Forward error correction for high speed optical transmission systems

• US 6,683,855 B1
• Filed: 08/31/1998
• Issued: 01/27/2004
• Est. Priority Date: 08/31/1998
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Sturm, Wolfram, Dohmen, Ralf, Bordogna, Mark Aldo
• Primary Examiner(s): TON, DANG T
• Application Number:
  US09/143,781
• Time in Patent Office: 1,975 Days
• Field of Search: 370/244, 370/465, 370/474, 370/503, 370/351, 370/352, 370/241, 370/242, 370/356, 370/389, 714/746, 714/747, 714/751, 714/752, 714/753, 714/754, 714/758, 714/759, 714/764, 375/243, 375/253, 375/250, 375/246, 359/139, 359/147
• US Class Current: 370/244
• CPC Class Codes: H04J 2203/0089 Multiplexing, e.g. coding, scrambling, SONET
• CPC Class Codes: H04J 3/14 Monitoring arrangements for SDH/SONET rings H04J3/085
• CPC Class Codes: H04J 3/1611 Synchronous digital hierarchy [SDH] or SONET H04J3/1664 takes precedence for interactions with OTN
• CPC Class Codes: H04L 1/0043 Realisations of complexity reduction techniques, e.g. use of look-up tables
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control

Abstract

Memory requirements and processing delays associated with the application of forward error correction in high speed optical transmissions are substantially reduced by mapping a forward error correction code on a row-by-row basis into unused overhead bytes in a high bit rate signal frame. By applying the forward error correction code to an entire row of the signal frame on a row by row basis, approximately one row needs to be stored at a time thereby reducing the total memory requirements for forward error correction processing. Using SONET as an exemplary application, approximately {fraction (1/9)}th of the entire SONET frame (e.g., one of nine rows) needs to be buffered for forward error correction processing. In an illustrative embodiment, four forward error correction (FEC) blocks are provided for each row for a total of 36 FEC blocks for a frame. Each FEC block comprises four bytes of correction bits for a total of 32 correction bits. These 32 correction bits are mapped to unused overhead and are used for correcting errors in one block of one row of a signal frame, wherein one block covers ¼th of the row. Other unused overhead bytes in the row can be used to carry error detection codes for detecting multiple errors in a row to determine when forward error correction should be disabled. For example, if a single bit error correcting code is employed, then error correction can be disabled to avoid false corrections if more than one error is detected.

Claims

1. A method of improving the bit error rate performance of an optical transmission system, wherein a signal supplied by the system comprises a plurality of signal frames, each signal frame having a predetermined number of rows, the method comprising the steps of:

inserting a predetermined number of forward error correction bytes into predetermined overhead bytes in a signal frame on a row-by-row basis, such that the forward error correction bytes in a particular row apply to data in a preceding row of the signal frame; and

processing only the forward error correction bytes in the particular row to detect and correct errors within the preceding row.

2. The method according to claim 1, further comprising the step of, prior to processing the forward error correction bytes in a row, storing approximately one row of the signal frame.

3. The method according to claim 1, wherein the optical transmission system is a system selected from the group consisting of a SONET-based system and a SDH-based system.

4. The method according to claim 3, wherein the signal is selected from the group consisting of a STS-192 signal and a STM-64 signal, both operating at a transmission rate of approximately 10 Gb/s.

5. The method according to claim 4, wherein the predetermined number of rows is nine.

6. A method of providing forward error correction for signals supplied by an optical transmission system, each signal comprising a plurality of signal frames, each signal frame having a predetermined number of rows, the method comprising the steps of:

partitioning each row in a signal frame into a predetermined number of segments;

inserting forward error correction bytes into predetermined overhead bytes in the signal frame on a row-by-row basis, wherein a predetermined number of forward error correction bytes apply to each segment within a row and wherein the forward error correction bytes in a particular row apply to data in a preceding row of the signal fame; and

processing only the forward error correction bytes in the particular row to detect and correct errors within the preceding row.

7. The method according to claim 6, further comprising the step of, prior to processing the forward error correction bytes in a row, storing approximately one row of the signal frame.

8. The method according to claim 7, wherein the predetermined number of segments is four so that each segment is representative of approximately one-fourth of a row of data.

9. The method according to claim 8, wherein the predetermined number of forward error correction bytes is four.

10. The method according to claim 6, wherein the optical transmission system is a system selected from the group consisting of a SONET-based system and a SDH-based system.

11. The method according to claim 10, wherein the signal is selected from the group consisting of a STS-192 signal and a STM-64 signal, both operating at a transmission rate of approximately 10 Gb/s.

12. The method according to claim 11, wherein each segment comprises approximately 34,560 bits.

14. The method according to claim 6, further comprising the step of inserting error detection bytes into predetermined overhead bytes of the signal frame on a row-by-row basis, wherein a predetermined number of error detection bytes apply to each segment within a row.

15. The method according to claim 14, wherein the error detection bytes are processed to detect a total number of errors in each segment, and wherein forward error correction processing is enabled and disabled on a row-by-row basis as a function of the number of errors detected within a row.

16. The method according to claim 15, wherein, if the total number of errors detected exceeds a predetermined threshold, forward error correction processing is disabled to avoid false corrections, and wherein, if the total number of errors detected is less than or equal to the predetermined threshold, forward error correction processing is enabled.

17. The method according to claim 16, wherein the error detection bytes comprise bit interleaved parity bytes.

18. The method according to claim 14, further comprising the step of compensating particular overhead bytes to account for parity changes resulting from insertion of the forward error correction bytes and insertion of the error detection bytes.

19. The method according to claim 6, further comprising the steps of:

inserting a forward error correction start byte into a predetermined overhead byte in the signal frame; and

enabling and disabling forward error correction processing as a function of the value of the start byte.

20. The method according to claim 6, further comprising the steps of:

rearranging overhead bytes in selected rows in the signal frame to preserve the contents thereof, wherein the step of rearranging includes copying and moving contents of overhead bytes between selected rows in the signal frame prior to inserting the forward error correction bytes in the selected rows; and

compensating particular overhead bytes to account for parity changes resulting from rearranging the overhead bytes in selected rows.

21. The method according to claim 6, wherein the forward error correction bytes corresponding to each of the segments within a row are bit interleaved within the predetermined overhead bytes, wherein each forward error correction byte includes forward error correction bits from each of the segments within the row so that multiple contiguous errors within a row of the signal frame are detectable and correctable.

22. The method according to claim 10, wherein the forward error correction processing can be selectively enabled and disabled at a section layer or at a line layer.

13. The method according to claim wherein 11, for a particular row in the signal frame, the step of inserting the forward error correction bytes comprises inserting the forward error correction bytes on a bit-by-bit basis into at least one bit location of a succeeding number of overhead bytes.

23. An apparatus for improving the bit error rate performance of an optical transmission system, wherein a signal supplied by the system comprises a plurality of signal frames, each signal frame having a predetermined number of rows, the apparatus comprising:

means for inserting forward error correction bytes in predetermined overhead bytes in a signal frame on a row-by-row basis, such that the forward error correction bytes in a particular row apply to data in a preceding row of the signal frame; and

means for processing only the forward error correction bytes in the particular row to detect and correct errors within the preceding row.

24. The apparatus according to claim 23, wherein the means for inserting comprises a forward error correction encoder and the means for processing comprises a forward error detection decoder.

25. The apparatus according to claim 23, wherein the means for processing further comprises memory for storing approximately one row of the signal frame prior to processing the forward error correction bytes in a row.

26. The apparatus according to claim 23, wherein the optical transmission system comprises a system selected from the group consisting of a SONET-based system and a SDH-based system.

27. The apparatus according to claim 26, wherein the signal is selected from the group consisting of a STS-192 signal and a STM-64 signal, both operating at a transmission rate of approximately 10 Gb/s.