Method and apparatus for receive channel noise suppression

• US 6,675,004 B1
• Filed: 08/25/2000
• Issued: 01/06/2004
• Est. Priority Date: 08/25/2000
• Status: Expired due to Term

• Current Assignee: CommScope Technologies, LLC (CommScope Holding Company, Inc.)
• Original Assignee: Interwave Communications International SA (Alvarion Limited)
• Inventors: Waylett, Nicholas S.
• Primary Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US09/648,259
• Time in Patent Office: 1,229 Days
• Field of Search: 455/296, 455/298, 455/310, 455/303, 455/315, 455/209, 455/306, 455/307, 455/313, 455/317, 455/318, 455/324, 455/207, 455/256, 455/305, 455/278.1, 455/304, 455/285, 455/284, 455/283
• US Class Current: 455/304
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

A noise suppression apparatus for use in a receiver includes an input terminal adapted to receive an inbound signal. A channel splitter is coupled to the input terminal and configured to split the inbound signal into a substantially identical first signal and second signal. A first mixer coupled to the channel splitter and configured to receive the first signal, and a second mixer coupled to the channel splitter and configured to receive the second signal. A first local oscillator is coupled to the first mixer and configured to generate a first LO frequency signal, and a second local oscillator coupled to the second mixer and configured to generate a second LO frequency signal, where the first LO frequency signal and second LO frequency signal differ from one another. The first mixer is configured to mix the first signal with the first LO frequency signal to create a first mixed signal, and the second mixer is configured to mix the second signal with the second LO frequency signal to create a second mixed signal. A combiner is coupled to the first mixer and the second mixer and configured to combine the first mixed signal with the second mixed signal to create a noise suppressed output signal. Advantages of the invention include a high quality signal with an improved signal-to-noise ratio.

Claims

1. A noise suppression apparatus for use in a receiver, comprising:

an input terminal adapted to receive an inbound signal comprising a desirable signal component and an internal noise component;

a channel splitter coupled to the input terminal and configured to split the inbound signal into a substantially identical first signal and second signal;

a first mixer coupled to the channel splitter and configured to receive the first signal, and a second mixer coupled to the channel splitter and configured to receive the second signal;

a first local oscillator coupled to the first mixer and configured to generate a first LO frequency signal, and a second local oscillator coupled to the second mixer and configured to generate a second LO frequency signal, where the first LO frequency signal and second LO frequency signal differ from one another by an offset in frequency;

wherein the first mixer is coupled to the first local oscillator and configured to mix the first signal with the first LO frequency signal to create a first mixed signal, and the second mixer is coupled to the second local oscillator and configured to mix the second signal with the second LO frequency signal to create a second mixed signal;

a first bandpass filter coupled to the first mixer having a first passband frequency range and configured to generate a first filtered signal;

a second bandpass filter coupled to the second mixer having a second passband frequency range and configured to generate a second filtered signal;

wherein said first LO frequency signal, said second LO frequency signal, and said first and second passband frequency ranges are selected such that said first filtered signal comprises said desirable signal component and said second filtered signal consists essentially of said internal noise component;

a first phase shifting structure coupled to the second bandpass filter and configured to shift the phase of the second filtered signal approximately 180 degrees from the phase of the second filtered signal to create a phase-shifted second filtered signal;

a second phase shifting structure coupled to the first bandpass filter and configured to shift the phase of the first filtered signal to create a phase-shifted first filtered signal that corrects for the offset in frequency; and

a combiner coupled to the first filter and the second filter and configured to combine the phase-shifted first filtered signal with the phase-shifted second filtered signal to generate a noise suppressed output signal having said desirable signal component and wherein said internal noise component is substantially suppressed

2. The noise suppression apparatus of claim 1, further comprising:

a reference signal generator coupled to the first oscillator and the second local oscillator.

3. The noise suppression apparatus of claim 1, wherein:

the first and second LO signals differ in frequency sufficiently to prevent the desirable signal component from passing through the second band pass filter.

4. The noise suppression apparatus of claim 1, wherein:

the first and second LO signals differ in frequency by at least one adjacent channel.

5. The noise suppression apparatus of claim 1, wherein:

the first and second LO signals differ in frequency by approximately 0.1%.

6. The noise suppression apparatus of claim 1, further comprising:

an analog to digital convertor coupled to the input terminal; and

wherein the first mixer, second mixer, first phase shifting structure, second phase shifting structure and combiner are structured in a digital signal processor.

7. The apparatus of claim 1, further comprising:

a low-noise amplifier coupled to said input port, wherein said internal noise component comprises internal noise generated in said low-noise amplifier.

8. The apparatus of claim 7, further comprising:

a third filter coupled to said low-noise amplifier, and wherein said internal noise component further comprises internal noise generated in said third filter.

9. A method in a receiver of suppressing noise, comprising the steps of:

receiving an inbound signal comprising a desirable signal component and an internal noise component;

splitting the inbound signal into substantially identical first signal and second signals;

generating a first LO frequency signal and a second LO frequency signal, where the first LO frequency signal and second LO frequency signal differ from one another by an offset in frequency;

mixing the first signal with the first LO frequency signal to create a first mixed signal, and mixing the second signal with the second LO frequency signal to create a second mixed signal;

filtering the first mixed signal by a first bandpass filter thereby generating a first filtered signal;

filtering the second mixed signal by a second bandpass filter thereby generating a second filtered signal, wherein said second filtered signal consists substantially of said internal noise component and said first filtered signal comprises said desirable signal component;

shifting the phase of the second-filtered signal approximately 180 degrees to create a phase-shifted second filtered signal;

shifting the phase of the first filtered signal to create a phase-shifted first filtered signal that corrects for offset in frequency; and

combining the phase-shifted first filtered signal and the phase-shifted second filtered signal to create a noise suppressed output signal having said desirable signal component wherein said internal noise component is substantially suppressed.

10. The method of claim 9, further comprising the step of:

supplying the first local oscillator and the second local oscillator with a common reference signal.

11. The method of claim 9, wherein:

the first and second LO signals differ in frequency sufficiently to prevent inbound signal of interest from passing through the second band pass filter.

12. The method of claim 9, wherein:

the first and second LO signals differ in frequency by at least one adjacent channel.

13. The method of claim 9, wherein:

the first and second LO signals differ in frequency by approximately 0.1%.

14. The method of claim 9, further comprising the step of:

converting the inbound signal from analog to digital; and

wherein the mixing steps and combining step are performed by a digital signal processor.

15. The method of claim 14, wherein the phase shifting steps are performed by the digital signal processor.

16. A noise suppression apparatus for use in a receiver, comprising:

an input terminal adapted to receive an inbound signal comprising a desirable signal component and an internal noise component;

a mixer coupled to the input terminal and configured to receive the inbound signal;

a local oscillator coupled to the mixer and configured to generate a LO frequency signal;

wherein the mixer is configured to mix the inbound signal with the LO frequency signal to create a mixed signal;

a channel splitter coupled to the mixer and configured to split the mixed signal into a substantially identical first signal and second signal;

a first bandpass filter coupled to the channel splitter having a first passband frequency range and configured to generate a first filtered signal;

a second bandpass filter coupled to the channel splitter having a second passband frequency range and configured to generate a second filtered signal;

wherein LO frequency signal and said first and second passband frequency ranges are selected such that said first filtered signal comprises said desirable signal component and said second filtered signal consists essentially of said internal noise component;

a first phase shifting structure coupled to the second band pass filter and configured to shift the phase of the second filtered signal approximately 180 degrees to create a phase-shifted second filtered signal;

a second phase shifting structure coupled to the first bandpass filter and configured to fine tune the phase of the first filtered signal to create a phase-shifted first filtered signal that corrects for an offset in phase between the first filtered signal and the second filtered signal; and

a combiner coupled to the first bandpass filter and the second bandpass filter and configured to combine the phase-shifted first filtered signal with the phase-shifted second filtered signal to create a noise suppressed output signal having said desirable signal component and wherein said internal noise component is substantially suppressed.

17. The noise suppression apparatus of claim 16, wherein:

the first bandpass filter and second bandpass filter differ in passband frequency sufficiently to prevent the desirable signal component of the inbound signal from passing through the second bandpass filter.

18. The noise suppression apparatus of claim 16, wherein;

the first and second bandpass filters differ in passband frequency by at least one adjacent channel.

19. The noise suppression apparatus of claim 16, wherein:

the first and second bandpass filters differ in passband frequency by approximately 0.1%.

20. The noise suppression apparatus of claim 17, wherein:

the first and second bandpass filters differ in passband frequency by at least one adjacent channel.

21. The noise suppression apparatus of claim 17, further comprising:

an analog to digital convertor coupled to the input terminal; and

wherein the mixer, splitter and combiner are structured in a digital signal processor.

22. The noise suppression apparatus of claim 21, wherein the first phase shifting structure and second phase shifting structure are structured in the digital signal processor.

23. The apparatus of claim 16, further comprising:

a low-noise amplifier coupled to said input port, wherein said internal noise component comprises internal noise generated in said low-noise amplifier.

24. The apparatus of claim 23, further comprising:

a third filter coupled to said low-noise amplifier, and wherein said internal noise component further comprises internal noise generated in said third filter.

25. A method in a receiver of suppressing noise, comprising the steps of:

receiving an inbound signal comprising a desirable signal component and an internal noise component;

mixing the inbound signal with an LO frequency signal to create a mixed signal;

splitting the mixed signal into a substantially identical first signal and second signal;

filtering the first mixed signal by a first bandpass filter thereby generating a first filtered signal;

filtering the second signal by a second bandpass filter thereby generating a second filtered signal, wherein said second filtered signal consists substantially of said internal noise component and said first filtered signal comprises said desirable signal component;

shifting the phase of the second filtered signal approximately 180 degrees to create a phase-shifted second filtered signal;

shifting the phase of the first filtered signal to create a phase-shifted first filtered signal that corrects for an offset in phase between the first filtered signal and the second filtered signal; and

combining the phase-shifted first filtered signal with the phase-shifted second filtered signal to create a noise suppressed output signal having said desirable signal component and wherein said internal noise component is substantially suppressed.

26. The method of claim 25, wherein:

the first bandpass filter and second bandpass filter differing passband frequency sufficiently to prevent the desirable signal component of said inbound signal from passing through the second band pass filter.

27. The method of claim 25, wherein;

the first and second bandpass filters differ in passband frequency by at least one adjacent channel.

28. The method of claim 25, wherein:

the first and second bandpass filters differ in passband frequency by approximately 0.1%.