Joint service improvement and content placement for cache-enabled heterogeneous cellular networks

Caching popular contents in the storage of base stations (BSs) has emerged as a promising solution for reducing the transmission latency and providing extra-high throughput. This study tackles the optimal trade-off problem between the sum of effective rates and backhaul saving through joint service improvement and content placement in cache-enabled heterogeneous cellular networks while guaranteeing the quality-of-service requirements of all user terminals (UTs) and backhaul traffic constraints of all BSs. However, there exists an intractable issue of mixing the integer nature into the feasible region in the nonlinear optimisation problem. To this end, the authors decompose the optimisation problem into three subproblems by alternately fixing two of three classes of variables (i.e. UT association, power control, and content placement). Aiming at these subproblems, they, respectively, convert them into the tractable forms and propose the corresponding algorithms. By combining them, they propose a three-tier iterative algorithm for jointly optimising UT association and cache placement. Finally, numerical results have verified the effectiveness of proposed schemes.