Patent FR-2808361-A1 (FR)
Title: Method and device for digital signal coding for transmission by modulation of at least one carrier, for use in protected telecommunication system
Inventor: ROUSSELIN SAMUEL
IPC: H04L27/34
Filed: 2000-04-27
Abstract: The method for coding a digital signal composed of consecutive binary elements is by mapping onto a set of points of a predetermined constellation having a whole number CC of points, which can be different from a power of two. The device for coding contained in the transmission block (38) of a peripheral station (SPi) in a telecommunication system with a base station (SB) comprises means in the form of markers insertion and data control circuit for regrouping the binary elements of the digital signal into successive binary words of length L, which is obtained from the equation: L = N+C-2N, where N is an integer such that C is in the range from 2N to 2N+1; and mapping circuit utilized for each binary word for mapping on a point among 2N points of the constellation, representing N binary elements in an absolute manner, so that C-2N other binary elements are deductible from former utilization or non-utilization of C-2N points of the constellation, named special points, each representing in a differential manner a binary element among C-2N binary elements of binary word.  Each of C-2N binary elements is represented by the special point of corresponding constellation, as a function of occurrence of a predefined event with respect to the value of the considered binary element in a set of consecutive binary words. The predefined event corresponds to a change of value of the considered binary element with respect to its value in the preceding binary word, or to a conservation of value of the considered binary element. The other binary elements are removed from the digital signal and replaced by markers designed to indicate at least one event relative to the other binary elements, and the markers are coded by the intermediary of special points. A predetermined sequence of markers changes the rule of coding. The digital signal is transmitted by the quadrature amplitude modulation (QAM) of a unique carrier, when each binary word modulates consecutively the carrier according to the predetermined constellation, or of a set of carriers, when a set of binary words modulates simultaneously at least one subset of carriers. The digital signal is transmitted according to the method of orthogonal frequency division multiplexing (OFDM). Each point of the constellation corresponds to an amplitude and to a phase of modulation of carrier by the digital signal, and one of the points is situated at the origin of complex plane. The modulation of carrier is controlled by mapping according to the constellation of points. The number of points of the constellation associated with each carrier is calculated as a function of an information representative of the quality of transmission in that channel. The information is received preliminary to the transmission of the digital signal, following a preceding transmission of a digital signal. The reception of digital signal comprises the steps of demodulation of carriers in a manner to obtain a constellation point for each, and of decoding the constellation points according to the rule of coding utilized in transmission in order to obtain binary words of digital signal. The decoding of each constellation point comprises a step of deducing the decoding of special points, as a function of value of binary elements in binary words preliminary received on the same carrier, and a step of extracting from the reconstituted data signal the control data indicative of the quality of transmission, for modifying the rule of coding. The telecommunication system comprises at least one digital signal transmission device, and at least one digital signal reception device. A telecommunication network comprises at least two telecommunication systems.