In this paper, we mainly study how to improve the secure transmission performance of cell-free massive multiple-input multiple-output (MIMO) systems by using location technology. In cell-free massive MIMO systems, active pilot attacks will contaminate the uplink channel estimation and affect the downlink precoding of access points (APs). In order to effectively reduce the impact of active pilot attacks on user transmission, this paper respectively proposes an user location estimation method based on fingerprint positioning and a channel estimation algorithm based on location information. Firstly, under the imperfect channel state information, the location information of users and eavesdropper is obtained by using fingerprint positioning method and K-means clustering algorithm. Then, combined with location information, AP selection strategy and channel estimation method based on non-overlapping angle of arrival (AOA) criterion are proposed respectively. Based on the location information of users and eavesdropper, we use discrete Fourier transform (DFT) to distinguish the uplink channels of legitimate user and eavesdropper from the angle domain, thus eliminating the pilot contamination caused by active pilot attacks. The results show that compared with the traditional transmission method, the proposed secure transmission strategy can increase the secrecy rate of up to 2 b/s/Hz, which effectively enhances the secure transmission performance of cell-free massive MIMO in strong interference environment.

中文翻译：

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无细胞大规模MIMO系统中基于指纹定位的安全传输方案

在本文中，我们主要研究如何利用定位技术提高无蜂窝大规模多输入多输出（MIMO）系统的安全传输性能。在无蜂窝大规模 MIMO 系统中，主动导频攻击会污染上行信道估计并影响接入点 (AP) 的下行预编码。为了有效降低主动导频攻击对用户传输的影响，本文分别提出了一种基于指纹定位的用户位置估计方法和一种基于位置信息的信道估计算法。首先，在信道状态信息不完善的情况下，利用指纹定位方法和K-means聚类算法得到用户和窃听者的位置信息。然后结合位置信息，分别提出了基于非重叠到达角(AOA)准则的AP选择策略和信道估计方法。基于用户和窃听者的位置信息，我们使用离散傅里叶变换（DFT）从角度域区分合法用户和窃听者的上行信道，从而消除主动导频攻击造成的导频污染。结果表明，与传统传输方法相比，所提出的安全传输策略可以提高高达2 b/s/Hz的保密率，有效提升了强干扰环境下无蜂窝Massive MIMO的安全传输性能。基于用户和窃听者的位置信息，我们使用离散傅里叶变换（DFT）从角度域区分合法用户和窃听者的上行信道，从而消除主动导频攻击造成的导频污染。结果表明，与传统传输方法相比，所提出的安全传输策略可以提高高达2 b/s/Hz的保密率，有效提升了强干扰环境下无蜂窝Massive MIMO的安全传输性能。基于用户和窃听者的位置信息，我们使用离散傅里叶变换（DFT）从角度域区分合法用户和窃听者的上行信道，从而消除主动导频攻击造成的导频污染。结果表明，与传统传输方法相比，所提出的安全传输策略可以提高高达2 b/s/Hz的保密率，有效提升了强干扰环境下无蜂窝Massive MIMO的安全传输性能。