Bluetooth® LE Channel Sounding: Accurate Distance Measurement Without Adding UWB

Why Distance Measurement is Still a Challenge in Bluetooth LE

In most Bluetooth LE designs, connectivity is easy. Distance measurement is not.

If you’ve worked on proximity-based applications—like smart locks, asset tracking, or digital keys—you already know the limitations of RSSI. It looks fine on paper, but in real environments, it fluctuates a lot. Walls, reflections, human movement—everything affects it.

That’s why many designs moved to UWB for accurate ranging. But UWB brings its own trade-offs: higher cost, extra hardware, and more complex integration.

Now, with Bluetooth LE Channel Sounding, there’s a more practical option.

Introduced by Nordic Semiconductor, this feature allows you to measure distance accurately and securely using standard Bluetooth LE hardware.

What is Bluetooth LE Channel Sounding?

Bluetooth LE Channel Sounding is a method to measure the actual distance between two BLE devices, without depending on signal strength.

Instead of asking “how strong is the signal?”, it asks:
“how did the signal behave while travelling?”

By analyzing signal characteristics across multiple frequencies, it gives a much more stable and realistic estimate of distance.

How Channel Sounding Works

The concept is straightforward, but the implementation is quite smart. It combines two techniques—each solving a different part of the problem.

Phase-Based Ranging (PBR)

PBR looks at how the phase of a signal changes when it travels from one device to another.

Since Bluetooth LE operates across multiple channels, the system measures phase differences across these frequencies. These differences are then used to estimate distance.

Why this works better:

• Multiple frequencies reduce error
• Less sensitive to reflections compared to RSSI
• More stable in indoor environments

Round Trip Time (RTT)

RTT measures time, not signal behavior.

• Device A sends a packet
• Device B responds
• Total time taken is measured

Since radio waves travel at a known speed, this time directly relates to distance.

Why Combine PBR and RTT?

Using both together improves reliability.

• PBR gives accuracy
• RTT adds validation
• Combined, they make it harder to manipulate the system

This is important for security-sensitive applications, where distance is used to make decisions.

Security Matters: Not Just Accuracy

One of the practical benefits of Bluetooth LE Channel Sounding is its ability to reduce relay attacks.

In a relay attack, a signal is extended artificially to make a device appear closer than it actually is. This is a known risk in systems like digital keys. By analyzing both phase and timing, the system can detect inconsistencies. This makes proximity-based access more trustworthy.

Nordic Devices Supporting Channel Sounding

Nordic Semiconductor has introduced support for Channel Sounding in its nRF54L Series.

Here’s how the lineup fits different roles:

• nRF54L05
  Best suited for simple reflector roles with minimal processing
• nRF54L10
  Supports reflector functionality with added features and basic initiator capability
• nRF54L15
  Designed for initiators with built-in ranging algorithms and more advanced use cases

Future support is expected in the nRF54H Series, which will further expand performance and flexibility.

What Kind of Accuracy Can You Expect?

In practical terms:

• Around 0.5 meter accuracy for short distances (under 5 meters)
• Around 1 meter accuracy up to 20 meters

That’s a significant improvement over RSSI-based methods, and good enough for most proximity-based applications.

Key Advantages in Real Designs

• No Additional Hardware: You don’t need to add UWB. Existing Bluetooth LE hardware can handle it.
• Better Accuracy Than RSSI: More stable results, especially indoors.
• Low Power: Still fits within typical BLE power budgets.
• Improved Security: Helps detect relay attempts and abnormal signal behavior.

Where This Fits in Real Applications

• Smart Locks: Door unlock decisions can be based on actual distance, not just connection.
• Find My Devices: More precise location of personal items.
• Asset Tracking: Useful in warehouses where knowing “nearby” is not enough.
• Smart Home Devices: Devices can respond based on proximity—without false triggers.
• Digital Keys: Critical for automotive systems where both accuracy and security matter.

BLE Channel Sounding vs UWB

UWB still has an edge in ultra-high precision. But it comes at a cost.

Bluetooth LE Channel Sounding sits in a very practical middle ground:

• Much better than RSSI
• Good enough for most use cases
• No extra hardware
• Easier to scale

For many products, this balance makes more sense.

Strategic Takeaway

Bluetooth LE Channel Sounding is not about replacing everything—it’s about solving a very specific problem in a more practical way.

If your application needs reliable distance measurement without increasing BOM cost, this is worth serious consideration.

With platforms from Nordic Semiconductor, getting started is straightforward, especially if you’re already working within the BLE ecosystem.

Need Support for Your Design?

If you’re planning to work on Bluetooth LE Channel Sounding or evaluating Nordic’s nRF54 series, having the right support early can save time.

Millennium Semiconductors can help with:

• Device selection
• Technical guidance
• Faster prototyping

📩 Reach out at info@millenniumsemi.com