Algorithm II.

walking speed estimation:

Band pass filter (freq_low, freq_high) to limit the frequency range reasonable based on human gait speed Compute spectrogram Reduce spectral noise with average filter Select frequency with peak energy at time t as the torso frequency shift F (t)f → max[P (t, f)] Refine outlier torso frequency beyond (mean + 3*std dev) Update freq_low, freq_high based on obtained torso frequency, and repeat step 1–5 three times with updated freq_low, freq_high Suppress no-motion (sum energy at time t < threshold) torso frequency to zero Compute the walking speed $v=\frac{F_{d}c}{2F_t}$