High Spectral and Energy Efficient Multi-User Large MIMO (MU-MIMO) Wireless Systems

第四代以上无线系统(或第五代无线系统)的主要关注点将是提供无缝的全球漫游、宽带接入、高度交互的多媒体(数据/语音/互联网)服务，如视频会议、多方和随时随地的虚拟远程呈现。要以节能的方式实现这种无处不在的高容量可接受质量的传输/接收，需要在无线信道(AIR)上传输几吉比特每秒(Gbps)。为了实现这一点，人们提出了不同的先进技术，其中大型多输入多输出(MIMO)技术最近被认为是提高系统容量和能量的重大突破，远远超出了目前使用的系统。 特别是，已经证明，具有大量天线的无线系统可以获得数据速率/频谱效率和通信可靠性的指示性增加，以及总发射能量的过度减少。近年来，业界也有很多关于大量天线的MIMO系统的制作和测试的报告，例如NTT DoCoMo的12发射12接收天线(12X12)，单用户MIMO系统，在100兆赫兹(MHz)的带宽上可以获得5千兆比特/秒(Gbps)的数据吞吐速率。此外，WiFi标准的扩展(从IEEE 802.11n到IEEE 802.11ac以获得5 GHz频段的多吉比特速率传输)现在考虑8发射和8接收天线()多用户MIMO(MU-MIMO)操作。 大型MU-MIMO的两个主要优点如下：第一，在天线数量非常多的情况下，信道向量几乎是正交的，因此可以显著降低多用户干扰。因此，利用高数据速率和较少的发送能量，可以同时服务多个用户。具体地说，利用相干处理，由于阵列增益，发射能量可以显著降低。 其次，大型MU-MIMO系统的这一方面非常重要，因为基站的运行能量消耗导致温室气体排放加速增加。事实上，节能设计是下一代通信网络的主要目标之一。特别是，GreenTouch联盟(由Alcatel-Lucent Bell Lab.创建，由领先的电信公司和研究小组组成的联盟)最近推出了具有大量天线的无线系统，作为高频谱效率和高能效无线系统的关键解决方案。 该计划的第一个目标是研究在无线信道的实际约束/限制下，大型MU-MIMO系统的潜在利益是否以及在多大程度上仍然能够得到保障。第二个目标是设计低复杂度的信号处理算法和技术，以确保实际受限的大型MU-MIMO系统的潜在好处。已有研究表明，大型MU-MIMO系统可用于进一步降低无线通信的能耗。虽然人们对这一主题越来越感兴趣，但到目前为止还没有进行全面的研究，以研究如何选择天线阵列的大小、调制大小和发射功率来实现能量和频谱高效的通信，因此我们的第三个目标。第四个目标是开发新的物理层安全概念。为此，将考虑到高效、准确和快速的估计技术，并考虑到信道时间一致性，以确保安全通信。

A major concern in beyond 4th generation wireless systems (or 5th generation wireless systems) will be providing seamless global roaming, broadband access, highly interactive multimedia (data/voice/internet) services such as video-conference, multi-party and virtual tele-presence any-time everywhere. Achieving such ubiquitous high-capacity acceptable-quality transmission/reception with energy efficient usage requires several giga bits per second (Gbps) to be transmitted over the wireless channel (air). To acquire this, different advanced techniques have been proposed, among which Large Multiple-Input-Multiple-Output (MIMO) has recently come into view as a significant breakthrough for improving the capacity and energy far beyond systems in use today. In particular, it has been proven that wireless systems with a large number of antennas can attain an indicative increase in data rate/spectral efficiency and communication reliability, and excessive reduction in the amount of total transmitted energy. In recent years, there have also been many reports from the industry, regarding fabrication and testing of the MIMO systems with a large number of antennas, for example, the 12 transmit and 12 receive antenna (12X12), single-user MIMO system by NTT DoCoMo, which can gain a data throughput rate of 5 gigabits-per-sec (Gbps) over a bandwidth of 100 mega-hertz (MHz). Furthermore, the expansion of WiFi standards (the progression from IEEE 802.11n to IEEE 802.11ac to obtain multi-gigabit rate transmissions in 5 GHz band) now considers the 8 transmit and 8 receive antenna (8X8) Multi-user MIMO (MU-MIMO) operation. The main two advantages of Large MU-MIMO are as follows: First, with a very large number of antennas, the channel vectors are nearly-orthogonal and as a result, multi-user interference can be dramatically reduced. Consequently, with high data rate and less transmit energy, many users can be simultaneously served. In particular, with coherent processing, transmit energy can be reduced considerably due to the array gain. Second, this aspect of Large MU-MIMO systems is of great importance, due to the accelerated increase in greenhouse gas emissions resulting from operational energy consumption in base stations. Indeed, energy-aware design is one of the main objectives for the next generation of communication networks. Particularly, the GreenTouch Consortium (a consortium founded by Alcatel-Lucent Bell Labs., and consisting of leading telecommunication companies and research groups), recently introduced wireless systems with a large number of antennas as a key solution for high spectral efficiency and power efficient wireless systems. The first objective of this proposed program is to examine whether and to what extent the promising benefits of Large MU-MIMO systems can still be secured under practical constraints/limitations of the wireless channels. The second objective is to design low-complexity signal processing algorithms and techniques which can secure the potential benefits of practically constrained Large MU-MIMO systems. It has been shown that Large MU-MIMO systems could be used for achieving further reductions of the energy consumption of wireless communications. Although there is increasing interest in this topic, no comprehensive study has been undertaken so far to examine how the antenna array size, the modulation size and transmission power need to be selected in order to attain energy and spectral efficient communications, hence our third target. The fourth objective is to develop new physical-layer security concepts. To do so, efficient, accurate and fast estimation techniques, taking into account the channel time coherence, will be considered to ensure secure communications.