Patent GB-1288233-A (GB)
IPC: H04B7/212
Filed: 1969-09-16
Abstract: 1288233 Radio-communications system KOKUSAI DENSHIN DENWA CO Ltd and FUJITSU Ltd 16 Sept 1969 [16 Sept 1968] 45644/69 Heading H4L In a P.C.M., T.D.M., satellite communication system, e.g. for carrying telephone messages, the N ground stations transmit their signals in respective bursts B1 ... BN, Fig. 1, successively arranged in a repetitive frame period T. Each burst, Fig. 2, e.g. that from station i, comprises a plurality n of satellite channels CH 1  ... CH n , and a control information portion. The satellite channels are grouped according to the destination ground station of the information they carry : e.g. channels CH1, CH2 are destined for station 1; CH 3 , CH 4 , CH 7  for station 2, &c. Each satellite channel is further made up of a plurality of T.D.M. ground channels or trunks TK, ... TKm. Due to a change in traffic at one or more of the ground stations, it may become necessary to change the number of satellite channels grouped for any one destination station, e.g. a change from format (b) to (c). This new arrangement has to be communicated to all the other ground stations for ideally simultaneous change over of their received information distribution system. The distribution information for any one burst is contained in a block of M words, SW, W1 ... (W m -1), Fig. 5 (a), word SW indicating the beginning of the block. Each word, of length TW = (TB/m), is made up of 1 successive word parts and each control information section of a burst includes an order word channel DL by means of which one word part is transmitted at a time. A plurality of frames T are thus needed before all the distribution information can be given out. The change in distribution information is signalled by a switching command signal Ex, Fig. 5(b), from a standard ground station SL, the station furthest from the satellite SA. The switching signal Ex is received back at the nearest and furthest ground stations SS and SL respectively at respective times SE and LE. Each ground station, Fig. 3, comprises a channel rearrangement unit C.R.U. which receives and gives out ground channels TK, arranges these in the respective satellite channels CH and arranges the satellite channels according to their destination station. A burst synchronizing unit BSU then arranges the burst into its correct slot so as not to cause overlapping with others at the satellite. Control information is also given by BSU. Units CRU and BSU are controlled according to the distribution information as supplied by order word unit DLU. CMU is an overall command unit. Unit CRU, (transmitter section) is shown at Fig. 4(a) and unit CRU (receiver section) is shown at Fig. 4 (b). Two stores C t  and D t  are provided, one of which is in use and determines by read out where the ground channels are to be placed in the satellite channels, and the other one of which is in reserve and memorizes whether a ground channel is being used in a ground channel is being used in a particular satellite channel. The change over from one distribution information to the next is thus brought about by the change over of the store in use. Unit B T  determines the channel number to be used in the stores CT, or DT and correspondingly controls the write-in of the ground channels TRK into talking into memory AT. This memory distributes the ground channels TRK into the satellite channels CH. The read out of memoryAT is controlled by unit E T . After the signal E x  has been received back at the furthest (standard) ground station SL, a delay Tp elapses, for the new distribution to be written into the reserve memory CT or DT before the transmitter can be changed from the old distribution LTO to the new distribution LTN. The ground station SL then transmits the nth block, beginning word SWi + n, which causes the nearest station SS to change over to its new distribution. The invention is stated to lie in the selection of block period T B  such that nT B #T 1 +T p  (n-1)T B #T s  or T B #T 1 +T p -T s  whereby all the stations have time to change over simultaneously. Each station changes over its receiver to the new distribution, i.e., LRO to LRN and SRO to SRN, after counting (nTB) after signal E x  is received, i.e. on receiving word SWi+n.