Abstract: In order to achieve low-latency data transmission in the cloud wireless access network (C-RAN), a base station caching and fronthaul link multicast transmission mode is proposed to minimize the system transmission delay by jointly optimizing fronthaul link beamforming and access link beamforming. The non-convex time delay minimization problem is transformed into a convex one by using L0 norm approximation, successive convex approximation and semi-definite relaxation techniques. An effective iterative algorithm is proposed to obtain the solution of the problem. The proposed scheme can determine the service status of base stations, which are suspended service, continuing service status according to the content cached by base stations and the channel quality of fronthaul link. They are different from the traditional multicast transmission for cache-enabled C-RAN. Simulations show that compared with the traditional scheme, the proposed scheme can effectively reduce the system transmission delay.

Key words: cloud radio access network, base-station caching, beamforming, multicasting, convex optimization