| 摘要 |
A loudspeaker (116) transmits an ultrasonic signal x(n) into a spatial region. A microphone (118) transduces ultrasonic sound, including an echo u(n) of the transmitted ultrasonic signal, received from the spatial region into a received ultrasonic signal y(n). A controller (404, 406, 407, S, 408, 410) transforms the ultrasonic signal and the received ultrasonic signal into respective time-frequency domains that cover respective ultrasound frequency ranges. The controller computes an error signal Z(m,k), representative of an estimate of an echo-free received ultrasonic signal, based on the transformed ultrasonic signal X(m,k) and the transformed received ultrasonic signal Y(m,k). The controller computes power estimates of the error signal over time, and detects a change in people presence in the spatial region based on a change in the power estimates of the error signal over time. |
