Embedder for embedding a watermark into an information
representation, detector for detecting a watermark in an
information representation, method and computer program
and information signal
Embodiments of the present invention relate to embedders for embedding a watermark into
an information representation, to detectors for detecting a watermark in an information
representation, to methods for embedding a watermark into an information representation,
to methods for detecting a watermark in an information representation, to corresponding .
computer programs and to an information signal.
Some embodiments of the present invention relate to devices and methods for repeated
watermark embedding and watermark extraction.
In many fields of information processing, it is desirable today to add a watermark to the
information. A watermark is, for example, a piece of information which may be added to
the actual useful information without substantially interfering with the actual information.
When adding a watermark, for example the data format of the useful information may be
maintained, for example by overlaying the watermark onto the useful information. In some
known methods, overlaying the watermark onto the useful information is executed such
that an interference with the useful information is kept so low that, for example, it does not
interfere, or only very weakly, in a reproduction of the useful information.
Watermarks may, for example, be added to an information representation which represents
an audio signal. Further, watermarks may, for example, be added to an information
representation representing a video signal. A watermark may, however, also be added to an
information representation, for example representing a computer program. Still further
information representations representing different data forms may be provided with a
watermark.
Special challenges result when several watermarks are to be embedded into one single
useful information. In this case, frequently a mutual influencing of the watermark results,
whereby in some case detection is made more difficult or even impossible. The mutual
influencing of the watermarks may further lead to an interference of the actual useful
information becoming unacceptably high.

Further, in some conventional methods the effort required to extract several watermarks
from an information representation is strongly increased.
It is thus the object of the present invention to provide a concept facilitating embedding a
watermark into an information representation or improving the detection of a watermark in
an information representation.
This object is achieved by an embedder for embedding a watermark to be embedded into
an input information representation according to claim 1, by a detector for detecting at
least one watermark in an input information representation provided with a watermark
according to claim 20, by a method for embedding a watermark to be embedded into an
input information representation according to claim 32, by a method for detecting at least
one watermark in an input information representation to be provided with a watermark
according to claim 33, by a computer program according to claim 34, and by an
information signal according to claim 35.
According to one aspect, the present invention provides an embedder for embedding a
watermark to be embedded into an input information representation having an information
adder which is implemented to provide the input information representation with the
watermark and an additional information to be added, to obtain an information
representation provided with the watermark and the additional information to be added.
The additional information to be added includes a descriptive information regarding an
embedding of at least one watermark into the input information representation.
The mentioned aspect is based on the finding that an extraction of a watermark embedded
into the information representation by a descriptive information describing the embedding
of at least one watermark into the input information representation may be facilitated. By
adding the additional information, thus, within the information representation provided
with the watermark to be embedded, information is provided which may be used by a
watermark detector for controlling the watermark detection and/or watermark extraction.
The describing additional information may, for example, carry information about whether,
how, when or from whom the watermark was added to the input information
representation. Thus, the additional information may serve a watermark detector or
watermark extractor for deciding whether the watermark is to be extracted and/or in which
way (e.g. using which detection parameters) the watermark is to be extracted. The presence
of the additional information describing the embedding of a watermark into the
information representation provided with the watermark may, for example, make it
unnecessary to search the information representation provided with the watermark to be

embedded for any possible watermarks known to the watermark detector. Rather, the
watermark detector may, for example, already detect, using the additional information,
which watermarks are contained at all in the information representation provided with the
watermark. Thus, the watermark detector may, for example, accordingly narrow a search,
whereby the effort in the search for watermarks in the watermark detector is considerably
reduced. The additional information may further include, for example, information on
resources used in the embedding (e.g. frequency resources, time resources or code
resources), so that, in the detection of a watermark in the information representation
provided with the watermark to be embedded, the detector may evaluate the additional
information to set detection parameters suitably and/or pointedly for a detection of the
watermark to be detected.
The additional information may further, for example, carry information about how many
watermarks are embedded in the information representation. Thus, for example a
watermark detector, after evaluating the corresponding information, may obtain a
termination criterion, so that the watermark detector may, for example, terminate a search
for watermarks when so many watermarks have been found as are described by the
additional information.
In summary it may thus be stated that, by adding additional information describing the
embedding of watermarks into the input information representation or into the information
representation provided with the watermark to be embedded, efficiency in the detection of
watermarks may be substantially improved in a watermark detector.
Accordingly, according to a further aspect, the present invention provides a detector for
detecting at least one watermark in an input information representation, wherein the
detector comprises an embedding information extractor which is implemented to extract
embedding information including descriptive information regarding the embedding of at
least one watermark into the input information representation (or into the information
representation provided with the watermark) from the information representation. The
corresponding detector further includes a watermark extractor which is implemented to
extract one or several watermarks contained in the input information representation
depending on the embedding information.
The corresponding detector is, for example, able to extract the additional information
added by the above-described embedder to the information representation as embedding
information from the information representation and to control the watermark extraction
depending on the embedding information. Thus, the mentioned detector is, for example,

able to use the additional information and to realize the advantages described above with
reference to the corresponding embedder.
According to some further embodiments, the present invention provides an information
signal including at least one watermark and a descriptive information regarding the
embedding of the at least one watermark into the information signal. The corresponding
information signal, due to the presence of the descriptive information regarding the
embedding of the at least one watermark into the information signal, enables a
substantially easier (for example faster or more resource-economical) extraction of the
watermark embedded into the information signal than is conventionally possible.
In the following, embodiments of the present invention are described in more detail with
reference to the accompanying drawings, in which:
Fig. 1 shows a block diagram of a watermark embedder according to an embodiment of
the invention;
Fig. 2 shows a block diagram of a watermark detector according to an embodiment of
the invention;
Fig. 3a shows a block diagram of a watermark embedder according to an embodiment of
the invention;
Fig. 3b shows a block diagram of a watermark embedder according to an embodiment of
the present invention;
Fig. 3c shows a block diagram of a watermark embedder according to an embodiment of
the invention;
Fig. 4 shows a block diagram of a watermark detector according to an embodiment of
the invention;
Fig. 5 shows a block diagram of a watermark embedder according to an embodiment of
the invention;
Fig. 6 shows a block diagram of a watermark detector according to an embodiment of
the invention;

Fig. 7a shows a block diagram of a watermark embedder having a watermark
information detector and an embedding parameter determiner according to an
embodiment of the present invention;
Fig. 7b shows a schematical illustration of an information signal having an embedded
watermark according to an embodiment of the invention;
Fig. 7c shows a schematical illustration of a determination of a value sequence using a
one-way function;
Fig. 7d shows a graphical illustration of a procedure of calculating an embedding code
based on an initial value;
Fig. 8 shows a block diagram of a watermark detector according to an embodiment of
the invention;
Fig. 9 shows a block diagram of a watermark embedder according to an embodiment of
the invention;
Fig. 10 shows a block diagram of a watermark detector according to an embodiment of
the invention;
Fig. 11 shows a flowchart of a method for embedding a watermark according to an
embodiment of the invention;
Fig. 12 shows a flowchart of a method for detecting a watermark according to an
embodiment of the invention;
Fig. 13 shows a graphical illustration of a step for embedding a watermark according to
an embodiment of the invention;
Fig. 14 shows a flowchart of a method for detecting a watermark according to an
embodiment of the invention;
Fig. 15 shows a flowchart of a method for embedding a watermark according to an
embodiment of the invention; and

Fig. 16 shows a flowchart of a method for detecting a watermark according to an
embodiment of the invention.
Fig. 1 shows a block diagram of an embedder for embedding a watermark to be embedded
or to be added into an input information representation. The embedder according to Fig. 1
is designated by 100 in its entirety. The embedder 100 is implemented to receive an input
information representation 110. The embedder 100 includes a watermark information
detector 120 which is implemented to detect watermark information already contained in
the input information representation 110. Thus, the watermark information detector 120 for
example provides information 122 about watermark information detected in the input
information representation 110. The embedder 100 further includes a watermark adder 130
which is implemented to provide the input information representation 110, depending on
the watermark information detected by the watermark information detector 120, with a
watermark 132 to be added, to obtain an information representation 134 provided with the
watermark 132 to be embedded. The watermark adder 130 may thus, for example, be
implemented to receive the input information representation 110 and the information 122
from the watermark information detector 120. Further, the watermark adder 130 may, for
example, be implemented to receive the watermark 132 to be added. The watermark 132 to
be added may, however, also be firmly stored in the watermark adder 130.
Regarding the functioning of the embedder 100, it is to be noted that the watermark adder
130 may add the watermark 132 to be added depending on the watermark information
already contained in the input information representation 110, to the input information
representation 110. The embedder 100 thus enables the watermark 132 to be added to be
added to the input information representation 110 not in a random way but considering the
watermark already contained in the input information representation 110.
Regarding the way in which the watermark already contained in the input information
representation 110 is considered by the watermark adder 130, different possibilities exist
which are explained in the following, for example with reference to Figs. 7a - 7d in more
detail.
Fig. 2 shows a block diagram of a detector for detecting at least two watermarks in an
information representation provided with one watermark. The detector according to Fig. 2
is designated by 200 in its entirety. The detector 200 is implemented to receive an
information representation 210 provided with a watermark. The detector 200 further
includes a detection information detector 220 which is implemented to identify reusable
watermark information in the information representation 210 provided with the watermark.

The detection information detector 220 is thus, for example, implemented to receive the
information representation 210 and to provide information 222 about reusable watermark
information. The detector 200 further includes a watermark extractor 230 which is
implemented to extract a first watermark using the reusable watermark information from
the information representation 210 and to extract a second watermark using the reusable
watermark information from the input information representation 210. The watermark
extractor 230 is, for example, implemented to receive the information representation 210
and the information 222 provided by the detection information detector 220 and, based
thereon, to provide information 232 about a first watermark and information 234 about a
second watermark.
Regarding the functioning of the detector 200, it is to be noted that the watermark extractor
230 is, for example, implemented to use information common to both watermarks for the
detection of the first watermark described by the information 232 and for the detection of
the second watermark described by the information 234. For example, the common
reusable information may be synchronization information which is for both watermarks.
Thus, it is sufficient in this case, for example, to detect the synchronization information
only once, whereupon the detection of the at least two watermarks may be executed based
on the common synchronization information.
The common, reusable information may, for example, additionally or alternatively be
information which indicates that the first watermark and the second watermark may be
detected with at least one common detection parameter. For example, the information
representation 210 may contain information which indicates that at least two watermarks
were embedded into the information representation 210 according to a common embedding
method, so that the watermark extractor 230 may assume that at least two watermarks may
be extracted with a corresponding common extraction method from the information
representation 210.
Further, for example, the information representation 210 may carry information about how
many watermarks are embedded in the information representation 210. The corresponding
number information may, for example, be regarded as common information which
commonly describes the at least two watermarks contained in the information
representation 210. The number information may, for example, be extracted by the
detection information detector 220 and may further be used, for example, to set one or
several extraction parameters for the watermark extractor 230 to correctly extract several
watermarks from the information representation 210. In other words, the number

information may be used to correctly set detection parameters of the watermark extractor
230 for the extraction of two different watermarks.
If it is know, for example, that three watermarks are contained in the information
representation 210, then, for example, in the extraction of the first watermark and in the
extraction of the second watermark such detection parameters which are provided for
embedding a fourth to nth watermark may be left out of consideration. Rather, it is
sufficient to limit the range of detection parameters to be considered according to the
number of watermarks present.
Further details are again described in the following, for example with reference to Figs. 7a
-7d.
Fig. 3 a shows a block diagram of an embedder for embedding a watermark to be embedded
into an input information representation according to an embodiment of the invention. The
embedder according to Fig. 3a is designated by 300 in its entirety. The embedder 300 is
implemented to receive an input information representation 310 and to provide an
information representation 320 provided with a watermark and additional information. The
embedder 300 includes an information adder 330 which is implemented to receive the
input information representation 310 and to provide the information representation 320
provided with the watermark and the additional information. The information adder 330 is
all in all implemented to provide the information representation 310 with the watermark
341 to be added and additional information 343 to be added to obtain the information
representation 320 provided with the watermark and the additional information. The
additional information to be added includes descriptive information regarding an
embedding of at least one watermark into the information representation. For example, the
descriptive information describes embedding at least one watermark into the information
representation.
Fig. 3a shows an exemplary topology of the information adder 330. The information adder
330 may, for example, in a parallel structure, comprise a watermark adder 340 and an
additional information adder 342. For example, both the watermark adder 360 and also the
additional information adder 342 may receive the input information representation 310 to
add the watermark to be added or the additional information to be added. For example, the
watermark adder 340 may be implemented to receive the input information representation
310 and the watermark 341 to be added or to be embedded and, based thereupon, to
generate an information representation 344 provided with the watermark to be added. The
additional information adder 342 may, for example, be configured to receive the input

information representation 310 and the additional information to be added 343 and, based
thereupon, to generate an information representation 346 provided with the additional
information. The information representation 344 provided with the watermark may further,
for example, be combined with the information representation 346 provided with the
additional information to obtain the information representation 320 provided with the
watermark and additional information, as is indicated in Fig. 3a. Alternatively, it is also
possible, however, that the watermark adder 340 provides as an output signal watermark
information adapted to the information representation 310, that the additional information
adder 342 provides additional information adapted to the information representation 310
and that the output signals of the watermark adder 340 and the additional information
adder 342 are subsequently combined with the input information representation 310 to
obtain the information representation 320 provided a watermark and additional
information.
Alternatively, the information adder 330 may also comprise other structures, as are
described, for example, in Figs. 3b and 3c. For example, the information adder of the
embedder 300 may be replaced by an information adder 330b according to Fig. 3b. The
information adder 330b includes, for example, a series arrangement of a watermark adder
340b and an additional information adder 342b. The watermark adder 340b is configured,
for example, to receive the input information representation 310 and to provide the input
information representation 344b provided with a watermark to the additional information
adder 342b. The additional information adder 342b may be configured, for example, to add
the additional information to be added to the information representation 344b provided
with the watermark and to thus provide the information representation 320 provided with
the watermark and additional information.
As it may be gathered from Fig. 3c, the order of the additional information adder and the
watermark adder may, of course, also be changed with respect to the order illustrated with
reference to Fig. 3b. In this case, an additional information adder 342c is, for example,
arranged in front of a watermark adder 340c.
In summary, it is to be noted that different structures may be used to add both the
watermark to be added and also the additional information to be added to the input
information representation 310. Adding these two pieces of information may, apart from
that, also be done by a common information adder in which the blocks "watermark adder"
and "additional information adder" are combined or summarized. In other words, no
separate adder is required for the watermark and the additional information.

However, the additional information to be added may well depend on embedding
parameters of the watermark adder. Thus, for example, the additional information may
encode how the watermark adder is configured or parametrized to add the watermark to be
added. For example, the additional information may contain information on which
watermark method the watermark adder used for adding the watermark to be added.
Further, the additional information may also describe individual parameters which the
watermark adder uses when providing the input information representation 310 with the
watermark to be added. Thus, the additional information may, for example, carry
information about which embedding code the watermark adder 340 is using, which
frequency resources (e.g. frequency bands) the watermark adder 340 is using for
embedding the watermark, or which time resources (e.g. time slots) the watermark adder is
using for embedding the watermark. Further, the watermark adder 340 and the additional
information adder 342 may, for example, also use different embedding methods when it is,
for example, requested according to a specification that the additional information is
always to be embedded according to a predetermined embedding method, independent of
which embedding method the watermark adder 340 is using. In this case, the watermark
adder 340 and the additional information adder 342 are, for example, implemented such
that no substantial mutual interference results when adding the watermark and when
adding the additional information.
Further details regarding the embedding of a watermark and additional information are
explained in more detail in the following, for example with reference to Figs. 7a - 7d.
Fig. 4 shows a block diagram of a detector for detecting at least one watermark in an input
information representation provided with a watermark. The detector according to Fig. 4 is
designated by 400 in its entirety. The detector 400 is implemented to receive an
information representation (or input information representation) provided with a
watermark. The detector 400 includes an embedding information extractor 420 which is
implemented to receive the information representation 410 provided with the watermark
and to extract embedding information 422, including descriptive information regarding the
embedding of at least one watermark into the information representation, from the
information representation 410.
The detector 400 further includes a watermark extractor 430 which is implemented to
receive the information representation 410 provided with the watermark and the
descriptive information 422 with respect to the embedding of at least one watermark into
the information representation 410. The watermark extractor 430 is further implemented to
extract one or several watermarks contained in the information representation 410

depending on the embedding information 422 and to thus provide information 432 about at
least one watermark.
The watermark extractor 430 may thus pointedly identify a watermark in the information
representation 410 based on the embedding information 422. Based on the descriptive
information 422, the watermark extractor 430 has, for example, information 422 regarding
the fact using which embedding method a watermark present in the information
representation 410 is embedded into the information representation. Alternatively or
additionally, information 422 may, for example, be provided to the watermark extractor
430 from the embedding information extractor 420 about the fact which detection code or
extraction code is to be used for the extraction of a watermark from the information
representation 410. Further, the embedding information extractor 420 may, for example,
provide information to the watermark extractor 430 about how many watermarks are
contained in the information representation 410.
The embedding information extractor 420 may, for providing the descriptive information
422, evaluate, for example, additional information contained in the information
representation. Additional information may, for example, be information not belonging to
the actual information content of the watermark but describing in which way one or several
watermarks are embedded in the information representation 410.
Fig. 5 shows a block diagram of an embedder for embedding a watermark into an
information representation or into an input information representation according to an
embodiment of the invention. The embedder according to Fig. 5 is designated by 500 in its
entirety. The embedder 500 is implemented to receive an input information representation
510 and to generate an information representation 534 provided with a watermark to be
embedded or to be added. The embedder 500 includes an embedding parameter determiner
520. The embedding parameter determiner is implemented to apply a schematically
indicated derivation function 522 one or several times to an initial value 524 to obtain an
embedding parameter 526 for embedding the watermark to be embedded into the
information representation. The embedder 500 further includes a watermark adder 530
which is implemented to receive the input information representation 510 and the
embedding parameter 526. Further, the watermark adder 530 may be implemented to
receive the watermark 532 to be added or to be embedded. The watermark to be added or
to be embedded may further also be firmly stored in the watermark adder 530.

Thus, the watermark adder 530 provides, for example by embedding the watermark 532 to
be added into the input information representation 510 using the embedding parameters
526, an information representation 534 provided with the watermark to be embedded.
The embedder 500 thus enables the determination of the embedding parameters 526 based
on an initial value 524, wherein a derivation function 522 is evaluated. By the possibility
of evaluating the derivation function 522 several times, there is the possibility, based on
one single initial value 524, of generating different sets of embedding parameters 526 in a
simple way. By the use of a derivation function, which may, for example, be a
cryptographic one-way function, it may be achieved that access rights are allocated to
different embedders. Details in this respect are given in the following.
Fig. 6 shows a block diagram of a detector for detecting a watermark in an information
representation provided with a watermark. The detector according to Fig. 6 is designated
by 600 in its entirety. The detector 600 is implemented to receive an information
representation or an input information representation 610 provided with a watermark and
to provide information 634 about a watermark contained in the information representation
610.
The detector 600 includes a detection parameter determiner 620. The detection parameter
determiner 620 is implemented to apply a schematically illustrated derivation function 622,
one or several times, to an initial value 624 which may be given externally or which may
be stored in the detection parameter determiner 620, and thus obtain a detection parameter
626 for the detection of the watermark in the information representation.
The detector 600 further includes a watermark extractor 630 which is implemented to
receive the information representation 610 provided with the watermark and the detection
parameter 626. The watermark extractor 630 is further configured to extract the
information 634 about a watermark contained in the information representation 610 from
the information representation 610 provided with the watermark using the detection
parameter 626. In other words, the detection parameter 626 serves for setting the
watermark extractor 630. The detection parameter may here, for example, indicate which
resources (e.g. which time slots or frequency bands) are applied in the detection of the
watermark. Alternatively or additionally, the detection parameter 626 may, for example, be
used to determine a detection code, if, for example, in the information representation 610
different watermarks with different codes are separate from each other.

Further, the detection parameter determiner 620 may, for example, be implemented to
decide, for example, based on an (optional) index parameter 640, how often the derivation
function 622 is to be applied to the initial value 624 to obtain the detection parameter 626.
Apart from that, it is to be noted that, when determining the detection parameter 626 from
the initial value 624, also additional algorithms may be used, for example. Thus, for
example, an intermediate result obtained by the application of the derivation function to the
initial value may serve as an input value for a calculation regulation which maps the
intermediate result to a detection code. By the application of the corresponding function
regulation it may, for example, be achieved that the thus obtained detection parameter
comprises certain characteristics which are advantageous, or required, for a watermark
extraction. For example, the intermediate value, obtained by an application, once or several
times, of the derivation function 622 to the initial value 624, may serve as an initial value
(seed) for a spread code generator which determines different spread codes based on
different seeds, wherein the spread codes are, for example, at least approximately
orthogonal to each other. The corresponding spread codes may serve, for example, as
detection parameters 626.
However, many other possibilities are possible for mapping the intermediate result,
obtained by the application of the derivation function to the initial value, to a detection
parameter 626.
Fig. 7a shows a block diagram of an embedder for embedding the watermark to be added
into an information representation or into an input information representation. The
embedder according to Fig. 7a is designated by 700 in its entirety. The embedder 700 is
implemented to receive an input information representation 710 and to generate, based
thereon, an information representation 720 provided with a watermark. The information
representation 720 provided with the watermark may further be optionally provided with
additional information, for example describing the embedding.
The embedder 700 includes a watermark information detector 730 which is implemented to
receive the input information representation 710 and to obtain information regarding the
embedding of a watermark therefrom. The embedder 700 further includes a watermark
adder 740 which is implemented, for example using information provided by the
watermark information detector 730, to add a watermark to be added to the input
information representation 710 to obtain the information representation 720 provided with
the watermark. The embedder 700 further includes, for example, an embedding parameter
determiner 750 which is implemented to receive information from the watermark

information detector 730 and to thus provide one or several embedding parameters to the
watermark adder 740 so that, for example, the watermark adder 740 may be set depending
on the setting parameters provided by the embedding parameter determiner 750.
The embedder 700 further includes an additional information provider 760 which is
implemented to receive, from the watermark information detector, information regarding a
watermark contained in the input information representation 710 and to provide additional
information to the watermark adder 740 which may, for example, be added by the
watermark adder 740 to the input information representation 710, so that the information
representation 720 provided with the watermark further includes the additional
information.
In the following, details are described regarding which information may be obtained by the
watermark information detector 730 from the input information representation 710, and
how this information may be used by the watermark adder 740, the embedding parameter
determiner 750 and the additional information provider 760.
The watermark information detector 730 may, for example, include a detector 731 for the
detection of reusable watermark information. The detector 731 for reusable watermark
information may, for example, be implemented to detect synchronization information in
the input information representation 710. The synchronization information may, for
example, exist when a watermark is already present in the input information representation
710. The synchronization information may, for example, be a certain pattern contained in
the input information representation 710 which may, for example, precede a watermark
embedded into the input information representation 710 or which may, for example, be
interleaved with a watermark embedded into the input information representation 710. The
synchronization information may, for example, be a firmly given pattern which may be
contained in the input information representation 710 encoded according to a certain
encoding. For example, the synchronization information may be embedded into the input
information representation 710 according to a predetermined synchronization embedding
code. For example, the synchronization information may occur simultaneously (or at least
overlapping in time) in several individual frequency bands in the information
representation, whereby the synchronization information is, for example, especially well
detectable. The detector 731 for the reusable watermark information may thus, for
example, provide information 732 about the reusable watermark information to the
watermark adder 740. The watermark adder 740 may, for example, be implemented, in
response to the presence of reusable watermark information in the input information
representation, to prevent a renewed embedding of the reusable watermark information.

For example, the watermark adder 740 may be configured to only add synchronization
information to the input information representation 710 when the information 732 of the
detector 731 for the reusable watermark information indicates that in the input information
representation 710 no watermark information is yet present or detectable.
If the information 732 of the determiner 731 for reusable watermark information indicates,
for example, that in the input information representation 710 synchronization information
is already present, then the watermark adder 740 may, for example, add the watermark to
be added synchronized with the already existing synchronization information in the input
information representation. For this purpose, the detector 731 may, for example, provide
information for the reusable watermark information to the watermark adder 740 with
regard to where in the input information representation (for example at what time or in
which frequency bands) synchronization information already exists. Based thereon, the
watermark adder 740 may, for example, calculate or determine where (for example in
which time interval or in which frequency bands) the watermark to be added is to be added
to the input information representation 710.
Further, the watermark adder 740 may be configured to add synchronization information to
the input information representation 710 when the information 732 of the detector 731 for
reusable watermark information indicates that, in the input information representation 710,
no reusable synchronization information was detected.
By the repeated use of the synchronization information when embedding a further
watermark by the watermark adder 740 into an input information representation, in which
synchronization information (and thus in many cases also watermark information) already
exists, on the one hand a negative influencing of the information representation 710 by
embedding the watermark to be embedded may be minimized and, on the other hand, a
resource-saving detection of several watermarks may be enabled in the information
representation 720 provided with a watermark. Thus, conventionally, the influence on an
information representation is less, the less information is embedded into the same. If thus
synchronization information already existing in the information representation 720 is
reused instead of embedding new additional synchronization information, an influence on
the information content of the information representation may be minimized. On the side
of a watermark detection it is, apart from that, sufficient in the reuse of the synchronization
information to detect the synchronization information once. Thus, the detection effort may
be kept low as compared to when two different pieces of synchronization information
would have to be detected.

The watermark information detector may further comprise, for example, a detector 733 for
detecting additional information contained in the input information representation 710. The
detector 733 may, for example, provide information 734 about the additional information.
The additional information may, for example, be page information describing the
embedding of one or several watermarks into the input information representation 710. For
example, the additional information may carry information about how many watermarks
are already embedded in the input information representation 710. The additional
information here does not necessarily have to describe the overall number of embedded
watermarks, but may be restricted to indicating how many watermarks were embedded
according to a certain watermark embedding method into the input information
representation. The information about the number of the existing watermarks may further
be restricted to indicate how many watermarks were embedded by a certain watermark
embedder into the input information representation. In an ideal case which may, however,
not always be achieved, the information about the number of existing watermarks may also
carry information about an overall number of watermarks. In some embodiments, thus the
information about the number of existing watermarks at least provides information about a
minimum number of existing watermarks, wherein more watermarks may in fact exist.
The detector 733 may further be implemented, for example, to detect additional
information which indicates according to which watermark embedding method or
according to which watermark embedding methods the watermarks existing in the input
information representation 710 are embedded. This information may, for example, exist in
connection with the synchronization information in the input information representation
710. For example, the synchronization information may contain information, for example
by the selection of the synchronization pattern, according to which watermark embedding
method the watermark information contained in the information representation 710 is
embedded. Alternatively or additionally, also subsequent to the synchronization
information or parallel to the synchronization information, corresponding additional
information may exist in the input information representation 710 which indicates
according to which watermark embedding method one or several watermarks are
embedded in the input information representation 710.
Alternatively or additionally, the additional information may, for example carry
information about what resources (e.g. time slots, frequency bands or embedding codes or
spread codes) were used for embedding one or several watermarks into the input
information representation. This information may be contained in additional information
which may, for example, comprise the above-described structure. In other words,
corresponding additional information may, for example, be contained within the

synchronization information, parallel in time to the synchronization information or
subsequent to the synchronization information (for example directly subsequent to the
synchronization information) in the input information representation. In some
embodiments, the additional information is encoded separately to the associated watermark
information described by the additional information. While the watermark information
thus, for example, encodes a certain useful information which is, for example, freely
selectable on the embedder side, the additional information may, for example, be
determined on the basis of the fact by which parameters the actual useful information of
the watermark is encoded or embedded. In other words, in some embodiments a strict
logical separation between the additional information directed to the type of representation
of the useful information in the watermark, and the actual useful information itself which is
encoded by the watermark may exist. In other words, using the additional information, for
example embedding parameters, using which the useful information to be encoded by the
water was embedded into the information representation, are identified without having to
decode the useful information of the watermark. In other words, the additional information
is in some embodiments independent of the useful information encoded by the watermark
and only depends on parameters according to which an embedder is operated.
In some embodiments, the watermark information detector 730 includes a detector 735 for
embedding parameters of embedded watermarks. The detector 735 may, for example,
receive the input information representation 710 and thereupon provide information 736 on
embedding parameters, using which one or several watermarks are embedded into the
input information representation 710. The detector 735 may, for example, be implemented
to analyze the input information representation 710 in order to find out, using which
settings or parameters watermarks were embedded into the input information
representation 710. For this purpose, the detector 735 may, for example, also analyze the
watermarks themselves. For example, the detector may apply a pattern recognition method
to the input information representation in order to determine whether watermarks were
embedded into the input information representation 710 according to a certain embedding
method. As a pattern-recognizing method, for example a correlation method may be used,
according to which the input information representation 710 is correlated with one or
several comparative values. Further, the detector may also apply other algorithms in order
to obtain information 736 on an embedding parameter of at least one watermark already
contained within the input information representation 710.
In other words, while the detector 733 may, for example, be implemented to evaluate
additional information which is different from the useful information represented by the
watermark, the detector 735 may, for example be implemented to analyze the watermark

information represented by the useful information. Thus, different possibilities exist as to
the way in which information may be obtained on a watermark contained in the input
information representation 710. Apart from evaluating the additional information by the
detector 733, also a direct analysis of the watermark information (or, in some
embodiments, of the complete watermark information including the useful information) is
available.
In one further embodiment, the watermark information detector 730 may (alternatively or
additionally) include a detector 737 which is implemented to determine a number of
watermarks embedded in the input information. The detector 737 may, for example, be
implemented to receive the input information representation 710 and to provide
information 738 about the number of embedded watermarks (or detected embedded
watermarks).
As was already described above, it is not compulsory for the information 738 to describe
all the watermarks contained in the input information representation. Rather, it is sufficient
in some embodiments if the information 738 describes a number of watermarks detected in
the input information representation.
In summary it is to be noted that there is a multitude of possibilities for obtaining
information by the watermark information detector 730 which describes the embedding of
watermarks in the input information representation 710. The corresponding information
732, 734, 736, 738 may be used in different ways, as is described in the following.
For example, the information 732 may directly be transferred to the watermark adder 740
via reusable watermark information, so that the same may decide, for example based on the
information on reusable watermark information, whether reusable watermark information
is contained in the input information representation 710. The possibly reusable information
may then be directly used by the watermark adder 740.
Further, the additional information provider 760 may receive the information 732, 734,
736, 738 provided by the watermark information detector 730 (or maybe only one or
several pieces of the mentioned information) and derive therefrom additional information
to be added to the input information representation 710. The additional information may,
for example, include information regarding the embedding of watermarks or watermark
information already contained in the input information representation 710. For example,
the additional information 762 may comprise a reference to the additional information 734
already contained in the input information representation 710 and detected by the detector

733. Further, the additional information 762 to be added may, for example, include a copy
of the additional information 734 contained in the input information representation 710 and
further be supplemented by other information related, for example, to the embedding of the
watermark to be added. Further, the additional information 732 may, for example, describe
a number of watermarks contained in the information representation 720 provided with the
watermark to be added. If thus, by the watermark information detector 730, information
about a number of watermarks embedded in the input information representation 710 is
provided, then, for example, the additional information provider 760 may increment the
mentioned number and thus generate the additional information 762 so that the same
describes a number of watermarks contained after adding the watermark to be added in the
information representation 720. Further, the additional information 762 may include
information on embedding parameters of watermarks already contained in the input
information representation 710 about embedding parameters, according to which the
watermark to be added is embedded.
It is to be noted that the additional information 762 does, of course, not have to include all
of the mentioned information, but that it is sufficient if the additional information only
includes one or several of the mentioned pieces of information.
In some embodiments, however, advantages result when the additional information 762 not
only describes how the watermark to be added is added to the input information
representation 710, but when the additional information 762 further also includes
information on watermarks already contained in the input information representation 710.
This combined information describing both the watermarks already existing in the input
information representation 710 and also the embedding of the watermark to be embedded
may be evaluated in an especially efficient way by a detector. Thus, a detector may, for
example, by evaluating one single additional information, obtain extensive information on
the embedding of all watermarks contained in the input information representation 710 (or
at least with respect to a plurality of watermarks contained in the input information
representation). It is thus not required to evaluate many individual pieces of additional
information and to compile their information.
The embedding parameter determiner 750 may further be implemented to set or adapt
embedding parameters for the embedding of the watermark to be added by the watermark
adder 740 depending on one or several pieces of information 732, 734, 736, 738 provided
by the watermark information detector 730. If, for example, the additional information 734
includes information on using which resources (e.g. using which time slots, using which
frequency bands or using which embedding codes) the watermarks already contained in the

input information representation 710 are embedded, then the embedding parameter
determiner 750 may, for example, select suitable embedding parameters or embedding
resources for embedding the watermark to be added. For example, the embedding
parameter determiner 750 may be configured to select the resources for the embedding of
the watermark to be added so that no unacceptable intersections whatsoever result between
the resources used in the embedding of the watermark to be added and the resources used
in the embedding of the already existing watermarks. Based on the information regarding
which time slots are used by the watermarks already contained in the input information
representation 710, the embedding parameter determiner 750 may, for example, select a
free time slot for the embedding of the watermark to be added. In a similar way, the
embedding parameter determiner 750 may select suitable (free or only relatively weakly
occupied) frequency bands for the embedding of the watermark to be added, when the
information provided by the watermark information detector 730 indicates the occupation
of frequency bands.
If the information provided by the watermark information detector 730 indicates which
embedding code or which embedding codes were used for embedding information into the
input information representation 710, then the embedding parameter determiner 750 may,
for example, further select an embedding code for embedding the watermark to be added
which is, for example, different from the embedding codes used in the input information
representation 710. For example, the embedding parameter determiner 750 may select an
embedding code for the embedding of the watermark to be added, which is at least
approximately orthogonal to embedding codes which were used for the embedding of
watermarks already contained in the input information representation. Thus it may, for
example be guaranteed by the evaluation of the input information representation 710 by the
watermark information detector 730 that the watermark to be added is embedded using an
embedding code which is different from the embedding codes of the already existing
watermarks.
In one embodiment, the embedding parameter determiner may be implemented to also
generate embedding parameters for an embedding of additional information as is, for
example, provided by the additional information provider 760. In this case, the embedding
parameter determiner 750 may, for example, be configured to set the embedding
parameters for the embedding of the additional information 762 such that the additional
information 762 is embedded substantially using the same embedding parameters as
additional information already contained in the input information representation 710. For
this purpose, for example the watermark information detector 730 may also provide
information on embedding parameters, using which additional information already

contained in the information representation 710 was embedded into the input information
representation 710. In this way, it may, for example, be enabled that both the additional
information already contained in the input information representation 710 and also the
additional information 762 to be added may be detected efficiently by a detector.
In a further embodiment, the information 738 about the number of embedded watermarks
may be evaluated to determine or specify the embedding parameters. For example, the
embedding parameter determiner 750 may comprise a functionality, corresponding to a
functionality of the embedding parameter determiner 520, as was explained with reference
to Fig. 5. The information 738 about the number of embedded watermarks (which may, for
example, be determined either based on additional information in the input information
representation or based on an analysis of the input information representation) may, for
example, be used to decide how often the derivation function 522 is applied to the initial
value 524 in order to obtain the embedding parameter 526.
In summary it may thus be noted that, by the embedding parameter determiner 750, for
example one or several embedding parameters 752 may be generated which may then be
supplied to the watermark adder 740. The embedding parameters may here, for example,
be selected based on information 732, 734, 736, 738 on watermarks already contained in
the input information representation 710. The embedding parameters may, for example,
serve for selecting an embedding method. Further, the embedding parameters may also
describe details regarding the embedding, e.g. an embedding code, an embedding time slot
or an embedding frequency band.
Further details regarding individual aspects of the embedder 700 are described in the
following with reference to Figs. 7b - 7d. Thus, Fig. 7b shows a graphical representation
of resources which are available for an embedding of watermark information. The
graphical illustration of Fig. 7b is designated by 770 in its entirety. The graphical
illustration 770 illustrates a time/frequency band representation of an information
representation. At an abscissa 772, for example time is plotted, and at an ordinate 774, for
example frequency is plotted. The time/frequency representation may, for example,
represent an audio signal which may be divided into individual time sections and
frequency bands. A corresponding representation of an audio signal may, for example, take
place by a spectral analysis as may, for example, be achieved by a filter bank. Different
time sections are, for example, designated by 776a - 776f. Different frequency bands are,
by the way, designated by 777a - 777g.

In one time section 776b, for example in the frequency bands 777a - 777f, basically
synchronization information (SYNC) is contained. Further, for example in another
frequency band 777g in the time section 776b (i.e. parallel in time to the synchronization
information), additional information may be contained describing the embedding of a
watermark. The additional information in the frequency band 777g during the time interval
776b may, of course, be regarded as optional. Further, additional information may also, for
example, be contained in a time slot after the synchronization information (SYNC). For
example, the synchronization information in the frequency bands 777a - 777f may be
contained during the time section 776c.
For example, the additional information for different embedded watermarks may be
contained in different frequency bands (or time slots). For example, the additional
information describing a first embedded watermark or inserted in a first watermark
embedding, may be contained in the frequency band 777f during the time section 776c.
Additional information relating to the embedding of a second watermark, or added in the
embedding of a second watermark, may, for example, be inserted in the frequency band
776e during the time section 776c. In general, additional information describing the
embedding of different watermarks, or those which are embedded in different embedding
steps, may be added to the information representation using different resources (here: using
different frequency bands). Thus, for example when adding a further watermark, the
existing additional information is supplemented by adding further additional information,
for example using hitherto unused resources. Thus, for example an overlapping of
additional information is prevented, whereby it is, for example, achieved that the
information representation is not unnecessarily strongly affected, and whereby it is further
achieved that the individual additional information is readable without mutual
interferences. In this respect it is to be noted that, in the embedding of watermark
information in an information representation, it is generally difficult or even impossible to
remove or change information (e.g. additional information) again once inserted into the
information representation. For this reason, in some embodiments of the invention, when
adding a watermark to be added, additional additional information is added to possibly
already existing additional information.
The graphical illustration 770 further shows different resources used for the embedding of
different watermarks. For example, useful information of the first watermark may be
inserted into resource sections designated by a first hatching 778a. For example, the
information of the first watermark in the first time section 776d may be contained in the
frequency bands 777b, 777d and 777f. Further, the information of the first watermark
during the fourth time section 776f may be contained in the frequency bands 777b, 777d

and 777f. Information of a second watermark may, for example, be contained, or encoded,
using the resources designated by a second hatching 778b (time section 776d: frequency
bands 777a, 777c, 777e; time section 776f: frequency bands 777a, 777c, 777e). Useful
information of the third watermark may, for example, be contained in resources designated
by a third hatching 778c, and useful information of a fourth watermark may, for example,
be contained in resources designated by a fourth hatching 778d.
From the graphical illustration 770 it may, for example, be gathered that the useful
information of the watermarks (described by the fields of the graphical illustration 770
designated by hatchings 778a, 778b, 778c, 778d) saved separate from corresponding
additional information in the watermark.
In summary it may be noted that the graphical illustration of Fig. 7b may describe an
information signal, wherein, in addition to underlying useful information (for example
including an audio signal, image information, text information or computer program
information), a watermark and, for example, additional information is contained in the
information signal. The information signal may be supplemented by all those features and
aspects described within the scope of the present specification with regard to the
embedders or detectors.
Fig. 7c shows a graphical illustration of a procedure in a determination of an embedding
parameter using a one-way function. The graphical illustration according to Fig. 7c is
designated by 780 in its entirety. In the following it is first of all assumed that a first value
782 is known to an embedder (or a detector), wherein the first value 782 may also be
regarded as the first initial value, or "initial value 1". By applying the mentioned one-way
function, a second value 784 may, for example, be obtained from the first value 782. Here,
for example, an algorithm is known as to how the second value 784 may be obtained from
the first value 782 with comparatively low computational effort. In some embodiments,
however, it is not possible, or only possible with extreme effort, to calculate the first value
782 from the second value 784. For this reason, the one-way function is partially also
referred to as a "cryptographic one-way function".
From the second value 784, however, by a further application of the one-way function, for
example a third value 786 may be obtained. In other words, the same algorithm is applied
to the second value 784 which was applied to the first value 782 for determining the
second value 784, and thus, for example, from the second value 784 the third value 786 is
obtained. By a further application of the one-way function to the third value 786, for
example a fourth value 788 may be obtained. The one-way function is again applied to the

fourth value 788, and thus, for example, a fifth value 789 is obtained. It thus remains to be
noted that it is sufficient to know the first value 782 and the one-way function (or the
algorithm described by the one-way function) to obtain the second to fifth values 784 -
789 from the first value 782 by a repeated application of the one-way function.
The values 782 - 789 may, apart from that, for example be used to serve as a description
for embedding parameters or detection parameters of an embedder or detector, as was
already explained above.
Further, an administration of different access rights may be implemented. If, for example, a
first embedder (or detector) knows the first value 782 (initial value 1), it may, based
thereon, using the one-way function, determine all the values 782 - 789 with low
computational effort. If, however, an embedder (or detector) only knows the third value
786 (initial value 2), then the corresponding embedder (or detector) may only determine
the fourth value 788 or the fifth value 789 (or subsequent values) using reasonable
computational effort. The mentioned detector, which only knows the third value 786
(initial value 2) and the one-way function, but not the first value 782 or the second value
784, can thus not determine the first value 782 and the second value 784 using reasonable
computational effort. Accordingly, the mentioned detector only knowing the initial value 2
cannot execute the embedding or detection of a watermark, so that the embedding
parameters correspond to the embedding parameters belonging to the first value 782 or the
second value 784. Thus, it may, for example, be guaranteed that an embedder which only
knows the third value 786 (initial value 2) may not execute in an unauthorized way an
embedding of a watermark according to the embedding parameters belonging to the first
value 782 or according to the embedding parameters belonging to the second value 784.
In the following it is briefly described with reference to Fig. 7d how, using a one-way
function, an embedding parameter may be obtained. For this purpose, Fig. 7d shows a
graphical illustration of a procedure when determining an embedding code or a detection
code from an initial value using a one-way function. The graphical illustration according to
Fig. 7d is designated by 790 in its entirety. The graphical illustration 790 shows that, based
on an initial value 792, an intermediate result 794 may be obtained by the application of a
one-way function once or several times. The intermediate result 794, for example,
corresponds to the second value 784, the third value 786, the fourth value 788 or the fifth
value 789 according to Fig. 7c. The intermediate result 794 may, of course, also
correspond to other values, which may, for example, be obtained by an application of the
one-way function more than four times to the first value 782 or to the initial value 782. The
intermediate result 794 may, for example, serve as a seed (starting parameter) for an

embedding code generation. For example, based on the intermediate result 794, an
embedding code may be generated by supplying the intermediate result as a seed to a code
generator. As a code generator, here, for example, a feedback shift register arrangement
may serve, as it may be known for the generation of pseudo-random numbers. Different
initial values for the feedback shift register arrangement in some embodiments leads to
different code sequences at an output of the feedback shift register arrangement, wherein
the different code sequences may, for example, form the different embedding codes. In
other words, for example a first code sequence is generated by a feedback shift register
arrangement when the feedback shift register arrangement is provided or pulsed with the
first initial value. Further, a second bit sequence or code sequence is generated when the
feedback shift register arrangement is provided with a second initial value. The different
bit sequences, for example, form the different code sequences.
For the determination of the embedding code or detection code 796 from the intermediate
result 794, however, generally any algorithm may be used which enables obtaining
different codes based on different seeds 794, wherein the codes, for example at least
approximately, comprise default characteristics (e.g. stochastic characteristics). For
deriving an embedding parameter from the intermediate result 794, also other algorithms
may be applied. For example, individual bits of the intermediate result 794 may be directly
used to directly form the embedding parameters. Further, different mappings (which may,
for example, be defined by associated mapping tables or logic tables) are possible for
determining an embedding parameter from the intermediate result 794.
Fig. 8 shows a block diagram of a detector for extracting a watermark from an information
representation provided with a watermark. The detector according to Fig. 8 is designated
by 800 in its entirety. The detector 800 is, for example, implemented to receive an
information representation 810 provided with a watermark and to provide at least one
watermark contained in the information representation 810. In some embodiments, the
detector 800 may be implemented, however, to provide information on a plurality of
watermarks contained in the information representation 810. For example, the detector 800
may be implemented to provide information 820 on a first watermark and to provide
information 822 on a second watermark.
The detector 800 includes, for example, a watermark information detector 830 which is
implemented to receive the information representation 810 provided with the watermark
and to provide, based thereupon, information on watermark information contained in the
information representation 810. For example, the watermark information detector 830 may
comprise the same basic functionality as the watermark information detector 730 of the

embedder 700. Apart from that, the watermark information detector 830 may, for example,
correspond to the detection information detector 220 according to Fig. 2.
Thus, the watermark information detector 830 may, for example, be implemented to
provide information 832 on the reusable watermark information. Further, the watermark
information detector 830 may be implemented to provide additional information 834, for
example corresponding to the additional information 734, based on the information
representation 810 provided with at least one watermark. Further, the watermark
information detector 830 may be implemented to provide, based on the information
representation 810, information 836 on embedding parameters basically corresponding to
the information 736, for example. Alternatively or additionally, the watermark information
detector 830, based on the information representation 810, may provide information 838 on
a number of watermarks embedded in the information representation 810. In this respect it
is to be noted that it is, for example, sufficient for the watermark information detector to
provide one of the mentioned pieces of information 832, 834, 836, 838. However, there are
embodiments in which the watermark information detector provides all mentioned
information, wherein in this case an especially powerful overall system results.
The detector 800 further includes a watermark extractor 840 which is implemented to
receive the information representation 810 provided with a watermark. The watermark
extractor 840 may further be implemented, for example, to receive information 832 on
reusable watermark information, as far as such information is provided by the watermark
information detector 830. Further, the watermark extractor is, for example, implemented to
receive embedding parameter information 852 from an embedding parameter determiner
850. The watermark extractor 840 is thus, for example, implemented, based on the
information representation 810 and depending on the information 832 and the embedding
parameters 852, to extract at least one watermark and to provide corresponding
information 820 on the extracted watermark. A synchronization of the watermark extractor
840 may here, for example, take place through the information 832 on reusable watermark
information if the information 832, for example, relates to the presence of synchronization
information. In this case, for example, the watermark extractor 840 may be instructed by
the information 832 to extract two different watermarks using the same synchronization
information. If only one watermark is to be extracted, for example the evaluation of the
information 832 on reusable watermark information may be rendered unnecessary.
The embedding parameter determiner 850 may, for example, be implemented to determine
the embedding parameters or detection parameters 852 based on the information 832, 834,
836, 838. The embedding parameter determiner 850 may, of course, also evaluate only one

of the mentioned pieces of information 832, 834, 836, 838 to determine the embedding
parameter 852. The embedding parameter determiner 850 is, for example, implemented to
set the embedding parameters 852 such that a watermark is extracted from the information
representation 810 which is actually contained in the information representation 810 or the
presence of which is indicated by at least one of the pieces of information 832, 834, 836,
838. In other words, the embedding parameter determiner 852 may, for example, be
configured to prevent the attempt to extract a watermark from the information
representation 810 which is not contained in the information representation 810 or the
presence of which is not indicated by at least one of the pieces of information 832, 834,
836, 838. Thus, the embedding parameter determiner 852, based on the information 832,
834, 836, 838 may control the watermark extractor 840 to extract the existing watermarks
pointedly. Thus, a substantial advantage regarding power or advantage regarding speed
may be achieved as compared to arrangements in which the information representation 810
is searched for any possible watermarks.
The detector 800 further includes, for example, a sequence control 860 which is
implemented, for example, to control an extraction of several watermarks. The sequence
control 860 may, for example, be configured to terminate a watermark extraction from the
information representation 810 when all watermarks assumed to exist in the information
representation 810 have been identified. If the watermark information detector 830, for
example, provides information 838 on a number of watermarks embedded in the
information representation, then, for example, the sequence control 860 may terminate a
search for watermarks in the information representation if a number of watermarks has
been identified which is the same as the number described by the information 838.
Although the watermark information detector 830 may fail when providing the information
838, i.e. for example indicates the presence of less watermarks than are actually contained
in the information representation 810, the information 838 may still in many cases be
regarded as a reliable termination criterion for terminating a search for further watermarks.
By a corresponding sequence control terminating the search for watermarks depending on
the information 838, apart from that an unnecessary and futile search for further
watermarks may be avoided if, for example, all watermarks have already been extracted by
the watermark extractor 840.
It may be gathered from the above description that the detector 800 offers substantial
advantages as compared to conventional detectors. By employing reusable watermark
information, a watermark extraction may be accelerated. By employing the information
provided by the watermark information detector 830, apart from that the search for
embedded watermarks may take place in a very systematic way, so that, for example, only

actually existing watermarks are extracted, and a futile search for non-existing watermarks
is not required.
Further advantages may, for example (optionally), be achieved when the embedding
parameter determiner 850 is implemented to determine one or several embedding
parameters using a one-way function. Here, for example, the initial value may be given,
and the information 838 on the number of embedded watermarks may be used in order to
decide how often the one-way function is to be applied to the initial value. If the
information 838 indicates, for example, that three watermarks are contained in the
information representation 810, the one-way function may, for example, be applied to the
initial value once to obtain the extraction parameters for the extraction of the first
watermark. Extraction parameters for the extraction of the second watermark are, for
example, obtained by applying the one-way function again to the value which was obtained
by the first application of the one-way function to the initial value. Thus, for example, a
detection parameter for the extraction of a subsequent watermark may be derived from the
detection parameters for the extraction of a preceding watermark, which leads to an
especially efficient realization of a mechanism for determining the detection parameters.
Apart from that, it is to be noted that the terms embedding parameter and detection
parameter may be basically used synonymously regarding the detection of a watermark. If,
for example, embedding parameters are known, using which a watermark was embedded
into an information representation or into an information signal, in many cases it may be
assumed that thus also detection parameters are known, using which the watermark may be
detected or extracted again. Determining or detecting of extraction parameters or detection
parameters thus in many cases corresponds to the determination of embedding parameters.
Fig. 9 shows a block diagram of an embedder for embedding a watermark into an audio
signal. The embedder according to Fig. 9 is designated by 900 in its entirety. The
embedder 900 is implemented to embed watermark information, i.e. for example a useful
signal which is to be embedded into a watermark, via a data input 910. The embedder 900
further includes a data stream generator 920 which is implemented to receive the
watermark useful information from the data input 910 and to generate, based thereupon, a
parallel data stream, for example including m bits. The data stream generator 920 is, for
example, implemented to apply a forward error correction (FEC) to the watermark useful
information from the data input 910, to obtain an error-protected data stream representing
the watermark useful information. Further, the data stream generator 920 is, for example,
implemented to apply a time interleaving to the error-protected data stream to thus obtain a
time-interleaved data stream. The time-interleaved data stream is less prone to certain

errors (e.g. bundling errors) than the mere error-protected data stream. Further, the data
stream generator 920 is, for example, implemented to spread the interleaved data stream
with a first spread code (spread code C). For example, the data stream generator 920 may
be implemented to generate a plurality of bits from one bit of the time-interleaved data
stream by applying a spread code. Thus, from the watermark useful information from the
data input 910 a once spread data stream results, as is, for example, known from
telecommunications. In summary it may be noted that the once spread data stream, by
applying a forward error correction (FEC), by applying time interleaving and by applying a
first spread procedure using spread code C, results from the watermark useful information
from the data input 910. The individual bits of the once spread data stream are then divided
into a parallel data stream, for example including m parallel data streams having associated
bits (bit 1, bit 2, ..., bit m-1, bit m). The mentioned bits are, for example, designated by
9221 - 922m. Each of the parallel bits 9221 - 922m is then subjected to spreading. The
corresponding spreading takes place in respective spreaders 9301 - 930m. In one of the
spreaders 9301 - 930m, for example, depending on the value of the associated bit 9221 -
922m, a first sequence (sequence 1) or a second sequence (sequence 2) is selected. The first
sequence and the second sequence may, for example, be complementary to each other. The
sequences may, for example, be a spread sequence M and the inverse of the spread
sequence M. Thus, for example, each bit 9221 - 922m is spread by the associated spreader
9301 - 930m so that, for example, m spread bit sequences 9321 - 932m result. The spread bit
sequences 9321 - 932m are then supplied to respective level setters 9401 - 940m so that
corresponding level-controlled and spread bit sequences 9421 - 942m result. In one
embodiment, a level of each level-controlled, spread bit sequence 9411 is individually
settable as compared to the level of the associated non-level-controlled spread bit sequence
932i (i = 1, ..., n). However, a level setting may also take place for a group of spread bit
sequences together.
The embedder 900 further includes a synthesis filter bank 950 which may, for example be
implemented to execute an inverse Fourier transformation. The synthesis filter bank 950 is,
for example, configured to receive the level-controlled and spread bits 9421 - 942m.
Further, the synthesis filter bank 950 may additionally be implemented to receive one or
several (e.g. level-controlled) synchronization frequencies. The synthesis filter bank 950 is
thus, for example, implemented to receive the level-controlled bit sequences 9421 - 942m
and the level-controlled synchronization bit sequences, for example as frequency range
input signals and, based thereupon, for example by forming an inverse Fourier
transformation, generate a corresponding time signal 952.

The embedder 900 further includes a summator 960 which is, for example, implemented to
add the output signal 952 of the synthesis filter bank 950 to a main audio signal 962 to
obtain an audio signal or sum audio signal 964 provided with a watermark (according to
the watermark useful information).
The embedder 900 further includes, for example, a psychoacoustic control unit 970. The
psychoacoustic control unit 970 is, for example, implemented to receive the main audio
signal 962 and to generate level control signals 972 for the level setters 9401 - 940m. For
this purpose, the psychoacoustic unit 970 may, for example, process the main audio signal
962 to determine masking thresholds in the main audio signal. In other words, the
psychoacoustic unit 970 may, for example, determine according to a psychoacoustic model
how loud a signal (e.g. the output signal 952 of the synthesis filter bank 950) added to the
main audio signal 962 may be in different frequency bands, so that no substantial
interference results in the sum audio signal 964. The psychoacoustic unit 970 is thus, for
example, implemented to set the level setter 9401 —940m such that an interference of a
hearing impression in the sum audio signal 964 by the output signal 952 of the synthesis
filter bank 950 does not exceed a certain boundary. In other words, the output signal 952 of
the synthesis filter bank 950 ought to be embedded into the main audio signal 962 so that
the signal 952 only slightly impairs a hearing impression caused by the sum audio signal
964 as compared to a hearing impression caused by the main audio signal 962.
The embedder 900 further includes, for example, a synchronization sequence generator
980 which is implemented to generate one or several bit sequences, for example serving
for a synchronization in a watermark extraction from the sum signal 964. The
synchronization sequence generator 980 thus generates one or several synchronization
sequences 982 which are, for example, in a level setter 990, subjected to a level setting (for
example controlled by the psychoacoustic unit 970). Thus, level-controlled
synchronization sequences result which, as explained above, may be supplied to the
synthesis filter bank 950.
The embedder 900, as already indicated above, may be improved in different ways. For
example, the synchronization sequence generator may be controlled depending on whether
a synchronization sequence is already present in the main audio signal 962. In other words,
the main audio signal 962 corresponds, for example, to the input information
representation 110 according to Fig. 1, the input information representation 310 according
to Figs. 3a - 3c, the input information representation 510 according to Fig. 5 or the input
information representation 710 according to Fig. 7a. If the embedder 900 is thus provided
with a corresponding watermark information detector which is implemented to identify a

synchronization signal present in the main audio signal 962, the synchronization sequence
generator 980 may, for example, be activated or deactivated depending on the presence of
a synchronization signal in the main audio signal 962. If, in the main audio signal 962, a
synchronization sequence already exists, no additional synchronization sequence has to be
embedded into the audio signal. Further, apart from that, also the generation of the bit
streams (e.g. the bit streams 9221 - 922m and the bit streams derived therefrom) may be
synchronized with the synchronization signal detected in the main audio signal 962.
Further, parameters of the embedder 900, for example the used spread sequences or the
frequency bands used for the generation of the signal 952, may be set depending on
information describing a watermark contained in the main audio signal 962.
Apart from that, the selection of these parameters used by the embedder 900 may be done
using an embedding parameter, as was explained, for example, with reference to Figs. 5
and 7a.
Regarding details as to how spreading a signal using different spread codes may be
achieved, reference is, for example, made to the textbook "Digital Communication" by J.G.
Proakis (third edition, Mc Graw-Hill, New York, 1995). Also adding a forward error
correction and time interleaving are described in the above-mentioned book and further in
the conventional textbooks on telecommunications. Also the realization of a synthesis filter
bank, for example executing an inverse Fourier transformation or a similar transformation,
may be gathered from the telecommunication textbooks.
Fig. 10 shows a block diagram of a watermark detector according to one embodiment of
the invention. The watermark detector according to Fig. 10 designated by 1000 in its
entirety. The watermark detector 1000 is implemented to receive an audio signal provided
with at least one watermark at a signal input 1010 and to form, based thereupon, a
watermark useful information 1020. The detector 1000 includes an analysis filter bank
1030 which is implemented to receive the audio signal provided with the watermark and
divide the same into individual spectral bands. For example, the analysis filter bank 1030
may be implemented to execute a Fourier transformation or a fast Fourier transformation.
At an output of the analysis filter bank, thus, for example, individual signals for a plurality
of bands are applied, some of which serve as useful signal frequency band signals 1032[ -
1032m and some of which serve as synchronization frequency band signals 10341 - 1034n.
The detector 1000 further includes a plurality of , for example, m despreaders and
normalizers 1040i. An i-th despreader and normalizer 1040j may, for example be
implemented to correlate an associated useful signal frequency band signal 1034 to a

detection spread code (in general: a detection code or extraction code) to thus reverse the
spreading by the spreader 9301 - 930m. By the correlation with the corresponding spread
code, or detection code or extraction code, for example one bit may be detected. The
detection of the bit may, apart from that, also include normalizing, for example to reverse
the level setting in the embedder-side level setters 9401 - 940m. At the outputs of the
despreaders and normalizers 10401 - 1040m, for example bit information 10421 - 1042m
may be applied, for example carrying bit information normalized and despread by the
despreader and normalizer 10401 - 1040m. The detector 1000 further includes a watermark
recovery unit 1050, for example implemented to receive the bit signals 10421 - 1042m and
to recover based thereupon the watermark useful information 1020. The watermark
recovery unit 1050 may, for example, comprise a despreader which is, for example,
implemented to reverse the spreading (Spreizen-C; spreading C) executed in the bit stream
generator 920 of the watermark embedder 900. The watermark recovery unit 1050 may
further comprise, for example, a de-interleaver which is implemented to reverse the time
interleaving of bits executed in the bit stream generator 920. Further, the watermark
recovery unit 1050, for example, includes an error corrector, or a forward error correction,
which is implemented to use the error correction information added by the bit stream
generator 920 to thus obtain the watermark useful information 1020 based on the bit
signals 10421 - 1042m, so that in the watermark useful information 1020 the effects of bit
errors in the bit signals 10421 - 1042m are reduced or eliminated.
The decoder 1000 further includes a synchronizer 1080 which is implemented to receive
the synchronization signals 10341 - 1034n. The synchronizer includes, for example, one or
several synchronization correlators 10821 - 1082n, wherein the synchronization correlators
10821 - 1082n are implemented to receive respective synchronization signals 10341 -
1034n and correlate the same with a predetermined synchronization signal detection code.
Thus, the synchronization correlators 10821 - 1082n may detect the presence of a
synchronization mark in the synchronization signals 10341 - 1034n. The synchronization
unit 1080 further includes, for example, a post-processing 1084 which is, for example,
implemented to receive, from the synchronization correlators 10821 - 1082n, information
on whether a correlation between the synchronization signals 10341 - 1034n and
predetermined synchronization codes reaches or exceeds a threshold value to provide,
based on the information provided by the synchronization correlators 10821 - 1082n, an
extracted synchronization signal 1086 which indicates a position, regarding which a
synchronization mark occurs in the synchronization signals 10341 - 1034n.
The extracted synchronization signal 1086 is then, for example, supplied to the despreaders
and normalizers 10401 - 1040m to synchronize the function of the despreaders and

normalizers 10401 - 1040m with the synchronization information contained in the input
signal 1010.
The decoder 1000 may be expanded in many ways to achieve one or several of the above-
described additional functionalities. For example, the decoder 1000 may be supplemented
by a detector which is implemented to identify reusable information in the input signal
1010 and to provide the reusable identification for an extraction of several watermarks. If
the detector, for example, detects for the reusable information that in the input signal 1010
synchronization information is contained which may be used for a detection or extraction
of several watermarks, the detector may provide the corresponding information (e.g. the
corresponding synchronization information) for the detection of several watermarks. In this
case, for example, a first set of despreaders and normalizers may receive the reusable
information (e.g. synchronization information) to extract a first watermark. A second set of
despreaders and normalizers may receive the reusable information to extract a second
watermark. The first set of despreaders and normalizers is, for example, configured to
detect a watermark which is embedded according to a first embedding method or according
to a first embedding code into the input information 1010. The second set of despreaders
and normalizers may further, for example, be implemented to extract from the input
information 1010 a watermark which, according to a second embedding method or using a
second embedding code, is embedded into the input information 1010. Thus, the reusable
information may again be used and a one-time detection of the synchronization
information for a detection of several different watermarks is sufficient (e.g. embedded
using different embedding methods or using different embedding codes).
Further, in the decoder 1000 different advantageous concepts may be used to set extraction
parameters used for the extraction of a watermark. For example, the detector 1000 may
include a watermark information detector, for example corresponding to the watermark
information detector 830 of the detector 800. Further, the detector 1000 may, for example,
comprise an embedding parameter determiner, for example basically corresponding to the
embedding parameter determiner 850 of the detector 800. Apart from that, the detector
1000 may also comprise a sequence control, for example basically corresponding to the
sequence control 860 of the detector 800.
Thus, it may, for example, be determined by the embedding parameter determiner which
detection code is used for despreading the signals 10321 - 1032m. Alternatively or
additionally, it may, for example, be determined by the embedding parameter determiner
which detection code is used for despreading the signals 10421 - 1042m in the watermark
recovery unit 1050. Alternatively or additionally, it may also be determined by the

embedding parameter determiner which length the corresponding detection codes for
despreading the corresponding signals comprise. Apart from that, also information
regarding how the time interleaving in the watermark recovery unit 1050 may be reversed
may be determined by the embedding parameter determiner. Apart from that, by the
embedding parameter determiner also different detection methods for different watermarks
may be determined. Apart from that, the embedding parameter determiner may, for
example, also provide information on which frequency bands are to be used for the
extraction of the watermark.
In the following, briefly some details regarding an overall system consisting of the
embedder 900 and the detector 1000 are described. At the input of the embedder 900, for
example, PCM-encoded audio signals or audio signals encoded according to a pulse code
modulation are applied. This audio signal (for example the main audio signal 962) is
analyzed using a psychoacoustic method, for example by the psychoacoustic unit 970. The
psychoacoustic method, for example, guarantees inaudibility of the watermark to be
embedded or sees to it that the watermark to be embedded is only perceived very weakly.
Data to be transmitted, for example applied to the data input 910, are added to the original
audio signal (or the main audio signal 962). The embedder 900 is, for example, not
exclusively targeted to offline signal processing, i.e. for broadcasting applications also a
real-time embedding may take place. Only by internal block processing a certain delay
may, for example, be expected.
The input signal at the input 1010 of the extractor may, for example, be recorded by a
microphone. This microphone of the extractor may, for example, comprise a frequency
response from 10 Hz to 10 kHz (typically with a frequency response of +/- 5 dB). As a
suitable sampling rate, 24 kHz may, for example, be selected.
In the following, a basic functioning of the embedder 900 or the extractor 1000 is
described. A useful band for watermark transmission is, for example, delimited by the
microphone of the extractor to a frequency range from 100 Hz to 10 kHz. A lower
boundary frequency of the useful band is, for example, designated by fmin. An upper
boundary frequency is, for example, designated by fmax. In some embodiments, the
following applies: fmin < 100 Hz and fmax > 10 kHz. A frequency band from 0 to fmax is,
for example, divided into M subbands of equal width, and in these subbands watermark
partial signals are transmitted. A subband having the number k for example extends from
(k - 1) * fmax/M to k * fmax/M, with k = 1, 2, ..., M. Due to an attenuation of the
microphone at low frequencies, for example the subband having the number 1 (k = 1) is
not used for data transmission. A watermark may thus consist of M - 1 subband signals.

These subband signals are converted into the individual subbands by means of a synthesis
filter bank. A sampling rate of these subband signals at an input of the synthesis filter bank,
for example designated by fs1, is a fraction of a sampling rate at the output (fs1: = 24/K
kHz, K being an integer number).
As in one embodiment, in the watermark extractor 1000, the subband signals (i.e., e.g., the
signals 10321 - 1032m or 10341 - 1034m) are further processed at a sampling rate fsl, with
regard to a favorable realization of the watermark extractor it may be sensible to select fsl
to be as small as possible. A bandwidth of the subbands may, for example, be fmax/M,
wherein fmax may, for example, be smaller than 10 kHz. According to the sampling
theorem, for example the condition fsl > 2 fmax/M has to be fulfilled. Thus, for example
for a quotient 24 kHz/fs1 of the two sampling rates, the following applies:
24 kHz/fs1 ≥ M * 12 kHz/fmax.
An efficient implementation of the synthesis filter bank 950 is, for example, possible when
the quotient 24 kHz/fsl is an integer multiple of M. As fmax = 12 kHz is not an option, for
example fmax = 6 kHz is selected. Apart from that, M = 16 is set, for example. A
bandwidth of one single subband is thus 375 Hz, and from the request for a minimum
sampling rate for example fsl = 750 Hz results.
The M - 1 subband signals (for example the signals 9421 - 942m) together with the signals
provided by the synchronization generator 980 and the level setter 990 contain, for
example, encoded information (for example the useful information of the watermark) and
known training symbols which may, for example, be used on a receiver side, i.e., for
example, in the watermark extractor, for synchronization. In one embodiment, in every
subband data symbols may be transmitted with synchronization symbols in a time
multiplexing. In another embodiment, however, data symbols and synchronization symbols
are transmitted in separate subbands. There are thus r synchronization signals (e.g. with r =
3) and M - 1 - r data signals. The corresponding subbands are thus also referred to as data
channels or synchronization channels.
An output signal of the synthesis filter bank 950 is, for example, the actual watermark
(including synchronization information and watermark useful information), added to the
audio signal (e.g. to the main audio signal 962). For the watermark not to be audible, for
example the individual subband signals (for example the signals 9321 - 932m or 982) may
still be changed in the amplitude (i.e., e.g., decreased). This time-variable weighting (for
example by the level setters 9401 - 940m or 980) depends, for example, on the respective

audio signal (e.g. on the main audio signal 962) and on the psychoacoustic perception of a
person. In this connection, reference is made to psychoacoustic weighting.
Fig. 9 shows, for example, the basic setup of the watermark embedder. The encoded bits (0
and 1) (for example represented by the bit signals 9221 - 922m) are represented, for
example, by two orthogonal spread sequences of the length Spreizen-M (spreading-M)
(e.g. spreading-M = 32). These spread sequences consist, for example, of the symbols +1
or -1. Thus, the subband data signals before a psychoacoustic weighting (PAW) are BPSK
signals (each with a power of 1). Also the synchronization signals before the
psychoacoustic weighting are, for example, BPSK signals (each power 1).
In the following, briefly the mechanisms each regarding the forward error correction
(FEC), the spreading (spreading-M) and the synchronization frequencies are described. For
details, reference is made to the textbook "Digital Communications" by J.G. Proakis (3rd
Edition, Mc Graw-Hill, New York, 1995).
The bit stream generator 920 consists, for example, of three parts, or implements three
processing steps:
1. convolution encoder or turbo encoder having the code rate R
2. spreading by the factor Spreizen C (spreading-C)
3. time interleaver (interleaver).
The encoder (convolution encoder or turbo encoder) for example generates n > k encoded
bits from k information bits. A code rate is, for example, defined as a quotient R = k/n. If,
for example, the case k = 1 is considered, it is assumed that 1 < n < 5 applies.
Lower code rates may, for example, be generated by a spreading of the encoded bits with a
bit sequence of the length spreading-C. Here, for example, each code bit of the value 1 is
replaced by the bit sequence sc[k], and each code bit of the value 0 is replaced by the
negated bit sequence scnot[k] (k = 0, 1,..., spreading-C - 1). An effective code rate is then,
for example, R/spreading-C. For example, for R = 1/3 and spreading-C = 12 an effective
code rate of 1/36 results. In this number example, an information bit is represented by 36
code bits. By the interleaver, the sequence of the code bits is changed in a defined way.
Using an inverse operation, the reversal of the interleaving (de-interleaver), the bits in the
receiver (watermark extractor) are again brought into the correct order.

In the following, briefly the spreading "Spreizen-M" (spreading-M) is described. In one
embodiment, the encoded bits (0 or 1) coming from the bit stream generator 920 or from
the forward error correction (FEC) are represented by two orthogonal spread sequences of
the length spreading-M (e.g. spreading-M = 32). These spread sequences consist of the
symbols +1 or -1. Thus, for example the subband data signals before the psychoacoustic
weighting are BPSK signals (each with the power of 1).
For example, s0[k] or sl[k] (k = 0, 1, ..., spreading-M - 1) are the spread sequences
represented by a zero or a one, respectively. Orthogonality here means that the inner
product = 0.
In the following, some more details regarding the synchronization sequences are described,
as they are provided by the synchronization sequence generator 980, and as they are, for
example, evaluated by the synchronization unit 1080. For a decoding of the data on the
receiver side (for example in the watermark extractor) it is, for example, advantageous
when points in times are known at which a code word beings. These points in time may,
for example, be determined by a transmission of known sequences and by a correlation to
these sequences in the receiver. These sequences are, for example, transmitted on the
synchronization channels. Here, for example, the following procedure may be chosen:
A sequence p[k] ( k = 0, 1, ..., L - 1) is generated by L BPSK symbols with good
autocorrelation characteristics. By a periodic repetition of p[k], it results for the signal
u[n]: = p[n modulo L] (n = 0, 1, ...). In the embodiment, on all synchronization channels
the same signal u[n] is transmitted.
In the following, briefly some details regarding the psychoacoustic weighting are
described. It is, for example, enabled by a spread band modulation to reduce the average
signal power by spectral spreading. Additionally the data signal is evaluated and modified
according to psychoacoustic principles. Thereby, for example, the inaudibility of the signal
added to the original audio signal 962 is guaranteed. This inaudibility of the watermark
information in the combined audio signal 964 is, for example, guaranteed by the use of the
level setters 9401 - 940m and 990 under the control of the psychoacoustic unit 970, as
already explained briefly above. A detailed description is omitted here, as the same is not
essential for understanding the present invention.
In the following, some details regarding the watermark detector or watermark extractor
1000 are described. The watermark-including audio signal, for example generated by the

embedder 900, may, for example, be distributed conventionally via existing transmission
channels (e.g. via broadcasting or also via the internet) and is, for example, finally supplied
to the watermark detector or watermark extractor 1000.
An input signal at the input 1010 of the detector 1000 includes, for example, a sum signal
transmitted via the audio channel (for example the combined audio signal 964) including
an audio signal and a watermark.
By the analysis filter bank 1030 the input signal is, for example, divided by the input 1010
into M subband signals at a sampling rate of, for example, 12/M kHz. The signals in the
unused subbands (e.g. subbands Nos. 17 - 32) are, for example, not calculated. The
subband signal No. 1 is, for example, calculated but not evaluated, however, as it does not
carry any information. The remaining M - 1 subband signals, for example, are divided into
M - 1 - r data signals, for example, and r synchronization signals and subsequently further
processed.
From the synchronization signals (for example from the signals 10341 - 1034m) points in
time are determined, for example, by means of correlation, at which the data signals (for
example the signals 10321 - 1032m) are despread (Entspreizen-M; despreading-M).
Output signals of the blocks 10401 - 1040m designated by despreading-M are, for example,
logarithmic likelihood ratios (LLR), i.e. soft bits. A positive logarithmic likelihood ratio
(LLR) indicates one bit is a logical one, and a negative logarithmic likelihood ratio (LLR)
indicates, for example, that this is a logical zero. The higher the amount of a logarithmic
likelihood ratio, for example, the more reliable the value.
The logarithmic likelihood ratios are, for example, further processed in the watermark
recovery unit 1050 or in a forward error correction (FEC).
In the following, reference is briefly made to the characteristics of the received subband
signals (for example the signals 10321 - 1032m and 10341 - 1034m). Here, Xk[n] (k = 1, 2,
..., M) are the subband signals in the watermark embedder after spreading (spreading-M)
and before psychoacoustic weighting. yk[n] (k = 1, 2, ..., M) are the output signals of the
analysis filter bank. The signals xk[n] are interfered with by three effects:
psychoacoustic weighting
audio signal

audio channel.
For the received signals (for example received by the decoder 1000) generally, for
example, the following applies:

Here, Ck[n] is a (time-dependent) channel coefficient and rk[n] is additive noise. The effects
of distortions are, for example, characterized by an average signal-to-noise ratio per
channel, or by a mean signal/noise ratio averaged across all channels.
A useful signal from the point of view of telecommunications is, for example, the signal
Xk[n-D]. The rest are noise-type interferences. The ratio of effective power C to
interference power N, i.e. C/N, generally expressed in decibel, is, for example, the
signal/noise ratio.
In the following, a synchronization in the detection of a watermark or a processing of
synchronization signals (for example a processing of the synchronization signals 10341 -
1034m) is briefly described. In one embodiment, a transmitted synchronization sequence
p[k] (k = 0, 1,..., L-1) is known. In the following, x[n] refers to the input signal and y[n] to
the output signal of a correlator for synchronization. The output signal is, for example,
calculated by a filtering of the input signal with an FIR filter of an impulse response p[L -
1-n] (n = 0, 1,..., L-1), i.e. according to the regulation

Output signals of the individual correlators are, for example combined ("post processing")
to determine the position of a correlation peak. From the location of the correlation peak,
for example, the positions of the synchronization sequence p[k] within the synchronization
signals may be determined. From these positions, for example, the starting times for
despreading may be derived (entSpreizen-M; despreading-M). This information (for
example information 1086) is passed on from the synchronization unit 1080 to the
despreading-M blocks 10401 - 1040m.

In the following, the procedure for despreading-M is described. A processing unit
designated by despreading-M (for example one of the processing units 10401 - 1040m),
from a block of input values Spreizen-M (spreading-M), calculates exactly one output
value (for example in the form of a logarithmic likelihood ratio LLR). This is described in
the following.
In the following, for example, x[n] (n = 0, 1, ...,spreading-M) are the samples of a block of
the length spreading-M at an input of despreading-M (10401 - 1040m). In one embodiment,
first of all the power of the block is normalized to one. In this respect, for example, a signal
is formed

The signal y[n] is, for example, despread using a difference sl0[n]: = s1[n] - s0[n] of the
two spread sequences s1[n] and s0[n]. The result is, for example, a logarithmic likelihood
ratio LLR:

Due to an orthogonality of the spread sequences ( = 0), for example a logarithmic
likelihood ratio LLR = 1 results for y[n] = s1[n] and a logarithmic likelihood ratio LLR =
-1 results for y[n] - s0[n].
In the following, details with respect to a forward error correction or to a watermark
recovery are described. The processes described in the following may, for example, be
executed in the watermark recovery unit 1050. A forward error correction (FEC) in the
watermark extractor 1000 includes, for example, three parts or processing steps:
1. reversing time interleaving (for example by a so-called de-interleaver)
2. despreading by the factor spreading-C (also referred to as "despreading-C"); and
3. forward error correction decoding, for example in an FEC decoder.

In the following, details with respect to reversing time interleaving are described. The de-
interleaver, for example, reverses a change executed in the transmitter (or embedder) of a
sequence of bits by a corresponding (for example reversed) change of the sequence of the
logarithmic likelihood ratio (LLR).
In the following, despreading (Entspreizen-C; despreading-C) is described. A despreading
by the factor spreading-C may, for example, be executed in the way described in the
following. It is to be noted here that a spread sequence used in the watermark embedder
was referred to above by sc[k] (k = 0, 1, ..., spreading-C-1). This sequence consists of
zeros and ones. From sc[k], for example according to the regulation

a sequence sc1[k] only consisting of the numbers 1 and -1 is generated. Here, for example,
the number sc[k] = 0 is mapped into the number scl[k] = -1, and the number sc[k] = 1 is
mapped into the number sc1[k] = 1. Using the spread sequence scl[k] for example, the
logarithmic likelihood ratios are despread analog to the procedure described with reference
to despreading-M.
In the following xLLR[n] (n = 0, 1, ..., spreading-C) are the samples of a block of
logarithmic likelihood ratios (LLR) at the input of despreading-C. First of all, for example,
a power of a block is normalized to 1. In this respect, for example, the following signal is
formed

From the sequence yLLR[n], for example using the spread sequence sc1[k], the despread
logarithmic likelihood ratios are obtained


These despread logarithmic likelihood ratios are, for example, shifted into the forward
error correction decoder (FEC decoder) and decoded there.
In the following, details with respect to the forward error correction decoder (FEC
decoder) are described.
For decoding the logarithmic likelihood ratios (LLR) after despreading-C, for example a
forward error correction decoder may be used. For example, the following decoders
comprising low complexity and high efficiency are an option:
turbo decoder (for example with a short code word length);
Viterbi decoder, for example in connection with a Reed-Solomon decoder (here, for
example, in a transmitter or embedder a Reed-Solomon code is put downstream to
the convolution code); or
sequential decoder with a high inflow length (e.g. K = 41; for details, see textbook
"Digital Communications" by J.G. Proakis).
The logarithmic likelihood ratios after despreading-M and despreading-C, for example
with the code rate R (e.g. R = 1/3) represent encoded information bits. The forward error
correction decoder provides back, for example, at its output the decoded information bits.
To decode the information bits with an error likelihood which is as low as possible, it is
desirable for the ratio Eb/NO to be sufficiently high. Here, Eb designates an energy per
information bit and NO a one-sided noise power density. The following applies, for
example:
Eb/NO/dB = C/N/dB + 10 * loglO (Spreizen-M * Spreizen-C/R).
Here, C/N is an average signal/noise ratio across all data channels at an output of the
analysis filter bank 1030, i.e. before despreading-M. The second addend is, for example,
the sum of the spreading gain (spreading-M) and the encoding gain (Spreizen-C/R;
spreading-C/R). For example, for spreading-M = 32, spreading-C = 12 and R = 1/3, the
value of Eb/NO is above C/N by 30.6 dB.

In the mentioned textbook by Proakis, for example using simulation results for a sequential
decoder, it was indicated that a bit error likelihood Pb takes the value Pb = le-6, for
example, for the following values of Eb/NO:
R=1/3:Eb/N0 = 2.5dB;
R = 1/2: Eb/NO = 3 dB.
For the turbo decoder the same boundary values apply.
If, for example, a reserve of 2 - 3 dB is added to the above-mentioned values of Eb/NO to
compensate interfering noise, there is, for example, a request for Eb/NO to be 5 dB, for
example. Referring to the above-mentioned number values for spreading-M, spreading-C
and R, for example C/N before despreading-M may be -25 dB.
It may be seen from the above-mentioned description that, in particular by spreading the
watermark useful data in embedding and by despreading the watermark useful data in
decoding, it may be achieved that the watermark information is, for example, embedded in
an audio signal such that the audio signal, by the embedding of the watermark useful
information, is only changed in an inaudible or only slightly audible way. By the use of
different spread codes it may further be enabled to embed different watermarks into the
same audio signal (or into another information representation). A reliable decoding or
extraction of the watermark requires, however, on the side of the decoder or extractor, the
despreading (both despreading-M and also despreading-C) to take place using suitable
spread codes which are adapted at the embedder-side spread codes or which correspond to
the embedder-side spread codes. With reference to the consideration above, it is obvious
that the above-described mechanisms for setting extraction parameters, which are, for
example, suitable for the selection of spread codes used for the extraction, may be used
advantageously to enable despreading.
In the following, some aspects of the present invention are summarized. The concept
described within the scope of the present description may, for example, be used for
watermark embedding into carrier data and for the extraction, for example, of embedded
watermark data.
In conventional watermark embedding, the watermark embedding takes place, for
example, without examining a carrier signal (e.g. an audio signal or an image signal) with
respect to existing watermarks. In some embodiments, a watermark has the characteristic

of being able to contain several independent watermarks without an influence occurring.
Further, it is desirable in some conventional concepts for a detector to know about the
necessary embedding information of the different embedders.
If it is desired for a repeated embedding of watermarks to be possible, special requirements
exist. For example, each further inserted watermark may not make already existing
watermarks unusable. Further, a detector, or watermark detector, has to be able to
differentiate the watermarks of different embedders.
From the relevant expert publications, different watermark methods are known. The
following watermark methods, for example, can be used in conventional embedders or
extractors and also in the inventive embedders or extractors:
narrow band method
spread band method
echo hiding
multi-carrier method
phase modification.
In conventional methods, several disadvantages can arise. For example, conventionally,
every embedder adds information (or watermark information) independently to an
information representation (for example to an audio signal). Hence, conventionally, a
detector or watermark detector has to perform the complete detection method for every
embedder. Further, conventionally, a detector needs to have exact information on the
embedder that enables him to detect the watermark. For example, when using a spread
band method, a conventional detector requires the spread sequence used by the embedder.
Hence, in a conventional detector, a detection complexity and memory requirements
increase with each watermark since a conventional detector attempts, for example, one
extraction for every possible embedder. Hence, conventionally, it is not possible that a
number of possible embedders is, for example, unlimited (which does not necessarily mean
that an unlimited number of watermarks can exist in a carrier signal). Therefore,
conventionally, the embedders are frequently limited. If the number of possible embedders

is very high, conventionally, all embedders will have to be sought for, even when finally
only one watermark is contained (for example in the examined information representation).
Subsequently added embedders are, for example, not known to a conventional extractor
and, for example, an update of the detectors becomes necessary when an embedder is
subsequently added.
In the following, several aspects of the present invention will be summarized. According to
several embodiments of the invention, the detector or watermark detector can share all
information and detection methods necessitated for all watermarks as far as possible,
which reduces complexity, memory requirements, time requirements, and/or energy
requirements. In several embodiments, redundant information does not have to be
superimposed in the carrier signal (e.g. the audio signal).
Additionally, in several embodiments, the detector or watermark detector has information
on the embedders and can, for example, limit a search for watermarks to the significant
detection steps.
In several embodiments, necessary detection information (or detection parameters) can be
calculated dynamically by defined derivation steps of the embedder information. Thus, in
several embodiments, newly added embedders do not require a subsequent change of the
detector information.
In the following, several aspects of different embodiments will be described. The different
aspects can be combined within a detector, within an extractor or within an overall system
including a detector and an extractor.
1. According to one aspect, prior to every embedding process (or at least prior to
several embedding processes), a carrier signal (e.g. an audio signal or an image
signal or a video signal or a computer program signal, or generally an information
representation) is examined for possibly existing watermarks. If an already existing
watermark is detected, then, for example, the new watermarks will be inserted,
depending on the original watermark, in a manner that enables the detector to use
common computing operations for all watermarks. For example, a synchronization
sequence (generally: synchronization information) is not re-embedded, but an
existing synchronization sequence (or synchronization information) is used and
only the actual data (for example the watermark payload data) are embedded (for
example synchronously to the existing sequence or synchronization sequence).

Hence, for example, an extractor has to search for only a single synchronization
sequence (or synchronization information) that is the same (or the only one) for all
contained watermarks. At the same time, this synchronization sequence can, for
example, be an indication for existing watermarks for subsequent embedders.
2. According to one aspect, embedder information is added with a method that is the
same for every embedder. In other words, at least two different embedders use the
same method for embedding embedder information. The embedder information
can, for example, be generation information. The generation information can
describe, for example, a number of previous watermarks. Hence, for example, a
first embedder can indicate that it has added the first watermark. A second
embedder can indicate, for example, that now two watermarks are contained.
According to one aspect, this information (i.e. for example the generation
information) can be detected independent of the embedder.
3. According to one aspect, the data (or the watermark payload data or watermark
payload information) are now added by the embedder (for example to the carrier
signal), so that the watermarks do not (or only slightly) influence each other. For
that, different methods can be used. For example, a CDMA method or a code
multiplex multiple access method) can be used. In a respective spread method, for
example, every embedder (of a plurality of embedders) uses its own spread
sequence, which is orthogonal to the sequences or spread sequences of other
embedders. The data share, for example (but not necessarily), a common frequency
domain and also a common time domain.
Alternatively (or additionally), embedding can be performed in time multiplex,
frequency multiplex or by using a combination of the same. Since the sequences
overlap, for example when using the CDMA method, an overall embedded signal
energy will increase with every further watermark. Thereby, for example, the
watermark energy can increase to such an extent that detection of the watermark
becomes more likely. According to one aspect, every watermark can be embedded
in a different frequency band or in a different time slot to avoid an overlay. Here, it
is advantageous when every embedder knows what watermarks are already
contained, so that no overlay takes place (or only takes place to an acceptable
extent). In other words, here, the above-stated generation information is not only
helpful for the detector, but for every further embedder.

If multiple embedding of watermarks is to take place, further embedders will start
again, for example, at point 1.
4. In several embodiments, the detector extracts, similar to every further embedder,
the embedder information (that comprises, for example, information on the
embedding parameters used by the embedder or the detection parameters to be used
by the detector). According to one aspect, a detector can read out the generation
information of all embedders in the same manner with the same method or the same
spread sequence.
Information that can be used for all watermarks (also referred to as reusable
information) can, for example, also be obtained from the carrier signal. For
example, a synchronization signal valid for all watermarks (or at least for a plurality
of watermarks) can be obtained from the carrier signal. Further, based on the
embedder information, contained watermarks can be specifically searched for (e.g.
by the detector).
5. Since a conventional detector does not have any information on how many
watermarks are contained in the carrier signal, the detector would have to search for
all possible embedder information. In order to solve this problem, this number (i.e.
the number of possible watermarks) can, for example, be limited in advance.
According to one aspect of the invention, however, a certain time slot (or another
resource) can be left unoccupied, for example following the synchronization
sequence, where every embedder, for example, is allowed to insert generation
information.
According to one aspect, it is preferred that the embedding method (for several
embedders) is always the same. For example, every embedder of generation
information can use the same synchronization band. Further, for example, every
embedder of generation information can use the same spread sequence or the same
embedding method. Therefore, for example, an extractor can read out the
generation information of all embedders (or at least a plurality of embedders) with
the same method (or the same spread sequence) in the same manner without
increasing the extraction complexity. Therefore, it is advantageous when the
embedding method for the generation information is identical for all embedders.
Based on the knowledge of the generation information (i.e. the number of
watermarks) an extractor knows, for example, exactly how many watermarks it has

to search for. A (conventionally frequently occurring) useless search for non-
existing watermarks is hence unnecessary.
According to a further aspect, so-called derivation functions can be used for embedder
information. Details regarding this will be summarized below. In a spread band method, an
embedder embeds this sequence (for example a spread sequence) into the carrier signal.
Therefore, it is preferred that the sequence, or the spread sequence, is known to the
detector so that the same can detect the sequence, or spread sequence, existing in the
carrier signal and so that the detector can hence extract the watermark information
contained in the carrier signal. Therefore, every subsequently added embedder
(conventionally) causes an update of the extractors. In other watermark methods, it is also
sometimes required that the detector knows certain information from the embedder for
detection.
This requirement can, for example, be avoided when the stated information (in this
example the spread sequences) is calculated from a fixed data amount (e.g. from an initial
value) by means of an appropriate derivation function. A new embedder can, for example,
apply the derivation function to the initial value as often as there are already allocated
embedders and therefore also spread sequences.
In several cases, the value calculated in this manner (i.e. the value calculated from the
initial value by applying the derivation function once or several times) cannot be used
directly as a spread sequence. Hence, in a spread sequence, several requirements exist, e.g.
with regard to the correlation characteristics and the spectrum. In several embodiments, the
value calculated by applying the derivation function to the initial value can also serve as
"seed" for generating the actual spread sequence. In other watermark methods (that, for
example, do not use a spread sequence), the value obtained by applying the derivation
function to the initial value once or several times can also serve as a base for a respective
data modulation.
According to a further aspect, a further characteristic results by using so-called one-way
functions for the derivation. Thus, for example, only the hierarchically lower value can be
calculated from a derived value. Thereby, for example, access rights can be granted to the
extractor. If a detector has knowledge, for example, of the "uppermost" initial value, it will
then be able to extract all watermarks. A detector that knows, for example, only the value
that was derivated twice as the initial value, cannot generate the two sequences (lying
above) and hence it cannot read out the watermarks of two embedders. If, however, instead
of a one-way function a normal derivation function (for example convertible with little

computing effort) is used as the derivation function, a direct allocation of access rights will
not be possible. However, there is the possibility of being able to obtain the sequence of an
almost arbitrary amount of embedding parameter values or detection parameter values.
In the following, several improvements and advantages in relation to the prior art will be
described, which can be obtained according to several embodiments of the present
invention.
According to several embodiments described within the scope of the present invention, it is
possible to embed several watermarks into a carrier signal or to read out several
watermarks from a carrier signal. Thereby, for example, detection complexity can be
reduced or minimized with respect to independent detection. According to several
embodiments of the invention, memory requirements and/or energy requirements in a
detection of watermarks are reduced.
In several embodiments of the invention it is possible to embed several watermarks into a
carrier signal and to read them out in such a manner that only the watermarks are read out
that are actually contained or that are free to be accessed. In several embodiments, useless
detection efforts can be omitted.
In several embodiments, a detector does not have to know all embedder information
required for detection. Rather, in several embodiments, subsequently added embedders can
be detected without having to update the detector.
Further, in several embodiments, a detector (or even every detector) can implicitly obtain
access rights for these watermarks.
In the following, a further embodiment of the invention will be described. First, the
embedding will be described. According to an embodiment, the embedder searches, for
example, for existing watermarks in the carrier signal by searching for a synchronization
sequence. Since the embedder (for example in the first embedding of a watermark into a
carrier signal) is the first embedder, no such sequence is found. Therefore, the embedder,
or the first embedder, inserts the synchronization sequence. Additionally, the embedder, or
first embedder, can signalize that it is the first embedder. Thereby, the first embedder can
' also add the data (for example the signalization data indicating that it is the first embedder)
(for example to the carrier signal). For example, the first embedder can add the data in an
unoccupied time slot after the synchronization sequence or in a separate band in parallel to

the synchronization sequence. In one embodiment, the data are added in parallel to the
synchronization sequence.
In the following, a possible procedure in performing further embeddings is described. In
this case, the embedder can again, for example, search for the known synchronization
sequence. The known synchronization sequence can, moreover, be considered as an
indication of the existence of watermarks. If the embedder finds the known
synchronization sequence (for example during a further embedding), it can add, for
example after signalizing the first embedder, information indicating that it is the second
embedder. The respective data can again be added in parallel to the synchronization
sequence. Further, the data can also be added to the carrier signal in a different manner,
e.g. in a time slot following the synchronization sequence.
In the following, an exemplary procedure for detection will be described. A detector can
search, for example, for the embedder information and finds (for example after the above-
described embeddings) the synchronization signal and the signalizations from the first and
second embedders. Hence, the detector derives, for example, the necessary extraction
parameters required for detecting the watermark. Further, the detector extracts, for
example, exactly these two watermark data. Since, for example, both watermarks (i.e. for
example the watermark embedded by the first embedder and the watermark embedded by
the further, or second, embedder) are based on the same synchronization signal,- the
synchronization is, for example, performed only once for all watermarks. Further, no
further watermarks need to be searched for.
In summary, it is to be stated that the present invention according to several aspects
provides an apparatus and a method for multiple watermark embedding and watermark
extraction. Several embodiments of the invention solve the object to enable multiple
watermark embedding into carrier data, or a carrier signal, such that detection with limited
complexity or with lower complexity than with conventional arrangements is possible.
The respective concept can be used advantageously, since it is desired or even necessary
for the different cases of application to embed not only one single watermark but several
independent watermarks. Moreover, most watermark methods are designed for embedding
one watermark, even when the respective method basically allows multiple embedding.
Conventionally, detection complexity and memory requirements increase uniformly with a
number of possible watermarks. Further, conventionally, a detector usually has no

information on how many and what watermarks actually exist in carrier signals. Hence, it
has to attempt, for example, to detect all possible watermarks.
According to one aspect of the embodiments described in the present specification, the
carrier signal is examined for possibly existing watermarks prior to every embedding
process. If an already existing watermark is detected, the new watermarks will be inserted
independent of the original watermark in a manner enabling the detector to use common
methods for all watermarks equally.
According to a further aspect of several of the embodiments described herein, embedding
of additional information providing both the extractor with information on the original
embedders and providing a further embedder with information on every further (or
previous) embedding process, can take place. An extraction method for this information
can, for example, be independent of the embedder.
According to a further aspect of several of the embodiments described herein, the
embedder-dependent information is not selected arbitrarily but derived from each other in a
defined manner.
In the following, several methods according to different embodiments of the invention will
be described.
Fig. 11 shows a flow diagram of a method of embedding a watermark to be embedded into
an information representation. The method according to Fig. 11 is indicated by 1100 in its
entirety. In a first step 1110, the method 1100 comprises detecting watermark information
already contained in the information representation. Further, in the second step 1120, the
method 1100 comprises providing the information representation with the watermark
depending on the watermark information detected in the information representation, to
obtain an information representation provided with the watermark to be embedded.
Fig. 12 shows a flow diagram of a method of detecting at least two watermarks in an
information representation provided with watermarks. The method according to Fig. 12 is
indicated by 1200 in its entirety. In a first step 1210, the method 1200 comprises
identifying reusable watermark information in the information representation provided
with a watermark. Further, in a second step 1220, the method 1210 comprises extracting a
first watermark from the information representation using the reusable watermark
information. Further, in a third step 1230, the method 1200 comprises extracting a second
watermark from the information representation using the reusable watermark information.

Further, the second step 1220 and the third step 1230 can be performed one after the other.
Alternatively, the second step 1220 and the third step 1230 can also be performed in
parallel, simultaneously or at least in a temporally overlapping manner.
Fig. 13 shows a graphical illustration of a method of embedding a watermark to be
embedded into an input information representation. The method according to Fig. 13 is
indicated by 1300 in its entirety. The method 1300 comprises providing 1310 the input
information representation with a watermark and additional information to be added to
obtain an information representation provided with the watermark and the additional
information to be added. The additional information to be added comprises descriptive
information with regard to the embedding of at least one watermark into the input
information representation.
Fig. 14 shows a flow diagram of a method of detecting at least one watermark in an input
information representation. The method according to Fig. 14 is indicated by 1400 in its
entirety. In a first step 1410, the method 1400 comprises extracting embedding information
including descriptive information with regard to the embedding of at least one watermark
into the information representation, from the information representation. Further, in a
second step 1420, the method 1400 comprises extracting one or several watermarks
contained in the input information representation depending on the embedding
information.
Fig. 15 shows a flow diagram of a method of embedding a watermark into an information
representation. The method according to Fig. 15 is indicated by 1500 in its entirety. In a
first step 1510, the method 1500 comprises applying a derivation function, once or several
times, to an initial value to obtain an embedding parameter for embedding the watermark
into the information representation. Further, in a second step 1520, the method 1500
comprises providing the information representation with the watermark using the
embedding parameter.
Fig. 16 shows a flow diagram of a method of detecting at least one watermark in the
information representation provided with the watermark. The method according to Fig. 16
is indicated by 1600 in its entirety. In a first step 1610, the method 1600 comprises
applying a derivation function, once or several times, to an initial value to obtain a
detection parameter for detecting the watermark in the information representation. Further,
in a second step 1620, the method 1600 comprises extracting the watermark from the
information representation using the detection parameter.

The methods 1200 - 1600 according to Figs. 12-16 can further be supplemented by all
those steps and/or features discussed within the present description also with regard to the
described apparatuses. Further, the method illustrated within the present description may
also be realized by a computer program.
In other words, the inventive apparatus and the inventive method can be implemented in
hardware or in software. Implementation can be made on a digital memory medium, for
example a disc, a CD, a DVD, an ROM, a PROM, an EPROM, an EEPROM or a FLASH
memory with electronically readable control signals that can cooperate with a
programmable computer system such that the respective method is performed.
Generally, the present invention consists therefore also of a computer program product
with a program code stored on a machine-readable carrier for performing the inventive
method when the computer program product runs on a computer. In other words, the
invention can be realized as a computer program with a program code for performing the
inventive method when the computer program runs on a computer.

According to one embodiment, the invention provides an embedder 300; 700 for
embedding a watermark 341; 742 to be embedded into an input information representation
310; 710 representing an audio signal, or representing a video signal, or representing a
computer program, or representing an image, or representing a text, comprising: an
information adder 330; 740 implemented to provide the input information representation
310; 710 with the watermark 341; 742 to be embedded and additional information 343; 762
to be added to obtain an information representation 320; 720 provided with the watermark
to be embedded and the additional information to be added, wherein the additional
information to be added comprises descriptive information describing the embedding of at
least one watermark into the information representation 320; 720 provided with the
watermark to be embedded and the additional information; wherein the embedder is
implemented to provide the input information representation 310; 710 with the additional
information 343; 762 to be added such that the additional information to be added carries
information on how many watermarks are contained in the information representation 320;
720 provided with the watermark to be embedded and the additional information to be
added.
In a preferred embodiment of the embedder 300; 700, the information adder 330; 740
comprises a watermark adder 340; 340b; 340c implemented to provide the input
information representation or information derived therefrom with the watermark 341; 742
to be embedded, and an additional information adder 342; 342b; 342c implemented to
provide the input information representation or information derived therefrom with the
additional information to be added, wherein the watermark adder 340; 340b; 340c and the
additional information adder 342; 342b; 342c are configured to cooperate in order to
generate, during operation, an information representation provided with the watermark
341; 742 to be embedded and the additional information 342; 762 to be added.
In a preferred embodiment of the embedder 300; 700, the embedder is implemented to
provide the input information representation 310; 710 with additional information 343; 762
to be added such that the additional information to be added signalizes the existence of the
watermark 341; 742 to be embedded in the information representation 320; 720 provided
with the watermark to be embedded and the additional information to be added.
In a preferred embodiment of the embedder 300; 700, the embedder is implemented to
provide the input information representation 310; 710 with the additional information 343;
762 to be added such that the additional information to be added carries information on
how many watermarks are contained in the information representation 320; 720 provided
with the watermark to be embedded and the additional information to be added.

In a preferred embodiment of the embedder 300; 700, the embedder is implemented to
provide the input information representation 310; 710 with the additional information 343;
662 to be added such that the additional information to be added encodes at least one
parameter used by the information adder 330; 740 when providing the input information
representation with the watermark to be embedded.
In a preferred embodiment of the embedder 300; 700, the embedder is implemented to
provide the input information representation with the additional information 343; 762 to be
added such that the additional information 343; 762 to be added depends on a watermark
contained in the input information representation 310; 710.
According to an embodiment, the invention provides an embedder 300; 700 for embedding
a watermark 341; 742 to be embedded into an input information representation 310; 710
representing an audio signal, or representing a video signal, or representing a computer
program, or representing an image, or representing a text, comprising: an information
adder 330; 740 implemented to provide the input information representation 310; 710 with
the watermark 341; 742 to be embedded and additional information 343; 762 to be added
to obtain an information representation 320; 720 provided with the watermark to be
embedded and the additional information to be added, wherein the additional information
to be added comprises descriptive information describing the embedding of at least one
watermark into the information representation 320; 720 provided with the watermark to be
embedded and the additional information; wherein the embedder comprises a watermark
information detector 730, which is implemented to detect an existence of a watermark in
the input information representation 310; 710, and to provide information on an existence
of a watermark in the input information representation; and wherein the embedder is
implemented to determine the additional information 343; 762 to be added depending on
the information on the existence of a watermark in the input information representation
310; 710.
In a preferred embodiment of the embedder 300; 700, the watermark information detector
730 is implemented to detect the existence of a watermark synchronization sequence in the
input information representation 310; 710, and, when a watermark synchronization
sequence exists in the input information representation, to provide information indicating
the existence of at least one watermark in the input information representation.
In a preferred embodiment of the embedder 300; 700, the watermark information detector
730 is implemented to detect, in the input information representation 310; 710, an

existence of additional information describing an embedding of a watermark existing in the
input information representation, and, when additional information exists in the input
information representation, to provide, as the information on the existence of a watermark,
information based on the additional information existing in the input information
representation.
In a preferred embodiment of the embedder 300; 700, the information adder 330; 740 is
implemented to add the additional information 341; 762 to be added to the input
information representation 310; 710 in an additional information block, which is adjacent
to a synchronization information block.
In a preferred embodiment of the embedder 300; 700, the information adder 330; 740 is
implemented to add the additional information 341; 762 to be added in a timeslot following
synchronization information contained in the input information representation 310; 710.
According to one embodiment, the invention provides an embedder 300; 700 for
embedding a watermark 341; 742 to be embedded into an input information representation
310; 710 representing an audio signal, or representing a video signal, or representing a
computer program, or representing an image, or representing a text, comprising: an
information adder 330; 740 implemented to provide the input information representation
310; 710 with the watermark 341; 742 to be embedded and additional information 343; 762
to be added to obtain an information representation 320; 720 provided with the watermark
to be embedded and the additional information to be added, wherein the additional
information to be added comprises descriptive information describing the embedding of at
least one watermark into the information representation 320; 720 provided with the
watermark to be embedded and the additional information; wherein the embedder is
implemented to select resources for embedding the watermark 341; 742 to be embedded
depending on information on a number of watermarks already contained in the input
information representation 310; 710.
In a preferred embodiment of the embedder 300; 700, the embedder comprises an
embedding parameter determiner 750, which is implemented to apply a derivation function
depending on information on the number of watermarks already contained in the input
information representation 310; 710, once or several times, to an initial value to obtain an
embedding parameter for embedding the watermark into the input information
representation, and wherein the information adder 330; 740 is implemented to provide the
input information representation 310; 710 with the watermark to be embedded using the
embedding parameter.

In a preferred embodiment of the embedder 300; 700, the embedding parameter determiner
750 is implemented to use a value of the function obtained by applying the derivation
function to the initial value, once or several times, as an initial value for calculating an
embedding code according to a predetermined embedding code calculation regulation.
In a preferred embodiment of the embedder 300; 700, the derivation function is a
cryptographical one-way function.
An embodiment of the invention provides a detector 400; 800 for detecting at least one
watermark in an input information representation 410; 810 representing an audio signal, or
representing a video signal, or representing a computer program, or representing an image,
or representing a text, comprising: an embedding information extractor, which is
implemented to extract, from the input information representation, embedding information
comprising descriptive information with regard to the embedding of at least one watermark
into the input information representation; and a watermark extractor 630; 840, which is
implemented to extract one or several watermarks contained in the input information
representation 410; 810 depending on the embedding information; wherein the embedding
information extractor 420; 830 is implemented to detect, as embedding information,
additional information in the information representation 410; 810 comprising information
on a number of watermarks embedded in the information representation, and wherein the
detector is implemented to determine, depending on the additional information, how many
watermarks are to be extracted from the input information representation.
In a preferred embodiment of the detector 400; 800, the embedding information extractor
420; 830 is implemented to detect additional information in the information representation
410; 810 as embedding information, comprising information with regard to embedding at
least one watermark into the information representation, and wherein the detector is
implemented to select at least one extraction parameter for extraction of at least one
watermark contained in the input information representation 410; 810 depending on the
information with regard to the embedding of at least one watermark.
In a preferred embodiment of the detector 400; 800, the embedding information extractor
420; 830 is implemented to detect, as the embedding information, additional information in
the input information representation 410; 810 describing an allocation of an extraction
code to a watermark to be extracted from the input information representation 410; 810 by
the watermark extractor 430; 840, and wherein the detector is implemented to select an

extraction code for extracting the watermark to be extracted depending on the additional
information.
In a preferred embodiment of the detector 400; 800, the embedding information extractor
420; 830 is implemented to detect, as the embedding information, additional information in
the input information representation 410; 810 comprising information on a number of
watermarks embedded in the input information representation, and wherein the detector is
implemented to determine, depending on the additional information, how many
watermarks are to be extracted from the input information representation.
In a preferred embodiment of the detector 400; 800, the embedding information extractor
420; 830 is implemented to identify several embedding information units in the input
information representation 410; 810, wherein the embedding information units are
allocated to different watermark embeddings in the input information representation; and
wherein the embedding information extractor 420; 830 is implemented to select a latest
embedding information unit from the plurality of identified embedding information units to
derive the additional information from the latest embedding information unit.
In a preferred embodiment of the detector 400; 800, the embedding information extractor
420; 830 is implemented to extract, as the embedding information, a watermark number
belonging to the watermark to be extracted from the input information representation 410;
810; wherein the detector comprises a detection parameter determiner 850, which is
implemented to apply a derivation function depending on the watermark number, once or
several times, to an initial value to obtain an extraction parameter for extracting the
watermark to be extracted from the input information representation; and wherein the
watermark extractor 430; 840 is implemented to extract the watermark to be extracted
using the extraction parameter from the input information representation.
An embodiment of the invention provides an information signal 770, comprising at least
one watermark and one descriptive information with regard to the embedding of the at least
one watermark into the information signal, wherein the information signal comprises an
audio signal, an image signal, a text signal or a computer program signal; and wherein the
descriptive information is added in a timeslot following synchronization information
contained in the input information representation 310; 710.

In a preferred embodiment of the information signal 770, the descriptive information
describes an allocation of a timeslot of the information signal to the at least one watermark,
an allocation of a frequency band of the information signal to the at least one watermark,
an allocation of an extraction code to the at least one watermark or a number of
watermarks embedded in the information signal.

We-Claim:
1. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:
an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,
wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the embedder is implemented to provide the input information
representation (310; 710) with the additional information (343; 762) to be added such
that the additional information to be added carries information on how many
watermarks are contained in the information representation (320; 720) provided with
the watermark to be embedded and the additional information to be added.
2. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:
an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,

wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the embedder comprises a watermark information detector (730), which is
implemented to detect an existence of a watermark in the input information
representation (310; 710), and to provide information on an existence of a watermark
in the input information representation; and
wherein the embedder is implemented to determine the additional information (343;
762) to be added depending on the information on the existence of a watermark in
the input information representation (310; 710).
3. The embedder (300; 700) according to claim 2, wherein the watermark information
detector (730) is implemented to extract, when additional information exists in the
input information representation (310; 710), information describing the number of
watermarks contained in the input information representation from the existing
additional information, and
wherein the embedder is implemented to determine the additional information (343;
762) to be added such that the additional information to be added describes, based on
the information on the number of watermarks contained in the input information
representation, a number of after adding the watermark to be added in the
information representation provided with the watermark to be embedded and the
additional information to be added.
4. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:
an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,

wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the information adder (330; 740) is implemented to add the additional
information (341; 762) to be added to the input information representation (310; 710)
in the same embedding format in which additional information already existing in the
input information representation exists.
5. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:
an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,
wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the embedder comprises a watermark information detector (730), which is
implemented to detect watermark information already contained in the input
information representation (310; 710), and wherein the information adder (330; 740)
is implemented to provide the input information representation with the watermark,
depending on the watermark information detected by the watermark information
detector (330; 730).
6. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:

an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,
wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the embedder is implemented to select resources for embedding the
watermark (341; 742) to be embedded depending on information on a number of
watermarks already contained in the input information representation (310; 710).
7. A detector (400; 800) for detecting at least one watermark in an input information
representation (410; 810) representing an audio signal, or representing a video signal,
or representing a computer program, or representing an image, or representing a text,
comprising:
an embedding information extractor, which is implemented to extract, from the input
information representation, embedding information comprising descriptive
information with regard to the embedding of at least one watermark into the input
information representation; and
a watermark extractor (630; 840), which is implemented to extract one or several
watermarks contained in the input information representation (410; 810) depending
on the embedding information;
wherein the embedding information extractor (420; 830) is implemented to detect, as
embedding information, additional information in the information representation
(410; 810) comprising information on a number of watermarks embedded in the
information representation, and
wherein the detector is implemented to determine, depending on the additional
information, how many watermarks are to be extracted from the input information
representation.

8. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein the input information representation (310; 710) is provided with the
additional information (343; 762) to be added such that the additional information to
be added carries information on how many watermarks are contained in the
information representation (320; 720) provided with the watermark to be embedded
and the additional information to be added.
9. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein an existence of a watermark is detected in the input information
representation (310; 710), and information on an existence of a watermark in the
input information representation is provided; and

wherein the additional information (343; 762) to be added is determined depending
on the information on the existence of a watermark in the input information
representation (310; 710).
10. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein the additional information (341; 762) to be added is added to the input
information representation (310; 710) in the same embedding format in which
additional information already existing in the input information representation exists.
11. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein watermark information already contained in the input information
representation (310; 710) is detected, and wherein the input information
representation is provided with the watermark, depending on the detected watermark
information.

12. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein resources for embedding the watermark (341; 742) to be embedded are
selected depending on information on a number of watermarks already contained in
the input information representation (310; 710).
13. A method (1400) of detecting at least one watermark in an input information
representation representing an audio signal, or representing a video signal, or
representing a computer program, or representing an image, or representing a text,
comprising:
extracting (1410) embedding information comprising descriptive information with
regard to the embedding of at least one watermark into the input information
representation, from the input information representation; and
extracting (1420) one or several watermarks contained in the input information
representation depending on the embedding information;
wherein, as embedding information, additional information in the information
representation (410; 810) is detected, comprising information on a number of
watermarks embedded in the input information representation, and
wherein it is determined, depending on the additional information, how many
watermarks are to be extracted from the input information representation.

14. An information signal (770), comprising at least one watermark and one descriptive
information with regard to the embedding of the at least one watermark into the
information signal;
wherein the information signal comprises an audio signal, an image signal, a text
signal or a computer program signal; and
wherein the descriptive information carries information on how many watermarks
are contained in the information signal.
15. An embedder (300; 700) for embedding a watermark (341; 742) to be embedded into
an input information representation (310; 710) representing an audio signal, or
representing a video signal, or representing a computer program, or representing an
image, or representing a text, comprising:
an information adder (330; 740) implemented to provide the input information
representation (310; 710) with the watermark (341; 742) to be embedded and
additional information (343; 762) to be added to obtain an information representation
(320; 720) provided with the watermark to be embedded and the additional
information to be added,
wherein the additional information to be added comprises descriptive information
describing the embedding of at least one watermark into the information
representation (320; 720) provided with the watermark to be embedded and the
additional information;
wherein the information adder (330; 740) is implemented to add the additional
information (343; 762) to be added in a timeslot following synchronization
information contained in the input information representation (310; 710).
16. The embedder (300; 700) according to claim 15, wherein the information adder (330;
740) is implemented to add the additional information (341; 762) to be added to the
input information representation (310; 710) in a separate frequency band overlapping
in time with synchronization information.
17. A detector (400; 800) for detecting at least one watermark in an input information
representation (410; 810) representing an audio signal, or representing a video signal,

or representing a computer program, or representing an image, or representing a text,
comprising:
an embedding information extractor, which is implemented to extract, from the input
information representation, embedding information comprising descriptive
information with regard to the embedding of at least one watermark into the input
information representation; and
a watermark extractor (630; 840), which is implemented to extract one or several
watermarks contained in the input information representation (410; 810) depending
on the embedding information;
wherein the embedding information extractor (420; 830) is implemented to identify
several embedding information units in the input information representation (410;
810), wherein the embedding information units are allocated to different watermark
embeddings in the input information representation; and
wherein the embedding information extractor (420; 830) is implemented to select a
latest embedding information unit from the plurality of identified embedding
information units, and to derive the additional information from the latest embedding
information unit.
18. A detector (400; 800) for detecting at least one watermark in an input information
representation (410; 810) representing an audio signal, or representing a video signal,
or representing a computer program, or representing an image, or representing a text,
comprising:
an embedding information extractor, which is implemented to extract, from the input
information representation, embedding information comprising descriptive
information with regard to the embedding of at least one watermark into the input
information representation; and
a watermark extractor (630; 840), which is implemented to extract one or several
watermarks contained in the input information representation (410; 810), depending
on the embedding information;

wherein the embedding information extractor (420; 830) is implemented to extract,
as the embedding information, a watermark number belonging to the watermark to be
extracted, from the input information representation (410; 810);
wherein the detector comprises a detection parameter determiner (850), which is
implemented to apply a derivation function, depending on the watermark number,
once or several times, to an initial value to obtain an extraction parameter for
extracting the watermark to be extracted from the input information representation;
and
wherein the watermark extractor (430; 840) is implemented to extract the watermark
to be extracted using the extraction parameter from the input information
representation.
19. The detector (400, 800) according to claim 17 or 18, wherein the embedding
information extractor (420; 830) is implemented to detect, as the embedding
information, additional information in the input information representation (410;
810) describing an allocation of a timeslot of the input information representation to
a watermark to be extracted from the input information representation (410; 810) by
the watermark extractor (430; 840), and
wherein the detector is implemented to select a timeslot for the extraction of the
watermark to be extracted depending on the additional information.
20. The detector (400; 800) according to one of claims 17 to 19, wherein the embedding
information extractor (420; 830) is implemented to detect, as the embedding
information, additional information in the input information representation (410;
810) describing an allocation of a frequency band of the input information
representation to a watermark to be extracted from the input information
representation (410; 810) by the watermark extractor (430; 840), and
wherein the detector is implemented to select a frequency band for the extraction of
the watermark to be extracted depending on the additional information.
21. The detector (400; 800) according to one of claims 17 to 20, wherein the embedding
information extractor (420; 830) is implemented to search for the additional
information in a predefined timeslot of the input information representation (410;
810) following synchronization information in the input information representation.

22. The detector (400; 800) according to claim 17, wherein the embedding information
extractor (420; 830) is implemented to identify several embedding information units
in the input information representation (410; 810) describing different numbers of
watermarks, and
to select an embedding information unit describing a highest number of watermarks
as latest embedding information unit.
23. The detector (400; 800) according to claim 18, wherein the watermark number
indicates how often the derivation function is to be applied to the initial value.
24. The detector (400; 800) according to claims 18 to 23, wherein the derivation function
is a cryptographical one-way function.
25. A method (1300) of embedding a watermark to be embedded into an input
information representation representing an audio signal, or representing a video
signal, or representing a computer program, or representing an image, or representing
a text, comprising:
providing (1310) the input information representation with a watermark and
additional information to be added to obtain an information representation provided
with the watermark and additional information to be added,
wherein the additional information to be added comprises descriptive information
with regard to embedding at least one watermark into the input information
representation;
wherein the additional information (343; 762) to be added is added in a timeslot
following synchronization information contained in the input information
representation (310; 710).
26. A method (1400) of detecting at least one watermark in an input information
representation representing an audio signal, or representing a video signal, or
representing a computer program, or representing an image, or representing a text,
comprising:

extracting (1410) embedding information comprising descriptive information with
regard to the embedding of at least one watermark into the input information
representation, from the input information representation; and
extracting (1420) one or several watermarks contained in the input information
representation depending on the embedding information;
wherein several embedding information units are identified in the input information
representation (410; 810), wherein the embedding information units are allocated to
different watermark embeddings in the input information representation; and
wherein a latest embedding information unit is selected from the plurality of
identified embedding information units, and the additional information is derived
from the latest embedding information unit.
27. A method (1400) of detecting at least one watermark in an input information
representation representing an audio signal, or representing a video signal, or
representing a computer program, or representing an image, or representing a text,
comprising:
extracting (1410) embedding information comprising descriptive information with
regard to the embedding of at least one watermark into the input information
representation, from the input information representation; and
extracting (1420) one or several watermarks contained in the input information
representation, depending on the embedding information;
wherein, as the embedding information, a watermark number belonging to the
watermark to be extracted is extracted from the input information representation
(410; 810);
wherein, depending on the watermark number, a derivation function is applied, once
or several times, to an initial value to obtain an extraction parameter for extracting
the watermark to be extracted from the input information representation; and
wherein the watermark to be extracted is extracted using the extraction parameter
from the input information representation.

28. A computer program for performing a method according to one of claims 8 to 13 or
25 to 27, when the computer program runs on a computer.
29. An information signal (770), comprising at least one watermark and one descriptive
information with regard to the embedding of the at least one watermark into the
information signal.
wherein the information signal comprises an audio signal, an image signal, a text
signal or a computer program signal; and
wherein the descriptive information is added in a timeslot following synchronization
information contained in the input information representation (310; 710)

An embedder for embedding a watermark to be embedded into an input information
representation comprises an information adder, which is implemented to provide the input
information representation with the watermark and additional information to be added to
obtain an input information representation provided with the watermark and the additional
information. The additional information to be added comprises descriptive information
describing the embedding of the at least one watermark into the input information
representation.