| 摘要 |
PURPOSE:To make interception difficult and to improve secrecy by changing a unique word used for a communication line from a fixed station to a moving station at every call and setting an arbitrary frequency. CONSTITUTION:For setting a communication channel, MES selects the parameter of the unique word by a forward channel in a unique word signal machine 1 and generates a unique word parameter signal showing the parameter. The signal is supplied to a signalling generator 2 and a unique word signal detector 6, and the generator 2 generates the signalling signal in accordance with the parameter signal. The unique word used for the communication line is changed at every call. MES except for specified MES sets the arbitrary frequency and transmits it to the moving station MES from the fixed station LES via a satellite line 10. Since unique word patterns used at every word differ even if the same moving station MES is used, interception is difficult and secrecy can be improved. |
