Receiver of wideband digital signal in the presence of a narrow band interfering signal

• US 6,539,068 B2
• Filed: 01/21/2000
• Issued: 03/25/2003
• Est. Priority Date: 05/22/1997
• Status: Expired due to Term

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Hebron, Yoav, Raghavan, Sree A., Gurantz, Itzhak
• Primary Examiner(s): LIU, SHUWANG
• Application Number:
  US09/489,284
• Publication Number:
  US 20020097821A1
• Time in Patent Office: 1,159 Days
• Field of Search: 375/346, 375/232, 375/216, 375/235, 375/347, 370/335, 342/383, 342/362, 348/472, 455/266
• US Class Current: 375/346
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04B 1/7101 with estimation filters
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/03471 Tapped delay lines H04L2025/03464 takes precedence
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

A desired signal having a wide frequency band and including sequential symbols representing digital values is discriminated from a narrow band interfering signal having a carrier frequency in the wide band by initially applying both signals to a filter so both signals are passed to an output of the filter. In response to the filter output, estimates of the values of received symbols of the desired signal are derived and compared to the filter output to derive an error representing signal. A characteristic of the filter is controlled in response to the error representing signal so the filter is adjusted to reject the interfering signal and pass the desired signal.

Claims

1. A method of discriminating a desired Direct Broadcast Satellite (DBS) signal from a narrow band interfering signal, said DBS signal including sequential symbols representing digital values, the desired signal being discriminated from a narrow band interfering signal and said narrow band signal having a carrier frequency in the wide band, the method comprising:

initially applying the DBS and narrow band interfering signals to a digital demodulator, wherein the DBS and narrow band interfering signals are amplified as a single, composite signal;

passing the single, composite signal to a filter responsive to C-band signals so the single, composite signal is passed to an output of the filter, the filter having inputs for baseband I and Q components of the single, composite signal only and no other inputs;

responding to the filter output to derive estimates of the values of received symbols of the desired single, composite signal;

comparing the filter output with the estimated values of the received symbols to derive an error representing signal; and

adjusting the filter in response to the error representing signal to reject the interfering signal and pass the desired signal.

2. The method of claim 1, wherein the filter includes multiple cascaded delay elements, and said comparing of the filter output with the estimated values of the received symbols to derive an error representing signal further comprising:

supplying the symbols to the cascaded delay elements so the delay elements contain values representing the amplitudes of successive received symbols,

combining signal values determined by the values in the elements with signal values representing the errors to derive an output signal for each element, and

combining values representing the output signals for each of the at least several elements to derive the filter output.

3. The method of claim 1, wherein the filter includes a delay arrangement, the desired signal including orthogonal I and Q channels, which include sequential symbols of simultaneous I and Q components, the method further comprising:

applying signals representing the I and Q components to the delay arrangement so the signals representing the I and Q components are progressively delayed in the elements for equal intervals, said intervals being equal to an integral multiple of the interval between adjacent symbols,

combining signals representing;

(1) the I and Q components as delayed for corresponding times with each other and

(2) errors between I and Q channel outputs of the filter with estimates of the I and Q components of the emitted symbols to derive I and Q output signals for each of several of the delay intervals,

combining the I output signals of several of the delay intervals to derive the I channel output of the filter, and

combining the Q output signals of several of the delay intervals to derive the Q channel output of the filter.

4. The method of claim 3, wherein the I and Q channel estimates are derived by supplying the I and Q channel outputs of the filter to a derotator that assigns I and Q channel estimates based on the quadrants of the I and Q channel outputs.

5. The method of claim 1, wherein the filter includes a delay arrangement, the desired signal being modulated with a variable phase and including at least one channel, the filter being responsive to orthogonal I and Q channels derived in response to reception of the wide and narrow band signals and having I and Q channel outputs, each of the I and Q channels to which the filter is responsive including information about the interfering signal, at least one of the I and Q channels to which the filter is responsive including information about the values of sequential symbols in the desired signal, the method further comprising:

applying the interfering signal information and the symbols to the delay arrangement so they are progressively delayed in the elements for intervals determined by the interval between adjacent symbols;

combining signals representing;

(1) the symbols and information in the I and Q channels as delayed for corresponding times with each other and

(2) errors between I and Q channel outputs of the filter with estimates of the emitted symbols in the derived signal to derive I and Q output signals for each of several of the delay intervals,

combining the I output signals of several of the delay intervals to derive the I channel output of the filter; and

combining the Q output signals of a plurality of the delay intervals to derive the Q channel output of the filter.

6. The method of claim 5, wherein the delay arrangement includes first and second delay devices respectively responsive to the I and Q channels and each having (N+1) cascaded stages 0, 1 . . . i . . . N, where N is an even integer, the method further comprising:

initially setting the signal values for the combined signals representing the combined values of (1) and (2) to a first binary value except that one of the signal values for the combined signals representing the combined values of (1) and (2) is set to a second binary value,

loading binary zero values in each of the stages except stage $\left(\frac{N}{2}+1\right),$

initially loading a non-zero finite value in stage $\left(\frac{N}{2}+1\right).$

7. The method of claim 6, wherein the signal value for the I channel output $\left(\frac{N}{2}+1\right)$

 



or

 



(N2)

for the combined values of (1) and (2) is set to the second binary value.

8. The method of claim 5, wherein the delay arrangement includes first and second delay devices respectively responsive to the I and Q symbols and each including (N+l) delay taps 0,1 . . . i . . . N, on which are derived at time k signals p_kⁱ and q_kⁱ, the I and Q errors at time k being respectively represented by Re(e)k and Im(e)k, the combining step to derive the output signal for each element being performed by combining the p_kⁱ, q_kⁱ, Re(e)k and Im(e)k signals as well as a scaling factor d to derive (1) signals representing real and imaginary coefficients in accordance with:

9. Apparatus for receiving Direct Broadcast Satellite (DBS) satellite broadcasts from a first geosynchronous satellite in the presence of a narrow band emission from a second geosynchronous satellite having a relatively close arcuate spacing from the first satellite, the DBS broadcasts and narrow band emissions being capable of having overlapping spectra such that the narrow band can have a carrier frequency that is variable in the spectrum of the DBS broadcasts, the apparatus comprising:

an antenna having a beamwidth such that the DBS broadcasts and narrow band emissions from the first and second satellites are respectively transduced into first and second simultaneously occurring electrical signals having amplitudes with the same order of magnitude, wherein the first and second simultaneously occurring electrical signals are amplified as a single, composite signal;

a digital demodulator for receiving the single, composite signal; and

an adaptive filter responsive to signals in the C-band for attenuating substantially the second signal relative to the first signal so the first signal as coupled to an output terminal of the filter has an amplitude that can produce a perceptible response in an output device and the second signal as coupled to the output terminal has an insufficient amplitude to produce a perceptible response in the output device even though the carrier frequency is variable in the wide band, the adaptive filter having inputs for baseband I and Q components of the single, composite signal only and no other inputs.

10. The apparatus of claim 9, wherein the filter is operated in response to the first and second signals so it passes most frequencies in the bandwidth of the first signal and attenuate substantially all frequencies in the bandwidth of the second signal.

11. The apparatus of claim 10, wherein the means for passing and substantially attenuating performs a statistical analysis of symbols in a signal at the filter output terminal and of first transduced signal.

12. The apparatus of claim 11, wherein the statistical analysis is based on minimum least mean square error techniques.

13. The apparatus of claim 12, wherein the means for passing and substantially attenuating includes a means for delaying the first and second signals, the means for delaying including multiple outputs having different delay times.

14. The apparatus of claim 13, further including means responsive to an output of the filter for deriving estimates of the value of an information symbol in the wide band emissions and for deriving indications of errors between the filter output and the estimates, the filter responding to the errors and the multiple outputs for controlling the filter output.

15. The apparatus of claim 10, wherein the means for passing and substantially attenuating includes means for delaying the first and second signals, the means for delaying including multiple outputs having different delay times.

16. The apparatus of claim 15, further including means responsive to an output of the filter for deriving estimates of the value of an information symbol in the wide band emissions and for deriving indications of errors between the filter output and the estimates, the filter responding to the errors and the multiple outputs for controlling the filter output.

17. The apparatus of claim 10, wherein the wide band emission includes sequential symbols, means responsive to an output of the filter for deriving estimates of the emitted symbols and for deriving error signals indicating deviations between sequential outputs of the filter and the estimates of the emitted symbols, the filter including:

multiple cascaded delay elements responsive to sequential signal values derived in response to the symbols so the delay elements contain values representing the amplitudes of successive received symbols,

an electronic device for combining data values representing the values in the elements with information values representing the errors to derive an output signal for each of the at least several elements, and

means for combining values representing the output signals of each of the at least several elements to derive the filter output.

18. The apparatus of claim 10, wherein the desired signal includes orthogonal I and Q channels, each channel including simultaneous sequential I and Q symbols, the filter including:

a delay arrangement, signals representing the I and Q symbols being applied to the delay arrangement so signals representing the I and Q symbols propagate in the delay arrangement so they are progressively delayed for intervals determined by the propagation time interval of adjacent symbols between pairs of the elements, and

means for combining signals;

(1) representing the I and Q symbols as delayed for corresponding times with each other and signals representing the I and Q errors to derive I and Q output signals for each of several delay intervals,

(2) the I output signals of each of the several delay intervals to derive an I channel filter output signal, and

(3) the Q output signals of each of the several delay intervals to derive a Q channel filter output signal.

19. The apparatus of claim 18, wherein the delay arrangement includes first and second delay devices respectively responsive to the I and Q symbols and each including (N+1) delay taps 0,1 . . . i . . . N, on which are derived at time k signals p_kⁱ and q_kⁱ, the I and Q errors at time k being respectively represented by Re(e)k and Im(e)k, the combining means responding to the p_kⁱ, q_kⁱ, Re(e)k and Im(e)k signals as well as a scaling factor d for;

(1) deriving signals representing real and imaginary coefficients in accordance with;

20. The apparatus of claim 19, wherein the estimates of the emitted symbols are derived by determining the quadrant of the I and Q channel filter output signals such that predetermined combinations of the values of the estimates of the emitted symbols for the I and Q channels are derived depending on the values of the I and Q channel filter output signals.

21. A method of terrestrially receiving a first electromagnetic wave in the Direct Broadcast Satellite (DBS) frequency band, the first electromagnetic wave emitted from a first geosynchronous satellite spaced from a second geosynchronous satellite by a predetermined arc, the second geosynchronous satellite emitting a second electromagnetic wave having (a) a narrower frequency band than the first wave, and (b) a carrier frequency that is variable in the frequency band of the first wave, the first and second waves being simultaneously emitted from the first and second satellites, the method comprising:

simultaneously transducing the first and second waves into first and second simultaneously derived electrical signals that are substantial replicas of variations of the waves, wherein the first and second simultaneously derived electrical signals are amplified as a single, composite signal, with a receiver including a terrestrial antenna pointed generally at the first satellite and having a beamwidth so the first and second waves are transduced into signals having the same order of magnitude, the receiver also including a digital demodulator for receiving the single, composite signal from the antenna; and

responding to said single, composite signal using an adaptive filter responsive to signals in the C-band to substantially attenuate the second signal relative to the first signal so the first signal is passed to an output device, the output device producing a perceptible output in response to the first signal and failing to produce a perceptible output in response to the second signal or producing an output that does not significantly adversely affect the performance of the output device, the adaptive filter receiving baseband I and Q components of the single, composite signal only and receiving no other inputs.

22. The method of claim 21, wherein the substantial attenuation of the second signal is provided by discriminating its frequency band from that of the first signal.

23. The method of claim 21, wherein the substantial attenuation of the second signal is provided by discriminating its frequency band from that of the first signal and performing a statistical analysis of symbols in (a) the first signal substantially as passed to the output device and (b) the first signal substantially as transduced.

24. The method of claim 23, wherein the statistical analysis is based on minimum least mean error square techniques.