On the Design of Downlink Multi-user Multi-antenna OFDMA Systems with Imperfect CSIT

MIMO-OFDMA is a promising technology to accommodate multi-user transmission over frequency selective fading channels with high spectral efficiency. In multi-user MIMO-OFDMA systems, cross layer scheduling is very important to exploit the multi-user selection diversity over the spatial and frequency domains. In this paper, we focus to investigate the design and performance of downlink multi-user MISO-OFDMA cross layer scheduler for time-division duplex (TDD) systems. We propose a systematic framework for the optimal design of the cross layer scheduling with imperfect knowledge of CSIT. We first exam the optimal solution for the scheduling problem. Because of its huge complexity, some sub-optimal algorithms are proposed to achieve reasonable performance-complexity tradeoff. We found that while the ideal schedulers (designed for perfect CSIT) fails to exploit the spatial multiplexing and cross-layer gains, the proposed cross-layer scheduling algorithms designed for imperfect CSIT achieves significant spectral efficiency even at large CSIT errors