This paper presents a content-centric transmission design in a cloud radioaccess network (cloud RAN) by incorporating multicasting and caching. Usersrequesting a same content form a multicast group and are served by a samecluster of base stations (BSs) cooperatively. Each BS has a local cache and itacquires the requested contents either from its local cache or from the centralprocessor (CP) via backhaul links. We investigate the dynamic content-centricBS clustering and multicast beamforming with respect to both channel conditionand caching status. We first formulate a mixed-integer nonlinear programmingproblem of minimizing the weighted sum of backhaul cost and transmit powerunder the quality-of-service constraint for each multicast group. Theoreticalanalysis reveals that all the BSs caching a requested content can be includedin the BS cluster of this content, regardless of the channel conditions. Thenwe reformulate an equivalent sparse multicast beamforming (SBF) problem. Byadopting smoothed $\ell_0$-norm approximation and other techniques, the SBFproblem is transformed into the difference of convex (DC) programs andeffectively solved using the convex-concave procedure algorithms. Simulationresults demonstrate significant advantage of the proposed content-centrictransmission. The effects of three heuristic caching strategies are alsoevaluated.
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