Measuring Channel Occupancy with an SDR

[Pavel]

Short answer: Channel occupancy is the fraction of defined observation time in which a channel exceeds a stated detection rule. Publish the channel bandwidth, threshold, time resolution, noise treatment and missing-data policy or the percentage cannot be reproduced.

Before you start​

• Define authorized bands, observation period, minimum signal duration and the measurement you need before selecting hardware.
• Use shielding or conducted RF paths for active security tests whenever over-the-air transmission is unnecessary.

Step-by-step method​

1. Step 1: Define channel center and bandwidth, then calibrate frequency and estimate noise across representative times. Exclude receiver overload before setting a threshold.
2. Step 2: Choose a detector such as power above noise by a fixed margin for a minimum duration. Include hysteresis so noise near threshold does not chatter between states.
3. Step 3: Sample or sweep fast enough for the shortest event, recording timestamps and gaps. Mark maintenance and dropped data rather than counting it as idle.
4. Step 4: Validate against a known test transmission, then calculate occupied seconds divided by valid observed seconds for each channel and time interval.

Concrete example​

If a channel is above threshold for 900 valid seconds during a 3,600-second window with no gaps, occupancy is 25%. If 600 seconds of data are missing, the denominator is 3,000 valid seconds unless the policy explicitly handles gaps differently.

How to judge the result​

A credible occupancy result is stable under a small threshold sensitivity test and includes enough detector parameters and valid-time accounting to repeat it.

What to record​

• Calibrate amplitude with a known source and record frequency-dependent correction; an SDR display is not automatically a traceable power meter.
• Store enough metadata to reproduce each observation: receiver, clock, antenna, gain, bandwidth, location precision and software configuration.
• For occupancy, define threshold, time resolution and treatment of noise before calculating percentages.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Using one fixed dBFS threshold across frequency without calibrating receiver gain and noise response can create artificial busy and quiet channels.

Final check​

Run a known controlled signal through the monitoring method and verify detection, calibration, timestamps and gaps. Keep authorization and data-handling records with the measurement.