Due to the severe pathloss experienced by electromagnetic waves in the millimeter wave (mmWave) band, a substantial challenge in their design is to have an adequate coverage area. With the objective of improving the coverage area and the sum rate attained, we conceive new full-duplex (FD) mmWave multiple-input multiple-output (MIMO) multiple-relay systems. Specifically, we propose a novel two-timescale analog-digital hybrid beamforming scheme for maximizing the sum rate, while reducing the system’s complexity and the channel state information (CSI) signalling overhead, as well as mitigating both the effects of self-interference and that of outdated CSIs caused by the associated delays. In the proposed scheme, the long-timescale analog beamforming matrices are designed based on the available channel statistics and updated in a frame-based manner, where a frame contains a fixed number of time slots. By contrast, the short-timescale digital beamforming matrices are optimized more frequently – namely for each time slot – based on the low-dimensional effective CSI matrices available on a real-time basis. We develop both an efficient analog beamforming algorithm based on the cut-set bound as well as on stochastic successive convex approximation (SSCA) and an innovative digital beamforming algorithm that relies on the theory of penalty dual decomposition (PDD), where our design objective is to maximize the system’s sum rate. Both the convergence properties and the computational complexity of the proposed algorithms are also examined. Our simulation results show that the proposed two-timescale hybrid beamforming design significantly outperforms the conventional beamformers both in terms of requiring a lower CSI-signalling overhead and a higher sum rate in the face of realistic outdated CSIs.

中文翻译：

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用于毫米波全双工 MIMO 多中继辅助系统的两时间尺度混合模拟-数字波束成形

由于毫米波 (mmWave) 频段中的电磁波会经历严重的路径损耗，因此其设计中的一个重大挑战是拥有足够的覆盖区域。为了提高覆盖区域和达到的总速率，我们构思了新的全双工 (FD) 毫米波多输入多输出 (MIMO) 多中继系统。具体来说，我们提出了一种新颖的双时间尺度模拟-数字混合波束成形方案，用于最大化总速率，同时降低系统的复杂性和信道状态信息 (CSI) 信令开销，以及减轻自干扰的影响和由相关延迟引起的过时 CSI。在所提出的方案中，基于可用信道统计数据设计长时标模拟波束成形矩阵，并以基于帧的方式更新，其中一帧包含固定数量的时隙。相比之下，基于实时可用的低维有效 CSI 矩阵，更频繁地优化短时间尺度数字波束成形矩阵（即针对每个时隙）。我们开发了一种基于割集边界和随机逐次凸逼近 (SSCA) 的高效模拟波束成形算法，以及一种依赖于惩罚对偶分解 (PDD) 理论的创新数字波束成形算法，我们的设计目标是以最大化系统的总和率。还检查了所提出算法的收敛特性和计算复杂度。