  In this paper, optimal content caching strategy is proposed to jointly
minimize the cell average outage probability and fronthaul usage in cloud radio
access network (Cloud-RAN). At first, an accurate closed form expression of the
outage probability conditioned on the user's location is presented, and the
cell average outage probability is obtained through the composite Simpson's
integration. The caching strategy for jointly optimizing the cell average
outage probability and fronthaul usage is then formulated as a weighted sum
minimization problem, which is a nonlinear 0-1 integer NP-hard problem. In
order to deal with the NP-hard problem, two heuristic algorithms are proposed
in this paper. Firstly, a genetic algorithm (GA) based approach is proposed.
Numerical results show that the performance of the proposed GA-based approach
with significantly reduced computational complexity is close to the optimal
performance achieved by exhaustive search based caching strategy. Secondly, in
order to further reduce the computational complexity, a mode selection approach
is proposed. Numerical results show that this approach can achieve near-optimal
performance over a wide range of the weighting factors through a single
computation.
