Correlation across transmit antennas in multiple-input multiple-output (MIMO) systems has been studied in various scenarios and has been shown to be detrimental or provide benefits depending on the particular system and underlying assumptions. In this dissertation, we investigate the effect of transmit correlation on the capacity of the Gaussian MIMO broadcast channel (BC), with a particular interest in the large-scale array (or massive MIMO) regime. To this end, we introduce a new type of diversity, referred to as transmit correlation diversity, which captures the fact that the channel vectors of different users may have different, and often nearly mutually orthogonal, large-scale channel eigen-directions. In particular, when taking the cost of downlink training properly into account, transmit correlation diversity can yield significant capacity gains in all regimes of interest. Our analysis shows that the system multiplexing gain can be increased by a factor up to [M/r], where M is the number of antennas and r ≤ M is the common rank of the users transmit correlation matrices, with respect to standard schemes that are agnostic of the transmit correlation and treat the channels as if they were isotropically distributed. Thus, this new form of diversity reveals itself as a valuable “new resource” in multiuser communications.
This work further investigates how user grouping, more specifically, group partitioning, affects the sum-rate performance of a two-stage multiuser MIMO precoding scheme referred to as joint spatial division and multiplexing (JSDM). Taking both independent and clustered user geometry models into account, we propose new criteria for user grouping to noticeably improve the sum-rate performance of JSDM. Numerical results confirm that user grouping based on the proposed criteria yields substantial performance enhancement.
다중입출력 안테나 시스템에서 공간 상관도는 특정 채널환경과 전제에 따라 시스템 성능에 이로울수 도 해로울수도 있다고 알려져 있다. 본 학위논문에서는 공간 상관도가 대규모 안테나 다중사용자 채널에 미치는 영향을 정보이론적으로 분석한다. 이를 위해 공간 상관 다양성을 정의하고 파일럿 신호 자원소모를 고려할 때 본 다양성이 채널용량을 크게 증대시킬 수 있음을 보이고 이러한 공간 상관 다양성은 다중사용자 통신에서활용가능한새로운자원이될수있음을보이고자한다. 이와더불어본논문은공간분리및 다중화 결합 기술의 성능에 중요한 단말 분류 기술을 제안하고 두 가지 사용자 분포 모델에 따라 빔형성 행렬의 최적화 및 시스템 성능에 미치는 영향을 분석한다. 또한 대규모 안테나 및 대규모 사용자 시스템에서 스케줄링 복잡도를 줄이기 위한 통계적 스케줄링 기법을 제안하다.
