On achievable rates in a multi-antenna Gaussian broadcast channel

A Gaussian broadcast channel with r single-antenna receivers and t antennas at the transmitter is considered. Both transmitter and receivers have perfect knowledge of the channel. Despite its apparent simplicity, this model is in general a non-degraded broadcast channel, for which the capacity region is not fully known. We propose a novel transmission scheme based on "ranked known interference" (RKI). In brief, the transmitter decomposes the channel into an ordered (or ranked) set of interference channels for which the interference signal of the i-th channel is generated as a linear combination of the signals transmitted in channels j