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Claims  |
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What is claimed is:
1. An apparatus for classifying an input signal as either a voice or data
signal in a communication system, wherein said apparatus comprises:
a frequency estimator that receives the input signal and generates a
frequency estimate value representing both an estimated central frequency
of the input signal and an estimated energy level of input signal;
an energy estimator that receives the input signal and generates an energy
estimate value representing an estimate of the energy level of the input
signal; and
a classification unit in electrical communication with both said frequency
and energy estimators, wherein said classification unit receives the
frequency and energy estimate values and classifies the input signal as
either a voice or data signal based on the frequency and energy estimate
values and a data threshold value.
2. An apparatus according to claim 1, wherein said classification unit
further comprises a normalizer in electrical communication with both said
frequency and energy estimators, and wherein said normalizer generates a
normalized frequency estimate value representing an estimate of the
central frequency of the input signal.
3. An apparatus according to claim 2, wherein said normalizer divides the
frequency estimate value by the energy estimate value and generates a
normalized frequency estimate value representing an estimate of the
central frequency of the input signal.
4. An apparatus according to claim 2, wherein the data threshold value
defines a frequency value, wherein said classification unit further
comprises a frequency detector in electrical communication with said
normalizer, and wherein said frequency detector compares the normalized
frequency estimate value to the data threshold value and classifies the
input signal as a data signal if the normalized frequency estimate value
is at least as great as the data threshold value.
5. An apparatus according to claim 2, wherein said classification unit
further comprises:
a frequency detector in electrical communication with said normalizer;
a switch in electrical communication with both said normalizer and said
frequency detector for selectively connecting the normalizer and the
frequency detector; and
an energy detector in electrical communication with said energy estimator
and said switch, wherein said energy detector initially compares the
energy estimate value to an energy threshold value defining a minimum
energy level, wherein if the energy estimate value is at least as great as
the energy threshold value, said energy detector controls said switch to
connect said normalizer and said frequency detector, such that the
frequency detector may classify the input signal as either voice or data.
6. An apparatus according to claim 1, wherein said classification unit
further comprises an energy detector in electrical communication with said
energy estimator, wherein said energy detector initially compares the
energy estimate value to an energy threshold value defining a minimum
energy level, and wherein said energy detector classifies the input signal
as a voice signal if the energy estimate value is no greater than the
energy threshold value.
7. An apparatus according to claim 1, wherein said classification unit
comprises:
a frequency detector in electrical communication with said frequency
estimator;
an energy detector in electrical communication with both said energy
estimator and said frequency detector; and
a memory device in electrical communication with said energy detector, said
memory device storing a table that includes a plurality of differing data
threshold values, wherein said energy detector receives the energy
estimate value and selects a data threshold value from the plurality of
differing threshold values in said table based on the amplitude of the
energy estimation value, and wherein said frequency detector receives the
data threshold value from said energy detector and classifies the input
signal as a data signal if the frequency estimate value is at least as
great as the selected data threshold value.
8. An apparatus according to claim 1, wherein said frequency estimator
comprises:
a delay that receives the input signal and generates a delayed input
signal;
a difference integrator in electrical communication with said delay and the
input signal, wherein said difference integrator receives the delayed and
input signals and generates a frequency estimate value representing both
the estimated central frequency of the input signal and the estimated
energy of the input signal.
9. An apparatus according to claim 8, wherein said frequency estimator
further comprises an absolute value device in electrical communication
with said delay, wherein said absolute value device receives the frequency
estimate value and generates an absolute value of the frequency estimate
value.
10. An apparatus according to claim 8, wherein said frequency estimator
further comprises an accumulator device in electrical communication with
said delay, wherein said accumulator device receives the frequency
estimate value and generates a frequency estimate value.
11. An apparatus according to claim 1, wherein said energy estimator
comprises:
an absolute value device that receives the input signal and generates an
absolute value of the input signal; and
an accumulator device in electrical communication with said absolute value
device, wherein said accumulator device generates an energy estimate value
representing the amplitude of the input signal.
12. A method for classifying an input signal as either a voice or data
signal in a communication system, wherein said method comprises the steps
of:
receiving an input signal;
generating a frequency estimate value representing both an estimated
central frequency of the input signal and an estimated energy of the input
signal;
generating an energy estimate value representing an estimate of the energy
level of the input signal; and
classifying the input signal as either a voice or data signal based on the
frequency and energy estimate values and a data threshold value.
13. A method according to claim 12, wherein said classifying step further
comprises the step of initially normalizing the frequency estimate value
based on the energy estimate value to thereby generate a normalized
frequency estimate value representing an estimate of the central frequency
of the input signal.
14. A method according to claim 13, wherein said normalizing step comprises
dividing the frequency estimate value by the energy estimate value to
thereby generate a normalized frequency estimate value representing an
estimate of the central frequency of the input signal.
15. A method according to claim 13, wherein the data threshold value
defines a frequency value, wherein said classifying step comprises the
steps of:
comparing the normalized frequency estimate value to the data threshold
value; and
classifying the input signal as a data signal if the normalized frequency
estimate value is at least as great as the data threshold value.
16. A method according to claim 13, wherein said classifying step further
comprises initially comparing the energy estimate value to an energy
threshold value defining a minimum energy level, wherein if the energy
estimate value is at least as great as the energy threshold value, said
classifying step comprises comparing the normalized frequency estimate
value to the data threshold value, and classifying the input signal as a
data signal if the normalized frequency estimate value is at least as
great as the data threshold value.
17. A method according to claim 12, wherein said classifying step further
comprises initially comparing the energy estimate value to an energy
threshold value defining a minimum energy level, and wherein said
classifying step classifies the input signal as a voice signal if the
energy estimate value is no greater than the energy threshold value.
18. A method according to claim 12, wherein said classifying step comprises
the steps of:
receiving the energy estimate value;
selecting a data threshold value from a plurality of differing threshold
values based on the amplitude of the energy estimate value; and
classifying the input signal as a data signal if the frequency estimate
value is at least as great as the selected data threshold value.
19. A method according to claim 12, wherein said generating a frequency
estimate value step comprises the steps of:
delaying the input signal to thereby generate a delayed input signal;
determining a difference between the delayed input signal and the input
signal; and
generating a frequency estimate value representing both the estimated
central frequency of the input signal and the estimated energy of the
input signal.
20. A method according to claim 19, wherein said generating a frequency
estimate value step further comprises the step of generating an absolute
value of the frequency estimate value.
21. A method according to claim 19, wherein said generating a frequency
estimate value step further comprises the step of accumulating the
frequency estimate value.
22. A method according to claim 12, wherein said generating an energy
estimate value step comprises the steps of:
generating an absolute value of the input signal; and
generating an energy estimate value representing the amplitude of the input
signal.
23. An apparatus for classifying an input signal as either a voice or data
signal in a communication system, wherein said apparatus comprises:
a delay that receives the input signal and generates a delayed input
signal;
a difference integrator in electrical communication with said delay and the
input signal, wherein said difference integrator receives the delayed and
input signals and generates a frequency estimate value representing both
the estimated central frequency of the input signal and the estimated
energy of the input signal; and
a classification unit in electrical communication with said difference
integrator, wherein said classification unit classifies the input signal
as either a voice or data signal based on the frequency estimate value and
a data threshold value.
24. An apparatus according to claim 23, wherein said classification unit
comprises a normalizer in electrical communication with said difference
integrator, wherein said normalizer normalizes the frequency estimate
value based on an energy estimate value representing the energy of the
input signal and generates a normalized frequency estimate value
representing an estimate of the central frequency of the input signal.
25. An apparatus according to claim 24, wherein said normalizer divides the
frequency estimate value by the energy estimate value and generates a
normalized frequency estimate value representing an estimate of the
central frequency of the input signal.
26. An apparatus according to claim 24, wherein said classification unit
further comprises a frequency detector in electrical communication with
said normalizer, wherein said frequency detector compares the frequency
estimate value with a data threshold value, and wherein said detector
classifies the input signal as a data signal if the frequency estimate
value is at least as great as the data threshold value.
27. An apparatus according to claim 23 further comprising:
an absolute value device in electrical communication with said difference
integrator, wherein said absolute value device generates an absolute value
of the input signal; and
an accumulator device in electrical communication with said absolute value
device, wherein said accumulator device generates a frequency estimate
value representing both the estimated central frequency of the input
signal and the estimated energy of input signal.
28. A method for classifying an input signal as either a voice or data
signal in a communication system, wherein said method comprises the steps
of:
delaying the input signal to thereby generate a delayed input signal;
generating a frequency estimate value representing both the estimated
central frequency of the input signal and the estimated energy of the
input signal based upon the input signal and the delayed input signal; and
classifying the input signal as either a voice or data signal based on the
frequency estimate value and a data threshold value.
29. A method according to claim 28 further comprising after said generating
step normalizing the frequency estimate value based on an energy estimate
value representing the energy of the input signal to thereby generate a
normalized frequency estimate value representing an estimate of the
central frequency of the input signal.
30. A method according to claim 29, wherein said normalizing step comprises
dividing the frequency estimate value by the energy estimate value to
thereby generate a normalized frequency estimate value representing an
estimate of the central frequency of the input signal.
31. A method according to claim 29, wherein said classifying step comprises
comparing the frequency estimate value with a data threshold value and
classifying the input signal as a data signal if the frequency estimate
value is at least as great as the data threshold value.
32. A method according to claim 28 further comprising after said generating
step:
generating an absolute value of the input signal; and
generating a frequency estimate value representing both the estimated
central frequency of the input signal and the estimated energy of input
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates generally to signal processing in a
communication system and more particularly to classifying an input signal
as either voice or data.
BACKGROUND OF THE INVENTION
For the most part, telecommunication systems were originally envisioned for
voice signal transmission. Following its inception and implementation,
however, pronounced changes have occurred in the telecommunication
industry. Not only has voice communication via the telecommunication
system become prolific through out the world, the presence of preexisting
telephone lines has also made the telecommunication system a major media
for data signal transmission. For example, many households and businesses
in the United States and many foreign countries include telecommunication
systems that are used for both the transmission of voice signals via a
telephone and data signals via modem technology. As such, today's
telecommunication systems not only transmit an increasing number of voice
signals, but are also used as a major throughput for data signals.
With the increased use of the telephone communication system for both voice
and data signals, systems and methods have been developed to narrow the
required bandwidth needed to transmit voice signals, such that more voice
and data may be transmitted on existing telephone lines. For example, many
of today's telecommunication systems use encoding techniques to encode
voice signals for transmission in telecommunication systems. These
encoding techniques allow more information to be transmitted within the
limited bandwidth of the telecommunication system.
Although encoding of voice signals is advantageous, implementation of voice
encoding techniques in telecommunication systems can be somewhat
problematic. Specifically, most telephone lines are used for both voice
and data transmission. However, encoding techniques used for encoding of
voice signals may introduce errors if used to encode data signals. In
light of this, voice/data discrimination systems and techniques have been
developed to discern voice and data signals, such that voice signals may
be encoded, while data signals may be left unaffected or encoded by a
different encoding procedure. These voice/data discrimination systems
typically analyze signals transmitted on the telecommunication system and
classify communication signals as either voice or data. Voice signals are
then encoded prior to transmission to increase the amount of voice and
data that may be transmitted in the telecommunication system.
Although conventional voice/data discrimination systems provide viable
methods for voice and data signal discrimination, they do have some
drawbacks. For example, one drawback with conventional voice/data
discriminators is that they are typically computational intensive and may
require an undesired amount of energy for voice/data discrimination. For
example, many conventional voice/data discrimination systems use
multipliers, dividers, Fast Fourier Transform systems, neural networks,
and many other types of computational schemes to analyze signals
transmitted on telecommunication systems and accurately characterize the
signals as either voice or data. While these conventional voice/data
discrimination systems typically provide a system for accurately
characterizing communication signals as either voice or data, the energy
consumed in analysis of the communication signals may be unacceptable.
Specifically, many telecommunication systems are comprised of either
thousands or millions of communication lines used for transmission of both
voice and data signals. A dedicated voice/data discrimination systems is
typically needed to discriminate between voice and data for each
communication line. Although the energy consumption of each individual
voice/discriminator due to computationally intensive analysis of the
signals may be negligible, the use of a plurality of these conventional
voice/data discriminators in a telecommunication system may consume an
unacceptable amount of energy. This may be particularly problematic in
systems where energy conservation is at a premium.
An additional problem is that some conventional systems differentiate
between voice and data signals based on specific characteristics of the
data signals. Specifically, in many telecommunication systems, such as
systems that use modems, an initial set of tones may be transmitted across
the telecommunication line to inform systems that a data signal, as
opposed to a voice signal, is being transmitted. In light of this fact,
some conventional voice/data discrimination systems analyze the initial
portion of a telecommunication signal and classify the signal as either
voice or data based on whether these initial tones are present. While
these conventional voice/data discrimination systems typically provide
convenient apparatus and methods for discriminating between voice and data
signals, they are somewhat limited. Specifically, these conventional
voice/data discrimination systems must be activated prior to transmission
of the telecommunication signal in order to classify the data as either
voice or data.
SUMMARY OF THE INVENTION
As set forth below, the apparatus and method of the present invention may
overcome many of the deficiencies identified with discriminating between
voice and data signals in a communication system. In particular, the
present invention provides apparatus and methods for classifying
communication signals as either voice or data with a limited number of
computational instructions, (i.e., multipliers, dividers, etc.), such that
the communication signals may be classified with reduced energy
consumption. Additionally, the present invention, provides apparatus and
methods that may discriminate between voice and data signals based on the
communication signal, as opposed to specific signal characteristics at the
beginning of the signal. As such, the apparatus and methods of the present
invention may classify a telecommunication signal as either voice or data
without requiring activation prior to beginning transmission of the
telecommunication signal.
The present invention provides several embodiments for classifying a
communication signal as either voice or data in a communication system.
For example, one embodiment of the present invention provides an apparatus
and method for classifying an input signal based on both an estimation of
the central frequency of an input signal and the energy level of the input
signal. The apparatus of this embodiment includes a frequency estimator
for generating a frequency estimate value representing both the estimated
central frequency of an input signal and the estimate of the energy level
of an input signal. The apparatus also includes an energy estimator for
generating an energy estimate value representing an estimate of the energy
level of the input signal. Additionally, the apparatus of this embodiment
includes a classification unit in electrical communication with both the
frequency and energy estimators for classifying the input signal as either
a voice or data signal.
In operation, both the frequency and energy estimators receive the input
signal and generate respective frequency and energy estimate values of the
input signal. These estimate signals are received by the classification
unit and compared to a data threshold value. If the frequency estimate
value is at least as great as the data threshold value, the classification
unit classifies the input signal as data. Otherwise, the input signal is
classified as a voice signal.
Importantly the apparatus of this embodiment uses both the frequency and
energy estimate of the input signal to classify the input signal as either
voice or data. Because the present invention uses rough estimates of these
values, as opposed to more accurate estimations provided by computational
intensive systems, the apparatus and method of the present invention can
typically classify the communication signal as either voice or data with
less energy consumption. Additionally, because the present invention
analyzes the communication signal, as opposed to initial tones appearing
at the beginning of the signal, the apparatus and method of the present
invention can typically classify the communication signal even if the
apparatus and method of the present invention is activated during
mid-transmission of the signal.
As discussed above, the present invention classifies the input signal based
on both the frequency estimate and the energy estimate value of the input
signal. In one embodiment, the present invention classifies the input
signal based on an estimate of the central frequency of the input signal.
To determine an estimate of the central frequency of the input signal, the
classification unit of this embodiment further includes a normalizer in
electrical communication with both the frequency and energy estimators.
The normalizer generates an estimate of the central frequency of the input
signal by comparing the frequency and energy estimate values generated by
the frequency and energy estimators. Specifically, the frequency estimator
of the present invention generates a composite signal representing both
the estimated central frequency of the input signal and the estimated
energy level of the input signal. The normalizer of this embodiment,
compares the frequency and energy estimate values and generates a
normalized frequency estimate value representing an estimate of the
central frequency of the input signal.
To analyze the estimated central frequency of the input signal, the
classification unit of this embodiment further includes a frequency
detector in electrical communication with the normalizer. In this
embodiment of the present invention, the frequency detector compares the
normalized frequency estimate value generated by the normalizer to a data
threshold value representing a threshold frequency value. Input signals
having estimated central frequencies value equal to and above the data
threshold value are considered data signals. As such, if the frequency
estimate value of the input signal is at least as great as the data
threshold value, the frequency detector classifies the input signal as
data. Otherwise, the frequency detector classifies the input signal as
voice.
As discussed, the classification unit of this embodiment includes a
normalizer for normalizing the frequency estimate signal. In one
embodiment of the present invention, the normalizer comprises a divider in
electrical communication with both the frequency and energy estimators. In
this embodiment of the present invention, the divider divides the
frequency estimate value representing both an estimate of the central
frequency of the input signal and the energy level of the input signal by
the energy estimate value representing an estimate of the energy level of
the input signal. As such, the normalizer generates a normalized frequency
estimate value representing an estimate of the central frequency of the
input signal.
As an alternative to the use of a normalizer, which may be energy
consuming, the apparatus of the present invention may use an energy
detector and a look-up table stored in a memory device to normalize the
energy estimate signal. Specifically, in this embodiment, the
classification unit of the present invention may include an energy
detector in electrical communication with both the energy estimator and
the frequency detector. Additionally, the classification unit of this
embodiment may also include a look-up table stored in a memory device in
electrical communication with the energy detector. The look-up table of
this embodiment includes a plurality of differing data threshold values,
each representing a selected threshold value for a given energy level of
the input signal, (i.e., the selected threshold value multiplied by the
given energy level).
In this embodiment of the present invention, the energy detector receives
the energy estimation value and selects a frequency threshold value from
the plurality of differing threshold values in the look-up table.
Specifically, the energy detector selects the frequency threshold value
corresponding to the energy level of the input signal. This frequency
threshold value is supplied to the frequency detector of the
classification unit. The frequency detector, in turn, uses the selected
frequency threshold value to classify the input signal as either voice or
data. Importantly, the classification unit of this embodiment uses a
selected frequency from the look-up table to compensate for the energy
level of the input signal, as opposed to the use of a normalizer. As such,
the apparatus and method of this embodiment can typically classify the
input signal with reduced computational instructions and reduced energy
consumption due to the elimination of the normalizer.
As discussed above, the present invention typically classifies the input
signal as either voice or data based on the estimated frequency value.
However, in some embodiments, the present invention may initially evaluate
the estimated energy level of the input signal to determine whether the
input signal has sufficient energy for classification as a data signal. In
this embodiment, if the input signal has an energy level that is less than
a predetermined energy threshold value, the input signal is considered to
have an insufficient energy level to be a data signal and classifies the
input signal as voice, without further evaluating the frequency estimate
value.
In this embodiment of the present invention, the classification unit
further includes a switch in electrical communication with both the
normalizer and the frequency detector for selectively connecting the
normalizer and the frequency detector. The apparatus of this embodiment
also includes an energy detector in electrical communication with the
energy estimator and the switch. In operation, the energy detector
initially compares the energy estimate value to an energy threshold value
defining a predetermined minimum energy level. If the energy estimate
value is less than the energy threshold value, the energy detector
classifies the input signal as voice and the frequency estimate value is
not further analyzed by the frequency detector. However, if the energy
estimate value is at least as great as the energy threshold value, the
energy detector controls the switch to connect the normalizer and the
frequency detector, such that the frequency detector analyzes the
frequency estimate value and classifies the input signal as either voice
or data.
As detailed above, the present invention includes a frequency estimator for
generating a frequency estimate value representing both the estimated
central frequency of the input signal and the estimated energy level of
input signal. In one embodiment of the present invention, the frequency
estimator generates the frequency estimate value by taking the derivative
of the input signal. To take the derivative of the input signal, the
frequency estimator of this embodiment includes a delay in electrical
communication with the input signal and a difference integrator in
electrical communication with both the delay and the input signal. In
operation, the delay receives the input signal and generates a delayed
input signal. The difference integrator, in turn, receives the delayed, as
well as the input signal and generates a frequency estimate value
representing both the estimated central frequency of the input signal and
the estimated energy of the input signal. This frequency estimate value is
used by the classification unit as previously described above to classify
the input signal as either voice or data.
In a further embodiment of the present invention, the frequency estimator
may also include an absolute value device and an accumulator in electrical
communication with the difference integrator. In this embodiment of the
present invention, the absolute value device receives the frequency
estimate value and generates an absolute value of the frequency estimate
value and the accumulator device generates a smoothed or filtered
frequency estimate value.
As detailed above, the present invention includes an energy estimator for
generating an estimate of the energy level of the input signal. In one
embodiment of the present invention, the energy estimator may also include
an absolute value device and an accumulator in electrical communication
with the input signal. In this embodiment of the present invention, the
absolute value device receives input signal and generates an absolute
value of the input signal and the accumulator device generates a smoothed
or filtered energy estimate value.
As briefly discussed above and detailed in the various embodiments below,
the present invention provides apparatus and methods for classifying
communication signals as either voice or data with a limited number of
computational instructions, (i.e., multipliers, dividers, etc.), such that
the telecommunication signals may be typically classified with reduced
energy consumption. Additionally, the present invention, provides
apparatus and methods that may discriminate between voice and data signals
based on the communication signal, as opposed to specific signal
characteristics at the beginning of the signal. As such, the apparatus and
methods of the present invention may classify a telecommunication signal
as either voice or data without the prerequisite of the apparatus and
method of the present invention being activated prior to beginning
transmission of the communication signal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an apparatus for classifying an input signal
in a communication system as either voice or data according to one
embodiment of the present invention.
FIG. 2 is a block diagram of the operations performed to classify an input
signal in a communication system as either voice or data according to one
embodiment of the present invention.
FIG. 3 is a block diagram of the operations performed to estimate the
central frequency of an input signal according to one embodiment of the
present invention.
FIG. 4 is a block diagram of an apparatus for classifying an input signal
in a communication system as either voice or data using a look-up table
containing a plurality of data threshold values according to one
embodiment of the present invention.
FIG. 5 is a block diagram of the operations performed to classify an input
signal in a communication system as either voice or data using a look-up
table containing a plurality of data threshold values according to one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention now will be described more fully hereinafter with
reference to the accompanying drawings, in which preferred embodiments of
the invention are shown. This invention may, however, be embodied in many
different forms and should not be construed as limited to the embodiments
set forth herein; rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the scope
of the invention to those skilled in the art. Like numbers refer to like
elements throughout.
With reference to FIG. 1, one embodiment of an apparatus for classifying an
input signal as either voice or data in a communication system is
illustrated. The apparatus 10 of this embodiment includes a frequency
estimator 12 for receiving an input-signal transmitted via a communication
system. The apparatus of this embodiment also includes an energy estimator
14 that also receives the input signal. Connected to the output of both
the frequency and energy estimators is a classification unit 16.
With reference to FIG. 2, in operation, the frequency and energy estimators
both receive the input signal. (See step 100). The frequency estimator
generates a frequency estimate value representing both an estimate of the
central frequency of the input signal and an estimate of the energy level
of input signal. (See step 110). Likewise, the energy estimator generates
an energy value representing an estimate of the energy level of the input
signal. (See step 120). The classification unit receives both the
frequency and energy estimate values and compares the values to a data
threshold value. (See step 160). Based on this comparison, the
classification unit classifies the input signal as either voice or data.
(See steps 170 and 180).
As illustrated in FIG. 2, the present invention classifies the input signal
as either voice or data based on an estimate of the central frequency of
the input signal, an estimate of the energy level of the input signal, and
a data threshold value. An important aspect of the present invention, is
that the present invention classifies the input signal as either voice or
data with reduced energy consumption. Specifically, the apparatus and
method of the present invention use either no or few computational
instructions, (i.e., multipliers, dividers, etc.), to classify the input
signal. Instead, the apparatus and method of the present invention rely on
estimated frequency and energy values for the input signal to classify the
signal as either voice or data.
Additionally, the present invention, classifies the input signal as either
voice or data based on the input signal itself, as opposed to specific
signal characteristics at the beginning of the input signal. As such, the
apparatus and methods of the present invention may classify a
communication signal as either voice or data without requiring activation
of the apparatus and method of the present invention prior to beginning
transmission of the communication signal.
As discussed, the frequency estimator of the present invention generates a
frequency estimate value representing both an estimate of the central
frequency of the input signal and an estimate of the energy level of input
signal. With reference to FIG. 1, in one embodiment of the present
invention, the frequency estimator provides the frequency estimate value
with reduced computational instructions. Specifically, in this embodiment
of the present invention, the frequency estimator 12 includes a delay 18
in electrical communication with the input signal. Connected to the delay
is a difference integrator 20 that is in electrical communication with
both the delay and the input signal. Additionally, the frequency estimator
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