Layering techniques for space-time communication in multi-user networks

In this paper, we consider a multiuser communication network where all the nodes in the network are equipped with multiple antennas and different users are identified through their spatial signatures. We present some results on the capacity of such networks. We consider two cases of interest: (i) when the transmitter (the base) has full knowledge of the channel state information (CSI) between itself and the receiving nodes (users); and (ii) when the base does not have CSI, but it does know which users currently have the best channel (e.g., measured in terms of a condition number). In the first case, we establish coordinated beamforming between the base and a number of users to whom data is to be transmitted. In the second case, partial knowledge of the quality of the users' channels will be used to transmit data to the users with better channel condition, without performing any beamforming at the base. In both cases, the base transmits independent data streams to multiple users. This guarantees a higher minimum quality of service for all the users compared to the case where the user with the best channel is selected and all the available capacity is devoted to it. In addition, we show that this approach may increase the overall capacity/throughput of the network.