Wireless surveillance, in which untrusted communications links are proactively monitored by legitimate agencies, has started to garner a lot of interest for enhancing the national security. In this paper, we propose a new cell-free massive multiple-input multiple-output (CF-mMIMO) wireless surveillance system, where a large number of distributed multi-antenna aided legitimate monitoring nodes (MNs) embark on either observing or jamming untrusted communication links. To facilitate concurrent observing and jamming, a subset of the MNs is selected for monitoring the untrusted transmitters (UTs), while the remaining MNs are selected for jamming the untrusted receivers (URs). We analyze the performance of CF-mMIMO wireless surveillance and derive a closed-form expression for the monitoring success probability of MNs. We then propose a greedy algorithm for the observing vs, jamming mode assignment of MNs, followed by the conception of a jamming transmit power allocation algorithm for maximizing the minimum monitoring success probability concerning all the UT and UR pairs based on the associated long-term channel state information knowledge. In conclusion, our proposed CF-mMIMO system is capable of significantly improving the performance of the MNs compared to that of the state-of-the-art baseline. In scenarios of a mediocre number of MNs, our proposed scheme provides an 11-fold improvement in the minimum monitoring success probability compared to its co-located mMIMO benchmarker.

翻译：无线监控是一种由合法机构主动监控不可信通信链路的技术，近年来为提升国家安全而备受关注。本文提出了一种新型无蜂窝大规模多输入多输出(CF-mMIMO)无线监控系统，其中大量分布式多天线辅助的合法监控节点(MNs)可对不可信通信链路执行观测或干扰操作。为实现同步观测与干扰，部分MN被选为监控不可信发射机(UTs)，其余MN则被选为干扰不可信接收机(URs)。我们分析了CF-mMIMO无线监控系统的性能，推导了MN监控成功概率的闭式表达式。随后提出了一种用于MN观测/干扰模式分配的贪婪算法，并设计了基于长期信道状态信息的干扰发射功率分配算法，以最大化所有UT-UR对的最小监控成功概率。研究表明，与现有基线方案相比，所提出的CF-mMIMO系统能显著提升MN性能。在中等规模MN场景下，与共置式mMIMO基准系统相比，本方案的最小监控成功概率提升了11倍。