The demand for providing multicast services in cellular networks iscontinuously and fastly increasing. In this work, we propose a non-orthogonaltransmission framework based on layered-division multiplexing (LDM) to supportmulticast and unicast services concurrently in cooperative multi-cell cellularnetworks with limited backhaul capacity. We adopt a two-layer LDM structurewhere the first layer is intended for multicast services, the second layer isfor unicast services, and the two layers are superposed with differentbeamformers and decoded by each receiver using successive interferencecancellation. We formulate a joint multicast and unicast beamforming problemwith adaptive base station (BS) clustering that aims to maximize the weightedsum of the multicast rate and the unicast rate under per-BS power and backhaulconstraints. The problem is a non-convex mixed-integer non-linear programmingproblem. We first develop a branch-and-bound algorithm to find its globaloptimum. We then reformulate the problem as a sparse beamforming problem andpropose a low-complexity algorithm based on convex-concave procedure.Simulation results demonstrate the significant superiority of the proposedLDM-based non-orthogonal scheme over the orthogonal schemes in terms of theachievable multicast-unicast rate region.
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