The additional ultrasonic communication enables two functionalities:
– Because of the varying wavelength of US-communication to the RF-communication and the specific speed the exact Distance between both parties can be measured.
– The ultrasonic communication is encrypted and shares the specific communication parameters that is needed for the RF-communication. In that way, the system inhibit the crosstalk to other communicating couples.
– Unlimited numbers of station doors or bus doors.
– Up to 16 sender / receiver couples can be used at the same time within 5m. Which is the relevant distance of the US-length.