Recently, the first version of the fifth-generation (5G) new radio (NR) standard with massive multiple-input multiple-output (MIMO) has been finished by the 3rd Generation Partnership Project (3GPP), with initial deployments occurring in 2018. Despite the major advances in 5G, there are still many challenges remaining. 6G and beyond will require even higher data rates, lower latencies, better energy efficiency, and improved robustness. Multiple antenna technologies, which have played important roles in nearly all recent wireless standards, will be key to addressing these challenges. MIMO research continues to evolve, and new MIMO research topics such as enhanced massive MIMO techniques and array architectures hold much potential for 6G and beyond. Cell-free massive MIMO utilize a large number of distributed access points (APs) that jointly serve users in a coordinated fashion, using only local channel state information at each AP. While the performance of cell-free massive MIMO can be analyzed using a similar methodology as in cellular massive MIMO, the fundamental limits, signal processing, and resource allocation are substantially different. In order to reduce the hardware cost and energy consumption in millimeter wave (mmWave) massive MIMO systems, beamspace MIMO has been proposed to significantly reduce the number of required radio-frequency (RF) chains by using lens antenna arrays or phase shifters. Alternatively, the intelligent reflecting surface (IRS) concept involves electromagnetically controllable surfaces that can be integrated into large-scale infrastructure such as building walls, airports, and stadiums. There are active and partially passive forms of large intelligent surface (LIS), and variants with either large antenna spacing or continuous aperture. There are also some substantial differences between the new multiple antenna technologies and traditional MIMO systems, such as transceiver design and propagation models. This special issue aims to highlight recent research on multiple antenna technologies.

中文翻译：

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超越 5G 的多天线技术客座社论特刊——第一部分

近日，第三代合作伙伴计划（3GPP）完成了具有大规模多输入多输出（MIMO）的第五代（5G）新无线电（NR）标准的第一版，并于2018年进行了初步部署。尽管 5G 取得了重大进展，但仍然存在许多挑战。6G 及更高版本将需要更高的数据速率、更低的延迟、更高的能效和更高的稳健性。多天线技术在几乎所有最近的无线标准中都发挥了重要作用，将成为解决这些挑战的关键。MIMO 研究不断发展，新的 MIMO 研究主题（例如增强型大规模 MIMO 技术和阵列架构）对 6G 及更高版本具有很大潜力。无蜂窝大规模 MIMO 利用大量分布式接入点 (AP)，这些接入点以协调方式共同为用户提供服务，每个 AP 仅使用本地信道状态信息。虽然可以使用与蜂窝大规模 MIMO 类似的方法来分析无蜂窝大规模 MIMO 的性能，但基本限制、信号处理和资源分配却大不相同。为了降低毫米波 (mmWave) 大规模 MIMO 系统的硬件成本和能耗，已经提出波束空间 MIMO，以通过使用透镜天线阵列或移相器来显着减少所需的射频 (RF) 链的数量。或者，智能反射面 (IRS) 概念涉及电磁可控表面，可以将其集成到大型基础设施中，例如建筑墙体、机场和体育场。有大智能表面 (LIS) 的主动和部分被动形式，以及具有大天线间距或连续孔径的变体。新的多天线技术与传统 MIMO 系统之间也存在一些实质性差异，例如收发器设计和传播模型。本期特刊旨在重点介绍多天线技术的最新研究。新的多天线技术与传统 MIMO 系统之间也存在一些实质性差异，例如收发器设计和传播模型。本期特刊旨在重点介绍多天线技术的最新研究。新的多天线技术与传统 MIMO 系统之间也存在一些实质性差异，例如收发器设计和传播模型。本期特刊旨在重点介绍多天线技术的最新研究。