The purpose of the study is to investigate potential benefits of using Alamouti-like orthogonal space-time-frequency block codes (STFBC) in distributed multiple-input multiple-output (D-MIMO) systems to increase the diversity at the UE side when instantaneous channel state information (CSI) is not available at radio units (RUs). Most of the existing transmission techniques require instantaneous CSI to form precoders which can only be realized together with accurate and up-to-date channel knowledge. STFBC can increase the diversity at UE side without estimating the downlink channel. Under challenging channel conditions, the network can switch to a robust mode where a certain data rate is maintained for users even without knowing the channel coefficients by means of STFBC. In this study, it will be mainly focused on clustering of RUs and user equipment, where each cluster adopts a possibly different orthogonal code, so that overall spectral efficiency is optimized. Potential performance gains over known techniques that can be used when the channel is not known will be shown and performance gaps to sophisticated precoders making use of channel estimates will be identified.

翻译：本研究旨在探讨在分布式多输入多输出（D-MIMO）系统中采用类Alamouti正交空时频分组码（STFBC）的潜在优势，以在无线单元（RU）无法获取瞬时信道状态信息（CSI）的情况下提升用户设备（UE）侧的分集增益。现有大多数传输技术需要利用瞬时CSI设计预编码器，而这仅能通过精确且实时的信道知识实现。STFBC可在无需估计下行链路的情况下提升UE侧分集增益。在恶劣信道条件下，网络可切换至鲁棒模式，通过STFBC在未知信道系数的条件下仍能为用户维持特定数据速率。本研究重点聚焦于无线单元与用户设备的聚类方法，每个聚类可采用不同的正交码，从而优化整体频谱效率。将展示相较于现有未知信道条件下的技术所获得的潜在性能增益，并明确与采用信道估计的复杂预编码器之间的性能差距。