Interference detection and avoidance technique

• US 6,304,594 B1
• Filed: 07/27/1998
• Issued: 10/16/2001
• Est. Priority Date: 07/27/1998
• Status: Expired due to Term

• Current Assignee: General Dynamics Government Systems Corporation (General Dynamics Corporation)
• Original Assignee: General Dynamics Government Systems Corporation (General Dynamics Corporation)
• Inventors: Salinger, Sheldon Norman
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Bayard, Emmanuel
• Application Number:
  US09/123,203
• Time in Patent Office: 1,177 Days
• Field of Search: 375/219, 375/220, 375/222, 375/259, 375/284, 375/285, 370/278, 370/282, 370/286, 370/206, 455/65, 455/63, 455/296, 455/514, 455/501, 455/570, 455/557
• US Class Current: 375/222
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 17/26 using historical data, averaging values or statistics
• CPC Class Codes: H04B 17/345 Interference values signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/206 for modulated signals
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

The presence of interfering continuous-wave signals are automatically detected in the demodulated output of a quadrature amplitude modulation data communications receiver. The transmitter is re-tuned in order to avoid the detected interferer. Statistical information concerning the received signal is accumulated at a receiver and is analyzed to determine whether a reduction in the received bit-error-rate is due to the presence of an interferer. If an inteferer is determined to be present within the signal transmission bandwidth, then the potentially available transmission band is spectrum analyzed to find a new portion of that band in which the signal can be transmitted free of the interferer. The results of the statistical analysis and the spectral analysis are conveyed back to the transmitter which then readjusts the transmission parameters and forwards the new parameters to the receiver. The system resumes operation in the new transmission band with no interference and with the bit-error-rate restored to its required level.

Claims

1. In a communication apparatus, a method of detecting whether an interference signal is being received with a received signal of interest (SOI), said method being non-intrusive to a continued reception of the SOI and comprising steps of:

(a) accumulating statistical information associated with said SOI;

(b) determining whether an intrusive interference signal is present with said SOI, said step further comprising substeps of;

(i) determining a root mean square (RMS) cluster size of said intrusive interference signal;

(ii) determining a reciprocal constellation closure of said intrusive interference signal; and

(iii) determining a carrier-to-noise ratio (CNR) of said intrusive interference signal;

(c) analyzing, when an intrusive interference signal is present, said intrusive interference signal to determine the frequency thereof;

(d) identifying a spectral region free of interferers; and

(e) adjusting said communication apparatus to operate in said spectral region identified in step (d).

2. The method of claim 1 wherein said step (b) further comprises determining a symbol error rate of said intrusive interference signal.

3. The method of claim 1 wherein said step (b) further comprises determining a bit error rate of said intrusive interference signal.

4. The method of claim 1 wherein said step (b) further comprises determining an average cluster skewness associated with said intrusive interference signal.

5. The method of claim 1 wherein said step (b) further comprises determining an average cluster kurtosis associated with said intrusive interference signal.

6. A transceiver for transmitting and receiving data signals, said transceiver being capable of non-intrusively detecting an interference signal to said data signals, said transceiver comprising:

storage means for accumulating statistical information associated with said data signals;

interference determining means for determining whether an unacceptable interference signal is present with said data signals;

analysis means for spectrum analyzing said unacceptable interference signal and determining a frequency thereof and further locating a spectral region free of interferers;

conveyance means for communicating to a transmitter said spectral region free of interferers; and

means responsive to said conveyance means for changing operation of the transceiver and transmitter to said spectral region free of interferers.

7. The transceiver of claim 6 wherein said interference signal is a continuous wave signal.

8. The transceiver of claim 7 wherein said transceiver uses quadrature amplitude modulation.

9. The transceiver of claim 7 wherein said transceiver uses carrierless AM/PM data communication methods.

10. The transceiver according to claim 7 wherein said storage means accumulates both presliced quadrature amplitude coordinates and sliced symbol cell identification data.

11. The transceiver according to claim 10 wherein said analysis means processes a sequence of demodulated symbols to calculate the statistics of in-phase and quadrature mean coordinates and in-phase and quadrature sample variances for a subset of symbols in each decision cell from said sequence of demodulated symbols, said sliced data being used to assign said presliced data to a proper symbol cell.

12. The transceiver according to claim 11 wherein said analysis means further determines from said statistics a root mean square (RMS) cluster size for all the symbol clusters in a constellation, a constellation closure, a resulting carrier-to-noise-ratio, a resulting symbol error rate, and a resulting bit error rate (BER).

13. The transceiver according to claim 12 wherein said analysis means further tests the magnitude of said bit error rate to determine whether the quality of said demodulated signal is above an acceptable threshold and if not, then directing the commencement of further processing to determine whether the degradation of the quality of said demodulated signal is due to the presence of said continuous wave interfering signal.

14. The Transceiver according to claim 12 wherein said analysis means determines an average cluster skewness for the symbol clusters in said constellation and tests the magnitude of said skewness to decide whether an interferer is most likely present, which would be the cause of said degradation of said BER.

15. The transceiver according to claim 12 wherein said analysis means determines an average cluster kurtosis for the symbol clusters in said constellation and testing the magnitude of said kurtosis to decide whether an interferer is most likely present, which would be the cause of said degradation of said BER.

16. The transceiver according to claim 14, wherein said conveyance means transmits the results of said test of skewness back to said transmitter over a reverse channel, said transmitter temporarily turning off transmission while said receiver receives only the external interference signals in the RF environment, and spectrum analyzing said environment to determine the frequencies of said interference signals.

17. The transceiver according to claim 15 wherein said conveyance means transmits the results of said test of kurtosis back to said transmitter over a reverse channel, said transmitter temporarily turning off transmission while said receiver receives only the external interference signals in the RF environment, and spectrum analyzing said environment to determine the frequencies of said interference signals.

18. The transceiver according to claim 16 wherein said conveyance means transmits the results of said spectrum analysis back to said transmitter over a reverse channel, said transmitter determining new transmission parameters to avoid said interference signals, and said transmitter transmitting said new transmission parameters to said transceiver.

19. The transceiver according to claim 18 wherein said transceiver and said transmitter reconfigure to transmit and receive the desired data signals with said new transmission parameters and then resuming data transmission using said new transmission parameters.

20. The transceiver according to claim 18 wherein said new transmission parameters include a new carrier frequency, QAM modulation order, and data rate.

21. The transceiver according to claim 7 wherein said transceiver uses quadrature partial response modulation.

25. The modem according to claim 21 further comprising an analog-to-digital converter coupled for converting said data signal into a digital signal.

22. A modem capable of non-intrusively detecting an unwanted interferer during a receiving of a data signal, comprising:

a transmitter for transmitting information to a communications apparatus;

a receiver for receiving said data signal from said communication apparatus;

a memory coupled to said receiver for storing statistical information associated with said data signal; and

a processor for measuring constellation statistics from said statistical information, determining a carrier-to-noise ratio and bit error rate of said data signal, determining whether a continuous wave or narrowband interferer is present, determining whether said bit error rate exceeds an acceptable limit by testing whether a symbol cluster changes from a Rayleigh distribution to a Ricean distribution, and when said bit error rate exceeds said acceptable limit, interrupting said received data signal to spectrum analyze a transmission band for an interference free region of said transmission band and communicating said interference free region to said communications apparatus for adjustment.

23. The modem according to claim 22 wherein said testing comprises calculating a skewness associated with said symbol cluster.

24. The modem according to claim 22 wherein said testing comprises calculating a kurtosis associated with said symbol cluster.

26. The modem according to claim 23 further comprising a fast-Fourier-transform-analysis means for spectrum analyzing said analog signal.