Dear Sir or Madam,
We are currently evaluating and testing the **Channel Sounding feature on Nordic BLE devices**. During our measurements, we observed that the Channel Sounding results degrade significantly once the distance exceeds a certain range, which eventually prevents distance estimation. We would like to ask whether this behavior is expected, or if there are recommended configuration adjustments to improve the performance.
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Test Environment
* Device: nRF54L15
* Environment: Open office space (LOS, non-anechoic)
* Device setup: Both devices are static, with fixed antenna orientation
* Channel Sounding configuration: Enabled Channel Sounding with 72-channel frequency sweep
* Sample used: `samples/bluetooth/channel_sounding_ras_initiator`
* Configuration status: No modifications made; all default sample settings are used
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Observed Behavior
* When the distance is "below approximately 1 meter", Channel Sounding operates normally and ranging results can be obtained.
* When the distance is "greater than approximately 1 meter", signal quality frequently degrades, and the channel sweep results are often incomplete.
* Due to insufficient valid Channel Sounding data, the ranging algorithm is not executed, resulting in no distance output.
* We also observed that when the distance exceeds ~1 meter, the `tone_quality` field frequently reports `1 (fail)`, indicating that multiple channel tones do not pass the quality check.
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Preliminary Assessment and Questions
Based on our observations, we believe this issue is likely not caused by the ranging algorithm itself, but rather by insufficient received tone quality at longer distances, leading to an insufficient number of valid channels.
We would like to ask the following questions:
1. Under the test conditions described above, is the significant degradation of Channel Sounding performance beyond ~1 meter an expected behavior or known limitation?
2. In general, which factors most commonly cause `tone_quality = fail` (e.g., SNR thresholds, CS procedure duration, TX power, timing configuration)?
3. Are there any recommended Channel Sounding configuration adjustments (such as TX power, subevent/procedure interval, main mode repetition, or quality thresholds) to improve measurement robustness and extend the effective ranging distance?
4. Is there an internal requirement for a minimum number of valid channels or quality criteria, below which the Channel Sounding result is considered invalid and the ranging calculation is skipped?
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We would appreciate your guidance and experience to help us determine whether this behavior is an inherent system limitation or if there are further optimization opportunities.
Thank you very much for your support.
Best regards,
Mike
