Cloud and Edge Multicast Beamforming for Cache-Enabled Ultra-Dense Networks

For the cache-enabled ultra-dense networks, edge caching is a promising technique for realizing low-latency transmission. In this paper, we study cache-enabled ultra-dense networks with the wireless fronthaul, in which edge nodes (ENs) have the capability of caching and signal processing. Under such a setup, by exploiting the feature that users requesting the same content form a multicast group and can be served by a cluster of ENs, we first formulate a problem to optimize the cloud and edge multicast beamforming design for maximizing the minimum rate among the user groups. Due to the coupling of transmit and receive beamforming and the non-convex constraints of delivery rate, the formulated problem is difficult to be directly solved. To this end, we propose to use the weighted sum mean-square error minimization approaches and certain transformation techniques to convert the original problem into a convex one. An optimal solution is then obtained by using bisection search and second order cone (SOC) transformation. The results indicate that the performance of the proposed precoding scheme with wireless frothauling will close to that of the wired fronthauling.