Timesharing without Synchronization

Abstract

The capacity region of a multiple-access channel has recently been identified as the convex hull K̄ of a certain set K of points in the first quadrant of the (R₁,R₂) plane. For a pair of rates in K, a more or less standard random coding argument can be used to show the existence of a good pair of codes. But for points in K̄-K, it is apparently necessary for the two senders to use some form of timesharing to achieve the desired rates. However, in order to timeshare, at least one of the senders must have knowledge of the other's phase; and in many practical situations this knowledge does not exist. In this paper we investigate the problems which arise in coding for multiple access channels when the senders cannot synchronize with each other.