Data multiplexing for diversity operation

Abstract

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.

Description

[0001] The present application is a continuation application of application Ser. No. 09 / 959,815, filed Feb. 28, 2002, which application is based on International Application No. PCT / GB00 / 01880, filed May 17, 2000, claiming priority to European Patent Application No. 99303987.4, filed May 24, 1999, the entire contents of which are hereby incorporated by reference.FIELD OF THE INVENTION [0002] This invention relates to data multiplexing in a mobile telecommunications system, such as a satellite telecommunications system, which includes diversity operation, with particular but not exclusive application to multiplexing of link control data in a system which includes discontinuous transmission over diverse communication paths, BACKGROUND [0003] Terrestrial mobile telecommunications systems are well known and a number of different systems have developed which operate according to different standards, both analog and digital. In Europe and the Far East, excluding Japan, and elsewhere, the ...

AI Technical Summary

Benefits of technology

[0017] In accordance with this method, a user terminal is able to predict the arrival times of link control data for each of the diversity paths. The data burst transmission time can be set so that 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 the same frame, so that there is no delay in processing the two identical parts of the link control data. In discontinuous transmission mode, arrival of the link control data from diverse paths in the same frame minimises the number of frames in which data needs to be sent.

[0019] Multiplexing the data bursts in accordance with the method of the invention provides a staggering of the data burst transmission times at the ground station, so limiting the peak transmission power required at the ground station. This in turn avoids high peak to mean values of transmission power, i.e. power ripple, at the satellite which, in a satellite system, significantly limits the number of traffic channels capable of being supported.

Problems solved by technology

With this system, the satellite communications link does not permit communication between adjacent satellites.

For example, using the TN based multiplexing scheme explained above, the SACCH burst from the second satellite would arrive at the user terminal 4 frames after the burst from the first satellite, so introducing significant delays in processing the SACCH signals.

In addition, a TN based multiplexing scheme can impair the ability of the system to use the time alignment of the SACCH frames as a unique reference for functions such as measurement reporting and burst alignment in DTX operation.

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