Coding for the q-ary symmetric channel with moderate q

We study coding schemes for the q-ary symmetric channel with moderate alphabet sizes q that are much smaller than the q = 2²⁵⁶ considered as ldquoentry levelrdquo in some recently proposed packet-based schemes. First, we show theoretical optimality of a simple layered scheme, then we propose a practical coding scheme based on a simple modification of standard binary LDPC decoding.