Station relief arrangement for use in relieving operation of a reference station in a TDMA network without reduction of frame availability

In a time division multiple access satellite communication network comprising a plurality of earth stations each of which sends an up-link signal and receives a down-link signal, each of said up-link and said down-link signals being divisible into a succession of multiframes which have a multiframe period and each of which is divisible into a particular frame and at least one remaining frame, said particular and said remaining frames having a common frame period, a preselected one of said earth stations being used as a primary reference station for producing first reference bursts at a first predetermined time instant in said particular frame and second reference bursts at second predetermined time instants which correspond to said first predetermined time instant in each remaining frame, said second reference bursts being identified from said first reference bursts by said earth stations, said first and said second reference bursts defining said multiframe and said particular and said remaining frames in the up-link signals sent by said primary reference station, each of said earth stations establishing and maintaining frame synchronization with reference to said first and said second reference bursts in the down-link signal, placing a succession of synchronization bursts at a preassigned position at said multiframe period in the up-link signal sent thereby, and performing burst synchronization by detecting said synchronization bursts with reference to said first and said second reference bursts in the down-link signal received thereby, the improvement wherein:

• one of said earth stations except said primary reference station is a subsidiary reference station which can relieve operation of said primary reference station when said primary reference station becomes faulty, said relief station comprising:
• first means for producing at said multiframe period a particular one of said synchronization bursts that is specific to said subsidiary reference station and can be identified from the other synchronization bursts by said earth stations;
• and
• second means coupled to said first means for placing said particular one of the synchronization bursts at a third predetermined time instant within said multiframe at said multiframe period to keep said particular synchronization burst in the up-link signal sent thereby while said first and said second reference bursts disappear in the down-link signal received thereby, said primary reference station being relieved by keeping said particular synchronization burst during disappearance of said first and said second reference bursts.

A reception control circuit for use in a time division multiple access satellite communication network to carry out a succession of operations in a time division fashion by successively selecting a plurality of carrier frequencies one at a time, said operations being divisible into non-modifiable and modifiable operations, wherein the improvement comprises:

• internal control signal producing means for successively producing first and second internal control signals indicative of the carrier frequencies selected on said non-modifiable and said modifiable operations, respectively;
• indicating means for producing a condition indication which is representative of a request for said modifiable operation;
• code producing means for producing a modified code representative of a preselected one of said carrier frequencies;
• selecting means responsive to said internal control signals and said control indication, said indicating means, and said code producing means for selecting said modified code as a selected code when said internal control signal which is representative of said modifiable operation is active and said condition indication indicates the request for said modifiable operation;
• and
• means for successively selecting one of said carrier frequencies in accordance with said selected code.