Millimeter wave (mmWave) communication is expected to play a central role in next generation mobile systems (5G) and beyond, by providing multi-Gbps data rates. However, the severe pathloss and sensitivity to blockages at mmWave frequencies significantly challenge practical implementations. One effective way to mitigate these effects and to increase the communication range is beamforming in combination with relaying. In this paper, we study the beam scheduling problem for mmWave half-duplex (HD) relay networks, where the relay topology can be arbitrary. Based on theoretically optimal scheduling results, we first implement a network simplification procedure to reduce the network topology complexity, and then propose two practically relevant beam scheduling schemes: the deterministic edge coloring (EC) scheduler and the adaptive backpressure (BP) scheduler. The former consists of a very simple one-time computation of the sequence of scheduling states, which is then repeated periodically. The one-time computation depends on the underlying network topology, and therefore it must be repeated when such topology changes. As such, this approach is more suited to quasi-static scenarios. The latter is an “online” approach which updates scheduling weights and solves at each time slots a weighted sum rate maximization. Hence, it's computational complexity may be significantly higher than that of EC, but it is better suited to dynamic time-varying scenarios. With the aid of computer simulations, we show that both the proposed schedulers guarantee network stability within the network capacity. Particularly, in comparison with two baseline schemes, the proposed schedulers achieve much smaller queuing backlogs, much smaller backlog fluctuations, and much lower packet end-to-end delays.

中文翻译：

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半双工毫米波中继网络的高效波束调度


通过提供数 Gbps 的数据速率，毫米波 (mmWave) 通信预计将在下一代移动系统 (5G) 及更高版本中发挥核心作用。然而，毫米波频率下严重的路径损耗和对阻塞的敏感性对实际实施提出了重大挑战。减轻这些影响并增加通信范围的一种有效方法是将波束成形与中继相结合。在本文中，我们研究了毫米波半双工（HD）中继网络的波束调度问题，其中中继拓扑可以是任意的。基于理论上的最优调度结果，我们首先实现网络简化过程以降低网络拓扑复杂性，然后提出两种实际相关的波束调度方案：确定性边缘着色（EC）调度器和自适应背压（BP）调度器。前者由调度状态序列的非常简单的一次性计算组成，然后定期重复。一次性计算取决于底层网络拓扑，因此当拓扑发生变化时必须重复计算。因此，这种方法更适合准静态场景。后者是一种“在线”方法，它更新调度权重并在每个时隙求解加权和速率最大化。因此，它的计算复杂度可能明显高于EC，但它更适合动态时变场景。借助计算机模拟，我们表明所提出的两种调度器都保证了网络容量内的网络稳定性。特别是，与两种基线方案相比，所提出的调度器实现了更小的排队积压、更小的积压波动和更低的数据包端到端延迟。