DMT achieving schemes for the Isotropic Fading Vector Broadcast Channel

In this paper, we consider the isotropic fading broadcast channel. This channel refers to the case when no directional information is available at the transmitter side, and was studied by Jafar et al in [1]. It was shown that the isotropic vector broadcast channel (BC-V) can be reduced to an equivalent scalar broadcast channel (BC-S). It is well known from [2]http://www.pimrc2008.org/ that BC-S is degraded in the same order as the channel magnitude. This implies that the optimal strategy that maximizes the sum capacity for BC-S and BC-V consists on allocating the whole power to the strongest user. Based on these results, we derive in this paper the Diversity Multiplexing Tradeoff (DMT) of the isotropic fading BC-S and BC-V, and we propose optimal schemes that achieve these DMT.