Effects of Digital Precoding Schemes on Performance of Holographic MIMO Systems

Multiple-input multiple-output (MIMO) has made significant contributions to the improvement of system performance. To support increasing connection density, it is promising to deploy more antenna elements with closer spacing on the MIMO array, which is called holographic multiple-input multiple-output (HMIMO). Due to the inevitable coupling effects in HMIMO systems, it needs to determine whether digital pre-coding can bring performance gains as it did in MIMO systems. In this paper, the system performance of HMIMO systems is investigated based on different digital precoding schemes. Moreover, a radio channel model is utilized to analyze the signal propagation process of HMIMO systems and the antenna coupling effects are considered. Six common digital precoding schemes for HMIMO systems are proposed and the sum rate based on these digital precoding schemes is analyzed. The results show that when the antenna array element density increases, the coupling effect plays a significant role and cannot be eliminated by digital precoding. Hence, digital precoding schemes cannot offer performance improvements in HMIMO systems.