Coded data generation or conversion – Digital code to digital code converters – To or from multi-level codes
Patent
1997-08-27
1999-08-24
Hoff, Marc S.
Coded data generation or conversion
Digital code to digital code converters
To or from multi-level codes
34082544, H03M 520
Patent
active
059429941
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to methods and apparatuses for decoding multivalent electrical signals, and to receiver assemblies including such decoding apparatuses.
BACKGROUND OF THE INVENTION
More particularly, the invention relates to a method of decoding a multivalent electrical signal capable of taking up a number n of states greater than 2, said signal having a characteristic electrical magnitude U which varies over time to take up successive values each representing one of the n states of the electrical signal, the characteristic electrical magnitude substantially retaining said successive values during pause periods each of predetermined constant duration T, the method including the following steps: signal during each pause period; and
In such a method, it is difficult to choose the instant at which to perform each measurement. A measurement performed too near the beginning or the end of a pause can be falsified by the fact that the characteristic electrical magnitude does not remain exactly constant over the entire pause. Under such circumstances, identification of the state represented by the measured value can itself be falsified.
A particular object of the present invention is to mitigate these drawbacks.
To this end, according to the invention, a method of the kind in question is essentially characterized in that the characteristic electrical magnitude U is measured at instants that are separated from a time origin by an integer number of durations T, the time origin being determined by performing close-together measurements of said characteristic electrical magnitude during a predetermined synchronization period at instants that are spaced apart from one another by a duration T/m, where m is an integer not less than 3, said close-together measurements being used to identify the pause periods in the characteristic electrical magnitude U, with the time origin being set substantially in the middle of one of said pause periods.
In addition, unlike decoding a bivalent signal where it is easy to discriminate between a high level and a low level of the signal, identification of the state represented by each measured value can be disturbed relatively easily by variations in said characteristic electrical magnitude, which variations may be due, in particular to temperature variations of the electronic circuits processing the signal, and to aging of these circuits.
Also, when the decoding method is applied to an electrical signal that is the result of demodulating a previously picked-up radio signal, e.g. when the radio signal is modulated in frequency, in amplitude, or in phase, the disturbing variations in the characteristic electrical magnitude can also be due to the better or worse quality of reception of the radio signal.
SUMMARY OF THE INVENTION
In an advantageous embodiment of the invention, in order to adapt to disturbing variations in the characteristic electrical magnitude of the multivalent electrical signal, above-mentioned step b) is performed by comparing the measured value with n-1 thresholds S.sub.1, S.sub.2, . . . , S.sub.n-1 which define n ranges of values each corresponding to one state of the electrical signal, said thresholds being previously fixed at least as a function of a minimum value U.sub.1 and of a maximum value U.sub.n of the characteristic electrical magnitude U as measured during a predetermined adaptation period.
In other preferred implementations of the method of the invention, use is made of one or more of the following dispositions: not only as a function of the measured values U.sub.1, U.sub.2, . . . , U.sub.n, but also as a function of ideal values U.sub.1 0, U.sub.2 0, . . . , U.sub.n 0 that the characteristic electrical magnitude U ought to take for the various states of the signal; ##EQU1## where k is an integer lying in the range 1 to n-1, U.sub.1 0 being the smallest of the above-mentioned ideal values, U.sub.n 0 being the largest of the above-mentioned ideal values, and U.sub.k 0 and U.sub.k+1 0 being respectively the k-th and the (k+1)
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Carreel Eric
Lewiner Jacques
Hoff Marc S.
Jean-Pierre Peguy
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