Multiplex communications – Communication techniques for information carried in plural...
Patent
1997-09-29
2000-05-02
Kizou, Hassan
Multiplex communications
Communication techniques for information carried in plural...
370431, 375259, 375295, H04J 1500
Patent
active
060581182
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The field of the invention is that of the transmission of digital signals (or sampled and digitized analog signals) to one or more receivers. More specifically, the invention can be applied to transmission systems enabling the transmission of a multiplex that is generally (but not exclusively) formed by several independent source signals, according to a multiplex structure that can be redefined according to need, and implementing a time interleaving of the data elements that form these source signals.
A particular field of the invention is that of the transmission of signals that simultaneously implement a plurality of carrier frequencies, each encoded by distinct digital data elements.
Signals of this kind are generally designated by the term FDM (frequency division multiplex) signals. A particular example of these signals to which the invention can be applied is that of OFDM (orthogonal frequency division multiplex) signals.
An OFDM signal is used for example in the digital broadcasting system described for example in the French patent application FR-86 09622 filed on Jul. 2nd 1986 and in the document by M. Alard and R. Lassalle, "Principes de modulation et de codage canal en radiodiffusion numerique vcrs les mobiles" (Principles of channel modulation and encoding in digital broadcasting to moving bodies), Revue de l'U.E.R., No. 244, August 1987, pp. 168-190, known as the COFDM (coded orthogonal frequency division multiplex) system.
This COFDM system has been developed in particular within the framework of the European DAB (digital audio broadcasting) project. It is also a candidate for standardization for the terrestrial broadcasting of digital television.
The signals transmitted by such systems take the form of successive frames, each frame comprising all the carrier frequencies. Several source signals can therefore be conveyed simultaneously, each source signal being for example, at a given instant, associated with a set of frequencies. The term "source signal" is understood of course to mean both signals that are quite independent, corresponding to various applications (sound, images, telematics, data, etc.) and distinct signals (or fluxes) of one and the same application (for example the right-hand and left-hand channel for a stereophonic signal, subtitling, translation, images associated with a main signal, etc.).
It can easily be understood that it is desirable that the structuring of the frame into data channels (corresponding to each source signal) should be modifiable as a function of need. For example, it may be the case that a station may make transmission only occasionally, and may therefore not have need for transmission resources except at its transmission times. It may also happen that the needs relating to an application may vary in the course of time: for example with the stereophonic transmission of music and the monophonic transmission of speech, the addition of a translation sound signal, the transmission of an illustration, etc. Yet another example is that of radio-message networks, where needs constantly vary. More generally, the administrator of the network may, for one reason or another, wish to change the structure of the frames.
One technique used to manage the structuring in frames and its reconfiguration is described in the patent FR-90 16383 dated Dec. 19th 1990 filed on behalf of the same Applicants and entitled "System for the transmission of data by distribution in the time-frequency space with channel structuring". According to this technique, at least certain frames periodically include a description of the current structure. Thus, any receiver may have knowledge of this structure so as to extract the signal or signals pertaining to it therefrom.
This technique has been introduced into the DAB standard. In this standard, the frame is divided into sub-channels. This terminology shall be preserved hereinafter without however thereby restricting the scope of the invention. It must be noted that, on the contrary, the invention can be applied to
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Bauduin Jean-Pierre
Lemesle Jean-Michel
Rault Jean Christophe
France Telecom & Telediffusion de France
Kizou Hassan
Pezzlo John
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