Universal coding for multiple access channels

The problems of universal coding and decoding for multiple-access channels are examined. The hypothetical mutual information functions are used to prove that rate vectors R=(R_{1},R_{2}) in a subregion \hat{\cal C} of the capacity region \cal C are universally achievable in the sense that there exist codes of rate R that are asymptotically optimum for all multiple-access channels with finite fixed input alphabets X_{1},X_{2} , and output alphabet Y .