Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-10-05
2003-06-24
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Spread spectrum
C380S252000, C381S073100
Reexamination Certificate
active
06584138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coding method and to a coder for introducing a non-audible data signal into an audio signal.
2. Description of the Related Art
The transmission of non-audible data signals in an audio signal is employed for example in range research for broadcasting. Range research serves to reliably determine the listener distribution of individual radio stations. The prior art knows various solutions for ascertaining the listener distribution of individual radio stations.
A first method operates such that a microphone, carried by a listener, is used for recording ambient noise which is compared by means of a reference receiver. On the basis of this comparison it is possible to determine the receiving frequency of the radio receiver.
A second method records the ambient noise in compressed form along with the information of the exact time in a memory and then transmits the same to a central station. In the latter, the data are compared by powerful computers with program examples recorded during a predetermined period of time, for example a day. The station listened to can be ascertained in this manner.
The methods described hereinbefore display the following deficiencies.
The system described first is not applicable to multi-band reception, multi-standard reception or multi-media reception, since it is restricted to the transmission of frequency-modulated signals only. Additional local broadcasting of other media via free FM channels is possible in individual cases only due to the multiplicity of program sources. Furthermore, with this method the same receiving strength as that of the receiver of the listener is necessary. In case of good receiving equipment or e. g. in cars, this requirement cannot be fulfilled. Another disadvantage consists in the reaction time for tuning the reference receiver and the correlation, since this increases with the numbers of programs offered and is in the range of minutes. The current consumption of such a method is considerable due to the components used, the receiver, signal processing etc. Moreover, the receiver cannot be designed in any economic manner desired, since the current consumption of the reference receiver directly determines the large-signal strength. Again another disadvantage consists in that the comparison principle is capable only of determining the frequency of the signal received, with the frequency occupancy, however, being dependent upon the momentary location. It is thus necessary to obtain information concerning the location of the listener, for example via the current transmitter tables.
The second method described hereinbefore involves the disadvantage of a considerable memory need since in case of recording over 24 hours, a net data quantity of about 150 MB results. Even in case of good compression e.g. by the factor of 10, a data amount of about 15 MB arises each day. The memories to be utilized are thus large and consequently expensive, and they also have a high current demand. In addition thereto, the determination of the reference programs causes difficulties since this needs to be performed in distributed manner all over the country. Still another problem consists in the problematic nature concerning data protection, as the audio information is collected directly from the environment of the test person and is conveyed further to a central evaluation.
For avoiding the problems outlined hereinbefore, the prior art has already suggested several methods in which an identification signal of a station is introduced in the form of a data signal into the audio signal to be transmitted. The data signal to be transmitted in this case is not audible for the listener.
Such methods are described for example in WO 94/11989, GB 2260246 A, GB 2292506 A and WO 95/04430. The disadvantage of these methods consists in that it cannot be ensured that the data signal is not audible to the listener at all times during transmission of the audio signal.
U.S. Pat. No. 5,450,490 describes an apparatus for and a method of embedding codes in audio signals and decoding the same. This system makes use of various symbols that are coded by means of interleaved frequency lines. To ensure that the data signals transmitted are not audible at any time, a masking assessment is carried out with respect to the individual frequencies of which the symbols to be transmitted are composed. The disadvantage of this method consists in that the generation of signals to be transmitted is very complex.
U.S. Pat. No. 5,473,631 refers to a communication system for transmitting at the same time data and audio signals via a conventional audio communication channel, making use of psycoacoustic coding techniques (perceptual coding). A first network is used which monitors the audio channel for detecting possibilities for introducing the data signal into the audio channel in such a manner that the signals introduced are masked by the audio signal. There is provided a control by means of which a data signal is provided which thereafter is stored in RAM memories. The data signal is coded either by a spread-spectrum coder. The data signal stored in the RAM memory is entered into a modulo2-coder in which it is mixed with a synchronous pseudo-noise code from a PN code generator. The resulting signal is introduced into a head signal generator, and the signal output from this generator is applied to an adjustable attenuation member. The output of the adjustable attenuation member is connected to a summer which serves to combine the audio signal and the data signal so as to issue the audio and data signal at the output thereafter. The network is used for establishing possibilities of introducing a data signal into the audio signal in such a manner that the data signals are not perceived by a human listener.
SUMMARY OF THE INVENTION
The object of the present invention resides in providing a method of coding a data signal contained in an audio signal in non-audible manner, in which it is ensured that the data signal to be transmitted is not perceptible to the human ear, and which is not susceptible with respect to interference phenomena and establishes good channel exploitation while permitting safe and simple decoding of the data signal.
According to a first aspect, the present invention is a coding method for introducing a non-audible data signal into an audio signal. The method has the following steps:
a) transforming the audio signal to the spectral range;
b) determining the spectrum of the masking threshold exclusively on the basis of the audio signal;
c) providing a pseudo-noise signal;
d) providing the data signal;
e) multiplying the pseudo-noise signal by the data signal so as to provide a frequency-spread data signal;
f) weighting the spectrum of the spread data signal with the spectrum of the masking threshold;
g) transforming the weighted data signal to the time domain; and
h) superimposing the audio signal and the weighted signal.
According to a second aspect, the present invention is a coding method for introducing a non-audible data signal into an audio signal, the method having the following steps:
a) transforming the audio signal to the spectral range;
b) determining the spectrum of the masking threshold exclusively on the basis of the audio signal;
c) providing a pseudo-noise signal;
d) providing the data signal;
e) multiplying the pseudo-noise signal by the data signal so as to provide a frequency-spread data signal;
f) weighting the spectrum of the spread data signal with the masking threshold;
g) superimposing the audio signal and the weighted signal in the spectral range; and
h) transforming the weighted data signal to the time domain.
Another object of the present invention resides in providing a coder for introducing and extracting a data signal contained in an audio signal in non-audible manner, in which it is ensured that the data signal to be transmitted is not perceived by the human ear, and which is not susceptible with respect to interference phenomena and establishes good channe
Eberlein Ernst
Gerhäuser Heinz
Heuberger Albert
Neubauer Christian
Perthold Rainer
Corrielus Jean
Fraunhofer-Gesellschaft zur Foerderung der Angewandten Forschung
Glenn Michael A.
Glenn Patent Group
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