Massive multiple-input-multiple-output (M-MIMO) is a key technology for 5G networks. Within this research area, new types of deployment are arising, such as the extremely-large regime (XL-MIMO), where the antenna array at the base station (BS) has extreme dimensions. As a consequence, spatial non-stationary properties appear as the users see only a portion of the antenna array, which is called visibility region (VR). In this challenging transmission–reception scenario, an algorithm to select the appropriate antenna-elements for processing the received signal of a given user in the uplink (UL), as well as to transmit the signal of this user during downlink (DL) is proposed. The advantage of not using all the available antenna-elements at the BS is the computational burden and circuit power consumption reduction, improving the energy efficiency (EE) substantially. Numerical results demonstrate that one can increase the EE without compromising considerably the spectral efficiency (SE). Under few active users scenario, the performance of the XL-MIMO system shows that the EE is maximized using less than 20% of the antenna-elements of the array, without compromising the SE severely.

大规模多输入多输出（M-MIMO）是5G网络的一项关键技术。在这个研究领域内，出现了新的部署类型，例如超大型方案（XL-MIMO），其中基站（BS）的天线阵列具有极端的尺寸。结果，当用户仅看到天线阵列的一部分时，就会出现空间非平稳特性，这就是可见性区域（VR）。在这种具有挑战性的收发场景中，提出了一种算法，该算法选择适当的天线元件来处理上行链路（UL）中给定用户的接收信号，以及在下行链路（DL）中发送该用户的信号。在BS处不使用所有可用天线元件的优点是计算量大，电路功耗降低，大幅提高能源效率（EE）。数值结果表明，可以提高EE而不会大幅降低频谱效率（SE）。在极少活跃用户的情况下，XL-MIMO系统的性能表明，使用不到阵列天线元件的20％即可最大化EE，而不会严重损害SE。