Method for establishing communications in a network of frequency-jumping transmitter-receiver stations and a station for the utilization of said method
In order to establish communications in a conference network of transmitter-receiver stations, each station establishes a frequency-jumping standby law while a calling station transmits a frequency-diversity call sequence on said standby law and the other stations are listening in accordance with said standby law. Furthermore, each station establishes a second frequency law which is synchronous with the standby law but the stair-steps of which are of longer duration. At the end of a call sequence, the calling station and the stations which have detected this sequence are put in the listening state over a time interval t.sub.1 at the corresponding possible traffic frequency of the second frequency law. Each station which has detected a signal then transmits a jamming signal over a time interval t.sub.2 at the aforementioned traffic frequency and the stations which have not detected any signal extend the listening period by the same time interval t.sub.2. Non-reception of a signal during the time interval t.sub.2 makes it possible to establish a communication at the corresponding frequency.
A system for encoding and decoding an audio transmission signal comprises: (a) an encoder with a frequency-varying means to vary the carrier frequency of the audio signal according to an encryption algorithm; (b) a transmitter; (c) a receiver; and (d) a decoder with a multi-plexing filter for separating segments of the audio signal with identical carrier frequencies, and a demodulator corresponding to each carrier signal frequency. The separated segments of the audio signal are switched to the corresponding demodulators according to a decryption algorithm.
A communication system having a frequency hopping scheme which provides an improved initial synchronization in mobile stations of control channels. Special synchronization bursts are inserted into the hop sequence of the control channels which, when decoded, give the mobile station the hop sequence to follow for the control channel.
