The capacity region of multiple-rate codes for multiple-access channels

Investigates the limits imposed by information theory on multiple-access codes in which each user has multiple transmission rates, but where only certain combinations of users´ rates are desired to operate reliably at the same time. The capacity region for this problem is determined for both synchronous and frame-asynchronous multiple-access channels. Unlike the classic M-user multiple-access channel, the synchronous capacity region is not in general equal to the convex hull of the frame-asynchronous region. In the special case of T-out-of-M user codes, it is shown for symmetric multi-user channels that synchronism does not improve the symmetric capacity for M≫T