Rounding Algorithm of Minimizing Executing and Transmitting Time in Multiple CRANs

Recently, Cloud Radio Access Network (CRAN) is a technology for reducing communication load and improving the performance of user tasks. In a CRAN, remote radio heads (RRHs) are densely set up to enable users to connect to the network nearby, and baseband unit (BBU) pools are used to store and execute user contents and tasks. In this paper, our goal is to perform joint optimization when scheduling user tasks and assigning RRH to users in a multiple CRAN infrastructure. The joint problem is NP-hard and modeled as a 0/1 integer linear programming (ILP) with the objective of minimizing the total time of executing user tasks and transmitting user output contents under the constraints of RRH linked capacities and BBU pool computing resources. Then, an algorithm is designed by adopting the rounding technology to solve the 0/1 ILP. We will prove its approximation ratio competitively. The conducted simulations further show that the difference between its solution and the optimal one of the 0/1 ILP is very small, and its approximation ratio is between 1.09 and 1.17. In the conducted experiments, the results demonstrate that the proposed algorithm is indeed practical to be implemented in a multiple CRAN infrastructure.