Multiplex communications – Generalized orthogonal or special mathematical techniques – Particular set of orthogonal functions
Reexamination Certificate
1998-03-06
2001-05-01
Kizou, Hassan (Department: 2662)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Particular set of orthogonal functions
C375S286000
Reexamination Certificate
active
06226259
ABSTRACT:
The present invention concerns a device and a method for transmitting information and a device and a method for processing information.
It applies in particular to the transmission of information by modulation of electric signals transmitted on a channel, for example by radio means. Even more especially, the invention applies to an improvement to the devices and methods presented in the European patent applications EP-94 400 936.4 filed on Apr. 29, 1994 and EP-95 303693.6 filed on May 31, 1995.
By way of explanation, let the case be considered in which the information to be transmitted appears as an n-uple of sequences of symbols in a finite alphabet. These sequences will be referred to hereinafter as information sequences, even though they can represent redundancies designed to correct errors affecting information associated with these redundancies.
These sequences are supplied to a transmission device, also called an “encoder” hereinafter, which produces, from these sequences, the electric signal to be transmitted on the channel.
It can be advantageous for this output signal to occupy a spread-out frequency band, in comparison with the sole frequency f supplying sequences, and for the energy transmitted in this frequency band to be on average uniformly distributed in this frequency band.
The spectrum-spreading methods disclosed in the document EP-94 400 936.4 cited above produce signals whose amplitude can, at certain moments, be too high.
This is because, according to these methods, each of the information sequences, being able to be represented by a sequence of symbols able to take the values +1 and −1, enters the encoder at the rate of n symbols per period T, equal to 1/f. By using a Hadamard function, derived from square matrices whose elements can take only the values +1 and −1, a signal is produced to modulate a carrier in the time interval in question, an interval of duration T.
By way of example, if a Hadamard function is used which is based on a matrix having 8 rows and 8 columns, the time interval is divided into 8 sub-intervals of equal time (of durations equal to T/8). The signal emitted during the i-th of these sub-intervals is equal to the product of the i-th column of the Hadamard matrix and the row including the eight symbols of the sequence transmitted, each symbol taking one of the values +1 and −1.
On receipt of the corresponding signals, which may be affected by errors, a new Hadamard function identical to that effected in the encoder is effected and the sign of the successive elements of the resulting sequence gives the values of the estimated symbol sequence.
This method presents the following drawbacks:
on the one hand, the number of different values is equal to the number of symbols in each sequence, plus one. This large number of levels of modulation of the electric signal makes precise estimation of the levels received relatively difficult,
on the other hand, the largest modulation values are much less probable than the smallest values, and
furthermore, the maximum level of energy to be transmitted grows proportionally to the square of the average energy transmitted.
The invention aims to overcome these drawbacks. To this end, according to a first aspect, the invention relates to a device for transmitting sequences of information, by modulating a physical quantity, having a means of transforming sequences of information adapted to associate, with each sequence of information, a so-called “intermediate” sequence of n so-called “intermediate” symbols each able to take a first set of different values, characterised in that it has:
a means of transforming intermediate sequences taking into account a second set of values whose cardinal number is strictly less than that of the first set, and associating with each element of the first set an element of the second set referred to as the “modulation number” and
a modulator adapted to modulate the physical quantity by the numbers in each sequence of modulation numbers.
Correlatively, according to a second aspect, the invention relates to a method of transmitting sequences of information, by modulating a physical quantity, including a step of transforming sequences of information during which, with each sequence of information, there is associated a so-called “intermediate” sequence of n so-called “intermediate” symbols each able to take a first set of different values, characterised in that it includes:
a step of transforming intermediate sequences taking into account a second set of values whose cardinal number is strictly less than that of the first set, during which there is associated with each element of the first set an element of the second set referred to as the “modulation number” and
a modulation step during which the physical quantity is modulated by the numbers in each sequence of modulation numbers.
By means of these provisions, the number of different levels of modulation of the physical quantity is less than the number of different symbols able to form the information sequence. When the values of the highest levels are, statistically, the rarest, and when these values are mapped to low modulation values, the invention makes it possible to reduce significantly the maximum energy emitted by the modulator, without reducing to the same extent the differences between distinct sequences.
According to particular characteristics:
the sequences of information having k items of information each able to take two different values, the means of transforming sequences of information is adapted to use a sub-matrix of k rows of a Hadamard matrix of dimensions n x n, to represent each sequence of information by an intermediate sequence of n intermediate symbols each able to take k+1 different values,
the sequences of information having k items of information each able to take two different values, during the step of transforming sequences of information, a sub-matrix of k rows of a Hadamard matrix of dimensions n×n is used, to represent each sequence of information by an intermediate sequence of n intermediate symbols each able to take k+1 different values,
the means of transforming sequences of information is adapted to cause the said sub-matrix to work on sequences of numbers able to take only the values +1 and −1, and/or
during the step of transforming sequences of information, the said sub-matrix is made to work on sequences of numbers able to take only the values +1 and −1.
By means of these provisions, the present invention applies to transmission methods and devices exhibiting characteristics of spectrum spreading and, in particular, to improvements to the devices and methods presented in European patent applications EP-94 400 936.4 filed on Apr. 29, 1994 and EP-95 303693.6 filed on May 31, 1995.
According to other particular characteristics:
the values of the modulation numbers are lower than a first predetermined threshold and the means of transforming intermediate sequences is adapted to associate with each intermediate number higher than the said first threshold a number lower than the said first threshold,
the values of the modulation numbers are lower than a first predetermined threshold and, during the step of transforming intermediate sequences, there is associated with each intermediate number higher than the said first threshold a number lower than the said first threshold,
the values of the modulation numbers are higher than a second predetermined threshold and the means of transforming intermediate sequences is adapted to associate with each intermediate number lower than the said second threshold a number higher than the said second threshold,
the values of the modulation numbers are higher than a second predetermined threshold and, during the step of transforming intermediate sequences, there is associated with each intermediate number lower than the said second threshold a number higher than the said second threshold,
the values of the modulation numbers forming the second set, the means of transforming intermediate se
Canon Kabushiki Kaisha
Elallam Ahmed
Fitzpatrick ,Cella, Harper & Scinto
Kizou Hassan
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