Method and system for reducing amplitude modulation (AM) noise in AM broadcast signals
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.
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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
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.
SUMMARYDisclosed 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.
In the figures:
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).
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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.
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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.
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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,
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
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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 (μP), a microcontroller (μC), 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.
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.
Claims
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.
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Type: Grant
Filed: Dec 20, 2012
Date of Patent: Feb 23, 2016
Patent Publication Number: 20140177843
Assignee: Visteon Global Technologies, Inc. (Van Buren Township, MI)
Inventor: Yao H. Kuo (West Bloomfield, MI)
Primary Examiner: Vivian Chin
Assistant Examiner: Ubachukwu Odunukwe
Application Number: 13/721,396
International Classification: H03D 1/04 (20060101); H04H 20/88 (20080101); H04B 1/10 (20060101); H04B 1/04 (20060101); G10K 11/178 (20060101);