278 results found
Zhu Q, Qian Z, Clerckx B, et al., 2023, Rate-Splitting Multiple Access in Multi-Cell Dense Networks: A Stochastic Geometry Approach, IEEE Transactions on Vehicular Technology, Vol: 72, Pages: 15844-15857, ISSN: 0018-9545
In this article, the potential benefits of applying the Rate-Splitting Multiple Access (RSMA) in multi-cell dense networks are explored. Using tools of stochastic geometry, the sum-rate of RSMA-enhanced multi-cell dense networks is evaluated mathematically based on a Moment Generating Function (MGF) based framework to prove that RSMA is a general and powerful strategy for multi-antenna downlink systems. Further elaboration of the systematic performance metrics is undertaken by developing analytical expressions for area spectral efficiency and sum-rate in the RSMA-enhanced multi-cell dense networks. Based on the tractable expressions, we then offer an optimization framework for energy efficiency in terms of the number of antennas. Additionally, simulation results are shown to verify the accuracy of our analytical results and provide some insightful insights into system design. Analytically, it has been shown that: 1) the sum-rate of RSMA-enhanced multi-cell dense networks is significantly influenced by the power splitting ratio, and there is a unique value that maximizes the sum-rate; 2) the RSMA-enhanced multi-cell dense networks transmission scheme has superior sum-rate performance compared with Non-Orthogonal Multiple Access (NOMA) and Space-Division Multiple Access (SDMA) in a wide range of power splitting ratio; 3) By increasing the number of antennas and BS density in an RSMA-enhanced multi-cell dense network, the area spectral efficiency can be substantially enhanced; 4) As for energy efficiency, there exists an optimal antenna number for maximizing this performance metric .
Nerini M, Shen S, Clerckx B, 2023, Discrete-Value Group and Fully Connected Architectures for beyond Diagonal Reconfigurable Intelligent Surfaces, IEEE Transactions on Vehicular Technology, Vol: 72, Pages: 16354-16368, ISSN: 0018-9545
Reconfigurable intelligent surfaces (RISs) allow controlling the propagation environment in wireless networks through reconfigurable elements. Recently, beyond diagonal RISs (BD-RISs) have been proposed as novel RIS architectures whose scattering matrix is not limited to being diagonal. However, BD-RISs have been studied assuming continuous-value scattering matrices, which are hard to implement in practice. In this paper, we address this problem by proposing two solutions to realize discrete-value group and fully connected RISs. First, we propose scalar-discrete RISs, in which each entry of the RIS impedance matrix is independently discretized. Second, we propose vector-discrete RISs, where the entries in each group of the RIS impedance matrix are jointly discretized. In both solutions, the codebook is designed offline such as to minimize the distortion caused in the RIS impedance matrix by the discretization operation. Numerical results show that vector-discrete RISs achieve higher performance than scalar-discrete RISs at the cost of increased optimization complexity. Furthermore, fewer resolution bits per impedance are necessary to achieve the performance upper bound as the group size of the group connected architecture increases. In particular, only a single resolution bit is sufficient in fully connected RISs to approximately achieve the performance upper bound.
Cho H, Ko B, Clerckx B, et al., 2023, Coverage Increase at THz Frequencies: A Cooperative Rate-Splitting Approach, IEEE Transactions on Wireless Communications, Vol: 22, Pages: 9821-9834, ISSN: 1536-1276
Numerous studies claim that terahertz (THz) communication will be an essential piece of sixth-generation wireless communication systems. Its promising potential also comes with major challenges, in particular the reduced coverage due to harsh propagation loss, hardware constraints, and blockage vulnerability. To increase the coverage of THz communication, we revisit cooperative communication. We propose a new type of cooperative rate-splitting (CRS) called extraction-based CRS (eCRS). Furthermore, we explore two extreme cases of eCRS, namely, identical eCRS and distinct eCRS. To enable the proposed eCRS framework, we design a novel THz cooperative channel model by considering unique characteristics of THz communication. Through mathematical derivations and convex optimization techniques considering the THz cooperative channel model, we derive local optimal solutions for the two cases of eCRS and a global optimal closed form solution for a specific scenario. Finally, we propose a novel channel estimation technique that not only specifies the channel value, but also the time delay of the channel from each cooperating user equipment to fully utilize the THz cooperative channel. In simulation results, we verify the validity of the two cases of our proposed framework and channel estimation technique.
Li H, Shen S, Clerckx B, 2023, A Dynamic Grouping Strategy for Beyond Diagonal Reconfigurable Intelligent Surfaces With Hybrid Transmitting and Reflecting Mode, IEEE Transactions on Vehicular Technology, Vol: 72, Pages: 16748-16753, ISSN: 0018-9545
Beyond diagonal reconfigurable intelligent surface (BD-RIS) is a novel branch of RIS which breaks through the limitation of conventional RIS with diagonal scattering matrices. However, the existing research focuses on BD-RIS with fixed architectures regardless of channel state information (CSI), which limit the achievable performance of BD-RIS. To solve this issue, in this paper, we propose a novel dynamically group-connected BD-RIS based on a dynamic grouping strategy. Specifically, RIS antennas are dynamically divided into several subsets adapting to the CSI, yielding a permuted block-diagonal scattering matrix. To verify the effectiveness of the proposed dynamically group-connected BD-RIS, we propose an efficient algorithm to optimize the BD-RIS with dynamic grouping for a BD-RIS-assisted multi-user multiple-input single-output system. Simulation results show that the proposed dynamically group-connected architecture outperforms fixed group-connected architectures.
Park S, Choi J, Park J, et al., 2023, Rate-Splitting Multiple Access for Quantized Multiuser MIMO Communications, IEEE Transactions on Wireless Communications, Vol: 22, Pages: 7696-7711, ISSN: 1536-1276
This paper investigates the sum spectral efficiency maximization problem in downlink multiuser multiple-input multiple-output systems with low-resolution quantizers at an access point (AP) and users. We consider rate-splitting multiple access (RSMA) to enhance spectral efficiency by offering opportunities to boost achievable degree-of-freedom. Optimizing RSMA precoders, however, is highly challenging due to the minimum rate constraint when determining the common rate. The quantization errors coupled with the precoders make the problem more complicated. In this paper, we develop a novel RSMA precoding algorithm incorporating quantization errors for maximizing the sum spectral efficiency. To this end, we first obtain an approximate spectral efficiency in a smooth function. Subsequently, we derive the first-order optimality condition in the form of the nonlinear eigenvalue problem (NEP). We propose a computationally efficient algorithm to find the principal eigenvector of the NEP as a sub-optimal solution. We also extend the weighted minimum mean square error-based RSMA precoding to the considered quantization system. Simulation results validate the proposed methods. The key benefit of using RSMA over spatial division multiple access (SDMA) comes from the ability of the common stream to balance between the channel gain and quantization error in multiuser MIMO systems with different quantization resolutions.
Şahin MM, Dizdar O, Clerckx B, et al., 2023, Multicarrier Rate-Splitting Multiple Access: Superiority of OFDM-RSMA over OFDMA and OFDM-NOMA, IEEE Communications Letters, Vol: 27, Pages: 3088-3092, ISSN: 1089-7798
Rate-splitting multiple access (RSMA) is a multiple access technique generalizing conventional techniques, such as, space-division multiple access (SDMA), non-orthogonal multiple access (NOMA), and physical layer multi-casting, which aims to address multi-user interference (MUI) in multiple-input multipleoutput (MIMO) systems. In this study, we leverage the interference management capabilities of RSMA to tackle the issue of inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) waveform. We formulate a problem to find the optimal subcarrier and power allocation for downlink transmission in a two-user system using RSMA and OFDM and propose a weighted minimum mean-square error (WMMSE)- based algorithm to obtain a solution. The sum-rate performance of the proposed OFDM-RSMA scheme is compared with that of conventional orthogonal frequency division multiple access (OFDMA) and OFDM-NOMA by numerical results. It is shown that the proposed OFDM-RSMA outperforms OFDM-NOMA and OFDMA under ICI in diverse propagation channel conditions owing to its flexible structure and robust interference management capabilities.
Cerna Loli R, Dizdar O, Clerckx B, et al., 2023, Model-Based Deep Learning Receiver Design for Rate-Splitting Multiple Access, IEEE Transactions on Wireless Communications, Vol: 22, Pages: 8352-8365, ISSN: 1536-1276
Effective and adaptive interference management is required in next generation wireless communication systems. To address this challenge, Rate-Splitting Multiple Access (RSMA), relying on multi-antenna rate-splitting (RS) at the transmitter and successive interference cancellation (SIC) at the receivers, has been intensively studied in recent years, albeit mostly under the assumption of perfect Channel State Information at the Receiver (CSIR) and ideal capacity-achieving modulation and coding schemes. To assess its practical performance, benefits, and limits under more realistic conditions, this work proposes a novel design for a practical RSMA receiver based on model-based deep learning (MBDL) methods, which aims to unite the simple structure of the conventional SIC receiver and the robustness and model agnosticism of deep learning techniques. The MBDL receiver is evaluated in terms of uncoded Symbol Error Rate (SER), throughput performance through Link-Level Simulations (LLS), and average training overhead. Also, a comparison with the SIC receiver, with perfect and imperfect CSIR, is given. Results reveal that the MBDL receiver outperforms by a significant margin the SIC receiver with imperfect CSIR, due to its ability to generate on demand non-linear symbol detection boundaries in a pure data-driven manner.
Rizzello V, Nerini M, Joham M, et al., 2023, User-Driven Adaptive CSI Feedback With Ordered Vector Quantization, IEEE Wireless Communications Letters, Vol: 12, Pages: 1956-1960, ISSN: 2162-2337
We propose a user-driven method for adaptive quantization and feedback of channel state information (CSI) in frequency division duplexing systems. The approach can be combined with existing autoencoder neural networks and requires only a single codebook shared between the users and the base station. Users can provide feedback with different numbers of bits depending on their data rates, without system changes or additional storage requirements. We optimize CSI feedback by combining the nested dropout layer with vector quantization, resulting in a variable-length feedback approach. Simulation results show the proposed method outperforms state-of-the-art schemes in dynamically adapting to different feedback rates.
Nerini M, Clerckx B, 2023, Pareto Frontier for the Performance-Complexity Trade-Off in Beyond Diagonal Reconfigurable Intelligent Surfaces, IEEE Communications Letters, Vol: 27, Pages: 2842-2846, ISSN: 1089-7798
Reconfigurable intelligent surface (RIS) is an emerging technology allowing to control the propagation environment in wireless communications. Recently, beyond diagonal RIS (BD-RIS) has been proposed to reach higher performance than conventional RIS, at the expense of higher circuit complexity. Multiple BD-RIS architectures have been developed with the goal of reaching a favorable trade-off between performance and circuit complexity. However, the fundamental limits of this trade-off are still unexplored. In this letter, we fill this gap by deriving the expression of the Pareto frontier for the performance-complexity trade-off in BD-RIS. Additionally, we characterize the optimal BD-RIS architectures reaching this Pareto frontier.
Singh SK, Agrawal K, Singh K, et al., 2023, RSMA for Hybrid RIS-UAV-Aided Full-Duplex Communications With Finite Blocklength Codes Under Imperfect SIC, IEEE Transactions on Wireless Communications, Vol: 22, Pages: 5957-5975, ISSN: 1536-1276
In this work, we consider a hybrid aerial full-duplex (FD) relaying consisting of a reconfigurable intelligent surface (RIS) mounted over an FD unmanned aerial vehicle (UAV) relay operating in decode and forward mode to assist the information transfer between the base station and multiple users. For better spectral efficiency, we investigate the use of rate splitting multiple access (RSMA) in such networks and focus on joint optimization of RSMA parameters, 3D-coordinates of the UAV/RIS, and phase shift matrix at the RIS along with analyzing the outage probability, block error rate (BLER) and achievable weighted sum rate for finite blocklength (FBL) and infinite blocklength (IBL) codes under imperfect successive interference cancellation (SIC) at each user and residual-self interference (RSI) at the UAV. We first formulate the weighted sum rate maximization problem and adopt the block coordinate descent (BCD) method to deal with the non-convex nature of the problem. Thereafter, we propose a BCD-based algorithm that jointly optimizes these parameters using a heuristic approach for optimum power allocation, a Riemannian conjugate gradient-based algorithm to get the optimal phase shift at the RIS, and an iterative algorithm to obtain the optimal UAV/RIS position. It also distributes the common rate among the users optimally. Next, with obtained optimal parameters, we further analyze the performance of the network and derive the closed-form expressions of BLER, outage probability, and average weighted sum rate. We present Monte Carlo simulation-based results to validate the accuracy of the proposed algorithms and derived expressions, and demonstrate the superiority of RSMA over non-orthogonal multiple access (NOMA) and conventional orthogonal multiple access (OMA) schemes.
Liu Z, Aditya S, Li H, et al., 2023, Joint transmit and receive beamforming design in full-duplex integrated sensing and communications, IEEE Journal on Selected Areas in Communications, Vol: 41, Pages: 2907-2919, ISSN: 0733-8716
Integrated sensing and communication (ISAC) has been envisioned as a solution to realize the sensing capability required for emerging applications in wireless networks. For a mono-static ISAC transceiver, as signal transmission durations are typically much longer than the radar echo round-trip times, the radar returns are drowned by the strong residual self interference (SI) from the transmitter, despite adopting sufficient SI cancellation techniques before digital domain - a phenomenon termed the echo-miss problem. A promising approach to tackle this problem involves the ISAC transceiver to be full-duplex (FD), and in this paper we jointly design the transmit and receive beamformers at the transceiver, transmit precoder at the uplink user, and receive combiner at the downlink user to simultaneously (a) maximize the uplink and downlink communication rate, (b) maximize the transmit and receive radar beampattern power at the target, and (c) suppress the residual SI. To solve this optimization problem, we proposed a penalty-based iterative algorithm. Numerical results illustrate that the proposed design can effectively achieve up to 60 dB digital-domain SI cancellation, a higher average sum-rate, and more accurate radar parameter estimation compared with previous ISAC FD studies.
Liu Z, Bhandari A, Clerckx B, 2023, λ–MIMO: massive MIMO via modulo sampling, IEEE Transactions on Communications, ISSN: 0090-6778
Massive multiple-input multiple-output (M-MIMO) architecture is the workhorse of modern communication systems. Currently, two fundamental bottlenecks, namely, power consumption and receiver saturation, limit the full potential achievement of this technology. These bottlenecks are intricately linked with the analog-to-digital converter (ADC) used in each radio frequency (RF) chain. The power consumption in M–MIMO systems grows exponentially with the ADC’s bit budget while ADC saturation causes permanent loss of information. This motivates the need for a solution that can simultaneously tackle the above-mentioned bottlenecks while offering advantages over existing alternatives such as low-resolution ADCs. Taking a radically different approach to this problem, we propose λ–MIMO architecture which uses modulo ADCs ( M λ –ADC) instead of a conventional ADC. Our work is inspired by the Unlimited Sampling Framework. M λ –ADC in the RF chain folds high dynamic range signals into low dynamic range modulo samples, thus alleviating the ADC saturation problem. At the same time, digitization of modulo signal results in high resolution quantization. In the novel λ–MIMO context, we discuss baseband signal reconstruction, detection and uplink achievable sum-rate performance. The key takeaways of our work include, (a) leveraging higher signal-to-quantization noise ratio (SQNR), (b) detection and average uplink sum-rate performances comparable to a conventional, infinite-resolution ADC when using a 1-2 bit M λ –ADC. This enables higher order modulation schemes e.g. 1024 QAM that seemed previously impossible, (c) superior trade-off between energy efficiency and bit budget, thus resulting in higher power efficiency. Numerical simulations and modulo ADC based hardware experiments corroborate our theory and reinforce the clear benefits of λ–MIMO approach.
Katwe M, Singh K, Clerckx B, et al., 2023, Improved Spectral Efficiency in STAR-RIS Aided Uplink Communication Using Rate Splitting Multiple Access, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 5365-5382, ISSN: 1536-1276
Li H, Shen S, Clerckx B, 2023, Beyond Diagonal Reconfigurable Intelligent Surfaces: A Multi-Sector Mode Enabling Highly Directional Full-Space Wireless Coverage, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, Vol: 41, Pages: 2446-2460, ISSN: 0733-8716
Salem A, Masouros C, Clerckx B, 2023, Secure Rate Splitting Multiple Access: How Much of the Split Signal to Reveal?, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 4173-4187, ISSN: 1536-1276
Clerckx B, Mao Y, Jorswieck EA, et al., 2023, A Primer on Rate-Splitting Multiple Access: Tutorial, Myths, and Frequently Asked Questions, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, Vol: 41, Pages: 1265-1308, ISSN: 0733-8716
Cui H, Zhu L, Xiao Z, et al., 2023, Energy-Efficient RSMA for Multigroup Multicast and Multibeam Satellite Communications, IEEE WIRELESS COMMUNICATIONS LETTERS, Vol: 12, Pages: 838-842, ISSN: 2162-2337
Nerini M, Rizzello V, Joham M, et al., 2023, Machine Learning-Based CSI Feedback With Variable Length in FDD Massive MIMO, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 2886-2900, ISSN: 1536-1276
Mishra A, Mao Y, Thomas CK, et al., 2023, Mitigating Intra-Cell Pilot Contamination in Massive MIMO: A Rate Splitting Approach, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 3472-3487, ISSN: 1536-1276
Xu Y, Mao Y, Dizdar O, et al., 2023, Max-Min Fairness of Rate-Splitting Multiple Access With Finite Blocklength Communications, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, Vol: 72, Pages: 6816-6821, ISSN: 0018-9545
Katwe M, Singh K, Clerckx B, et al., 2023, Rate Splitting Multiple Access for Sum-Rate Maximization in IRS Aided Uplink Communications, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 2246-2261, ISSN: 1536-1276
Li H, Shen S, Clerckx B, 2023, Beyond Diagonal Reconfigurable Intelligent Surfaces: From Transmitting and Reflecting Modes to Single-, Group-, and Fully-Connected Architectures, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 2311-2324, ISSN: 1536-1276
Nerini M, Clerckx B, 2023, Overhead-Free Blockage Detection and Precoding Through Physics-Based Graph Neural Networks: LIDAR Data Meets Ray Tracing, IEEE WIRELESS COMMUNICATIONS LETTERS, Vol: 12, Pages: 565-569, ISSN: 2162-2337
Xu J, Dizdar O, Clerckx B, 2023, Rate-Splitting Multiple Access for Short-Packet Uplink Communications: A Finite Blocklength Analysis, IEEE COMMUNICATIONS LETTERS, Vol: 27, Pages: 517-521, ISSN: 1089-7798
Zhao Y, Wu Y, Hu J, et al., 2023, Energy Harvesting Modulation for Integrated Control State and Energy Transfer in Industrial IoT, IEEE WIRELESS COMMUNICATIONS LETTERS, Vol: 12, Pages: 292-296, ISSN: 2162-2337
Yin L, Clerckx B, 2023, Rate-Splitting Multiple Access for Satellite-Terrestrial Integrated Networks: Benefits of Coordination and Cooperation, IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, Vol: 22, Pages: 317-332, ISSN: 1536-1276
Park J, Lee B, Choi J, et al., 2023, Rate-Splitting Multiple Access for 6G Networks: Ten Promising Scenarios and Applications, IEEE Network, ISSN: 0890-8044
In the upcoming 6G era, multiple access (MA) will play an essential role in achieving high throughput performances required in a wide range of wireless applications. Since MA and interference management are closely related issues, the conventional MA techniques are limited in that they cannot provide near-optimal performance in universal interference regimes. Recently, rate-splitting multiple access (RSMA) has been gaining much attention. RSMA splits an individual message into two parts: a common part, decodable by every user, and a private part, decodable only by the intended user. Each user first decodes the common message and then decodes its private message by applying successive interference cancellation (SIC). By doing so, RSMA not only embraces the existing MA techniques as special cases but also provides significant performance gains by efficiently mitigating inter-user interference in a broad range of interference regimes. In this article, we first present the theoretical foundation of RSMA. Subsequently, we put forth four key benefits of RSMA: spectral efficiency, robustness, scalability, and flexibility. Upon this, we describe how RSMA can enable ten promising scenarios and applications along with future research directions to pave the way for 6G.
Mishra A, Mao Y, D'Andrea C, et al., 2023, Transmitter Side Beyond-Diagonal Reconfigurable Intelligent Surface for Massive MIMO Networks, IEEE Wireless Communications Letters, ISSN: 2162-2337
This letter focuses on a transmitter or base station (BS) side beyond-diagonal reflecting intelligent surface (BD-RIS) deployment strategy to enhance the spectral efficiency (SE) of a time-division-duplex massive multiple-input multiple-output (MaMIMO) network. In this strategy, the active antenna array utilizes a BD-RIS at the BS to serve multiple users in the downlink. Based on the knowledge of statistical channel state information (CSI), the BD-RIS coefficients matrix is optimized by employing a novel manifold algorithm, and the power control coefficients are then optimized with the objective of maximizing the minimum SE. Through numerical results we illustrate the SE performance of the proposed transmission framework and compare it with that of a conventional MaMIMO transmission for different network settings.
Shen S, Kim J, Clerckx B, 2023, Closed-loop wireless power transfer with adaptive waveform and beamforming: design, prototype, and experiment, IEEE Journal of Microwaves, Vol: 3, Pages: 29-42, ISSN: 2692-8388
A closed-loop far-field wireless power transfer (WPT) system with adaptive waveform and beamforming using limited feedback is designed, prototyped, and experimented. Spatial domain and frequency domain are jointly exploited by utilizing waveform and beamforming at the transmitter in WPT system to adapt to the multipath fading channel and boost the output dc power. A closed-loop architecture based on a codebook design and an over-the-air limited feedback with low complexity is proposed. The codebook consists of multiple codewords where each codeword represents particular waveform and beamforming. The transmitter sweeps through the codebook and the receiver then feeds the optimal codeword index back to the transmitter, so that the waveform and beamforming can be adaptive for maximizing the output dc power without requiring explicit channel estimation and the knowledge of accurate Channel State Information. The proposed closed-loop WPT with adaptive waveform and beamforming using limited feedback is prototyped using a Software Defined Radio equipment and measured in two real indoor environments. It is experimentally shown that the proposed closed-loop WPT with adaptive waveform and beamforming is able to enhance the output dc power by up to 14.7 dB in comparison with conventional 1-tone 1-antenna WPT system.
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