ON LIMITING CHARACTERIZATIONS OF MEMORYLESS MULTIUSER CAPACITY REGIONS

The restriction to Gaussian inputs in the limiting expression for the capacity regions of memoryless Gaussian interference and multiple-acce ss channels is shown to fall short of achieving capacity even if the i nputs are allowed to be dependent and nonstationary. In addition, the equality between the limiting and the single-letter characterizations of memoryless multiple-access channel capacity is established directly , without recourse to independent coding theorems.