2026· IEEE Open Journal of the Communications Society· Vol 7, pp. 9783-9797· 0 citations· 39 references
TL;DR
Simulation results show that the proposed method can significantly improve the sum rate of users as compared to benchmark with FPA + Optimized STAR-RIS, 6DMA + Random STAR-RIS, and FPA + Random STAR-RIS.
Abstract
Reconfigurable intelligent surfaces (RISs) and six-dimensional movable antennas (6DMAs) have emerged as promising technologies for enhancing wireless transmission by reconfiguring the propagation environment and antenna geometry, respectively. However, conventional RIS-assisted systems usually rely on fixed-position antenna arrays, whose spatial adaptability is limited when users are non-uniformly distributed in three-dimensional space. To address this limitation, this paper investigates a STAR-RIS-assisted six-dimensional movable antenna base station (6DMA-BS) communication system. In the considered system, the 6DMA-BS adjusts the positions and rotations of multiple antenna surfaces to exploit additional spatial degrees of freedom, while the STAR-RIS provides full-space coverage for users in both reflection and transmission zones. To enhance the system sum rate, a joint optimization problem is formulated by considering 6DMA surface positions and rotations, BS active beamforming, and STAR-RIS passive reflection/transmission beamforming under practical constraints. Since the formulated problem is highly non-convex with strongly coupled variables, an alternating optimization framework is developed. Specifically, the position and rotation subproblems are solved by conditional gradient methods, the active beamforming is obtained by MRT-based direction design and water-filling-based power allocation, and the passive beamforming is optimized via SDR and Gaussian randomization. Simulation results show that the proposed method can significantly improve the sum rate of users as compared to benchmark with FPA + Optimized STAR-RIS, 6DMA + Random STAR-RIS, and FPA + Random STAR-RIS.
The reconfigurable intelligent surface (RIS) is a promising technology for the beyond-5G and 6G wireless communication systems. It can improve the wireless communication performance, facilitate interference cancellation between users and other signals. In this paper, we present an active RIS-aided multiple-input multiple-output (MIMO) system, in which we configure an active RIS to assist point-to-point communication between a multiple-antenna base station (BS) and multiple-antenna user equipment (UE). Specifically, the transmit precoder at the BS and the reflecting coefficient matrix at the RIS are optimized to maximize the spectral efficiency (SE) at the UE based on an alternating optimization (AO) algorithm, where the precoder and reflecting coefficient are iteratively updated. First, the precoder at the BS is optimized using the singular value decomposition (SVD) method while keeping the RIS reflecting coefficient matrix fixed. Second, for the fixed transmit precoder, the RIS reflecting coefficient matrix is updated using the semidefinite relaxation (SDR) method. We evaluate the proposed algorithm against conventional passive and active RIS schemes and show that the proposed scheme outperforms the compared architectures in terms of SE for single-user MIMO systems.
George J. Nyahega, Kyung-In Lee· IEEE Access· 0 citations
This paper investigates a reconfigurable intelligent surface (RIS)-assisted movable antenna (MA) secure integrated sensing and communication (ISAC) system. In this architecture, the RIS establishes indirect transmission links to provide communication services for multiple legitimate users, while the high spatial diversity gain of MA is leveraged to enhance system security. Then, we formulate an optimization problem to maximize the system total secrecy rate by jointly optimizing the MA position selection, active beamforming design for base station and passive beamforming design for RIS. The problem also accounts for practical constraints including transmit power budget, sensing beampattern mean square error (MSE), RIS unit-modulus constraint. However, it is challenging to solve this problem due to its non-convexity and strong coupling of the optimization variables. Consequently, we propose an alternating optimization (AO) framework, employing techniques including discrete binary particle swarm optimization (BPSO), successive convex approximation (SCA) and difference-of-convex (DC) programming to transform the optimization problem into convex subproblems. Based on the solution above, the convex sub-problems are solved iteratively until convergence is achieved. Numerical results demonstrate that the proposed algorithm outperforms other baseline algorithms in terms of secure communication performance.
Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) can reconstruct indirect links when the direct link is blocked for millimeter wave (mmWave) communications. Moreover, the spectral efficiency of non-orthogonal multiple access (NOMA) can benefit from the highly directional transmission of mmWave. To capitalize on the complementarity of STAR-RIS, mmWave, and NOMA technologies, in STAR-RIS-assisted mmWave-NOMA downlink communication systems we propose the spectral efficiency optimization problem, considering the differences of the paired users’ channels. The problem is subject to maximum available transmission power, the constraints of the amplitude and phase-shift coefficients of each STAR-RIS element’s transmission and reflection, and so on. To solve the non-convex problem, the alternating iterative optimization algorithms (AIOAs) based on the successive convex approximation (SCA) and the semidefinite programming (SDP) are proposed, respectively. For the SCA-based AIOA algorithm, the effective channel gain is written as the sum of the square of the variable’ real part and the square of the variable’ imaginary part, which is further transformed into a convex expression after proving that the constraint on the sum of the amplitude coefficients of each STAR-RIS element’s transmission and reflection can be relaxed. For the SDP-based AIOA algorithm, the original problem is transformed into a SDP problem by introducing the auxiliary variables. Moreover, simulation results demonstrate that the two proposed algorithms improve spectral efficiency compared to existing algorithms, and NOMA is superior to orthogonal multiple access (OMA) in terms of spectral efficiency.
Fuyuan Xu, Ruirui Chen, Yong-Tao Liu et al.· IEEE Transactions on Green C...· 0 citations
High-capacity satellite network is the cornerstone of future space-air-ground integrated networks. However, the satellite uplink transmissions still face critical challenges, including severe path loss, complex multi-user interference, and payload constraints. Recently, Reconfigurable Intelligent Surfaces (RIS) and Fluid Antenna Systems (FAS) have shown promise for satellite communications through their dynamic signal reconfiguration. This paper proposes a multi-RIS-assisted satellite Compact Ultra-Massive Antenna Array (CUMA) architecture for multi-user satellite uplink transmission. Specifically, we deploy multiple RISs on the terrestrial side to separate interfering Line-of-Sight (LoS) channels via optimized phase shifts, and adopt a CUMA receiver on the satellite to further mitigate interference through FAS port selection. To solve a sum-rate maximization problem, we alternately optimize FAS port selection using a Forward-Backward Greedy Selection (FBGS) algorithm and RIS phase shifts based on Fractional Programming (FP). To the best of our knowledge, this is the first work to jointly optimize multi-RIS and CUMA in a satellite uplink context, where strong LoS and extreme path loss fundamentally distinguish the design from terrestrial counterparts. Simulation results confirm the effectiveness of the proposed architecture across frequency bands. At 6 GHz, our scheme achieves 181% and 32% rate gains over fixed antennas and traditional CUMA schemes, respectively, while the gains also reach 138% and 27% at 26 GHz, illustrating superiority in both interference-limited and noise-limited regimes.
Kai Feng, Runke Fan, Tianheng Xu et al.· IEEE Open Journal of the Com...· 0 citations
In this paper, a movable antenna enabled reconfigurable intelligent surface (RIS)-aided ISAC system is investigated, where the monostatic BS attempts to detect a single target while providing communication services for multiple users by utilizing a RIS. To characterize the inherent performance trade-off between sensing and communication, an optimization problem of maximizing the weighted sum of mutual information of sensing target and achievable rate of all users is formulated. Suffering from the self-interference from transmit to receive antennas of BS, it requires a joint design of transceiver beamforming, RIS phase shift and transceiver antenna positions. To address this highly non-convex problem with multiple coupled variables, an effective fractional programming-alternating optimization (FP-AO) framework is proposed, where FP is adopted to transform the original problem into several subproblems, and then an AO-based algorithm is proposed to iteratively solve them. Specifically, closed-form solutions of transceiver beamforming are derived through utilizing the Karush–Kuhn–Tucker conditions, and the transceiver antenna positions are optimized by the proposed two-stage method integrating coarse-grained search and projected gradient ascent. At 40 dBm BS transmit power, the proposed FP-AO framework outperforms the random phase shifts, direct gradient ascent, and fixed-position antenna by 4.2%, 7.4%, and 11.3% in ISAC performance, respectively.
Shuai Jin, Qiang Li, Ji-Liang Zhang et al.· IEEE Transactions on Communi...· 0 citations
This article studies transmissive reconfigurable intelligent surface (RIS)-assisted architectures. It compares them with electronically steered phased arrays for the deployment of vehicular direct-to-satellite (D2S) communications in future satellite networks. Rather than treating RIS as a direct replacement for phased arrays, we clarify the operating regimes in which RIS can serve as a low-power wavefront-shaping aperture and those in which phased arrays remain preferable because of their high gain and mature beam-tracking capability. Moreover, phased arrays can support multi-beam operation, which is particularly beneficial for dual connectivity and seamless handover. We distinguish analog, digital, and hybrid phased arrays, discuss the relationship between transmissive RIS and reconfigurable transmitarrays, and highlight practical profile, tracking, and link-budget constraints for mobile terminals. The comparison shows that passive RIS offers attractive power efficiency and aperture scalability, active RIS can partially improve the link budget, and phased arrays remain preferable for high-throughput.
W. Khan, Abdullah Abdullah, Juan Andres Vazquez-Peralvo et al.· 0 citations
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