Large Scale Antenna Systems Made Practical: Advanced Signal Processing for Compact Deployments [LSAS-SP]

本计画研究讯号处理技术，以实际及现实的方式实现大规模天线系统（LSAS）的高能效及频谱无线通讯。预计到2015年，蜂窝网络的能源账单将翻一番，因此人们越来越关注减少相关的运营支出（OPEX）以及所有通信领域的全球二氧化碳排放。无线通信物理层是电信系统链的核心组成部分，日益增长的服务质量需求直接反映在对相关信号处理技术的性能要求上。无线传播的物理限制形成了物理层传输的瓶颈。多输入多输出（MIMO）系统通过在物理通道中提供更多的数据流，已被证明在规避这一瓶颈方面特别有用。小规模MIMO系统目前是通信标准和商业设计的一部分。LSAS被设想用于下一代无线系统，利用多天线，并以节能的方式提供未来通信所需的传输速率。LSAS有几个关键的优点：发射功率被分散到许多低功率天线上，大约是毫瓦。-因此，射频（RF）前端组件的设计简化，因为可以部署低成本的功率放大器。- LSAS设计可以非常健壮，因为一个或几个天线单元的故障不会明显影响系统。-在信号处理方面，通过放大MIMO的维度，低复杂度的用户检测和预编码变得接近最佳。从信息论的角度来看，随着天线数量的无限大增长，MIMO信道的统计量趋向于确定性函数。以及相关的挑战：-为数百个天线提供馈电所需的大量射频链在其部署中提出了重要的实际挑战；-随着空间维度的增加，即使是最简单的信号处理技术的复杂性也显着增加-大规模天线阵列必须部署在基站和移动设备中可用的有限物理空间中。这就产生了在LSAS中特别相关的两个主要影响：由于天线作为信号源的接近而产生的空间相关性和由于天线作为电子元件的接近而产生的相互耦合。-对于大量天线，用于信道估计的导频序列必须在相邻单元之间重复使用。信道状态信息（CSI）的提供成为一个重要的负担，LSAS的性能受到由此产生的小区间干扰（导频污染问题）的限制。该项目通过以下方式解决大规模天线部署问题：a)具有现实建模的信息理论分析；b)致力于功率效率的信号处理和CSI采集；c)模拟-数字波束成形设计和减少射频链解决方案，旨在实现功率和成本效益。该项目旨在通过基于两个关键颠覆性概念的大规模天线系统实现节能传输：a)使用基于LSAS的电可操纵寄生阵列散热器（ESPAR）原理的模拟波束形成，b)利用建设性干扰。此外，本项目从天线阵列在有限物理空间中的实际部署的角度重新审视了LSAS的预期好处，这些天线阵列在密集部署的天线之间容易增加相关性和耦合。我们的目标是对LSAS对绿色通信的好处及其实际实施方案进行彻底和务实的调查。

This project investigates signal processing techniques for practical and realistic implementations of large-scale antenna systems (LSAS) for energy- and spectral- efficient wireless communication. It is expected that the energy bill for cellular networks will double by 2015 and therefore there is a growing concern to reduce the associated operational expenditure (OPEX) along with the global CO2 emission in all fields of communications. The physical layer of wireless communication is a core building block of the telecommunication system chain and the ever-increasing Quality-of-Service demands directly reflect on the performance requirements of the relevant signal processing techniques. The physical limitations of wireless propagation form the bottleneck of physical layer transmission. Multiple Input Multiple Output (MIMO) systems have proven particularly useful in circumventing this bottleneck by providing an increased number of data streams in the physical channel. Small scale MIMO systems are currently part of communication standards and commercial designs. LSAS are envisaged for the next generations of wireless systems, to capitalise on the utilisation of multiple antennas, and deliver the transmission rates required for future communications in a power-efficient manner. LSAS involve several critical benefits:- The transmit power is split to many low power antennas, of the order of milliWatts.- Hence, the design of the radio frequency (RF) front-end components is simplified as low cost power amplifiers can be deployed. - LSAS designs can be extremely robust in that the failure of one or a few of the antenna units would not appreciably affect the system. - In terms of signal processing, by scaling up the dimensions of MIMO low complexity user detection and precoding become close-to-optimal. - In information theoretic terms, as the numbers of antennas grow infinitely large, the statistics of the MIMO channel tend to deterministic functions. and associated challenges:- The massive amount of RF chains required to feed the hundreds of antennas poses an important practical challenge in their deployment, - With the increase of spatial dimensions the complexity of even the simplest signal processing techniques increases significantly - The massive antenna arrays must be deployed in the limited physical space that is available in both base stations and mobile devices. This creates two main effects which become particularly relevant in LSAS: spatial correlation due to the proximity of the antennas as signal sources and mutual coupling due to the proximity of the antennas as electrical components. - For large numbers of antennas pilot sequences for channel estimation have to be reused between adjacent cells. Channel State Information (CSI) provisioning becomes a significant burden and the performance of LSAS becomes limited by the resulting inter-cell interference (pilot contamination problem). This project tackles the issue of large scale antenna deployment by a) information theoretical analysis with realistic modelling, b) signal processing and CSI acquisition devoted to power efficiency and c) analogue-digital beamforming designs and reduced RF-chain solutions aimed at power- and cost- effective implementations. The project aims to achieve power-efficient transmission by large scale antenna systems based on two key disruptive concepts: a) using analogue beamforming using the principles of Electrically-Steerable Parasitic Array Radiators (ESPAR) based LSAS and b) exploiting constructive interference. In addition, this project re-examines the anticipated benefits of LSAS from the viewpoint of realistic deployments of the antenna arrays in limited physical space which are prone to increased correlation and coupling between the densely deployed antennas. We aim at a thorough and pragmatic investigation of the benefits of LSAS for Green Communications, and their practical implementation solutions.