On uncoded high rate transmission over synchronous Gaussian multiple-access channels

On Gaussian multiple-access channels a penalty in power efficiency 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 orthogonality of all users´ signal waveforms. In this paper, we show that keeping binary modulation and accepting some multiple-access interference, is a more power efficient strategy by presenting simulation results of transmission systems outperforming orthogonal schemes for rates between 1.25 and 1.75 bit/s/Hz, per dimension