US Patent 9245426 Control of lighting devices

A network of active sensors in a control system is considered. The active sensors, which may be fixed-infrastructure sensors, provide presence detection information to a distributed lighting system. The active sensors communicate by transmitting probe signals. The communication of probe signals may result in cross-interference which may vary in time. Cross-interference is detected, and can later be avoided, by determining a difference between signals received in a first part of a timeslot and signals received in a second part of the timeslot. In order to do so probe signals comprising two non-zero pulses are transmitted in respective parts of the timeslot. Applications are, for example, active presence sensors in lighting control applications in indoor as well as outdoor environments.