INCREASING ERROR CORRECTION IN DATA STREAMS ENCODED WITH LINEAR BLOCK CODE

• US 20080155376A1
• Filed: 02/27/2007
• Published: 06/26/2008
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Cable Television Laboratories Incorporated
• Original Assignee: Cable Television Laboratories Incorporated
• Inventors: Williams, Thomas H., Campos, Luis Alberto
• Granted Patent: US 7,921,351 B2
• Time in Patent Office: Days
• US Class Current: 714/760
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/0065 Serial concatenated codes

Abstract

Disclosed is an apparatus and method for increasing the error correction capabilities of a receiver circuit that receives a data stream of encoded data symbols that are encoded with a linear block code. Analog and digital comparator circuits are used to detect laser clipping or analog to digital converter overloading. Corrupted symbols are detected by comparing in-phase and/or quadrature phase baseband signals with pre-determined threshold limits that indicate that the in-phase and quadrature phase signals have exceeded the normal signal trajectory of an unimpaired signal. Corrupted symbols may also be detected by determining that the laser has been clipped. Corrupted symbols are marked for erasure prior to decoding and error correction. Erasure of corrupted signals increases the error correction capabilities of the decoder circuit.

Claims

1. A receiver that receives a data stream of modulated data symbols that have been encoded with a linear block code comprising:

a comparator that compares said data symbols with at least one limit that indicates impairment of said data symbols;

an output control signal generated by said comparator that marks said corrupt data symbols in said data stream; and

a decoder that is connected to said comparator that receives said output control signal and erases said corrupt data symbols that are marked by said output control signal prior to performing error corrections so as to increase error correction capabilities of said decoder.

2. The receiver of claim 1 wherein said comparator comprises an analog comparator.

3. The receiver of claim 1 wherein said comparator comprises a digital logic comparator.

4. The receiver of claim 1 wherein said data stream is transmitted by lasers in an optical transmission line and said at least one predetermined threshold value is set by a threshold limit of said lasers.

5. The receiver of claim 1 wherein said data stream is transmitted by lasers in an optical transmission line and said at least one limit is set by a saturation limit of said lasers.

6. The receiver of claim 3 further comprising:

an analog to digital converter that converts said data stream to a digital data stream; and

said at least one limit is set by clipping levels of said analog to digital converter.

7. A communication system for transmitting and receiving a stream of data comprising:

an encoder that encodes said stream of data into data symbols using a linear block code;

a transmitter that transmits said data symbols over an optical communication link using lasers;

a clipping detector that compares said data symbols with at least one threshold value that is determined in accordance with clipping levels of said lasers, and generates a clipping control signal that marks said corrupted data symbols;

a decoder that receives said clipping control signal that erases said corrupted data symbols in response to said clipping control signal prior to performing error correction to increase correction capabilities of said decoder.

8. The communication system of claim 7 wherein said transmitter uses an analog laser and said clipping detector is an analog comparator circuit.

9. The communication circuit of claim 7 wherein said transmitter uses an analog-to-digital converter and said clipping detector is a digital logic circuit.

10. A receiver for receiving a data stream of data symbols that have been encoded with a linear block code comprising:

a complex demodulator that demodulates said data symbols to produce an in-phase component and a quadrature phase component;

detectors that detect if said in-phase component and said quadrature phase component exceed thresholds that indicate in-band impairment of said data symbols and generate control signals that identify data symbols for erasure selected from the group consisting of data symbols that have;

in-phase components that exceed said predetermined thresholds, and quadrature phase components that exceed said predetermined thresholds;

a decoder that erases said data symbols that have been identified by said control signals prior to decoding by said decoder to increase data correction capabilities of said decoder.

11. The receiver of claim 10 further comprising:

low pass filters that are connected to said demodulator that low pass filter said in-phase component and said quadrature phase component to remove out of band energy.

12. The receiver of claim 10 wherein said data stream comprises a data stream from a satellite transmission.

13. The receiver of claim 10 wherein said data stream comprises a data stream from a cable transmission.

14. The receiver of claim 10 further comprising:

a wideband overload detector that detects if wideband energy of said data symbols exceed a wideband energy limit and generates an additional control signal that identifies impaired data symbols that have wideband energy that exceeds said wideband energy limit;

and wherein said decoder erases said data symbols that have been identified by the group consisting of said control signals and said additional control signal, prior to decoding by said decoder to increase data correction capabilities of said decoder.

15. A method of increasing error correction capabilities of a decoder that decodes and corrects linear block encoded symbols comprising:

transmitting said linear block encoded symbols in a composite signal through an optical transmission line using lasers;

comparing a composite signal level of said composite signal with at least one limit to identify corrupt data symbols in said data stream, said limit corresponding to at least one of the group consisting of;

a saturation limit of said lasers and a threshold limit of said lasers;

generating a control signal that marks said corrupt data symbols;

erasing said corrupt data symbols that have been marked by said control signal;

decoding said data stream after said corrupt data symbols have been erased from said data stream to increase said error correction capabilities of said decoder.

16. The method of claim 15 wherein said transmitter employs an analog laser and said process of comparing said data symbols with said limit comprises comparing said composite signal level with said limit in an analog comparator circuit.

17. The method of claim 15 wherein said transmitter employs an analog-to-digital converter and said process of comprising said data symbols with said limit comprises comparing said composite signal level with said limit in a digital comparator circuit.

18. A method of increasing error correction capabilities of a decoder that decodes and corrects linear block encoded symbols comprising:

converting an analog composite signal containing said linear block encoded symbols to a digital composite signal containing said linear block encoded symbols using an analog to digital converter;

comparing said digital composite signal with at least one limit to identify corrupt data symbols in said digital composite signal containing said linear block encoded symbols, said limit corresponding to clipping levels of said analog to digital converter;

generating a control signal that marks said corrupt data symbols;

erasing said corrupt data symbols that have been marked by said control signal;

decoding said digital composite signal containing said linear block encoded symbols after said corrupt data symbols have been erased from said digital composite signal to increase said error correction capabilities of said decoder.

19. The method of claim 18 wherein said process of comprising said digital composite signal with said at least one limit comprises comparing said digital composite signal with a saturation clipping level of said analog to digital converter.

20. The method of claim 18 wherein said process of converting said analog composite signal to a digital composite signal occurs prior to transmission of said digital composite signal.

21. The method of claim 18 wherein said process of converting said analog composite signal to a digital composite signal occurs after said analog data stream is transmitted.

22. A method of increasing error correction capabilities of a receiver that receives a data stream of data symbols that have been encoded with a linear block code comprising:

demodulating said data stream of said data symbols such that said data symbols have an in-phase component and a quadrature phase component;

detecting if said in-phase component exceeds in-phase limits that indicate an in-band impairment of said in-phase component;

detecting if said quadrature phase component exceeds quadrature phase limits that indicate in-band impairment of said quadrature phase component;

generating a control signal that identifies corrupt data symbols for erasure that have an in-phase component that exceeds said in-phase limits or a quadrature phase component that exceeds said quadrature phase limits;

erasing said corrupt data symbols that have been identified by said control signal;

decoding said data symbols after said corrupt data symbols that have been identified by said control signal have been erased, so as to increase data correction capabilities of said receiver.

23. The method of claim 22 further comprising:

low pass filtering said in-phase component and said quadrature phase component to eliminate out-of-band energy.

24. The method of claim 22 further comprising:

detecting if wideband energy of said data symbols exceeds wideband energy limits using a wideband overload detector;

generating an additional control signal that identifies data symbols for erasure if said data symbols have wideband energy that exceeds said wideband energy limits;

erasing said data symbols identified by said additional control signal prior to decoding said data symbols identified by said additional control signal so as to increase data correction capabilities of said receiver.

25. The method of claim 22 wherein said data stream comprises a data stream from a satellite transmission.

26. The method of claim 22 wherein said data stream comprises a data stream from a cable transmission.

27. The method of claim 24 wherein said data stream comprises a data stream from a satellite transmission.

28. The method of claim 24 wherein said data stream comprises a data stream from a cable transmission.