An active reconfigurable intelligent surface (RIS) has been shown to be able to enhance the sum-of-degrees-of-freedom (DoF) of a two-user multiple-input multiple-output (MIMO) interference channel (IC) with equal number of antennas at each transmitter and receiver. However, for any number of receive and transmit antennas, when and how an active RIS can help to improve the sum-DoF are still unclear. This paper studies the sum-DoF of an active RIS-assisted two-user MIMO IC with arbitrary antenna configurations. In particular, RIS beamforming, transmit zero-forcing, and interference decoding are integrated together to combat the interference problem. In order to maximize the achievable sum-DoF, an integer optimization problem is formulated to optimize the number of eliminating interference links by RIS beamforming. As a result, the derived achievable sum-DoF can be higher than the sum-DoF of two-user MIMO IC, leading to a RIS gain. Furthermore, a sufficient condition of the RIS gain is given as the relationship between the number of RIS elements and the antenna configuration.
翻译:已经证明,一个活跃的可重新校准的智能表面(RIS)能够增强两个用户多投入多输出干扰信道(IMO)的自由度总和(DoF),每个发射机和接收机的天线数量相等;然而,对于任何数目的接收和传输天线来说,一个活跃的RIS能够帮助改进总和-DoF的时间和方式仍然不明确;本文研究一个活跃的RIS援助的两用户IMO的双用户IMOC,具有任意天线配置的总和(DoF),特别是将RIS成形、传送零推进和干扰解码结合在一起,以对付干扰问题;为了最大限度地增加可实现的总量-DoF,形成了一个整数的优化问题,以优化RIS成型的干扰连接次数;因此,由此得出的可实现的总和F可以高于两个用户IMO的双用户的合成-DF,从而获得RIS的收益;此外,作为RIS数的天线之间的配置,还赋予了RIS获得的充足条件。