Energy-Efficient Transmission in Heterogeneous Wireless Networks: A Delay-Aware Approach

In this paper, we investigate the delay-aware energy-efficient transmission problem in dynamic heterogeneous wireless networks (HWNs) with time-variant channel conditions, random traffic loads, and user mobility. By jointly considering subcarrier assignment, power allocation, and time fraction determination, we formulate it as a stochastic optimization problem to maximize the system energy efficiency (EE) and to ensure network stability. By leveraging the fractional programming theory and the Lyapunov optimization technique, we first propose a general algorithm framework, referred to as the eTrans, to solve the formulation. Further, we exploit the special structure of the subproblem embedded in the eTrans to develop the extremely simple and low complexity but optimal algorithms for subcarrier assignment, power allocation, and time fraction determination. In particular, all of them have closed-form solutions, and no iteration is required, which paves the way for employing the eTrans to practical applications. The theoretical analysis and simulation results exhibit that eTrans can flexibly strike a balance between EE and average delay by simply tuning an introduced control parameter.