  Enabling caching capabilities in dense small cell networks (DSCNs) has a
direct impact on file delivery delay and power consumption. Most existing work
studied these two performance metrics separately in cache-enabled DSCNs.
However, file delivery delay and power consumption are coupled with each other
and cannot be minimized simultaneously. In this paper, we investigate the
optimal tradoff between these two performance metrics. Firstly, we formulate
the joint file delivery delay and power consumption optimization (JDPO) problem
where power control, user association and file placement are jointly
considered. Then we convert it to a form that can be handled by Generalized
Benders Decomposition (GDB). with GDB, we decompose the converted JDPO problem
into two smaller problems, i.e., primal problem related to power control and
master problem related to user association and file placement. An iterative
algorithm is proposed and proved to be $\epsilon$-optimal, in which the primal
problem and master problem are solved iteratively to approach the optimal
solution. To further reduce the complexity of the master problem, an
accelerated algorithm based on semi-definite relaxation is proposed. Finally,
the simulation results demonstrate that the proposed algorithm can approach the
optimal tradeoff between file delivery delay and power consumption.
