In this study, a new approach of random access and pilot allocation in crowded scenarios of massive multi-input multi-output (MIMO) systems is proposed. When the number of users in a cell is more than number of orthogonal pilots, random access to pilots (RAP) is a promising solution to solve the massive access problem of users; though the collision of pilots is a by-product of this method. There are several methods for pilot collision resolution such as strongest user collision resolution (SUCR), but they have one major limitation; i.e. they cannot serve users more than the number of orthogonal pilots simultaneously in coherent transmission mode. In this paper, angle of arrival (AOA) and angular spread (AS) of the received pilots in a compressed sensing approach are examined by applying sparsity of massive MIMO channels in angular domain. That allows to allocate same orthogonal pilot to non-overlapped users in spatial domain for coherent data transmission. By applying this approach in newly proposed protocol (SBPA), the limitation in number of adopted simultaneous users in crowded scenarios of a massive MIMO system would be resolved. Numerical results show improvement in access failures rate compared to SUCR in crowded massive MIMO systems.

在这项研究中，提出了一种在拥挤的大规模多输入多输出（MIMO）系统场景中进行随机访问和导频分配的新方法。当一个小区中的用户数量大于正交导频数量时，随机接入导频（RAP）是解决用户大规模接入问题的有前途的解决方案。尽管飞行员的碰撞是这种方法的副产品。有几种解决飞行员冲突的方法，例如最强的用户冲突解决方案（SUCR），但是它们有一个主要的局限性。即在相干传输模式下，它们不能同时为用户提供超过正交导频数目的服务。在本文中，通过在角域中应用大规模MIMO信道的稀疏性，研究了压缩感测方法中接收到的导频的到达角（AOA）和角扩展（AS）。这允许将相同的正交导频分配给空间域中的非重叠用户以进行相干数据传输。通过在新提议的协议（SBPA）中应用此方法，将解决大规模MIMO系统拥挤情况下同时采用的用户数量的限制。数值结果表明，在拥挤的大规模MIMO系统中，与SUCR相比，访问失败率有所提高。