Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-10-04
2004-02-24
Decady, Albert (Department: 2138)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S786000
Reexamination Certificate
active
06697985
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data telecommunications in general, and more particularly to forward error correction therefor.
BACKGROUND OF THE INVENTION
The use of Forward Error Correction (FEC) techniques in the design of digital communications and storage systems is well known. FEC is used to find and correct limited errors caused by a transport or storage system in order to ensure the validity of the received message without requiring retransmissions. In general, FEC encoding techniques, such as Reed-Solomon (RS) encoding, provide data redundancy by adding extra code symbols to a transmitted message which provide the necessary detection and correction information. The number of redundant symbols is determined by the amount and type of error correction required. RS encoding is an example of a block code where the data to be transmitted are divided into blocks, with each block comprising k symbols of data. An additional r redundancy symbols are then added to each block of k data symbols to form a code word of length n=k+r. The “code rate” of the code refers to the ratio k
, and is used to express the average amount of data symbols versus the amount of transmitted symbols. Thus, a code rate of 0.8 would indicate that the average over all time intervals T of the ratio of data symbols that were encoded in time interval T to the total number of transmitted symbols in time interval T, is 80%.
In general, the additional redundancy symbols must contain enough information to allow the position of an erroneous information symbol to be located and its value determined. For example, an RS decoder can detect and correct up to r/2 incorrect symbols if there are (r=n−k) redundant symbols in each code word, as one redundant symbol is used to detect and locate each error, and one more redundant symbol is used to identify the precise value of that error. Some symbols that are either known or suspected to be in error or otherwise unreliable may be labeled as “erasures.” The position of each erasure may be provided in advance to the decoder which then ignores the actual value of the erasure and instead reconstructs its value using the redundancy symbols. Since the position of each erasure is known, only one redundant symbol is needed to reconstruct the value of an erasure, and an additional redundant symbol to determine the location of the erasure is not required. In general, if a code word contains E symbols that are erasures whose locations are known and e symbols that are errors with unknown locations, the code word can be correctly decoded provided that (2e+E)<r. If the locations of all the errors are known to the decoder, the message can be correctly decoded provided that E<r, thus requiring half the number of redundant symbols needed to correct errors whose locations are not known.
While conventional FEC techniques may be used more or less successfully to correct errors, they generally must be designed with a redundancy that is greater than the number of errors they are expected to correct, with RS codes requiring up to twice as many redundancy symbols as error symbols. Thus, the greater the redundancy, the less room there is for data in each code word and the less throughput of the communication channel due to error correction overhead.
SUMMARY OF THE INVENTION
In one aspect of the present invention a forward error correction system is provided including a coder operative to encode a data stream into at least one primary code word and at least one secondary code word, where each primary code word is encoded at a first code rate, and each secondary code word is encoded at a second code rate that is greater than the first code rate, at least one transmitting modem for transmitting the code words, at least one receiving modem for receiving the code words, a decoder operative to detect errors in any of the code words, correct any of the errors and erasures in the code words, and communicate the positions of any of the errors, and a controller operative to receive the communication of the error positions, predict from any of the errors in the primary code word at least one error in the secondary code word, and report any of the predicted errors as erasure positions to the decoder.
In another aspect of the present invention the controller is operative to predict after determining that the number of errors detected in the primary code word exceeds a predetermined error threshold.
In another aspect of the present invention the coder is a Reed-Solomon coder.
In another aspect of the present invention the code words are either of systematic, non-systematic, and convolutional code words.
In another aspect of the present invention the code words are of different lengths.
In another aspect of the present invention the at least one transmitting modem includes a plurality of transmitting modems, and the system further includes a demultiplexer for demultiplexing the code words, thereby causing each of the transmitting modems to transmit a different portion of each of the code words.
In another aspect of the present invention the at least one receiving modem includes a plurality of receiving modems for receiving the different portions of each of the code words, and the system further includes a multiplexer for multiplexing the portions, thereby reconstructing the code words.
In another aspect of the present invention the controller is operative to predict after determining that the number of errors detected in any of the portions exceeds the predetermined error threshold, and any of the predicted errors corresponds to the portion exceeding the predetermined error threshold.
In another aspect of the present invention the system further includes an interleaver for interleaving the code words, and a deinterleaver for deinterleaving the interleaved code words.
In another aspect of the present invention the controller is operative to send a configuration signal to the decoder configuring the decoder for decoding either of the primary and the secondary code words.
In another aspect of the present invention a forward error correction system is provided including a coder operative to encode a data stream into at least one primary code word and at least one secondary code word, where each primary code word is encoded at a first code rate, and each secondary code word is encoded at a second code rate that is greater than the first code rate, a demultiplexer for demultiplexing each of the code words into a plurality of portions, a plurality of transmitting modems, each transmitting modem for transmitting a different one of the plurality of portions, a plurality of receiving modems for receiving the plurality of portions, a multiplexer for multiplexing the plurality of portions, thereby reconstructing the code words, a primary decoder operative to detect any errors in any of the primary code words, correct any of the errors, and communicate the positions of any of the errors, a controller operative to receive the communication of the error positions, predict from any of the errors in the primary code word at least one error in the secondary code word, and report any of the predicted errors as erasure positions, a secondary decoder operative to receive the report of erasure positions and correct any of the erasures in the secondary code words.
In another aspect of the present invention the controller is operative to predict after determining that the number of errors detected in the primary code word exceeds a predetermined error threshold.
In another aspect of the present invention the controller is operative to predict after determining that the number of errors detected in any of the portions exceeds the predetermined error threshold, and any of the predicted errors corresponds to the portion exceeding the predetermined error threshold.
In another aspect of the present invention the coder is a Reed-Solomon coder.
In another aspect of the present invention the code words are either of systematic, non-systematic, and convolutional code words.
In anothe
Actelis Networks Inc.
Chaudry Mujtaba
De'cady Albert
Eitan, Pearl, Latzer & Cohen Zedek LLP
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