Achieving Maximum Degrees of Freedom of Two-Hop MIMO Alternate Half-Duplex Relaying System For Linear Transceivers: A Unified Transmission Framework for DF and AF Protocols

In this paper, a novel unified transmission framework in the context of both decode-and-forward (DF) and amplify-and-forward (AF) protocols was proposed for a two-hop multiple-input–multiple-output (MIMO) alternate half-duplex (HD) relaying system with $M$ antennas for each node, which can achieve the maximum $M$ degrees of freedom (DoFs) of the system, compared with the existing interference alignment (IA) schemes that can only get $\hbox{3}M/\hbox{4} $ DoF. Furthermore, the proposed schemes require only two relays against three relays invoked in the existing IA schemes. Moreover, the proposed schemes are valid for the cases where the number of antennas $M$ can be either even or odd, whereas the existing IA schemes can only apply for an even number of antennas $M$.