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A method and apparatus are provided for measuring channel quality over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence. The method includes receiving a sequence of received symbols over the channel whose quality is to be

A method and apparatus are provided for measuring channel quality over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence. The method includes receiving a sequence of received symbols over the channel whose quality is to be measured. The sequence of received symbols is de-mapped based on a first channel quality indicator previously transmitted to a transmitter of the sequence of symbols. The method also includes decoding the de-mapped symbols to produce a decoded output sequence. In some embodiments, the decoding may be based on the first channel quality indicator. The method also includes re-encoding the decoded output sequence to produce a re-encoded output sequence. The method also includes correlating the de-mapped symbols with the re-encoded output sequence to produce a second channel quality indicator. The second channel quality indicator is transmitted to the transmitter to adaptively select a type of mapping based on the second channel quality indicator. In some embodiments, the transmitter may adaptively select a type of encoding based on the second channel quality indicator.

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1. A channel quality measurement apparatus adapted to measure a quality of a channel over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence, the apparatus comprising: a symbol de-mapper, receiving as input a sequence of rec

1. A channel quality measurement apparatus adapted to measure a quality of a channel over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence, the apparatus comprising: a symbol de-mapper, receiving as input a sequence of received symbols over the channel whose quality is to be measured, the symbol de-mapper being adapted to perform symbol de-mapping on the sequence of received symbols to produce a sequence of soft data element decisions, a type of the symbol de-mapping being based on a first channel quality indicator previously transmitted by the apparatus to a transmitter of the sequence of symbols;a soft decoder, receiving as input the sequence of soft data element decisions produced by the symbol de-mapper, the soft decoder being adapted to decode the sequence of soft data element decisions to produce a decoded output sequence;an encoder, receiving as input the decoded output sequence produced by the soft decoder, the encoder being adapted to re-encode the decoded output sequence with an identical code to a code used in encoding the source data element sequence to produce a re-encoded output sequence; anda correlator, receiving as input the sequence of soft data element decisions produced by said de-mapper, and the re-encoded output sequence produced by the encoder, said correlator being adapted to produce a second channel quality indicator by determining a correlation between the sequence of soft data element decisions and the re-encoded output sequence,wherein the apparatus is adapted to feed the second channel quality indicator back to the transmitter to apply a type of mapping of the source data element sequence based on the second channel quality indicator so that the type of mapping applied at the transmitter is based on the correlation between the sequence of soft data element decisions and the re-encoded output sequence. 2. The channel quality measurement apparatus of claim 1 wherein the symbol de-mapper is adapted to perform QPSK symbol de-mapping in response to the first channel quality indicator and is adapted to perform Euclidean distance conditional LLR symbol de-mapping in response to the second channel quality indicator. 3. The channel quality measurement apparatus of claim 1 wherein the symbol de-mapper is adapted to perform Euclidean distance conditional LLR symbol de-mapping in response to the first channel quality indicator and is adapted to perform QPSK symbol de-mapping in response to the second channel quality indicator. 4. The channel quality measurement apparatus of claim 1, wherein a type of decoding is based on the first channel quality indicator previously transmitted by the apparatus to the transmitter of the sequence of symbols. 5. The channel quality measurement apparatus of claim 4, wherein the second channel quality indicator is transmitted to the transmitter to adaptively select a type of coding of the source data element sequence. 6. A method of measuring channel quality of a channel over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence, the method comprising: receiving a sequence of received symbols over the channel whose quality is to be measured;symbol de-mapping said sequence of received symbols to produce a sequence of soft data element decisions;decoding said sequence of soft data element decisions to produce a decoded output sequence, the decoding being based on a first channel quality indicator previously transmitted to a transmitter of the sequence of symbols;re-encoding said decoded output sequence to produce a re-encoded output sequence using a code identical to a code used in encoding the source data element sequence; andcorrelating said re-encoded output sequence, and said sequence of soft data element decisions to produce a second channel quality indicator; andtransmitting the second channel quality indicator to the transmitter to adaptively select a type of coding to be applied to a source data element sequence based on the second channel quality indicator so that the type of mapping applied at the transmitter is based on the correlation between the sequence of soft data element decisions and the re-encoded output sequence. 7. The method of channel quality measurement of claim 6 wherein the symbol de-mapping of a sequence of received symbols is QPSK symbol de-mapping in response to the first channel quality indicator and wherein the symbol de-mapping of a sequence of received symbols is Euclidean distance conditional LLR de-mapping in response to the second channel quality indicator. 8. The method of channel quality measurement of claim 6 wherein the symbol de-mapping of a sequence of received symbols comprises Euclidean distance conditional LLR de-mapping in response to the first channel quality indicator, and wherein the symbol de-mapping of a sequence is QPSK symbol de-mapping in response to the second channel quality indicator. 9. An article of manufacture comprising a non-transitory computer-readable storage medium, the non-transitory computer-readable storage medium including instructions for implementing the method of claim 6. 10. A method of measuring OFDM channel quality of an OFDM channel over which has been transmitted a sequence of OFDM symbols, the OFDM symbols containing an encoded and constellation mapped source data element sequence, the method comprising: receiving a sequence of OFDM symbols over the OFDM channel whose quality is to be measured;symbol de-mapping said sequence of received symbols to produce a sequence of soft data element decisions, the symbol de-mapping being based on a first channel quality indicator previously transmitted to a transmitter of the sequence of OFDM symbols;decoding said sequence of soft data element decisions to produce a decoded output sequence pertaining to the source data element sequence, the decoding being based on the first channel quality indicator previously transmitted to the transmitter of the sequence of OFDM symbols;re-encoding said decoded output sequence to produce a re-encoded output sequence using a code identical to a code used in encoding the source data element sequence; andcorrelating said re-encoded output sequence, and said sequence of soft data element decisions to produce a second channel quality indicator; andtransmitting the second channel quality indicator to the transmitter to adaptively select a type of mapping and a type of coding to be applied to a source data element sequence based on the second channel quality indicator so that the type of mapping applied at the transmitter is based on the correlation between the sequence of soft data element decisions and the re-encoded output sequence. 11. The method of OFDM channel quality measurement of claim 10 wherein the symbol de-mapping of said sequence of received symbols is QPSK symbol de-mapping in response to the first channel quality indicator and wherein the symbol de-mapping of a sequence of received symbols is Euclidean distance conditional LLR de-mapping in response to the second channel quality indicator. 12. The method of OFDM channel quality measurement of claim 10 wherein the symbol de-mapping of said sequence of received symbols comprises Euclidean distance conditional LLR de-mapping in response to the first channel quality indicator, and wherein the symbol de-mapping of a sequence is QPSK symbol de-mapping in response to the second channel quality indicator. 13. The method of OFDM channel quality measurement of claim 10 wherein the decoding of said sequence of soft data element decisions to produce a decoded output sequence further comprises using a history of the soft data element decisions, and using information about encoding of the sequence of symbols transmitted over the channel. 14. An article of manufacture comprising a non-transitory computer-readable storage medium, the non-transitory computer-readable storage medium including instructions for implementing the method of claim 9. 15. A communication system comprising: a transmitter adapted to transmit a sequence of symbols produced by encoding and constellation mapping a source data element sequence over a channel; anda receiver comprising:a) a symbol de-mapper, receiving as input a sequence of received symbols over the channel, said symbol de-mapper being adapted to perform symbol de-mapping on said sequence of received symbols to produce a sequence of soft data element decisions, a type of the symbol de-mapping being based on a first channel quality indicator previously transmitted by the receiver to the transmitter of the sequence of symbols;b) a soft decoder, receiving as input the sequence of soft data element decisions produced by the symbol de-mapper, said soft decoder being adapted to decode the sequence of soft data element decisions to produce a decoded output sequence;c) an encoder, receiving as input the decoded output sequence produced by the soft decoder, said encoder being adapted to re-encode the decoded output sequence with an identical code to a code used in encoding the source data element sequence to produce a re-encoded output sequence; andd) a correlator, receiving as input the sequence of soft data element decisions produced by the de-mapper, and the re-encoded output sequence produced by the encoder, said correlator being adapted to produce a second channel quality indicator by determining a correlation between the sequence of soft data element decisions and the re-encoded output sequence,wherein the receiver is adapted to feed the second channel quality indicator back to the transmitter, and wherein the transmitter is adapted to apply a type of modulation of the source data element sequence based on the second channel quality indicator so that the type of modulation applied at the transmitter is based on the correlation between the sequence of soft data element decisions and the re-encoded output sequence. 16. The communication system of claim 15 wherein the symbol de-mapper is adapted to perform QPSK symbol de-mapping in response to the first channel quality indicator and is adapted to perform Euclidean distance conditional LLR symbol de-mapping in response to the second channel quality indicator. 17. The communication system of claim 15 wherein the first and second channel quality indicators correspond to a first and second bit error rate, respectively. 18. The communication system of claim 15, wherein a type of the decoding is based on the first channel quality indicator previously transmitted by the receiver to the transmitter of the sequence of symbols.