Optimal downlink multi-user MIMO cross-layer scheduling using HOL packet waiting time

Cross-layer design is a promising technique to achieve performance enhancement for wireless systems. In this paper, we seek to exploit the synergy between the PHY (physical) layer and the MAC (multiple access control) layer when a multiple-input multiple-output (MIMO) wireless system is operating at the PHY layer. We propose two optimal downlink multi-user MIMO scheduling algorithms which consider both the queueing state information from the MAC layer and the channel state information from the PHY layer when making scheduling decision. Our approaches are optimal in the sense that they can achieve maximum system throughput while at the same time guaranteeing the stability of the system. That is, they guarantee stability of the system whenever it is feasible with any other scheduling algorithm. Computer simulations demonstrate that significant gains are achieved by our cross-layer design compared to traditional strict-layered designs. Additionally, by making use of the HOL (head of line) packet waiting time our optimal scheduling algorithms can provide a more balanced delay performance for non-uniform traffic compared to the existing optimal scheduling algorithm which does not consider it