Joint wireless and backhaul load balancing in cooperative caches enabled small-cell networks

Distributed and cooperative caches (DCCs) enabled small-cell network (SCN) has been a common approach for improving QoE perceived by mobile users (UEs) and reducing backhaul traffic load. In this paper, we propose a joint wireless and backhaul load balancing (JWBLB) framework for DCCs enabled SCNs with the objective to minimizing the system content transmission delay. The JWBLB is achieved through content-request UEs and small-cell base stations re-association, and back-haul links and cooperative caches selection, with the knowledge of the cached content distribution, jointly considering traffic load of wireless and backhaul links. Specifically, 1) a software defined networking (SDN) inspired load balancing control architecture, consisting of the coordinator and DCCs, is designed. 2) The optimal JWBLB problem is formulated with the objective to minimizing the system content transmission delay, which is proved to be a quadratic assignment problem (QAP). 3) A joint Lagrangian relaxation and decomposition, and accelerated branch and bound algorithm is proposed to efficiently find the optimal binary solutions of the considered QAP. Simulation results show that JWBLB achieves great reduction in the average transmission delay and outgoing backhaul traffic load. For instance, 65% average transmission delay can be reduced as only 50% UEs with potential re-association possibility, and 48.4% outgoing traffic load caused by content fetches from Internet is reduced as the Zipf distribution parameter equals 0.6.