Multidirection multiplex communication systems

Claim 1

A multidirection multiplex communication system of a demand assign system including a central station (CS) and a plurality of subscriber stations (SSi, SS 2 ..... SS N ) cooperating therewith wherein only one of said subscriber stations is requesting to transmit an information signal, predetermined transmission time slots are assigned to said subscriber station, characterized in that said central station comprises: means (6) for generating a maintenance poling signal (109) requesting a subscriber station (SS 1 ) not requesting to transmit said information signal for sending a predetermined maintenance burst signal (120); means (2, 3, 7) for multiplexing said maintenance poling signal (109) into a main signal (102) constituted by a predetermined frame and transmitting the main signal; means (4, 5, 8) for extracting a transmission timing signal (107) out of said maintenance burst signal (120) sent as response to said maintenance poling signal (109) to said central station (CS) from said subscriber station (SS1) not requesting transmission of said information signal; means (4, 5, 8) comparing said transmission timing signal (107) with a predetermined timing signal (106) in said central station for detecting a time shift of said transmission timing signal (107) of said subscriber station to output said time shift as a time difference signal (108), and means (2, 3, 6, 7) for multiplexing said time difference signal (108) into a main signal (102) constituted by a predetermined frame to send said main signal to said subscriber station (SSl); and wherein each of said subscriber stations ( SS l , SS 2 ..... SS n ) comprises: means (15, 17, 19, 10) responsive to said maintenance poling signal (109) sent from said central station (CS) for generating a maintenance burst signal (120) under control of a predetermined transmission timing signal and sending back said maintenance burst signal (120) to said central station (CS); means (15, 17, 18, 19) for separating and extracting a time difference signal (123) between said transmission timing signal (107) sent from said central station (CS) and said reference timing signal (106) in said central station from said main signal (113); and means (15, 17, 18, 19) responsive to said time difference signal (126) for controlling a phase of said timing signal in said subscriber station (SS 1 ) to maintain said transmission timing signal in said subscriber station in a synchronous state commensurate with said reference timing signal in said central station.

Claim 5

The system according to any of claims 1 to 3 wherein said maintenance burst signal (120) from said subscriber station not requesting to transmit said information signal is constituted by an address code (204), an instruction response code (205) and an information code (206).

Claim 6

The system according to any of claims 1 to 4 wherein said means (15, 17, 18, 19) in said subscriber station for holding said transmission timing signal (107) in a synchronous state commensurate with said reference timing signal (106) in said central station includes-timing control means (18) that gives a delay time corresponding to said time difference signal (108) to said transmission timing signal (107).