PURPOSE: To prevent duplicated assignment of a channel by stopping the transmission of an old data burst after the reception acknowledge notice of both new/old data bursts is given from an earth station.

CONSTITUTION: The same data burst as a data burst transmitted from earth stations (A∼Z)34∼50 to the assigned channel is also transmitted newly to an idle channel assigned newly and the transmission of the old data burst is stopped when the earth station 35 receives the notice of the reception of the new data burst in the newly assigned channel in addition to the old data burst and the data burst is transmitted continuously only to the new channel. If no notice is received, when the transmission of the new data burst is stopped, the channel assignment is changed surely in the unit of channel and no duplicated assignment is applied.