A method and apparatus for measuring channel quality over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence. A sequence of received symbols is received over the channel. 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 de-mapped symbols are decoded to produce a decoded output sequence. In some embodiments, the decoding may be based on the first channel quality indicator. The decoded output sequence is re-encoded to produce a re-encoded output sequence. The de-mapped symbols are correlated 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.