Massive machine-type communications protocols have typically been designed under the assumption that coordination between users requires significant communication overhead and is thus impractical. Recent progress in efficient activity detection and collision-free scheduling, however, indicates that the cost of coordination can be much less than the naive scheme for scheduling. This work considers a scenario in which a massive number of devices with sporadic traffic seek to access a massive multiple-input multiple-output (MIMO) base-station (BS) and explores an approach in which device activity detection is followed by a single common feedback broadcast message, which is used both to schedule the active users to different transmission slots and to assign orthogonal pilots to the users for channel estimation. The proposed coordinated communication scheme is compared to two prevalent contention-based schemes: coded pilot access, which is based on the principle of coded slotted ALOHA, and an approximate message passing scheme for joint user activity detection and channel estimation. Numerical results indicate that scheduled massive access provides significant gains in the number of successful transmissions per slot and in sum rate, due to the reduced interference, at only a small cost of feedback.

中文翻译：

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大规模 MIMO 系统中大规模随机接入的调度与竞争

大规模机器类型的通信协议通常是在用户之间的协调需要大量通信开销并因此不切实际的假设下设计的。然而，最近在高效活动检测和无冲突调度方面取得的进展表明，协调成本可能远低于简单的调度方案。这项工作考虑了这样一种场景，即大量具有零星流量的设备寻求访问大规模多输入多输出 (MIMO) 基站 (BS)，并探索了一种方法，其中设备活动检测后跟单个常见的反馈广播消息，用于将活动用户调度到不同的传输时隙，并为用户分配正交导频以进行信道估计。所提出的协调通信方案与两种流行的基于竞争的方案进行了比较：编码导频接入，它基于编码时隙 ALOHA 的原理，以及用于联合用户活动检测和信道估计的近似消息传递方案。数值结果表明，由于减少了干扰，调度的大规模接入在每个时隙的成功传输数量和总速率方面提供了显着的收益，而且反馈成本很低。