Layered-division-multiplexing (LDM) is a spectrum-efficient physical-layer technology that can simultaneously support multiple services with diversified quality of service (QoS) requirements. In this paper, we propose a reconfigurable intelligent surface (RIS) assisted LDM system, where the base station (BS) simultaneously transmits non-orthogonal unicast and broadcast messages to multiple users. Our goal is to minimize the transmit power of the BS, while taking into account the QoS requirements of all messages and the unit modulus constraint of the RIS. To this end, we formulate a joint phase-shift matrix optimization as well as unicast and broadcast beamformer design problem. However, the formulated problem is a non-convex bi-quadratic programming problem. After utilizing alternating optimization and matrix lifting techniques, we transform the problem into an alternating sequence of rank-constrained semidefinite programming (SDP) problems. By introducing a difference-of-convex (DC) representation for the rank-one constraints, we develop an efficient DC algorithm to solve the low-rank optimization problem. Simulation results demonstrate the performance gains of the proposed algorithm over the state-of-art methods in reducing the BS transmit power.
Reconfigurable Intelligent Surface Assisted Non-Orthogonal Unicast and Broadcast Transmission
2020-05-01
169944 byte
Conference paper
Electronic Resource
English
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