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 vectorsR=(R_{1},R_{2})in a subregionhat{cal C}of the capacity regioncal Care universally achievable in the sense that there exist codes of rateRthat are asymptotically optimum for all multiple-access channels with finite fixed input alphabetsX_{1},X_{2}, and output alphabetY.