This paper studies the device activity detection problem in a multi-cell massive multiple-input multiple-output (MIMO) system, in which the active devices transmit signature sequences to multiple base stations (BSs) that are connected to a central unit (CU), and the BSs cooperate across multiple cells to detect the active devices based on the sample covariance matrices at the BSs. This paper demonstrates the importance of exploiting the knowledge of channel large-scale fadings in this cooperative detection setting through a phase transition analysis, which characterizes the length of signature sequences needed for successful device activity detection in the massive MIMO regime. It is shown that when the large-scale fadings are known, the phase transition for the multi-cell scenario is approximately the same as that of a single-cell system. In this case, the length of the signature sequences required for reliable activity detection in the multi-cell system can be made to be independent of the number of cells through cooperation, in contrast to the case where the large-scale fadings are not known. Further, this paper considers the case in which the fronthaul links between the BSs and the CU have capacity constraints and proposes a novel cooperation scheme based on the quantization of preliminary detection results at the BSs and the reconstruction of the sample covariance matrices at the CU. Simulations show that the proposed method significantly outperforms the scheme of directly quantizing the sample covariance matrices.

中文翻译：

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利用信道大规模衰落的多小区大规模 MIMO 中的稀疏活动检测


本文研究了多小区大规模多输入多输出 (MIMO) 系统中的设备活动检测问题，其中活动设备将签名序列传输到连接到中央单元 (CU) 的多个基站 (BS) ，并且BS跨多个小区协作以基于BS处的样本协方差矩阵来检测有源设备。本文通过相变分析证明了在这种协作检测设置中利用信道大规模衰落知识的重要性，相变分析描述了大规模 MIMO 体制中成功检测设备活动所需的签名序列的长度。结果表明，当大规模衰落已知时，多小区场景的相变与单小区系统的相变大致相同。在这种情况下，与大规模衰落未知的情况相反，通过协作可以使多小区系统中可靠的活动检测所需的签名序列的长度与小区的数量无关。此外，本文考虑了BS和CU之间的前传链路具有容量限制的情况，并提出了一种基于BS处初步检测结果的量化和CU处样本协方差矩阵重建的新型协作方案。仿真结果表明，该方法明显优于直接量化样本协方差矩阵的方案。