User admission in MIMO interference alignment networks

In this paper we consider an interference channel where a set of primary active users are cooperating through interference alignment over a constant multiple-input-multiple-output channel while a set of secondary users desire access to the channel. We present the conditions under which a secondary user can be admitted to the network. For the admitted users, we derive several beamforming designs maximizing approxi-mately the secondary users ’ sum-rate based on the number of the secondary users, the number of antennas at the secondary users and the total number of streams in the network of active users