Future wireless networks need to support massive machine type communication (mMTC) where a massive number of devices accesses the network and massive MIMO is a promising enabling technology. Massive access schemes have been studied for co-located massive MIMO arrays. In this paper, we investigate the activity detection in grant-free random access for mMTC in cell-free massive MIMO networks using distributed arrays. Each active device transmits a non-orthogonal pilot sequence to the access points (APs) and the APs send the received signals to a central processing unit (CPU) for joint activity detection. The maximum likelihood device activity detection problem is formulated and algorithms for activity detection in cell-free massive MIMO are provided to solve it. The simulation results show that the macro diversity gain provided by the cell-free architecture improves the activity detection performance compared to co-located architecture when the coverage area is large.

中文翻译：

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无小区大规模 MIMO 中无授权随机接入的基于聚类的活动检测算法


未来的无线网络需要支持大规模机器类型通信（mMTC），其中大量设备访问网络，而大规模 MIMO 是一项有前途的支持技术。针对共置大规模 MIMO 阵列的大规模接入方案已进行了研究。在本文中，我们研究了使用分布式阵列的无小区大规模 MIMO 网络中 mMTC 的无授权随机接入的活动检测。每个有源设备将非正交导频序列发送到接入点（AP），并且AP将接收到的信号发送到中央处理单元（CPU）以用于联合活动检测。阐述了最大似然设备活动检测问题，并提供了无小区大规模 MIMO 中的活动检测算法来解决该问题。仿真结果表明，当覆盖区域较大时，与共址架构相比，无小区架构提供的宏分集增益提高了活动检测性能。