标题： 近场全息MIMO在莱斯衰落信道下的谱效率分析 显示英文标题

标题： Spectral Efficiency Analysis of Near-Field Holographic MIMO over Ricean Fading Channels

摘要： 随着天线阵元分布的密集化，天线阵元之间的互耦效应会增强，这最终会影响通信性能。同时，由于全息阵列通常具有较大的物理尺寸，近场通信的可能性增加。 本文研究了一种近场多用户下行HMIMO系统，并在莱斯衰落信道下表征了谱效率（SE），考虑了互耦效应。两种情况都被考虑：完美信道状态信息（CSI）和非完美信道状态信息。 (i) 对于完美CSI的情况，首先建立了互耦和辐射效率模型。然后，在最大比传输（MRT）下推导出闭式SE。通过比较存在和不存在互耦情况下的SE，揭示了对于给定孔径大小，在低发射功率情况下，存在互耦的系统SE可能会优于不存在互耦的情况。此外，还揭示了除非阵列的物理尺寸增加到无穷大，否则无法消除用户间干扰。幸运的是，近场信道中的附加距离项可以用于用户间干扰抑制，特别是在最坏的情况下，用户的角位置重叠较多。 (ii) 对于非完美CSI的情况，在MRT下推导闭式SE时考虑了信道估计误差。结果显示，在低发射功率情况下，通过提高导频功率和增加天线阵元密度可以提升系统SE，而后者会导致严重的互耦。在高发射功率情况下，增加导频功率对提高系统SE的效果有限。然而，增加天线阵元密度仍然对提高系统SE非常有益。 显示英文摘要

摘要： With the denser distribution of antenna elements, stronger mutual coupling effects would kick in among antenna elements, which would eventually affect the communication performance. Meanwhile, as the holographic array usually has large physical size, the possibility of near-field communication increases. This paper investigates a near-field multi-user downlink HMIMO system and characterizes the spectral efficiency (SE) under the mutual coupling effect over Ricean fading channels. Both perfect and imperfect channel state information (CSI) scenarios are considered. (i) For the perfect CSI case, the mutual coupling and radiation efficiency model are first established. Then, the closed-form SE is derived under maximum ratio transmission (MRT). By comparing the SE between the cases with and without mutual coupling, it is unveiled that the system SE with mutual coupling might outperform that without mutual coupling in the low transmit power regime for a given aperture size. Moreover, it is also unveiled that the inter-user interference cannot be eliminated unless the physical size of the array increases to infinity. Fortunately, the additional distance term in the near-field channel can be exploited for the inter-user interference mitigation, especially for the worst case, where the users' angular positions overlap to a great extent. (ii) For the imperfect CSI case, the channel estimation error is considered for the derivation of the closed-form SE under MRT. It shows that in the low transmit power regime, the system SE can be enhanced by increasing the pilot power and the antenna element density, the latter of which will lead to severe mutual coupling. In the high transmit power regime, increasing the pilot power has a limited effect on improving the system SE. However, increasing the antenna element density remains highly beneficial for enhancing the system SE.