Method and apparatus for reduction of FM interference for FM in-band on-channel digital audio broadcasting system

• US 6,622,008 B2
• Filed: 05/18/2001
• Issued: 09/16/2003
• Est. Priority Date: 11/03/1998
• Status: Expired due to Term

• Current Assignee: USA Digital Radio, Inc. (Xperi Inc.)
• Original Assignee: iBiquity Digital Corporation (Xperi Inc.)
• Inventors: Kroeger, Brian William, Baird, Jeffrey Scott
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Taylor, Barry W
• Application Number:
  US09/860,246
• Publication Number:
  US 20010023175A1
• Time in Patent Office: 851 Days
• Field of Search: 455/61, 455/74, 455/143, 375/216, 375/226, 375/229, 375/316, 375/326, 375/346, 375/350, 370/207, 370/208, 370/350, 370/480
• US Class Current: 455/61
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04H 2201/183 FM digital or hybrid
• CPC Class Codes: H04H 40/27 specially adapted for broadcast systems covered by groups H04H20/53 - H04H20/95
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

This invention provides a method for reducing FM interference in an in-band on-channel digital audio broadcasting system. The method includes the steps of receiving a composite signal including a signal of interest and an interfering signal and normalizing the composite signal to produce a normalized composite signal. The composite signal is then multiplied by the complex conjugate of the normalized composite signal to produce a real signal. Then the real signal is filtered and the resulting filtered signal is multiplied by the normalized composite signal to produce an output signal. The adverse effects of the interfering signal in the output signal are reduced with respect to the magnitude of the signal of interest reducing FM interference in an in-band on-channel digital audio broadcasting system, thereby making it easier to detect the signal of interest. The output signal and the composite can be blended in response to the power of the real and filtered signals Radio receivers that utilize the above method are also included.

Claims

1. A method for processing a radio frequency signal, the method comprising the steps of:

receiving a composite signal including a signal of interest and an interfering signal;

processing the composite signal to produce an output signal;

controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed during the processing step; and

combining the output signal and the composite signal to produce a blended signal;

wherein the step of processing the composite signal to produce an output signal comprises the steps of;

normalizing the composite signal to produce a normalized composite signal;

multiplying the composite signal by a complex conjugate of the normalized composite signal to produce a real signal;

filtering the real signal to produce a filtered signal; and

multiplying the filtered signal by the normalized composite signal to produce the output signal.

2. A method for processing a radio frequency signal according to claim 1, wherein the step of controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed during the processing step comprises the steps of:

comparing the difference in power between the real signal and the filtered signal with upper and lower threshold values;

producing first and second control signals when the difference in power between the real signal and the filtered signal lies between the upper and lower threshold values;

multiplying the output signal by the first control signal; and

multiplying the composite signal by the second control signal.

3. A method for processing a radio frequency signal according to claim 1, wherein the step of filtering the real signal to produce a filtered signal comprises the steps of:

producing a carrier amplitude estimate signal;

delaying the real signal to produce a delayed real signal; and

subtracting the carrier amplitude estimate signal from the delayed real signal to produce the filtered signal.

4. A method for processing a radio frequency signal according to claim 3, wherein the step of producing a carrier amplitude estimate comprises the step of:

passing the real signal through a low pass filter.

5. A method for processing a radio frequency signal according to claim 1, wherein the step of filtering the real signal to produce a filtered signal delays the filtered signal, the method further comprising the step of:

delaying the normalized composite signal prior to the step of multiplying the filtered signal by the normalized composite signal.

6. A method for processing a radio frequency signal according to claim 1, wherein the step of controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed during the processing step comprises the steps of:

producing first and second control signals when the power of the signal component removed during the processing step lies between upper and lower threshold values;

multiplying the output signal by the first control signal; and

multiplying the composite signal by the second control signal.

7. A method for processing a radio frequency signal according to claim 6, wherein the first control signal represents a first percentage, and the second control signal represents a second percentage, the sum of the first and second percentages being 100 percent.

8. An apparatus for processing a radio frequency signal, the apparatus comprising:

means for receiving a composite signal including a signal of interest and an interfering signal;

means for processing the composite signal to produce an output signal;

means for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the means for processing the composite signal; and

means for combining the output signal and the composite signal to produce a blended signal;

wherein the means for processing the composite signal to produce an output signal comprises;

means for normalizing the composite signal to produce a normalized composite signal;

means for multiplying the composite signal by a complex conjugate of the normalized composite signal to produce a real signal;

means for filtering the real signal to produce a filtered signal; and

means for multiplying the filtered signal by the normalized composite signal to produce the output signal.

9. An apparatus for processing a radio frequency signal according to claim 8, wherein the means for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the means for processing the composite signal comprises:

means for comparing the difference in power between the real signal and the filtered signal with upper and lower threshold values;

means for producing first and second control signals when the difference in power between the real signal and the filtered signal lies between the upper and lower threshold values;

means for multiplying the output signal by the first control signal; and

means for multiplying the composite signal by the second control signal.

10. An apparatus for processing a radio frequency signal according to claim 8, wherein means for filtering the real signal to produce a filtered signal comprises:

means for producing a carrier amplitude estimate signal;

means for delaying the real signal to produce a delayed real signal; and

means for subtracting the carrier amplitude estimate signal from the delayed real signal to produce the filtered signal.

11. An apparatus for processing a radio frequency signal according to claim 10, wherein the means for producing a carrier amplitude estimate comprises:

a low pass filter.

12. An apparatus for processing a radio frequency signal according to claim 8, wherein the means for filtering the real signal to produce a filtered signal delays the filtered signal, further comprising:

means for delaying the normalized composite signal prior to multiplying the filtered signal by the normalized composite signal.

13. An apparatus for processing a radio frequency signal according to claim 8, wherein the means for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the means for processing the composite signal comprises:

means for producing first and second control signals when the power of a signal component removed by the means for processing the composite signal lies between upper and lower threshold values;

means for multiplying the output signal by the first control signal; and

means for multiplying the composite signal by the second control signal.

14. An apparatus for processing a radio frequency signal according to claim 13, wherein the first control signal represents a first percentage, and the second control signal represents a second percentage, the sum of the first and second percentages being 100 percent.

15. An apparatus for processing a radio frequency signal, the apparatus comprising:

an input for receiving a composite signal including a signal of interest and an interfering signal;

a processor for processing the composite signal to produce an output signal;

a controller for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the processor; and

a combiner for combining the output signal and the composite signal to produce a blended signal;

wherein the processor for processing the composite signal to produce an output signal comprises;

a divider for normalizing the composite signal to produce a normalized composite signal;

a first multiplier for multiplying the composite signal by a complex conjugate of the normalized composite signal to produce a real signal;

a filter for filtering the real signal to produce a filtered signal; and

a second multiplier for multiplying the filtered signal by the normalized composite signal to produce the output signal.

16. An apparatus for processing a radio frequency signal according to claim 15, wherein the controller for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the processor comprises:

a comparator for comparing the difference in power between the real signal and the filtered signal with upper and lower threshold values;

a signal generator for producing first and second control signals when the difference in power between the real signal and the filtered signal lies between the upper and lower threshold values;

a third multiplier for multiplying the output signal by the first control signal; and

a fourth multiplier for multiplying the composite signal by the second control signal.

17. An apparatus for processing a radio frequency signal according to claim 15, wherein the filter comprises:

a carrier amplitude estimator for producing a carrier amplitude estimate signal;

a time delay for delaying the real signal to produce a delayed real signal; and

a subtractor for subtracting the carrier amplitude estimate signal from the delayed real signal to produce the filtered signal.

18. An apparatus for processing a radio frequency signal according to claim 17, wherein the carrier amplitude estimator comprises:

a low pass filter.

19. An apparatus for processing a radio frequency signal according to claim 15, wherein the filter for filtering the real signal to produce a filtered signal delays the filtered signal, further comprising:

a time delay for delaying the normalized composite signal prior to multiplying the filtered signal by the normalized composite signal.

20. An apparatus for processing a radio frequency signal according to claim 15, wherein the controller for controlling the magnitude of the output signal and the magnitude of the composite signal in response to the power of a signal component removed by the processor comprises:

a signal generator for producing first and second control signals when the power of a signal component removed during the processing step lies between upper and lower threshold values;

a first multiplier for multiplying the output signal by the first control signal; and

a second multiplier for multiplying the composite signal by the second control signal.

21. An apparatus for processing a radio frequency signal according to claim 20, wherein the first control signal represents a first percentage, and the second control signal represents a second percentage, the sum of the first and second percentages being 100 percent.