Degrees of Freedom of Three-user MIMO-IC via Receiver Chain Alignment

Abstract

In this article, we propose a receiver-side chain alignment (RCA) method to evaluate the degrees of freedom (DoF) of symmetric three-user multiple input multiple output (MIMO) interference channel (IC). The interference observed atthe adjacent receivers is represented in a chain of optimal overlap subspaces, the dimension of which is determined merely by the topological information (antennas sharing) and the knowledge of local projection, that relaxes the need for explicit requirement of the channel state information at the transmitter (CSIT). The alignment chain continues as long as the optimal overlap interference subspaces are possible. The observed interference is expressed in terms of the length of the alignment chain (L), measured as a function of the transmit (M) and the receive (N) antennas. The DoF is evaluated for different values of M/N via RCA and the result for an example scheme is verified information theoretically.