Decoding carriers encoded using orthogonal frequency division multiplexing

• US 5,923,666 A
• Filed: 10/23/1996
• Issued: 07/13/1999
• Est. Priority Date: 10/24/1995
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: NDS Limited (Cisco Systems, Inc.)
• Inventors: Anikhindi, Santosh, Gledhill, Jeff
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): YAO, KWANG BIN
• Application Number:
  US08/735,868
• Time in Patent Office: 993 Days
• Field of Search: 370/203, 370/206, 370/207, 370/208, 370/343, 370/480, 370/503, 370/516, 370/481, 370/482, 370/483, 370/484, 375/260, 375/262, 375/340, 375/341, 371/69.1, 371/71
• US Class Current: 370/480
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/203 Details of error rate determination, e.g. BER, FER or WER
• CPC Class Codes: H04L 1/208 involving signal re-encoding
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

This invention relates to decoding symbols in the form of modulated carriers which are encoded using orthogonal frequency divsion multiplexing. The modulated carriers are supplied to a decoder which is preferably a Viterbi decoder. The decoder symbols are then recoded and passed to a comparator where they are compared with the incoming modulated carriers to locate errors between each recoded symbol and the corresponding modulated carrier symbol. The error rate for each carrier is derived by a counter and the indications of error rate and the modulated carriers are used to address entries in a look up table from which a decoder decodes the symbols represented by the modulated carriers.

Claims

1. A method of decoding modulated carriers encoded using orthogonal frequency division multiplexing to produce a steam of encoded symbols, the method comprising the step of:

supplying said modulated carries to a decoded effective to decode said encoded symbols to produce decoded symbols,

recoding said decoded symbols to produce recoded symbols;

comparing said modulated carriers with said recoded symbols to locate errors between each recoded symbol and a corresponding encoded symbol,

deriving an indication of an error rate for each of said modulated carriers, and

applying said indication of error rate to said decoder to effect decoding of each encoded symbol by reference to the modulation of one of said modulated carriers combined with said indication of error rate for one of said modulated carriers,

wherein said indication of error rate and said modulated carriers are used to address entries in a look up table from which said decoder decodes said encoded symbols represented by said modulated carriers.

2. The method as claimed in claim 1, wherein said decoder comprises a Viterbi decoder.

3. Apparatus for decoding modulated carriers comprising a stream of orthogonal frequency division multiplex encoded symbols and representing said stream of encoded symbols, the apparatus comprising:

a decoder having an input to receive said modulated carriers and being effective to decode said encoded symbols represented thereby to produce decoded symbols,

a recoder to recode said decoded symbols from said decoder to produce recoded symbols,

a comparator to compare said modulated carriers with said recoded symbols and to signal the location of errors between each recoded symbol and a corresponding encoded symbol and to output an indication of an error rate for each carrier, the decoder having an input to receive said indication of said error rate for each carrier and being effective to decode each of said encoded symbols by reference to the modulation of one of said modulated carriers and by reference to said indication of said error rate for said modulated carriers, and the decoder having a look up table, entries to which are addressed by said modulated carriers and said indication of said error rate and being effective to decode the symbols represented by said modulated carriers from said entries addressed in said look up table.

4. Apparatus as claimed in claim 3, wherein said decoder comprises a Viterbi decoder.