[email protected] <[email protected]> wrote:

>On Aug 19, 7:47*pm, Randy Yates <ya...@ieee.org> asked:

>>As a simple example, could a binary (7,4) Hamming code
>>be applied to 16-QAM, such that 4/7 codewords fit into one
>>symbol?

>Yes, though the implementation as well as any analysis would
>be messy. The first codeword would have its bits in the first
>and second QAM symbols transmitted, but the *second*
>codeword would have one bit in the second QAM symbol
>transmitted, the next four bits in the third QAM symbol, and
>two bits in the fourth QAM symbol. The 7 bits of the third
>codeword would have .... ; the whole cycle repeating
>after 7 QAM symbols (i.e. 4 codewords). Whether the
>increased complexity is worth the benefits reaped remains
>to be seen in 120 or so pages.

I would expect the Hamming code thus applied to exhibit
slightly less normalized coding gain than the same code
applied to a BPSK-modulated system.

There are two things that make the hit you're taking from
this mismatch smaller than one might think: in AWGN,
the noise vectors on the I and Q dibits are independent;
and if those dibits are grey-coded, as they typically
are, the bit errors within a dibit move closer to looking
independent of each other.

Still it would be worth placing an interleaver between
the code and the channel.

Steve