Traffic Off-Loading With Energy-Harvesting Small Cells and Coded Content Caching

We consider content delivery to users in a system consisting of a macro base station (BS), several energy-harvesting small cells (SCs), and many users. Each SC has a large cache and stores a copy of all contents in the BS. A user's content request can be either handled by the SC for free if it has enough energy, or by the BS that has a cost. Each user has a finite cache and can store some most popular contents. We propose an efficient coded content caching schemes and an optimal transmission schemes for this system to maximally off-load the data traffic from the macro BS to the energy-harvesting SCs, and therefore minimize the power consumption from the grid. Specifically, the proposed coded caching scheme stores fractions of some most popular contents, such that contents requested from multiple users can be simultaneously delivered by the BS or SC. Moreover, the optimal transmission policy is formulated and solved as a Markov decision process. Extensive simulation results are provided to demonstrate that the proposed coded caching and transmission schemes can provide significantly higher traffic off-loading capability compared with systems with no caching or with uncoded caching, as well as systems that employ heuristic-based transmission schemes.