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

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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.