User cooperation-assisted multi-cell MIMO networks

We explore the interplay between interference, cooperation, and feedback in multi-cell networks. Specifically, this paper focuses on G-cell multiple-input multiple-output Gaussian interfering broadcast channels (MIMO-IFBC) with K cooperating users on the cell-boundary of each base station. It corresponds to a downlink scenario for cellular networks with G base stations, and K users equipped with Wi-Fi interfaces enabling to cooperate among users on a peer-to-peer basis. In this scenario, we propose a novel interference alignment technique exploiting user cooperation. Our proposed algorithm obtains the total degrees of freedom (DoF) of GK to be achieved by transmitting one stream to each user from its corresponding BS, when each BS and cell-edge user has M = K + (G - 1)d_align transmit antennas and N = ⌊(M(G - 1)(K - d_align) + 1)/K⌋ receive antennas as a minimum antenna configuration, respectively, where ∀d_align ∈ {1,2,...K}. Furthermore, the algorithm requires only a small amount of channel feedback information with the aid of the user cooperation channels. The simulations demonstrate that not only are the analytical results valid, but the achievable DoF of our proposed algorithm also outperforms those of conventional techniques.