Data multiplexing for diversity operation
In a satellie mobile telecommunications system based on the GSM standard, and using a TDMA frame structure, discontinuous transmission (DTX) mode is used to take advantage of the substantial silences which occur during normal speech. In this mode, traffic channel (TCH) data is not sent, but control of the link between a ground station and a user terminal is maintained by sending control channel data bursts (SACCH) together with silence descriptor (SID) frames. To avoid high peak to mean values of transmission power at the satellite, the emission time of the bursts is controlled so as to be uniform over the available sending opportunities. Conventional techniques for doing this cannot be used in a system which includes diversity operation. Therefore, the burst transmission time at the ground station is set in dependence on a reference provided by the user terminal which is a modified version of the reference generated for contention resolution of random access requests.
1 . A method of data multiplexing in a mobile telecommunications system in which a ground station is in communication with each of a plurality of user terminals via a respective logical channel, each logical channel capable of carrying link control data to a respective user terminal over diverse communication paths using a multiple access scheme which includes time division, in which a frame comprises a sequence of time slots, each time slot being associated with a logical channel, the link control data being sent in bursts in selected time slots, the method comprising:
for each channel, setting the data burst transmission time from the ground station such that data bursts carrying link control data relating to the same channel and travelling over diverse paths to the same user terminal, arrive at the user terminal within a predetermined number of frames, and
distributing the ground station transmission time of data bursts carrying link control data for different channels over a plurality of frames, such that each frame which carries link control data includes link control data relating to a single logical channel only.
2 .- 22 . (canceled)