Consider a channel with an input alphabet that is finite but not necessarily binary. A method for approximating such a channel having a large output alphabet size by a degraded version of it having a smaller output alphabet size is presented and analyzed. The approximation method is used to construct polar codes for both single-user and multiple-access channels with prime input alphabet sizes.
['Ido Tal', 'Artyom Sharov', 'Alexander Vardy']
Constructing polar codes for non-binary alphabets and MACs