全双工无线回传UDN中的空域信号传输优化

Ultra-dense network (UDN) enhances system capacity and coverage significantly via the highly dense deployment of small base stations in hotspots. Since the small base stations are densely deployed in UDN, wireless backhauling can be an efficient solution in terms of lowering the cost and improving the flexibility of establishing UDN. The conventional wireless backhauling operates under the half-duplex mechanism, which does not fully exploit available time-frequency resources. In order to improve system spectrum efficiency, researchers have recently advocated novel wireless backhauling assisted by full-duplex transmission techniques. In this proposal, concerning the UDN adopting full-duplex wireless backhauls and multiple-input multiple-output (MIMO) technologies, we aim to conduct an in-depth study from the perspective of spatial-domain signal transmission optimization. Thus far, many valuable theoretical and practical problems regarding this topic still remain unsolved. We first investigate robust MIMO transceiver optimization for full-duplex wireless backhauled UDN by incorporating channel state information (CSI) errors and transmitted/received signal distortions. Furthermore, we introduce advanced millimeter wave (mmWave) massive MIMO techniques, and optimize MIMO transmission schemes with the emphasis on reducing hardware power consumptions and costs, where the sparsity of mmWave channels is also leveraged during the optimization. Finally, based upon the above work, we consider system energy efficiency oriented MIMO transceiver optimization.

超密集网络（UDN）技术通过在热点区域高密度部署小基站，显著提升系统容量以及覆盖能力。鉴于UDN中小基站密集分布的特点，采用无线回传能够有效降低组网成本并提高组网灵活度。传统无线回传建立在半双工机制上，并不能充分利用时频资源。为了提高系统频谱效率，最近研究人员提出基于全双工传输技术的新型无线回传方案。本课题将针对采用全双工无线回传的UDN，结合多输入多输出（MIMO）技术，从空域信号传输优化的角度展开深入研究。该研究方向目前尚存在大量重要的理论和实际问题未被解决。首先，结合实际系统中存在的信道状态信息（CSI）误差以及发射/接收信号畸变，探讨全双工无线回传UDN中的鲁棒MIMO收发机优化。进而，引入先进的毫米波（mmWave）大规模MIMO技术，以降低硬件功耗和成本为切入点，并利用毫米波信道的稀疏性优化MIMO传输方案。最后，在以上研究工作基础上，探究面向系统能量效率的MIMO收发机优化。

本项目围绕全双工无线回传超密集网络（UDN），通过融入信道状态信息（CSI）误差以及发射/接收信号畸变等实际因素，探讨高效的多输入多输出（MIMO）空域传输理论和方法。具体而言，从全双工中继MIMO传输技术入手，首先研究了对于CSI误差具有鲁棒性的全双工中继波束成形设计，提高系统在非理想CSI下的可达速率性能。进而，理论分析了全双工中继系统的能量效率性能，并提出了最大化能量效率的传输方法，以较低的复杂度逼近最优性能。进一步地，为了降低全双工中继MIMO节点所需的功耗，避免中继自干扰导致的系统性能损失，在上述研究工作的基础上研究了可重构智能表面（RIS）辅助的MIMO传输技术。针对该技术，首先研究了理想条件下的RIS辅助MIMO波束成形设计，显著提升传统MIMO系统的安全速率以及和速率性能。进而，探讨了对于信号畸变具有鲁棒性的RIS辅助MIMO波束成形设计，降低了信号畸变对系统误符号率性能的影响。最后，针对面向毫米波频段的宽带RIS通信系统，提出了低计算开销的波束成形方案，以获得优异的可达速率性能。本项目的研究成果为全双工无线回传在UDN中的应用提供了理论和技术支撑。