Improving Energy Efficiency for Multiuser MIMO Systems with Effective Capacity Constraints

In this paper, our aim is to devise energy efficient strategies for single and multiuser multiple-input multiple-output (MIMO) antenna systems with individual users' effective capacity (EC) constraints. The use of EC provides a metric to quantify the maximum achievable rate under a certain delay constraint and in particular, we formulate the problem as a cross-layer resource allocation problem that connects the link-layer parameters such as delay and source rate with the physical-layer parameters such as fading statistics and power control. The object is to minimize the transmission energy of the MIMO systems while meeting the EC constraints, with the aid of the channel statistics. By deriving a closed-form expression for the EC of a single-user link MIMO system, we address multiuser MIMO systems in the downlink, in which dynamic time (or spectrum) sharing and multiuser power control are performed if time-division multiple-access (TDMA) (or frequency-division multiple-access (FDMA)) is used. We show that the optimal resource-allocation solution can be obtained by a dynamic programming (DP) approach and more importantly, low-complexity near-optimal heuristic solutions are proposed.