390 research outputs found
Reconfigurable Intelligent Surfaces Aided mmWave NOMA: Joint Power Allocation,Phase Shifts, and Hybrid Beamforming Optimization
In this paper, an reconfigurable intelligent surface (RIS)-aided millimeter
wave (mmWave) non-orthogonal multiple access (NOMA) system is considered. In
particular, we consider an RIS-aided mmWave-NOMA downlink system with a hybrid
beamforming structure. To maximize the achievable sum-rate under a minimum rate
constraint for the users and a minimum transmit power constraint, a joint RIS
phase shifts, hybrid beamforming, and power allocation problem is formulated.
To solve this non-convex optimization problem, we develop an alternating
optimization algorithm. Specifically, first, the non-convex problem is
transformed into three subproblems, i.e., power allocation, joint phase shifts
and analog beamforming optimization, and digital beamforming design. Then, we
solve the power allocation problem under fixed phase shifts of the RIS and
hybrid beamforming. Finally, given the power allocation matrix, an alternating
manifold optimization (AMO)-based method and a successive convex approximation
(SCA)-based method are utilized to design the phase shifts, analog beamforming,
and transmit beamforming, respectively. Numerical results reveal that the
proposed alternating optimization algorithm outperforms state-of-the-art
schemes in terms of sum-rate. Moreover, compared to a conventional mmWave-NOMA
system without RIS, the proposed RIS-aided mmWave-NOMA system is capable of
improving the achievable sum-rate of the system
Joint Design for Simultaneously Transmitting And Reflecting (STAR) RIS Assisted NOMA Systems
Different from traditional reflection-only reconfigurable intelligent
surfaces (RISs), simultaneously transmitting and reflecting RISs (STAR-RISs)
represent a novel technology, which extends the half-space coverage to
full-space coverage by simultaneously transmitting and reflecting incident
signals. STAR-RISs provide new degrees-of-freedom (DoF) for manipulating signal
propagation. Motivated by the above, a novel STAR-RIS assisted non-orthogonal
multiple access (NOMA) (STAR-RIS-NOMA) system is proposed in this paper. Our
objective is to maximize the achievable sum rate by jointly optimizing the
decoding order, power allocation coefficients, active beamforming, and
transmission and reflection beamforming. However, the formulated problem is
non-convex with intricately coupled variables. To tackle this challenge, a
suboptimal two-layer iterative algorithm is proposed. Specifically, in the
inner-layer iteration, for a given decoding order, the power allocation
coefficients, active beamforming, transmission and reflection beamforming are
optimized alternatingly. For the outer-layer iteration, the decoding order of
NOMA users in each cluster is updated with the solutions obtained from the
inner-layer iteration. Moreover, an efficient decoding order determination
scheme is proposed based on the equivalent-combined channel gains. Simulation
results are provided to demonstrate that the proposed STAR-RIS-NOMA system,
aided by our proposed algorithm, outperforms conventional RIS-NOMA and RIS
assisted orthogonal multiple access (RIS-OMA) systems
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