U.S. patent number 9,270,393 [Application Number 13/721,396] was granted by the patent office on 2016-02-23 for method and system for reducing amplitude modulation (am) noise in am broadcast signals.
This patent grant is currently assigned to Visteon Global Technologies, Inc.. The grantee listed for this patent is Yao H. Kuo. Invention is credited to Yao H. Kuo.
United States Patent |
9,270,393 |
Kuo |
February 23, 2016 |
Method and system for reducing amplitude modulation (AM) noise in
AM broadcast signals
Abstract
A computer-implemented method for reducing a noise signal added
to an amplitude modulated (AM) broadcast signal while travelling
from a broadcasting antenna to a receiving antenna is provided. The
method includes capturing a signal representative of the AM
broadcast signal corrupted by the noise signal via the receiving
antenna, inverting the captured signal, and determining a carrying
frequency of the AM broadcast signal and delaying the inverted
waveform by a fraction of a cycle of the carrying frequency. The
method further includes generating a difference signal by
subtractively combining the captured signal and the delayed
inverted signal, generating an estimate noise signal by reducing an
amplitude of the generated difference signal using a
noise-reduction control multiplier, and minimizing the corrupting
noise signal component of the captured signal by subtractively
combining the captured signal and the generated estimate noise
signal.
Inventors: |
Kuo; Yao H. (West Bloomfield,
MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kuo; Yao H. |
West Bloomfield |
MI |
US |
|
|
Assignee: |
Visteon Global Technologies,
Inc. (Van Buren Township, MI)
|
Family
ID: |
50878887 |
Appl.
No.: |
13/721,396 |
Filed: |
December 20, 2012 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140177843 A1 |
Jun 26, 2014 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
1/1027 (20130101); H04H 20/88 (20130101); H04B
1/0483 (20130101); H04B 1/0475 (20130101) |
Current International
Class: |
H03D
1/04 (20060101); H04B 1/10 (20060101); H04H
20/88 (20080101); G10K 11/178 (20060101); H04B
1/04 (20060101) |
Field of
Search: |
;381/3,94.4,15,94.8,1,10,13,94.1,57
;455/226.1,222,223,296,3.01,3.02,277.2,142,143,3.06,67.13,67.11,67.7,132,135,272,502,313
;375/227,340,341,350,232,354,308,324,343,346,326,329
;342/174,203,601,603,613,614,159,175,89,92 ;379/399.01
;704/E21.004 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chin; Vivian
Assistant Examiner: Odunukwe; Ubachukwu
Attorney, Agent or Firm: Klintworth & Rozenblat IP
LLC
Claims
What is claimed is:
1. A computer-implemented method for reducing an externally
generated noise signal imposed on an amplitude modulated (AM)
broadcast signal, the AM broadcast signal travelling from a
broadcasting antenna to a receiving antenna, the method comprising:
capturing, via the receiving antenna, a signal representative of
the AM broadcast signal corrupted by the externally generated noise
signal; shifting the phase of the captured signal by 180 degrees;
determining a carrying frequency of the AM broadcast signal and
delaying the phase-shifted waveform by a fraction of a cycle of the
carrying frequency, the delaying of the waveform occurring after
the phase shifting of the captured signal; generating a difference
signal by combining the captured signal and the delayed phase-shift
signal; generating an estimate noise signal by reducing an
amplitude of the generated difference signal using a noise
amplifier control multiplier, wherein the generated estimate noise
signal represents an estimate of the corrupting noise signal;
minimizing the corrupting noise signal component of the captured
signal by combining the captured signal and the generated estimate
noise signal so as to compensate for the externally generated noise
signal imposed on the AM broadcast signal; and wherein shifting the
phase, determining the carrier frequency, generating a difference
signal, generating an estimate noise signal, and minimizing the
corrupting noise signal component, are performed on a continuous
basis operating on complete cycles of the captured signal and
without down-conversion of the signal.
2. The computer-implemented method of claim 1, wherein a fraction
of a cycle is equal to about a half cycle.
3. The computer-implemented method of claim 1, further comprising
filtering captured signal prior to the signal inversion.
4. The computer-implemented method of claim 1, further comprising
processing the captured signal through a low noise amplifying
unit.
5. The computer-implemented method of claim 1, further comprising
processing the captured signal through an analog to digital
converting unit to generate a digital version of the captured
signal prior to the signal inversion.
6. The computer-implemented method of claim 1, wherein the noise
amplifier control multiplier is equal to a rational number 1/n with
n being a number that is greater than a first value equal to one
(1) and is less than a second value equal to two (2).
7. A system for reducing an externally generated noise signal
imposed on an amplitude modulated (AM) broadcast signal, the AM
broadcast signal travelling from a broadcasting antenna to a
receiving antenna, the system comprising: a receiving unit for
capturing, by the receiving antenna, a signal representative of the
AM broadcast signal corrupted by the externally generated noise
signal; a signal inverting unit for shifting the phase of the
captured signal by 180 degrees; a signal frequency determining unit
for determining a carrying frequency of the AM broadcast signal and
delaying the phase-shifted waveform, using a delay circuit, by a
fraction of a cycle of the carrying frequency, the signal inverting
unit disposed in a signal processing path before the delay circuit;
a first signal differentiating unit for generating a difference
signal by combining the captured signal and the delayed
phase-shifted signal; a signal amplitude reducing unit for reducing
an amplitude of the generated difference signal using a noise
amplifier control multiplier to generate an estimate noise signal,
wherein the generated estimate noise signal represents an estimate
of the corrupting noise signal; a second signal differentiating
unit for minimizing the corrupting noise signal component of the
captured signal by combining the captured signal and the generated
estimate noise signal so as to compensate for the externally
generated noise signal imposed on the AM broadcast signal; and
wherein the signal inverting unit for shifting the phase, the
signal frequency determining unit for determining the carrier
frequency, the first signal differentiating unit for generating the
difference signal, the signal amplitude reducing unit for
generating an estimate noise signal, and the second signal
differentiating unit for minimizing the corrupting noise signal
component, continuously operate on complete cycles of the captured
signal and without down-conversion of the signal.
8. The system of claim 7, wherein a fraction of a cycle is equal to
about a half cycle.
9. The system of claim 7, further comprising a filtering unit for
filtering captured signal prior to the signal inversion.
10. The system of claim 7, further comprising a low noise
amplifying unit for amplifying a low noise component of the
captured signal.
11. The system of claim 7, further comprising an analog to digital
converting unit for generating a digital version of the captured
signal prior to the signal inversion.
12. The system of claim 7, wherein the noise-reduction control
multiplier is equal to a rational number 1/n with n being a number
that is greater than a first value equal to one (1) and is less
than a second value equal to two (2).
13. A non-transitory computer readable storage medium having stored
therein instructions executable by a computing element to cause the
computing element to perform functions to reduce an externally
generated noise signal imposed on an amplitude modulated (AM)
broadcast signal, the AM broadcast signal travelling from a
broadcasting antenna to a receiving antenna, the functions
comprising: capturing, by the receiving antenna, a signal
representative of the AM broadcast signal corrupted by the
externally generated noise signal; shifting the phase of the
captured signal by 180 degrees; determining a carrying frequency of
the AM broadcast signal and delaying the phase-shifted waveform by
a fraction of a cycle of the carrying frequency, the delaying of
the waveform occurring after the phase-shifted of the captured
signal; generating a difference signal by combining the captured
signal and the delayed phase-shifted signal; generating an estimate
noise signal by reducing an amplitude of the generated difference
signal using a noise-reduction control multiplier, wherein the
generated estimate noise signal represents an estimate of the
corrupting noise signal; minimizing the corrupting noise signal
component of the captured signal by subtractively combining the
captured signal and the generated estimate noise signal so as to
compensate for the externally generated noise signal imposed on the
AM broadcast signal; and wherein shifting the phase, determining
the carrier frequency, generating a difference signal, generating
an estimate noise signal, and minimizing the corrupting noise
signal component, are performed on a continuous basis operating on
complete cycles of the captured signal and without down-conversion
of the signal.
14. The non-transitory computer readable storage medium of claim
13, wherein a fraction of a cycle is equal to about a half
cycle.
15. The non-transitory computer readable storage medium of claim
13, further comprising filtering captured signal prior to the
signal inversion.
16. The non-transitory computer readable storage medium of claim
13, further comprising processing the captured signal through a low
noise amplifying unit.
17. The non-transitory computer readable storage medium of claim
13, further comprising processing the captured signal through an
analog to digital converting unit to generate a digital version of
the captured signal prior to the signal inversion.
18. A computing system comprising: at least one memory unit for
storing program instructions for reducing a noise signal imposed on
an amplitude modulated (AM) broadcast signal, the AM broadcast
signal travelling from a broadcasting antenna to a receiving
antenna, and at least one processing unit for executing the program
instructions; and wherein the program instructions comprise:
capturing, via the receiving antenna, a signal representative of
the AM broadcast signal corrupted by the externally generated noise
signal; shifting the phase of the captured signal by 180 degrees;
determining a carrying frequency of the AM broadcast signal and
delaying the phase-shifted waveform by a fraction of a cycle of the
carrying frequency, the delaying of the waveform occurring after
the inverting of the captured signal; generating a difference
signal by subtractively combining the captured signal and the
delayed inverted signal; generating an estimate noise signal by
reducing an amplitude of the generated difference signal using a
noise-reduction control multiplier, wherein the generated estimate
noise signal represents an estimate of the corrupting noise signal;
minimizing the corrupting noise signal component of the captured
signal by subtractively combining the captured signal and the
generated estimate noise signal so as to compensate for the
externally generated noise signal imposed on the AM broadcast
signal; and wherein shifting the phase, determining the carrier
frequency, generating a difference signal, generating an estimate
noise signal, and minimizing the corrupting noise signal component,
are performed on a continuous basis operating on complete cycles of
the captured signal and without down-conversion of the signal.
19. The computing system of claim 18, wherein a fraction of a cycle
is equal to about a half cycle.
20. The computing system of claim 18, further comprising filtering
captured signal prior to the signal inversion.
Description
BACKGROUND
Unless otherwise indicated herein, the materials described in this
section are not prior art to the claims in this application and are
not admitted to be prior art by inclusion in this section.
Amplitude modulation (AM) broadcasting is a process of radio
broadcasting that was the first method of impressing sound on a
radio signal and is still widely used today. As known to one
ordinary skill in the art, AM broadcasting signal has low immunity
from interfering signals. As shown in FIG. 1, during an AM signal
travel from a broadcasting antenna tower 102 to an AM receiver
antenna 104 coupled to an AM broadcast receiving device or
apparatus 106, many possible noise signals may become add-on or
interference signals to the original AM signal. These interference
noise signals can be generated by a number of sources, such as
power-line noise, lightning, other wireless communications, etc. .
. . . These interference noise signals are captured together with
the AM broadcast signal by the receiver circuit to become an
in-band noise.
In the case, for example, when AM broadcast receiving apparatus 106
is installed in a car, electrical motor noise and electromagnetic
interferences generated by the car's electrical circuits/devices
may increase the noise interference to the original AM broadcast
signal.
Therefore, there is a need for a system and method that can help
minimize AM broadcast interferences caused by noise signals.
SUMMARY
Disclosed herein are improved a method and system for reducing AM
noise in AM broadcast signals.
In one aspect, a computer-implemented method for reducing a noise
signal added to an amplitude modulated (AM) broadcast signal while
travelling from a broadcasting antenna to a receiving antenna is
provided. The method includes capturing a signal representative of
the AM broadcast signal corrupted by the noise signal via the
receiving antenna, inverting the captured signal, and determining a
carrying frequency of the AM broadcast signal and delaying the
inverted waveform by a fraction of a cycle of the carrying
frequency. The method further includes generating a difference
signal by subtractively combining the captured signal and the
delayed inverted signal, generating an estimate noise signal by
reducing an amplitude of the generated difference signal using a
noise-reduction control multiplier, and minimizing the corrupting
noise signal component of the captured signal by subtractively
combining the captured signal and the generated estimate noise
signal.
In another aspect, the computer-implemented method further includes
filtering captured signal prior to the signal inversion.
In another aspect, the computer-implemented method further includes
processing the captured signal through a low noise amplifying
unit.
In another aspect, the computer-implemented method further includes
processing the captured signal through an analog to digital
converting unit to generate a digital version of the captured
signal prior to the signal inversion.
In another aspect, the noise-reduction control multiplier is equal
to a rational number 1/n with n being a number that is greater than
a first value equal to about one (1) and is less than a second
value equal to about two (2).
In another aspect, a computer readable storage medium having stored
therein instructions executable by a computing element to cause the
computing element to perform the above-introduced method.
These as well as other aspects, advantages, and alternatives will
become apparent to those of ordinary skill in the art by reading
the following detailed description, with reference where
appropriate to the accompanying drawings. Further, it should be
understood that the disclosure provided in this summary section and
elsewhere in this document is intended to discuss the embodiments
by way of example only and not by way of limitation.
BRIEF DESCRIPTION OF THE FIGURES
In the figures:
FIG. 1 is a schematic diagram illustrating an embodiment of an AM
broadcast signal corrupted by a number of interfering signals and
captured by a receiver antenna;
FIGS. 2A-B are two graphs illustrating an uncorrupted AM broadcast
signal and one of its period that has been inverted and delayed by
a half-cycle;
FIG. 3 is a graph illustrating an AM broadcast signal with a
predetermined amplitude modulation on a signal carrier;
FIG. 4 is a graph illustrating a zoomed section of the AM broadcast
signal of FIG. 3;
FIG. 5 is a graph illustrating a near-symmetrical characteristics
of an upper half-cycle and of an inverted lower half-cycle of a
waveform cycle of the zoomed signal section of FIG. 4;
FIG. 6 is a block diagram illustrating an exemplary embodiment of a
system, that includes an analog signal processing unit, for
reducing AM noise captured by an AM receiver;
FIG. 7 is a flow chart illustrating an example embodiment of a
method for reducing AM noise using the analog signal processing
unit of FIG. 6;
FIG. 8 is a block diagram illustrating an exemplary embodiment of a
system, that includes a digital signal processing unit, for
reducing an in-band AM noise signal captured by an AM receiver;
FIG. 9 is a flow chart illustrating an example embodiment of a
method for reducing AM noise using the digital signal processing
unit of FIG. 8;
FIG. 10 is a block diagram illustrating another exemplary
embodiment of a system, that includes another digital signal
processing unit, for reducing an in-band AM noise signal captured
by an AM receiver;
FIG. 11A-C are three graphs that illustrate a corrupted AM
broadcast signal, and a demodulated noise signal that corrupted the
AM broadcast signal;
FIGS. 12A-C are three graphs that illustrate the corrupted AM
broadcast signal of FIG. 4A after a reduction of the demodulated
noise signal of FIG. 4C, which has been achieved with a value of an
adaptive control factor selected by one of the corresponding
systems shown in FIGS. 2 and 3;
FIGS. 13A-C are three graphs that illustrate the corrupted AM
broadcast signal of FIG. 4A after another reduction of the
demodulated noise signal of FIG. 4C, which has been achieved with
another value of the adaptive control factor selected by one of the
corresponding systems shown in FIGS. 2 and 3;
FIG. 14 is a graph illustrating an embodiment of another
uncorrupted AM broadcast signal;
FIG. 15 is a graph illustrating the AM broadcast signal of FIG. 14
as corrupted by a couple of interfering signals;
FIG. 16 is a graph illustrating a composite of the signals
interfering the AM broadcast signal of FIG. 15;
FIG. 17 is a graph illustrating an embodiment of an AM broadcast
signal output by one of systems of FIGS. 6, 8, and 10 after
reduction of the interfering signals of FIG. 16;
FIG. 18 is a graph illustrating an embodiment of an AM broadcast
signal output by one of systems of FIGS. 6, 8, and 10 after
reduction of the interfering signals of FIG. 16; and
FIG. 19 is a schematic drawing illustrating a computing network
system according to an exemplary embodiment.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the
accompanying figures, which form a part hereof. In the figures,
similar symbols typically identify similar components, unless
context dictates otherwise. The illustrative embodiments described
in the detailed description, figures, and claims are not meant to
be limiting. Other embodiments may be utilized, and other changes
may be made, without departing from the spirit or scope of the
subject matter presented herein. It will be readily understood that
the aspects of the present disclosure, as generally described
herein, and illustrated in the figures, can be arranged,
substituted, combined, separated, and designed in a wide variety of
different configurations, all of which are explicitly contemplated
herein.
Overview
Some conventional noise suppression systems are known to use a
noise generator coupled to a noise canceller. One such noise
suppression system may include a tuner configured to selectively
receive a radio wave signal and to transform it into an electric
signal, a field information detector to detect electric field
information of the radio wave signal received by the tuner, a noise
data generator that generate a noise pattern on the basis of the
detected electric field information, a noise canceler configured to
remove a noise component from the signal outputted from the tuner
on the basis of the noise pattern generated by the noise data
generator. However, these noise data generators are known to lack
the accuracy to generate a noise signal that can be considered a
substantial reproduction of the captured noise signal.
Accordingly, an embodiment of the proposed noise reducing method is
configured to process and analyze "near-symmetric" characteristics
of a received AM broadcast signal. As such, the proposed method is
configured to produce noise signals that are substantially similar
to the original add-on noise signals. The reproduced noise signals
are then used to cancel substantially all or at least the majority
of the add-on noise signals before the AM de-modulation process of
the received AM broadcast signal.
As known to one of ordinary skill in the art, in
telecommunications, a carrier wave or carrier is a waveform
(usually sinusoidal) that is modulated (modified) with an input
signal for the purpose of conveying information. This carrier wave
is usually a much higher frequency than the input signal. The
purpose of the carrier is usually either to transmit the
information through space as an electromagnetic wave (as in radio
communication), or to allow several carriers at different
frequencies to share a common physical transmission medium by
frequency division multiplexing (as, for example, a cable
television system).
Now referring to FIG. 2A, an exemplary embodiment 200 of a perfect
sinusoidal waveform 202 is illustrated. As an example, waveform 202
represents un-modulated AM carrier waveform at 300 KHz without
interference. As shown, waveform 202 is a smooth repetitive
oscillating waveform with a periodically constant amplitude, i.e.,
peak deviation from zero. As shown in FIG. 2A, waveform 202
includes a positive peak A 204 and a negative peak B 206. Because
waveform 202 is a perfect sine wave, if a half cycle delay is
applied to the waveform 202 then, as shown in FIG. 2B, peak A
becomes peak B and peak B becomes peak A, i.e., A=-B. That is,
waveform 202 at peak A is the same as at inverted peak B with a
half carrier cycle delay. Accordingly, peak A and peak B are
considered to be symmetrical with respect to waveform 202.
Now referring to FIG. 3, an exemplary embodiment 300 of an AM
broadcast signal waveform 302 with a predetermined amplitude
modulation on a signal carrier waveform (not shown) is illustrated.
As an example, AM broadcast waveform 302 has a frequency of 1.5 KHz
and a 95% amplitude-modulation on the waveform carrier with a 300
KHz frequency.
Now referring to FIG. 4, a waveform 402 representing a zoomed-in
section 304 of the waveform carrier of FIG. 3 is shown. Zoomed-in
section 304 corresponds to a waveform section associated with time
points T1 and T2, which are close to about 3.times.10.sup.-4
seconds and about 4.times.10.sup.-4 seconds, respectively.
Now referring to FIG. 5, a waveform 502 representing a zoomed-in
section 404 of waveform 402 of FIG. 4 is shown. The zoomed section
corresponds to a waveform section associated with time points T3
and T4, which are equal to about 374.times.10.sup.-6 seconds and
about 390.times.10.sup.-4 seconds, respectively. As shown in FIG.
5, waveform 502 includes an upper cycle peak "C" that has a
magnitude equal to +4.578062, and an adjacent lower cycle peak "D"
that has a magnitude equal to -4.81467. As such, upper cycle peak
"C" is close to but not exactly the same as "inverted lower cycle
peak "D." Thus, waveform 502 is a "Near Symmetrical" waveform. As
known to one of ordinary skill in the art, a lower modulation index
(%) leads to a more symmetrical waveform. Further, a higher audio
and carrier frequency ratio leads to a more symmetrical waveform.
Also, a lower modulation frequency leads to a more symmetrical
waveform.
Now referring to FIG. 6, a schematic diagram 600 illustrates an
exemplary embodiment of an analog system 602 for reducing noise
signals added to an AM broadcast signal. As shown, system 602
includes an antenna 604 for capturing an AM broadcast signal 606
augmented with add-on noise signals 608 and 610. Captured AM
broadcast signal 606 is a signal based on airwaves transmitted from
a broadcasting station (not shown). System 602 further includes a
cable unit 612 for communicating AM broadcast signal 606 to a
filter and low-noise amplifier combination unit 614, hereafter
referred to as F&LNA unit 614, and an analog signal processing
unit 616 for AM noise reduction. In one embodiment, the filter of
F&LNA unit 614 can be a two pole bandpass filter. As shown in
FIG. 6, analog signal processing unit 616, hereafter referred to as
analog AM noise reducing unit, includes a signal inverting unit
618, a signal delaying unit 620, a signal subtracting and reducing
unit 622, and a signal subtracting unit 624.
Now referring to FIG. 7, a flow chart 700 illustrates an example
embodiment of a method for reducing/minimizing add-on noises using
analog AM noise reducing unit 616. During operation, upon
initiation of the method at step 701, F&LNA unit 614 processes
AM broadcast signal 606 to output AM signal 607. At step 702, AM
noise reducing unit 616 is configured to provide AM signal 607 to
signal inverting unit 618. Upon receipt of AM signal 607, signal
inverting unit 618 processes it to output inverse AM signal 609, at
step 704. Then at step 706, AM noise reducing unit 616 provides AM
signal 609 to signal delaying unit 620 that is configured to delay
AM signal 609 by about a half carrier cycle and to output resulting
AM signal 611. Subsequently, AM noise reducing unit 616 provides
both AM signal 607 and AM signal 611 to signal subtracting and
reducing unit 622, which proceeds to subtractively combine them, at
step 708, and to change an amplitude of the resulting difference
signal by multiplying it with a rational number that is less than
or equal to one (1), at step 710. This rational number can be
selected to be equal to about 1/n where n satisfies the following
inequality: 1.ltoreq.n.ltoreq.2. In accordance with one embodiment,
the reduced difference signal 613 represents a generated or
re-produced noise signal that is substantially similar to combined
add-on noise signals 608 and 610. Then, at step 712, AM noise
reducing unit 616 provides both AM signal 607 and reduced
difference signal 613 to signal subtracting unit 624, which is
configured to subtractively combine them and output an AM
noise-reduced signal 615, which is desirably substantially similar
to AM broadcast signal 606.
Based on experimental results, AM noise reducing unit 616
substantially reduces add-on noise signals 608 and 610 when n is
close to 2. Moreover, an optimal control value of n can be
determined adaptively by this noise reduction approach during an
on-going processing of AM broadcast signal 606. This optimal
control value of n represents a value that best minimizes add-on
noise signals 608 and 610.
Now referring to FIG. 8, a schematic diagram 800 illustrates an
exemplary embodiment of a digital system 802 for reducing noise
signals added to an AM broadcast signal. As shown, system 802
includes an antenna 804 for capturing an AM broadcast signal 806
augmented with add-on noise signals 808 and 810. System 802 further
includes a cable unit 812 for communicating captured AM broadcast
signal 806 to a filter and low-noise amplifier combination unit
814, hereafter referred to as F&LNA unit 814, an analog to
digital (A/D) signal converting unit 819, and a digital signal
processing unit 816 for AM noise reduction. As discussed above, the
filter of F&LNA unit 814 can be a two pole bandpass filter. As
shown in FIG. 8, analog signal processing unit 816, hereafter
referred to as digital AM noise reducing unit, includes a signal
inverting unit 818, a signal delaying unit 820, a signal
subtracting and reducing unit 822, a delay compensation unit 823, a
signal subtracting unit 824, an AM demodulating unit 826, an error
control calibration unit 828, and a digital to analog (D/A)
converting unit 830.
Now referring to FIG. 9, a flow chart 900 illustrates an example
embodiment of a method for reducing/minimizing add-on noises using
digital AM noise reducing unit 816. During operation, upon
initiation of the method at step 901, F&LNA unit 814 processes
AM broadcast signal 806 to output AM signal 807. At step 902, A/D
signal converting unit 819 is configured to convert AM signal 807
to a digital signal 809. AM noise reducing unit 816 is configured
to provide AM digital signal 809 to signal inverting unit 818, at
step 904. Upon receipt of AM digital signal 809, signal inverting
unit 818 processes it to output inverse AM digital signal 811, at
step 906. Then, AM noise reducing unit 816 provides AM digital
signal 811 to signal delaying unit 820 that is configured to delay
AM digital signal 811 by about a half carrier cycle and to output
resulting AM signal 813, at step 908. Subsequently, AM noise
reducing unit 816 provides both AM signal 807 and AM signal 813 to
signal subtracting and reducing unit 822, which proceeds to
subtractively combine them, at step 910, and to change an amplitude
of the resulting difference signal by multiplying it with a
rational number that is less than or equal to one (1), at step 912.
As discussed above, alternatively, the rational number can be
selected to be equal to 1/n where n satisfies the following
inequality: 1.ltoreq.n.ltoreq.2. In accordance with one embodiment,
the reduced difference signal 815 represents a re-produced noise
signal that is desirably substantially similar to combined add-on
noise signals 808 and 810. Then, at step 914, AM noise reducing
unit 816 provides AM signal 809 to delay compensation unit 823,
which is configured to apply a compensating time delay to AM signal
809, and output AM delay-compensated signal 817. Subsequently, at
step 916, AM noise reducing unit 816 is configured to provide both
AM delay-compensated signal 817 and reduced difference signal 815
to signal subtracting unit 824, which is configured to
subtractively combine them and output an AM noise-reduced signal
819, which is substantially similar to AM broadcast signal 806.
Further, at step 918, AM noise-reduced signal 819 is demodulated by
AM demodulating unit 826, and the resulting demodulated signal 821
is provided to D/A converting unit 830 that converts it into an
analog waveform prior to being outputted as an audio signal by a
receiving speaker (not shown).
During this noise-reducing process, error control and calibration
unit 828 is recruited to analyze demodulated signal 819 and use
results of the analysis to adjust as needed the rational number 1/n
that is used by signal subtracting and reducing unit 822 in order
to improve on the minimization of add-on noise signals 808 and
810.
Now referring to FIG. 10, a schematic diagram 800 illustrates
another exemplary embodiment of a digital system 1002 for reducing
noise signals added to an AM broadcast signal. Digital system 1002
has substantially similar components as those of digital system
802, except that F&LNA unit 1014 further includes a radio
processing unit and error control and calibration unit 1028 is
further coupled to signal delaying unit 1020. In this configuration
of Digital system 1002, F&LNA unit 1014 is configured to
identity an intermediate frequency (IF) of AM broadcast signal
1006, to extract from it a signal, denoted IF signal 1007 having
the identified intermediate frequency as its main frequency. In one
embodiment, the coupling of error control and calibration unit 1028
to signal delaying unit 1020 serves to control the signal delaying
process to further improve on the noise reduction process. That is,
based on input received from error control and calibration unit
1028, signal delaying unit 1020 adaptively adjusts an amount of
signal delay that can be different from a half carrier cycle delay
and still leads to a better minimization of add-on noise signals
808 and 810.
Now referring to FIGS. 11A-C, three graphs are shown that
illustrate a corrupted AM broadcast signal 1102, a zoomed section
1104 of AM broadcast signal 1102, and an add-on noise signal 1106
that corrupted AM broadcast signal 1102. FIG. 11A illustrates AM
broadcast signal 1102 that was selected to represent AM broadcast
signal waveform 302 of FIG. 3 corrupted with add-on noise signals.
A zoomed section of AM broadcast signal 1102 is illustrated in FIG.
11B. Subsequent to processing AM broadcast signal 1102 using any
one of noise reducing systems 602, 802, and 1002, the add-noise
signal 1106 corresponding to the zoomed 1104 section is
substantially determined.
During a noise reduction process using any one of noise reducing
systems 602, 802, and 1002, and selecting adaptive control factor
"n" to be equal to 2.0, FIG. 12A illustrates a resulting AM
broadcast signal 1202 that represents AM broadcast signal 1102 with
the reduced add-on noise signal 1106. FIG. 12B illustrates the
zoomed section of AM broadcast signal 1102 shown in FIG. 11B after
the noise reduction, and FIG. 12C illustrates the reduced version
of add-on noise signal 1106.
To further reduce add-on noise signal 1106, noise reducing systems
602, 802, and 1002 are configured to adaptively vary the value of
adjusting control factor n. As such, based on a continuous analysis
of outputted noise-reduced AM signals, adjusting control factor n
was selected to be equal to 1.5, which lead to a further reduction
of add-on noise signal 1106 as illustrated in a further smoother
waveform of AM broadcast signal 1102, and a further reduced
amplitude-wise of add-on noise signal 1106, shown in FIGS. 13A and
13C.
Now referring to FIG. 14, a graph 1400 illustrates an embodiment of
an uncorrupted AM broadcast signal 1402 provided with a
substantially perfect signal modulation. As an example, AM
broadcast signal 1402 has a frequency of 1.7 KHz and is
amplitude-modulated by a 300 KHz waveform carrier (not shown).
During its broadcast travel, AM broadcast signal 1402 is corrupted
by a couple of add-on noise signals. These interfering noise
signals are both frequency modulated (FM) signals having
frequencies equal to 3.33 KHz and 2.0 KHz, respectively, whose
composite signal is illustrated by waveform 1602 of FIG. 16. The
corrupted version of AM broadcast signal 1402 is illustrated by
waveform 1502 of FIG. 15. By processing the corrupted version of AM
broadcast signal 1402 using any one of noise reducing systems 602,
802, and 1002, a noise-reduced signal version of AM broadcast
signal 1402 is generated as illustrated by waveform 1702, shown in
FIG. 17. The removed distorting component of waveform 1502 is
illustrated by waveform 1802 of FIG. 18.
In one embodiment, each of noise reducing systems 602, 802, and
1002 include a processing unit and a memory unit. Each of the
processing units can be implemented on a single-chip. For example,
various architectures can be used including dedicated or embedded
microprocessor (.mu.P), a microcontroller (.mu.C), or any
combination thereof. Each of the memory units may be of any type of
memory now known or later developed including but not limited to
volatile memory (such as RAM), non-volatile memory (such as ROM,
flash memory, etc.) or any combination thereof, which may store
software that can be accessed and executed by the processing units,
for example. Each of the memory units are configured to store
instructions that correspond to the processing functions of the
above discussed noise reducing systems.
In some embodiments, the disclosed method may be implemented as
computer program instructions encoded on a non-transitory
computer-readable storage media in a machine-readable format. FIG.
19 is a schematic illustrating a conceptual partial view of an
example computer program product 1900 that includes a computer
program for executing a computer process on a computing device,
arranged according to at least some embodiments presented herein.
In one embodiment, the example computer program product 1900 is
provided using a signal bearing medium 1901. The signal bearing
medium 1301 may include one or more programming instructions 1902
that, when executed by one or more processors may provide
functionality or portions of the functionality described above with
respect to FIGS. 7 and 9. Thus, for example, referring the
embodiments shown in FIGS. 7 and 9, one or more features of blocks
702, 704, 706, 708 and/or 710 and 902, 904, 906, 908, 910 and/or
912, respectively, may be undertaken by one or more instructions
associated with the signal bearing medium 1901.
In some examples, the signal bearing medium 1901 may encompass a
non-transitory computer-readable medium 1903, such as, but not
limited to, a hard disk drive, a Compact Disc (CD), a Digital Video
Disk (DVD), a digital tape, memory, etc. In some implementations,
the signal bearing medium 1901 may encompass a computer recordable
medium 1904, such as, but not limited to, memory, read/write (R/W)
CDs, R/W DVDs, etc. In some implementations, the signal bearing
medium 1901 may encompass a communications medium 1905, such as,
but not limited to, a digital and/or an analog communication medium
(e.g., a fiber optic cable, a waveguide, a wired communications
link, a wireless communication link, etc.).
While various aspects and embodiments have been disclosed herein,
other aspects and embodiments will be apparent to those skilled in
the art. The various aspects and embodiments disclosed herein are
for purposes of illustration and are not intended to be limiting,
with the true scope and spirit being indicated by the following
claims, along with the full scope of equivalents to which such
claims are entitled. It is also to be understood that the
terminology used herein is for the purpose of describing particular
embodiments only, and is not intended to be limiting.
* * * * *