Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Patent
1996-09-24
1998-10-13
Vu, Huy D.
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
370347, 370437, 370468, H04J 316
Patent
active
058223150
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The field of the invention is that of digital mobile radio systems. The invention applies in particular to cellular mobile radio systems such as GSM (Global System for Mobile communications) systems.
More particularly, the invention concerns the communication of digital data in systems utilizing time-division multiplexing, employing the TDMA (Time Division Multiple Access) technique.
The TDMA technique divides time into frames of predetermined fixed duration, the frames being in turn divided into time slots. One or more time slots are associated with each call. A burst can be transmitted in each time slot.
A frame comprises N time slots (i.e. N bursts) that can correspond to N calls. Each receiver is able to extract the bursts corresponding to the time slots that are addressed to it, in order to reconstruct the source signal. In this way, N calls can be transmitted in the same frequency band.
After transmission on a radio channel, in particular a mobile radio channel using frequency hopping and with a quasirandom distribution of the interference signals, the quality of the frames (and therefore of the bursts that they contain) is variable. The transmission channel may be subject to various disturbances, including rapid fading and impulsive interference, which cause sequences of errors in the frames.
To attempt to solve this problem, in one standard mode of transmission the data to be transmitted is organized into source blocks and is encoded and then distributed (i.e. interleaved) into bursts each of which belongs to a separate frame.
The encoding process, usually called error control coding or channel coding, is intended to protect the wanted data to be transmitted by judiciously converting it into encoded data. An encoded block is generally larger than a source block. At the receiver, the encoded data is processed to recover the wanted data, even in the presence of transmission errors due to the poor quality of the transmission channel.
The interleaving that follows encoding consists in dividing the data of the same encoded block between several bursts belonging to separate frames, so that they are transmitted at separate times. At the receiver, decoding is preceded by deinterleaving which breaks up the series of errors and, ideally, produces isolated errors that are more easily corrected upon decoding the codes used.
In the standard mode of transmission this interleaving, i.e. the distribution of the data from the same encoded block between several bursts, is mandatory since the size of the encoded blocks means that it is not possible to place all of an encoded block in one burst, in particular because they contain a relatively large amount of redundant data. The encoding process, and thus the amount of redundant data, are chosen to enable correct decoding when transmission channel quality is poor (i.e. in the worst case scenario).
This standard mode of transmission has various disadvantages, even though it enables effective and correct exchange of data regardless of the quality of the transmission channel.
First of all, it is clear that the standard mode of transmission, being designed to work in the worst case scenario, is not optimized when the transmission channel quality is reasonably good.
The interleaving at the transmitter implies a time-delay at the receiver which can be relatively large, since the corresponding deinterleaving process presupposes the arrival of several successive frames before an encoded block can be reconstituted.
An object of the invention is to overcome these various disadvantages of the prior art.
To be more precise, one object of the present invention is to provide a method of adapting the air interface in a mobile radio system to optimize the exchange of data bursts contained in frames, and in particular to reduce the amount of data transmitted.
Another object of the invention is to provide a method of this kind that reduces the time-delays.
A further object of the invention is to provide a method of this kind enablin
REFERENCES:
patent: 5214687 (1993-05-01), Kansakoski et al.
patent: 5481537 (1996-01-01), Gisler et al.
patent: 5619496 (1997-04-01), Weir
patent: 5644576 (1997-07-01), Bauchot et al.
de Seze Fabrice
Delprat Marc
Mourot Christophe
Alcatel Cit
Vu Huy D.
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