Transmission slot allocation and synchronization protocol for ultrasonic sensor systems

We consider an active ultrasonic sensor system for indoor presence detection. In such a system, a pulse sinusoid is used as an active transmission waveform and the received echoes are processed at the corresponding receiver to determine user presence within the detection region of a sensor. In a system with multiple sensors, cross-interference arises due to transmission from a sensor at the receiver of a different sensor and leads to degradation in detection performance. To address this, we propose a transmission slot allocation protocol to assign unique transmission slots to sensors within listening range, and a slot synchronization algorithm to ensure that assigned transmission slots are maintained in the presence of sensor clock drifts. A key characteristic of the presented solution is that it is distributed and does not require a central coordinator, and further does not need any explicit messaging. We evaluate the performance of the proposed solution in an ultrasonic presence sensing system.