Pilot contamination (PC) is a practical drawback of massive multiple-input multiple-output (mMIMO) systems. It prevents the exploitation of the inherent spectral-efficiency (SE) of mMIMO systems, especially in dense networks. In this letter, we consider multi-antenna users in a multi-cell network and propose a novel approach based on interference alignment (IA) to remove PC. We show that the extra degrees of freedom (DoFs), provided by multi-antennas at the users’ side, can be used efficiently when employed for pilot decontamination, especially in heavy-loaded networks. Thus, while the intra-cell interference is removed due to the properties of mMIMO the out-of-cell interference is eliminated by the proposed IA-based pilot decontamination. The proposed algorithm uses linear zero-forcing (ZF) and needs no continuous cooperation between the base stations (BSs). Moreover, the users need no channel state information (CSI). Our simulations show that the proposed method outperforms the conventional PC precoding algorithms significantly, particularly in heavy-loaded networks.

中文翻译：

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使用干扰对齐的大规模 MIMO 系统中的导频去污

导频污染 (PC) 是大规模多输入多输出 (mMIMO) 系统的实际缺陷。它可以防止利用 mMIMO 系统固有的频谱效率 (SE)，尤其是在密集网络中。在这封信中，我们考虑了多小区网络中的多天线用户，并提出了一种基于干扰对齐 (IA) 的新方法来去除 PC。我们表明，用户侧多天线提供的额外自由度 (DoF) 在用于导频去污时可以有效地使用，尤其是在重负载网络中。因此，虽然由于 mMIMO 的特性而消除了小区内干扰，但建议的基于 IA 的导频去污消除了小区外干扰。所提出的算法使用线性迫零（ZF）并且不需要基站（BS）之间的连续协作。此外，用户不需要信道状态信息（CSI）。我们的模拟表明，所提出的方法明显优于传统的 PC 预编码算法，特别是在重负载网络中。