On Uncoded High Rate Transmission

| On Gaussian multiple{access channels a penalty in power eeciency is to be paid if total transmission rate is higher than 1 bit/s/Hz per dimension. This usually results from the need for higher order modulation schemes required to maintain or-thogonality of all users' signal waveforms. In this paper , we show that keeping binary modulation and accepting some multiple{access interference, is a more power eecient strategy by presenting simulation results of transmission systems outperforming orthogonal schemes for rates between 1.25 and 1.75 bit/s/Hz per dimension. I. Introduction While total capacity and capacity region are well{known, the theoretical limits of uncoded transmission are still not completely analyzed. As data delay is considered to be a problem for many applications, investigation of eecient low{delay transmission is not only of theoretical interest. A rst step of insight into this problem will be given by understanding zero{delay (uncoded) multiple{access communication. In the following we consider all K users to apply linear bandlimited modulation. Thus, the users' signal waveforms can be described by their Nyquist sample vectors (signature