Hybrid adaptive Beamforming Systems using programmable Metasurfaces

为了应对移动通信网络中不断增长的数据流量，到2020年，移动通信网络中的数据流量将超过每年约335艾字节，缩小小区大小是一个持续的过程。现代的小蜂窝，典型的范围从10米到几百米，实现了高频谱重用，从而为每个用户提供了更高的带宽。因此，由于这些基站的密集布置，干扰问题变得越来越严重。此外，对于那些小蜂窝场景，例如在城市地区，对廉价、紧凑和节能的移动基站的需求也很大。为了应对这些挑战，我们引入了一种混合自适应波束形成系统，它使我们能够结合紧凑和负担得起的硬件来实现高频谱效率。该联合项目的主要目标是研究由多个数字通道和可编程元表面组成的混合自适应波束形成系统。高天线方向性和减少硬件工作量只是我们预测的两个好处。现代无线通信系统利用多输入多输出(MIMO)配置来提高容量和信号覆盖。最近的研究表明，对于第五代移动通信(5G)和以后的移动通信，毫米波频段将被视为满足客户对更高数据速率的需求。在使用更高的载波频率以获得更大带宽的同时，必须克服由此产生的自由空间路径损耗，这导致天线单元的数量增加，从而导致数字信道的数量增加。理论上，每个数字通道允许使用一个特定子通道，这可以极大地提高最大数据速率。然而，每个数字通道都需要自己的模拟前端或后端和一个强大的模数转换器(或发射机现场的数模转换器)，这导致了庞大而昂贵的设置。此外，数字信号处理器中的计算工作量随着每增加一个通道而增加，导致系统的高能量消耗。构建更紧凑和高效的系统的一种解决方案是形成由多个数字通道和一个模拟相移单元组成的混合波束形成系统，如所示。通过利用SEU提出的可编程元表面，天线的这种转向也可以被整合到系统概念中。由此得到的混合波束形成系统可以实现高方向性，同时仍然提供足够数量的数字信道以供应多个用户或增加单个用户的信道容量。根据实际情况，减少的数字信道数量对通信网络的整体性能没有负面影响。因此，比较纯数字波束形成系统和混合波束形成系统的性能是本文的主要研究目标之一。

To handle the growing data traffic in mobile communication networks, which will exceed roughly 335 Exabytes per year by 2020, the reduction of cell size is an ongoing process. Modern small cells, with a typical range from 10 meters to several hundred meters, enable a high spectral reuse and thus provide a much higher bandwidth per user. Hence, due to the dense arrangement of these base stations interference becomes more and more a problem. Furthermore, there is an enormous demand on cheap, compact and energy efficient mobile base stations for those small cell scenarios, for example in urban areas. To target upon these challenges, we introduce a hybrid adaptive beamforming system, which empowers us to achieve high spectral efficiency in combination with a compact and affordable hardware. The main objective of the joint project is the research on hybrid adaptive beamforming systems consisting of several digital channels in conjunction with programmable metasurfaces. A high antenna directivity as well as a reduction in hardware effort are only two of the benefits we predict.Modern wireless communication systems utilize a Multiple Input Multiple Output (MIMO) configuration to improve capacity and signal coverage. Recent studies have shown that for the fifth generations of mobile communication (5G) and beyond mmWave bands will be considered to satisfy the customer's demands on higher data rates. While going to higher carrier frequencies to obtain larger bandwidths the resulting free space path loss has to be overcome what leads to an increasing number of antenna elements and therefore digital channels. In theory, each digital channel enables the use of one particular subchannel, which can highly improve the maximum data rate. However, each digital channel needs its own analog front- or backend and a powerful analog-to-digital converter (or digital-to-analog converter at the transmitter site), which result in a large and expensive setup. Furthermore, the calculation effort in the digital signal processor increases with every added channel resulting in a high energy consumption of the system.One solution to build a more compact and efficient system is to form a hybrid beamforming system consisting of multiple digital channels in conjunction with an analog phase shifting unit as shown in. This steering of the antenna can also be integrated into the system concept by utilizing programmable metasurfaces as presented by SEU. The resulting hybrid beamforming system can achieve a high directivity, while still providing a sufficient number of digital channels to supply multiple users or to increase the channel capacity for a single user. The reduced number of digital channels has, depending on the practical scenario, no negative effects on the overall performance of the communication network. The performance comparison between the purely digital beamforming system and the hybrid approach is therefore one of the main research objectives.