.

The technology uses two complementary methods:

  • Phase-Based Ranging (PBR) The initiator sends a signal that the reflector returns. Repeating this process across multiple frequencies reveals phase differences that can be used for high-accuracy distance estimation.
  • Round-Trip Time (RTT) The system measures the travel time of cryptographically scrambled exchanges. RTT supplies an independent distance bound and helps detect sophisticated man-in-the-middle relay attempts.

PBR supports precise measurement, while RTT adds security-oriented cross-checking. The Bluetooth SIG reports early accuracy around ±20 cm and potential range up to 150 metres under favourable conditions. These are technology-level expectations, not product guarantees. Enclosure, antennas, multipath, orientation, calibration and algorithms determine performance.

Bluetooth does not establish a single distance-calculating algorithm that could be applied to all devices. Instead, it formalizes the metrics according to which the approximate distance can be calculated. This opens possibilities for the developers but complicates the task of developing algorithms, its validation and adjustment for each product.

Why Use the Nordic nRF54L Platform?

The nRF54L Series combines a low-power multiprotocol radio, efficient processing and modern security. The nRF54L15 provides a 128 MHz Arm Cortex-M33, 1.5 MB non-volatile memory, 256 KB RAM and a RISC-V coprocessor. It supports Bluetooth LE, Channel Sounding, Matter, Thread, Zigbee and proprietary 2.4 GHz.

Nordic has mentioned a 3.4mA receive current from nRF54L15 Tag while the transmit current is 4.8mA at 0dBm. Sleep states commence from just 0.7 μA at 3V.

The actual consumption is dependent upon the range schedule, amount of connected devices, sensors and power design.

The nRF54L15 Tag is a great example of a reference platform. It is designed in a coin-cell and contains sensors and two antennas making it possible for development teams to analyze trackers/wearables before custom hardware.

Using dual antennas is an advantage in situations where positions of the body or its obstructing parts lead to the interruption of the RF path.

Relevant Adequate Infosoft Case Studies

Explore real-world embedded, IoT, and software projects delivered by Adequate Infosoft. Our case studies provide insights into the approaches our engineering team has taken when handling various product development tasks.

Our projects range from hardware and firmware development through connectivity, cloud integration, and software applications and showcase our expertise in all technologies and product specifications.

The solutions we have created illustrate how we are able to create, test, integrate, and validate the efficiency of our products.

Our nRF54L Bluetooth Channel Sounding Development Services

Feasibility Analysis and Ranging Architecture

Initially, we present the requirements of the product and not just the required level of precision. For instance, a lock mechanism may require distinguishing between the outside and inside and avoiding any impersonation attempts.

Initially, we present the requirements of the product and not just the required level of precision. For instance, a lock mechanism may require distinguishing between the outside and inside and avoiding any impersonation attempts. In the case of a tool tracker, it may require reliable near and far zones.

An industrial controller must ensure that no unwanted activation is made before the operator reaches a safe location.

Feasibility study covers range, speed of update, latency, battery power, device roles, antennas, dependence upon phone and false acceptance and rejection limitations. We make a comparison between Channel Sounding with RSSI or Direction Finding whenever it is suitable, and create an architecture that can be tested.

nRF Connect SDK and Zephyr Firmware

We build C/C++ firmware with Nordic's nRF Connect SDK and Zephyr RTOS, including initiator and reflector configuration, secure connections, session control, measurement collection, state machines, power modes, diagnostics, recovery and firmware update.

We build C/C++ firmware with Nordic's nRF Connect SDK and Zephyr RTOS, including initiator and reflector configuration, secure connections, session control, measurement collection, state machines, power modes, diagnostics, recovery and firmware update.

A tag may use motion and coarse RSSI to avoid continuous ranging. A lock may require authentication, fresh ranging evidence and policy checks before activating. We profile memory, processor load and current on the selected SDK and hardware.

Distance Algorithm and Sensor Fusion Development

We develop or integrate algorithms that transform PBR and RTT data into distance, reject invalid samples, filter outliers and assign confidence. Channel Sounding may be fused with RSSI, IMU motion, door state or application context.

We develop or integrate algorithms that transform PBR and RTT data into distance, reject invalid samples, filter outliers and assign confidence. Channel Sounding may be fused with RSSI, IMU motion, door state or application context.

Products should not act on one noisy value. We implement hysteresis, confidence thresholds, time windows and state-aware rules, with diagnostic evidence for field investigation.

Custom PCB, RF and Antenna Design

Our hardware team handles schematics, power, sensors, antenna matching, PCB layout and design-for-manufacturing. Antenna placement, ground clearance, enclosure materials, batteries and the user's body can alter Channel Sounding observations.

Our hardware team handles schematics, power, sensors, antenna matching, PCB layout and design-for-manufacturing. Antenna placement, ground clearance, enclosure materials, batteries and the user's body can alter Channel Sounding observations.

We evaluate single- and dual-antenna designs and mechanical constraints before release. Deliverables can include design sources, Gerbers, BOM, assembly data, bring-up plans and test specifications.

Development of Secure Digital Key and Access Control Systems

Distance is just one factor for access control. In the process of delivering a control system, we take into consideration the use of pairing, authentication, verification, freshness and actuator safety together with PBR and RTT.

Distance is just one factor for access control. In the process of delivering a control system, we take into consideration the use of pairing, authentication, verification, freshness and actuator safety together with PBR and RTT. An authentication device such as a phone or fob should satisfy certain criteria in terms of zone, confidence and time window.

The models used by us allow for evaluating relay, replay, stolen devices and downgrade risks as well as devising secure booting, signed OTA, key protection, and controlled provisioning measures. Channel sounding helps reduce relay risk although it does not guarantee overall product security.

Mobile Application, Gateway and Cloud Connection

We develop native or cross-platform apps using .NET MAUI, Flutter and React Native for onboarding, identity, diagnostics, ranging status, history and updates.

We develop native or cross-platform apps using .NET MAUI, Flutter and React Native for onboarding, identity, diagnostics, ranging status, history and updates.

Applications can perform onboarding, identification, diagnostics, ranging, status monitoring, history, and updates. Additionally, if the mobile phone does not support certain functionalities, custom devices can be developed.

Cloud solutions enable the management of fleet, credential, configuration, firmware, and financial audit processes. However, personal information is kept local whenever necessary.

High-Value Channel Sounding Use Cases

Smart locks and digital keys

Verify that an authorized phone or fob is physically close before unlocking a door, vehicle, cabinet, bicycle or safe.

Find My and asset tracking

Provide finer distance feedback as a user approaches keys, luggage, tools, medical equipment or inventory.

Industrial safety

Enable machinery or HMIs only from an approved distance and add confidence to personnel/tool proximity workflows.

Smart home automation

Trigger context-aware lighting, room controls or appliance behaviour based on distance rather than unreliable RSSI alone.

Wearables and consumer devices

Locate small accessories, improve device handover or change operating modes as paired devices move closer or farther away.

Testing Accuracy, Security and Power in Real Environments

We measure previously established distances in visible paths free of hindrance, inside buildings, in places where metal is present, and in configurations worn on the body. The result is the tables of its distribution of errors, reliability, latency, and failure rate among all available data.

Testing includes the measurement of orientation, multipath propagation, noise, mobility, obstacles, battery condition, and the presence of Bluetooth signals concurrently. Security tests deal with replay, relaying, freshness, incorrect identification, and a rollback property.

Development Process and Deliverables

We progress through discovery, proof of concept, algorithm evaluation, hardware, firmware, app integration, bring-up, calibration, verification and manufacturing handover. Early prototypes must meet decision thresholds in representative environments before production tooling.

Deliverables can include architecture, source code, PCB files, ranging datasets, calibration, test reports, threat model, app, APIs and production instructions. Traceability supports future SDK and hardware revisions.

Frequently Asked Questions

Is Bluetooth Channel Sounding the same as RSSI ranging?

No. RSSI uses the received signal strength to determine location but can easily be affected by obstructions and other variables. Channel Sounding uses a variety of frequencies and other data to determine location more accurately.

Can an existing nRF52 product gain Channel Sounding through firmware alone?

Usually not. Channel Sounding introduces new controller and physical-layer capabilities, so an older product may require a compatible SoC such as an nRF54L device and corresponding hardware and firmware changes. We audit the existing design and create a migration plan.

Does Channel Sounding guarantee centimetre accuracy?

No. Nothing can be guaranteed unless tested in real life. Bluetooth has been designed with centimeter accuracy in mind but various factors come into play in the process of using it.

Editorial Sources

Ashok Patel
Ashok Patel
Senior Engineering Project Manager
AI/ML, DevOps, Data Science & Automation | IoT & C#/.NET | Azure & AWS Expert | Certified AI & Cloud Engineer | 1,500+ LinkedIn Followers
Facebook LinkedIn Stack Overflow