Energy–Delay Tradeoff in Adaptive Cooperative Caching for Energy-Harvesting Ultradense Networks

Abstract

Edge caching in collaborative edge computing (CEC) is a resource-friendly technique to improve energy efficiency and alleviate backhaul link congestion. Caching diverse contents based on the social features among users at energy-harvesting-powered (EH-powered) small base stations can further save on-grid energy, but it may lead to a longer delay to mobile users (MUs). In this article, we focus on an energy–delay tradeoff (EDT) problem in CEC-assisted and EH-powered ultradense networks and propose an EDT-oriented adaptive cooperative caching (EDT-ACC) scheme. We regard delay and energy as two types of cost and introduce a weighted cost function to transform the EDT problem into a cost minimization problem. An alternating optimization based on an improved quantum genetic algorithm (AO-IQGA) is proposed to solve the cost minimization problem. In AO-IQGA, the alternating optimization is utilized to divide the cost minimization problem into two subproblems (adaptive tuning weight subproblem and caching decision subproblem). We improve the quantum genetic algorithm in terms of repairing unfeasible solutions and adaptively updating quantum genes. Numerical results demonstrate the efficiency of the proposed AO-IQGA and illustrate the fundamental tradeoff between delay and energy consumption under different parameters, such as content popularity, storage size, and battery capacity.