the communication system , which is especially useful for pay tv , comprises a central station and a plurality of remote stations . the central station includes means for transmitting pay tv programs to the remote stations , and each remote station includes a circuit for transmitting information signals to the central station . each of the remote stations is adapted to transmit its information signals randomly to the central station so that a relatively large number of remote stations can operate , without interference , with a single central station . in one arrangement , the central station directly reads the information in the received signals to determine the status of the remote station . in a second system , the central station receives randomly transmitted signals from each room , and it also receives signals from the program transmitter . the central station equipment includes a computer which detects time or phase coincidence between the signal from the program transmitter and that from the remote stations , and uses that information as desired .