Feasibility conditions for interference neutralization in relay-aided interference channel

Interference neutralization (IN) is a new interference management mechanism found from and inherent in interference networks with relays. In this paper, we study the feasibility of IN for relay-aided multi-input-multi-output (MIMO) interference broadcast channel (MIMO-IBC) without symbol extension. Assuming linear transceiver with multiple amplify-and-forward relays, we consider fully connected symmetric systems, where each base station (BS), relay, and user is equipped with multiple antennas, and each user desires multiple data streams. We first present the necessary condition of generalized IN, which is the proper condition to ensure interference-free transmission with linear transceivers for general relay-aided MIMO-IBC. We then find and prove the necessary and sufficient condition of the feasibility of coordinated IN and pure IN for a class of relay-aided MIMO-IBC, where the sufficiency is proved by constructing a full rank coefficient matrix of interference-free transmission equation with sub-matrices of special structures. We show that when each BS and user has the minimal antenna configuration for data transmission, the sufficient and necessary condition for coordinated IN is the same as the necessary condition for generalized IN. When there is an arbitrary number of antennas at the BSs and users, the derived sufficient conditions give rise to the minimum relay configuration required by the coordinated IN and pure IN to support a given number of data streams without interference. Our proof sheds lights on how to use the relay resources to neutralize the interference in an efficient way. The results are applicable for both relay-aided MIMO-IBC and relay-aided interference channel (MIMO-IC).