Pulse or digital communications – Repeaters – Testing
Patent
1992-10-13
1994-07-12
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
H04L 2704, H04L 2712, H04L 2720
Patent
active
053295528
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of binary encoding the N points of a constellation corresponding to the discrete positions, in amplitude and in phase, associated with the encoding of digital words in the case of a multicarrier modulation of OFDM type (Orthogonal Frequency Division Multiplexing) of a digitized signal. It also relates to a method of assigning a constellation to a channel, especially when the points of the constellation are encoded by the method in accordance with the present invention.
BACKGROUND OF THE INVENTION 89/00546
In international patent application PCT/FR 89/00546, filed in the name of THOMSON-CSF, an especially powerful method of transmission has been described which uses a multicarrier modulation of OFDM type enabling a digitized signal to be transmitted with a high density. In the method of transmission described, a plurality of orthogonal frequencies are used and a pair (amplitude-phase) or (real part, imaginary part) is transmitted on each frequency, the amplitude-phase or real part-imaginary part pair being the one-to-one equivalent of the item of information to be forwarded. In order to produce the above one-to-one function, use is made of a constellation in a known manner. Indeed, each sub-carrier constituting the signal is modulated in amplitude and in phase in a discrete manner and the discrete positions, in amplitude and in phase, constitute a constellation in the complex plane. Several types of constellation can be used. Thus, in international patent application PCT/FR 89/00546 a circular constellation has been proposed. In this case, the amplitude-phase pairs corresponding to each digital word are distributed uniformly over concentric circles. The transcoding between the binary words of the digitized signal and a point of the constellation can be done in many ways without using any especially simple relationship. However, it is important for this encoding to make it possible to avoid, during reception, the maximum number of errors at the signal recovery level.
Thus, the aim of the present invention is to offer a novel method of binary encoding the points of a constellation which makes it possible to limit the number of errors during decoding.
SUMMARY OF THE INVENTION
Accordingly, the subject of the present invention is a method of binary encoding the N points of a constellation corresponding to the discrete positions, in amplitude and in phase, associated with the encoding of binary words in the case of a multicarrier modulation of OFDM type (Orthogonal Frequency Division Multiplexing) of a digitized signal, characterized in that two adjacent points of the constellation correspond to binary words which differ from one another by at most two bits.
According to a special embodiment applicable in particular when the points of the constellation are distributed over nested quadrilaterals, two horizontally and vertically adjacent points of the constellation correspond to binary words which differ from one another by a single bit, whereas two diagonally adjacent points of the constellation correspond to binary words which differ from one another by two bits.
Furthermore, in the case of a multicarrier modulation of OFDM type, if a single constellation is used for the all the channels, when all the carriers have maximum amplitude and are in phase, the transmitter must then pass a very high power spike with the risk of saturating this transmitter and thus of distorting the signal. This phenomenon occurs if no precaution is taken to avoid lengthy strings of "0"s or "1"s at the input of the device.
The aim of the present invention is also to provide a method of assigning a constellation to a channel which makes it possible to avoid the above disadvantages.
Accordingly, the subject of the present invention is a method of assigning a constellation to a channel, characterized in that a different constellation chosen from M constellations is assigned to each channel randomly in such a way as to avoid the phase-summation of signals.
Preferably, th
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Bingham, J. C., "Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come," May 1990, IEEE Communication Magazine, pp. 5-14.
Couasnon Tristan de
Fouche Yvon
Monnier Raoul
Rault Jean-Bernard
"Thomson-CSF"
Chin Stephen
Kobayashi Duane
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