Patent GB-1101513-A (GB)
Title: Time division multiplex radio communication system
IPC: H04B7/212
Filed: 1965-04-07
Abstract: 1,101,513. Multiplex pulse signalling. NIPPON ELECTRIC CO. Ltd. 7 April, 1965 [11 April, 1964], No. 14696/65. Heading H4L. In a time division multiplex system comprising a plurality of widely spaced ground stations and an earth satellite or other relay station, synchronizing means are provided which compensate for fluctuations in the position of the satellite or other faulty transmission conditions. General description.-The system described, Fig. 1 (not shown), includes a stationary satellite (S) and ground stations (A, B, M,) station (M) serving as a master station providing a synchronism standard for the whole system. The ground stations are not evenly spaced from the satellite and it is necessary to apply continuous time correction to ensure that signals arriving at the satellite from the respective ground stations appear in their correct time slots for retransmission. Intially the station (M) sends a coded signal which acts as a frame synchronizing signal and the time required for the return of this signal from the satellite is used by the station (M) to derive a signal representing the fluctuations of the position of the satellite to be sent as the next signal from station (M) via the satellite as a binary coded satellite-position-correction signal to the other ground stations. Each controlled ground station also transmits a coded search pulse signal which is received back by that ground station and if it is not received in the correct time position a correction is applied. Controlled ground stations.-Stations A and B, Fig. 3, include a radio receiver 12 supplying the demodulated time division multiplex P.C.M. or P.A.M. signal to a decoder and distributer 16 and also to a synchronizing signal gate 134 responsive to the sync. signal sent by station M, a search pulse gate 141 and a correction-signal gate 151, the gates being controlled by appropriately timed pulses from a tapped delay line 133 fed by a generator 131 via a frequency divider 132. The sync. signal is selected by a matched filter 135 and supplied via delay circuit 136D to a subtracting circuit 136H receiving also the signal from 135, the resulting timing correction signal being supplied via low pass filter 137 and amplifier 138 to control the frequency of the generator 131. Similarly, the search pulse is selected by a matched filter 142 co-operating with delay circuit 143D and subtracting circuit 143H, low pass filter 144 and amplifier 145 to provide a signal controlling variable delay 156 when switch 17 is in position 17P. The output of matched filter 142 is also supplied via low pass filter 146, and envelope detector 147 to a search pulse transmission control circuit 17W which controls switch 17 so that when the search pulses are within a predetermined range of the correct time position the switch 17 is in position 17P and when they are out of this range it is in position 17Q. The coded correction signal selected by gate 151 is converted into an analogue signal at 152, 153 and supplied to a programme generator 154 controlled by a standard clock 155. The device 154 produces a satellite-position representing analogue signal is known manner with reference to the standard time signal and the effects of the earth and other celestial bodies which is combined with the signal from 153 and is amplified in position 17Q of switch 17 to control the variable delay 156. The variable delay 156 controls the application of timing pulses from 133 to the transmitter synchronizing circuit 21. Circuit 21 controls a sync. generator 22 and a coder 23 receiving the input information signals, the coded output being supplied via switch 24 to the radio transmitter 25. The output of detector 147 is also supplied via a delay 27 to a control circuit 24W which keeps switch 24 open when the received search pulses are not in their correct time position. Master station.-Circuits 14 and 15 are omitted and a satellite-position-correction signal generator is included.