대량 다중 입력 다중 출력 시스템에서 에너지와 스펙트럼 효율을 높이 효율적인 파일럿 배정과 파워 할당

Abstract

Massive multiple-input-multiple-output (MIMO) has been considered as a promising transmission technique for future wireless networks (5G and beyond) since it has the ability to significantly improve both spectral efficiency and energy efficiency of the wireless systems. Moreover, base stations only need to use simple linear signal processing technique for both uplink signal detection and downlink pre-coding, such as zero forcing or maximum ratio, but they still are able to achieve nearly optimal performance. The huge potential of massive MIMO systems is undeniable; however, there are many aspects of massive MIMO systems should be deeply investigated and improved so that this technique can meet the huge demand for data transmission in the near future. Pilot contamination (PC) is one of the main drawbacks of massive MIMO systems. This PC happens due to the lack of resources since massive MIMO systems consist of many users and huge number of base station antennas. PC degrades the channel estimation quality, and eventually degrades spectral and energy efficiency of the massive MIMO system. Therefore, this thesis investigates some methods to mitigate the PC problems and also to improve the energy efficiency of the massive MIMO systems. Specifically, this thesis firstly focuses on how to allocate pilot sequence and pilot power to each user in a smart way to degrade the effect of PC problem, or in other words, to improve the spectral efficiency of the systems. Moreover, massive MIMO system consists of many users and a huge number of BS antennas. Therefore, using power efficiently is very important issue. Inspired by that, this thesis also investigates methods to improve the energy efficiency of the massive MIMO systems.