BEST READINGS

+ Basic Principles of RSMA

Overview


Multiple access (MA) is a crucial part of any wireless system and refers to techniques that make use of the resource dimensions to serve multiple users/devices/machines/services, ideally in the most efficient way. Given the needs of multi-functional wireless networks for integrated communications, sensing, localization, computing, coupled with the surge of machine learning / artificial intelligence (AI) in wireless networks, MA techniques are expected to experience a paradigm shift in 6G and beyond. In this paper, the authors provide a tutorial, survey and outlook of past, emerging and future MA techniques and pay a particular attention to how wireless network intelligence and multi-functionality will lead to a re-thinking of those techniques.

This paper proposes the 1-layer rate-splitting model for multi-antenna broadcast channels.

In this tutorial, the authors depart from the orthogonal multiple access (OMA) versus non-orthogonal multiple access (NOMA) discussion held in 5G, and the conventional multi-user linear precoding approach used in space-division multiple access (SDMA), multi-user and massive MIMO in 4G and 5G, and show how multi-user communications and multiple access design for 6G and beyond should be intimately related to the fundamental problem of interference management. The authors start from foundational principles of interference management and rate-splitting, and progressively delineate RSMA frameworks for downlink, uplink, and multi-cell networks. 

This paper presents the first comprehensive tutorial on RSMA providing a survey of the pertinent state-of-the-art research, detailing its architecture, taxonomy, and various appealing applications, as well as comparing with existing MA schemes in terms of their overall frameworks, performance, and complexities. An in-depth discussion of future RSMA research challenges is also provided to inspire future research on RSMA-aided wireless communication for beyond 5G systems. 

This letter is the first part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part I of the tutorial, the letter presents the basics of RSMA and its applications in light of 6G. The letter delineates the design principle and basic transmission frameworks of downlink and uplink RSMA. The letter then illustrates the applications of RSMA for addressing the challenges of various potential enabling technologies and use cases, consequently making it a promising next generation multiple access (NGMA) scheme for future networks such as 6G and beyond.  


This letter is the second part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part II of the tutorial, this letter addresses the interplay between RSMA and integrated radar sensing and communications (ISAC). In particular, the introduces a general RSMA-assisted ISAC architecture, where the ISAC platform has a dual capability to simultaneously communicate with downlink users and probe detection signals to a moving target.  


This letter is the third part of a three-part tutorial that focuses on rate-splitting multiple access (RSMA) for 6G. As Part III of the tutorial, this letter provides an overview of integrating RSMA and reconfigurable intelligent surface (RIS). 



Rate-splitting multiple access (RSMA) has appeared as a powerful transmission and multiple access strategy for multi-user multi-antenna communications. Uniquely, this paper studies the optimization of the sum-rate of RSMA with imperfect channel state information (CSI) at the transmitter (CSIT) and the receivers (CSIR). The robustness of the RSMA approach against imperfect CSIT has been investigated in the previous studies while there has been no consideration for the effects of imperfect CSIR. This motivates the paper to develop a robust design relying on RSMA in the presence of both imperfect CSIT and CSIR. Since the optimization problem for the design of RSMA precoder and power allocations to maximize the sum-rate is non-convex, it is hard to solve directly. To tackle the non-convexity, we propose a novel alternating optimization algorithm based on semidefinite relaxation (SDR) and concave-convex procedure (CCCP) techniques. By comparing simulation results with conventional methods, it turns out that RSMA is quite robust to imperfect CSIR and CSIT, thereby improving the sum-rate performance. 



Sum-Rate Optimization

This is the first paper that studies the performance of rate-splitting with partial CSIT and it proves that rate-splitting achieves the optimal sum-Degree-of-Freedom (DoF) of multiple-input single-output (MISO) broadcast channel (BC) with imperfect channel state information at the transmitter (CSIT).

This is the first paper that compares the DoF of MU–MIMO, MIMO NOMA and RS in a MIMO setting, studies the precoder optimization and the benefits of transmitting multiple commons streams in RS-assisted MIMO BC with perfect and imperfect CSIT, and designs the PHY-layer architecture to provide throughput performance of RS via the link level simulations (LLS) in MIMO settings. 


RSMA Generalizes NOMA and SDMA

This is the first paper that proposes the generalized framework of RSMA and compares its performance with non-orthogonal multiple access (NOMA) and dirty paper coding (DPC).


This paper illustrates the simplest two-user rate-splitting in MISO broadcast channel. Low-complexity precoding based on zero-forcing is adopted and the optimal power allocation between the common and private streams is calculated.


Next Generation Multiple Access

This letter is the first part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part I of the tutorial, the letter presents the basics of RSMA and its applications in light of 6G. The letter delineates the design principle and basic transmission frameworks of downlink and uplink RSMA. The letter then illustrates the applications of RSMA for addressing the challenges of various potential enabling technologies and use cases, consequently making it a promising next generation multiple access (NGMA) scheme for future networks such as 6G and beyond.   

This paper shows why non-orthogonal multiple access (NOMA) is inefficient in multi-antenna settings based on basic multiplexing gain analysis and highlights other non-orthogonal transmission frameworks, such as rate-splitting, exist which fully exploit the multiplexing gain and the benefits of successice interference cancellation (SIC) to boost the rate in multi-antenna settings.

Multiple access (MA) is a crucial part of any wireless system and refers to techniques that make use of the resource dimensions to serve multiple users/devices/machines/services, ideally in the most efficient way. Given the needs of multi-functional wireless networks for integrated communications, sensing, localization, computing, coupled with the surge of machine learning / artificial intelligence (AI) in wireless networks, MA techniques are expected to experience a paradigm shift in 6G and beyond. In this paper, the authors provide a tutorial, survey and outlook of past, emerging and future MA techniques and pay a particular attention to how wireless network intelligence and multi-functionality will lead to a re-thinking of those techniques.


Beyond Dirty Paper Coding

This is the first paper that shows that linearly precoded RSMA outperforms DPC with partial CSIT. A novel non-linear RSMA strategy, namely, dirty paper coded rate splitting (DPCRS) is proposed and shown to achieve a better rate region than DPC. 

+ Information Theoretic Analysis of RSMA

Two-user Interference Channel


It proposes rate-splitting for two-user single-input single-output (SISO) interference channel (IC).



This work shows that rate-splitting based on the HK scheme achieves rate regions within 1 bit/s/Hz of the capacity region in SISO IC.



Multiple Access Channel (Uplink)


This is the first work of rate-splitting in the uplink. It shows that rate-splitting based on successive single-user decoding and interference cancellation achieves the capacity region of the K-user Gaussian multiple access channel without the need for time sharing.



Two-User MISO BC with Partial CSIT


     This work calculates the two-user DoF for MISO BC with imperfect CSIT.



     This work calculates the two-user achieves constant-gap optimal to the sum-capacity of the two-user MISO BC. 



This paper shows rate-splitting achieves constant-gap optimal to the whole capacity region of the two-user MISO BC. But the constant-gap optimality is not guaranteed in general. 



Sum-GDoF of the K-User Underloaded MISO BC with Partial CSIT


This work proves that rate-splitting-assisted interference enhancement approach achieves the entire generalized DoFs (GDoFs) region of the two-user underloaded MISO BC with imperfect CSIT.



Sum-DoF Optimality of K-user MISO BC with Partial CSIT


This work provides a tight sum-DoF upperbound for the K-user MISO BC with arbitrary levels of partial CSIT.



RS achieves the optimum sum-DoF of the K-user underloaded MISO BC with imperfect CSIT, which coincides with the sum-DoF upperbound shown in the previous paper (Davoodi and Jafar, TIT, 2016).



DoF Region Optimality of K-user MISO BC with Partial CSIT


This work proves that RS achieves the entire DoF region of the underloaded MISO BC with imperfect CSIT.



This work proposes an alternative approach to prove the optimality of the DoF region achieved by rate-splitting.



Symmetric DoF of K-user MISO BC with Partial CSIT


This work shows that rate-splitting achieves a higher symmetric (max-min) DoF than space division multiple access (SDMA) based on multi-user linear precoding for the K-user underloaded MISO BC with imperfect CSIT.



Overloaded Transmission


This work proves that rate-splitting achieves the entire DoF region of the K-user overloaded MISO BC with imperfect heterogeneous CSIT qualities.



Multi-Antenna Wireless Networks


This work calculates DoF region of rate-splitting for the K-cell MISO IC with imperfect CSIT.



DoF Optimality for MIMO Networks


This work proposes an achievable scheme based on rate-splitting for the two-user multiple input multiple output (MIMO) networks with imperfect CSIT, and shows optimality under certain antenna-configurations and CSIT qualities.



This work derives the upperbound of the DoF region of the two-user MIMO networks with imperfect CSIT and shows the DoF region of rate-splitting achieved by the previous paper (Hao et al. TIT 2017) coincides with the upperbound.



Symmetric DoF in Multigroup Multicast Transmission


This work shows that rate-splitting achieves the highest symmetric DoF compared with that of SDMA based on MU-LP and NOMA based on superposition coding (SC) and successive interference cancellation (SIC) for the K-user overloaded MISO BC with perfect CSIT.



This paper characterizes the MMF DoF achieved by RSMA in multigroup multicast transmission with imperfect CSIT and demonstrates the benefits of RS strategies for both underloaded and overloaded scenarios.

+ Physical Layer Design and Optimization of RSMA

PHY Layer Design and Link-Level Simulations

This paper designs the physical layer of RSMA, accounting for modulation, coding (using polar codes), message split, adaptive modulation and coding, and SIC receiver. 


This paper studies the uncoded link level performance of rate-splitting. Bit error rate (BER) performance of RSMA is provided.


Space-Time Coding

This paper proposes a particular RS scheme which relies on space-time block coding to transmit the common message.  The proposed scheme is shown to be suited in the absence of full CSIT.


Quantized Feedback

This paper focuses on a two-user multiple-input single-output (MISO) broadcast channel (BC) with quantized channel state information at the transmitter (CSIT) (based on random vector quantization). It shows the potential of RSMA to reduce the feedback overhead.


This paper focuses on a K-user MISO BC with quantized CSIT (based on random vector quantization). Rate-splitting is shown to achieve significant sum-rate gain over conventional schemes.


Global Optimization



This work considers globally optimal precoder design for RSMA in Gaussian MISO downlink channels with respect to weighted sum rate and energy efficiency maximization. 


Energy Efficiency Optimization

This is the first paper that shows the energy efficiency performance of RSMA. 


This paper shows that RSMA achieves a superior trade-off between spectral and energy efficiency than SDMA and NOMA.


Robust Optimization


This work shows that RS achieves higher max-min (symmetric) Degree-of-Freedom (DoF) compared with conventional SDMA based on MU-LP for CSIT uncertainty regions that scale with SNR (e.g., by scaling the number of feedback bits). For the special case of non-scaling CSIT (e.g., fixed number of feedback bits), RS achieves a non-saturating max-min rate which is contrary to MU-LP. 


This is the first paper that studies the performance of rate-splitting with partial CSIT and it proves rate-splitting achieves the optimal sum-DoF of MISO BC with imperfect CSIT.


Joint Decoding Receiver


This paper investigates the achievable rates of RSMA in MISO BC with imperfect CSIT with joint decoding receivers. 

+ Superiority of RSMA over SDMA and NOMA

Multi-User Multi-Antenna Communications

This is the first paper that proposes the generalized framework of RSMA and compares its performance with non-orthogonal multiple access (NOMA) and dirty paper coding (DPC).


This paper illustrates the simplest two-user rate-splitting in MISO broadcast channel. Low-complexity precoding based on zero-forcing is adopted and the optimal power allocation between the common and private streams is calculated.

This is the first paper that compares the DoF of MU–MIMO, MIMO NOMA and RS in a MIMO setting, studies the precoder optimization and the benefits of transmitting multiple commons streams in RS-assisted MIMO BC with perfect and imperfect CSIT, and designs the PHY-layer architecture to provide throughput performance of RS via the link level simulations (LLS) in MIMO settings.  


This paper studies the sum-rate maximization problem of RSMA in SISO BC.


Multigroup Multicast


This is the first paper of RSMA in multigroup multicast transmission. This work characterizes the max-min fairness (MMF) DoF achieved by RSMA in multigroup multicast with perfect CSIT. It also shows that RS exhibits strictly higher MMF-rates in partially and fully overloaded scenarios.



This paper illustrates the MMF gain of RSMA over SDMA and NOMA in multigroup multicasting scenarios.


Energy Efficiency Optimization

This is the first paper that shows the energy efficiency performance of RSMA. 



This is the first paper investigating RSMA in NOUM. A novel system model based on RSMA is proposed for NOUM which better reuses the SIC for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user.



This paper investigates the energy efficiency of the RSMA and NOMA schemes in a millimeter-wave (mmWave) downlink UAV-assisted network. Numerical results indicates that RSMA is superior to NOMA in terms of overall energy efficiency.


Coordinated Multi-Point (CoMP)


This is the first paper that studies RSMA in multi-cell networks. Specifically, it studies RSMA in downlink coordinated multi-point (CoMP) joint transmission (JT) networks and shows that RSMA outperforms SDMA and NOMA in a wide range of inter-user and inter-cell channel strength disparities.


Nou-Orthogonal Unicast and Multicast (NOUM) Transmission


This is the first paper investigating RSMA in NOUM. A novel system model based on RSMA is proposed for NOUM which better reuses the SIC for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user.



This paper investigates non-linear precoding of RSMA in NOUM. A novel dirty paper coded rate splitting (DPCRS) strategy is proposed, which achieves larger rate regions than DPC-assisted NOUM in MISO BC with partial CSIT.


Reconfigurable Intelligent Surface (RIS)


This is the first paper of RSMA for RIS, in which RSMA is shown to enhance the energy efficiency of RIS-assisted transmission networks.


Simultaneous Wireless Information and Power Transfer (SWIPT)


This paper shows that rate-splitting achieves a better rate-energy tradeoff in MISO SWIPT BC with separated information users and energy users. 


Cooperative Transmission with User Relaying


This is the first paper that proposes cooperative rate-splitting (CRS) with user-relaying in the two-user case. 


Imperfect CSIT

This is the first paper showing that linearly precoded RSMA outperforms DPC with partial CSIT. A novel non-linear RSMA strategy, namely, dirty paper coded rate splitting (DPCRS) is proposed and shown to achieve a better rate region than DPC. 


Link-Level Simulations

This paper designs the physical layer of RSMA, accounting for modulation, coding (using polar codes), message split, adaptive modulation and coding, and SIC receiver. 


Cloud-Radio Access Network (C-RAN) 


This paper studies RSMA in C-RAN with fronthaul compression and fronthaul capacity constraint.



This paper studies RSMA in C-RAN with statistical CSIT (i.e., the transmitter only knows the distribution information of user channels).


Visible Light Communication (VLC)


This is the first paper that introduces RSMA to the multi-cell visible light communication (VLC) networks. By taking into account the specific constraints of optical signals and the LED effect, 1-layer RSMA is able to enhance the system spectral efficiency.



This paper provides an overview of the key multiple access techniques used in VLC systems. It also discusses the capabilities and potentials of RSMA in VLC systems. 


Secrecy Rate


This paper employs CRS technique to enhance the secrecy sum rate for the MISO BC with two legitimate users and one eavesdropper.



This paper studies the max-min fairness for a downlink two-user MISO system with imperfect CSIT by taking into account a potential eavesdropper.


Aerial Networks


This paper investigates energy efficiency of RSMA and NOMA in a millimeter-wave (mmWave) downlink UAV-assisted network. Numerical results indicates that RSMA is superior to NOMA in terms of overall energy efficiency.



This paper gives a comprehensive survey of key multiple access techniques for aerial networks. It also studies RSMA in a two-user MISO BC with UAV serving as an aerial transmitter.


Imperfect CSIT and Imperfect CSIR


This paper investigates sum rate maximization of RSMA with imperfect CSIT and imperfect CSIR.


Network Performance Analysis


This paper provides an analytical framework on rate-splitting which captures spatial randomness and provides closed-form expressions for the distributions of the SINR at the receivers. Results highlight the flexibility of RSMA against NOMA in terms of fairness performance.


Spectral and Energy Efficiency Tradeoff


This paper shows the significant performance gains of RSMA over SDMA and NOMA in terms of energy efficiency, spectral efficiency, as well as their tradeoff in multi-antenna broadcast channels.



This paper shows that RSMA is more flexible in achieving a better spectral and energy efficiency tradeoff than SDMA and NOMA in the multicell system.

+ Interplay Between RSMA and Other Emerging Technologies

Symbol-Level Precoding

This paper derives new analytical expressions for the ergodic sum-rate of rate-splitting based on finite constellations with constructive interference (CI) and zero-forcing (ZF) precoding schemes for the private messages.


Millimeter-wave (mmWave)


This is the first paper investigating rate-splitting in mmWave systems. This paper shows that rate-splitting enables remarkable saving in the second-stage training and feedback overhead in multi-user mmWave systems.



This paper investigates the energy efficiency of RSMA and NOMA in a millimeter-wave (mmWave) downlink UAV-assisted network. Numerical results indicates that RSMA is superior to NOMA in terms of overall energy efficiency.


Massive MIMO


This is the first paper investigating rate-splitting in massive MIMO networks.This paper proposes hierarchical rate-splitting (HRS) that is particularly suited to massive MIMO. HRS is shown to achieve significant sum rate gain in this work.



This paper shows that rate-splitting is robust to hardware imperfection resulting from oscillator phase noise and amplified thermal noise in time division duplex (TDD)-based massive MISO systems.



This paper considers a multi-pair decode-and-forward full-duplex relay channel, where the relay station is deployed with a large number of antennas. Relay stations employ a large number of antennas (massive MIMO). Rate-splitting is shown to achieve enhanced sum rate in both cases of half-duplex and full-duplex relaying.  



In this work, the authors study the performance of RSMA under the important setup of imperfect Channel State Information at the Transmitter (CSIT) originating from user mobility and latency/delay (between CSI acquisition and data transmission) in the network.   



This paper aims to integrate RSMA with TDD MaMIMO for downlink transmission and investigate its SE performance in the presence of pilot contamination. The paper shows that RSMA is significantly more robust to pilot contamination and always achieves a SE performance that is equal to or better than the conventional linearly precoded MaMIMO transmission strategy.



This letter focuses on integrating RSMA with TDD Cell-free Massive MIMO for massive machine-type communications. 


Cognitive Radio


This paper addresses the problem of resource allocation for systems in which a primary and a secondary link share the available spectrum by an underlay or overlay approach.



This paper studies secure communication in RSMA-based cognitive satellite-terrestrial network (CSTN) with imperfect wiretap CSI.


Simultaneous Wireless Information and Power Transfer (SWIPT)


This paper shows that rate-splitting achieves a better rate-energy tradeoff in MISO SWIPT BC with separated information users and energy users. 



This paper proposes a RS based robust design for MISO interference channel with SWIPT.



This paper studies rate-splitting in SWIPT with colocated information users and energy users. 


Nou-Orthogonal Unicast and Multicast (NOUM) Transmission


This is the first paper investigating RSMA in NOUM. A novel system model based on RSMA is proposed for NOUM which better reuses the SIC for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user.



This paper investigates non-linear precoding of RSMA in NOUM. A novel dirty paper coded rate splitting (DPCRS) strategy is proposed, which achieves larger rate regions than DPC-assisted NOUM in MISO BC with partial CSIT.


Cooperative Transmission with User Relaying


This is the first paper that proposes cooperative rate-splitting (CRS) with user-relaying in the two-user case. 



This paper generalises the two-user CRS to the K-user case. 



This paper employs CRS technique to enhance the secrecy sum rate for the MISO BC with two legitimate users and one eavesdropper.


Cloud-Radio Access Network (C-RAN) 


This paper studies RSMA in C-RAN with fronthaul compression and fronthaul capacity constraint.



This paper studies a hybrid UAV-assisted C-RAN. Multiple UAVs act as the transmitters and cooperatively serve multiple users using RSMA.



This paper studies rate-splitting in MIMO C-RAN when each user is equipped with multiple receive antennas.



This paper studies the performance of the generalized RS framework in C-RAN.



The paper addresses the problem of minimizing the weighted transmit power subject to minimum QoS and fronthaul capacity constraints.



This paper studies the energy efficiency (EE) maximization problem of rate-splitting in C-RAN. The global optimal EE solution is provided as a baseline to show the effectiveness of the proposed polynomial-time complexity algorithm.



This paper studies RSMA in C-RAN with data-sharing and fronthaul capacity constraint.



This paper studies RSMA in C-RAN with statistical CSIT (i.e., the transmitter only knows the distribution information of user channels).



This paper utilizes the rate-splitting technique to mitigate interference (including the interference amplified by the intelligent reconfigurable surface) within the network. 


Coordinated Multi-Point (CoMP)


This is the first paper that studies RSMA in multi-cell networks. Specifically, it studies RSMA in downlink coordinated multi-point (CoMP) joint transmission (JT) networks and shows that RSMA outperforms SDMA and NOMA in a wide range of inter-user and inter-cell channel strength disparities.


Multigroup Multicast


This is the first paper of RSMA in multigroup multicast transmission. This work characterizes the max-min fairness (MMF) DoF achieved by RSMA in multigroup multicast with perfect CSIT. It also shows that RS exhibits strictly higher MMF-rates in partially and fully overloaded scenarios.



This paper studies joint coordinated beamforming and antenna selection in multi-cell multi-user multigroup multicast MISO BC. Rate-splitting is shown to be achieve significant energy efficiency gain than conventional schemes. 



This paper studies the optimal MMF achieved by RSMA in multicarrier multigroup multicasting scenarios. 



This paper characterizes the MMF DoF achieved by RSMA in multigroup multicast transmission with imperfect CSIT and demonstrates the benefits of RS strategies for both underloaded and overloaded scenarios.



This paper studies MMF-rate performance of RSMA for multigroup multicast transmission with a system-wide common message.



This paper studies joint precoder design and subcarrier allocation for multi-carrier multigroup multicast systems. Rate-splitting is shown to achieve explicit max-min fairness improvement than conventional schemes.



This paper evaluates the error performance of the RS based transmission strategies with constellation-constrained coding/modulation.


Reconfigurable Intelligent Surface (RIS)


This letter is the third part of a three-part tutorial that focuses on rate-splitting multiple access (RSMA) for 6G. As Part III of the tutorial, this letter provides an overview of integrating RSMA and reconfigurable intelligent surface (RIS). 



This is the first paper of RSMA for RIS, in which RSMA is shown to enhance the energy efficiency of RIS-assisted transmission networks.



This article presents the potential of synergy between IRS and RSMA. Three important improvements achievable by IRS-RSMA schemes are identified, supported by insightful numerical examples, and mapped to beyond 5G use cases, along with future research directions. 


Physical Layer Security 


This paper employs CRS technique to enhance the secrecy sum rate of MISO BC with two legitimate users and one eavesdropper.



This paper studies the max-min fairness for a downlink two-user MISO system with imperfect CSIT by taking into account a potential eavesdropper.


Non-linear Precoding


This is the first paper that studies the non-linear precoding of RSMA in multi-antenna networks.


Satellite Communications


This paper shows the capability of rate-splitting to increase the spectral efficiency gains of multibeam satellite systems, while significantly reduces the feedback overhead. 



This paper studies the beamforming design problem to achieve max-min fairness (MMF) in multibeam satellite communications.



This paper studies the achievable rate of RSMA for multigroup multicast and multibeam satellite systems. It shows that RSMA is promising for multibeam satellite systems to manage inter-beam interference, taking into account practical challenges such as CSIT uncertainty, per-feed constraints, hot spots, uneven user distribution per beam, and overloaded regimes.


Joint Communication and Radar Transmission


This letter is the second part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part II of the tutorial, this letter addresses the interplay between RSMA and integrated radar sensing and communications (ISAC). In particular, the introduces a general RSMA-assisted ISAC architecture, where the ISAC platform has a dual capability to simultaneously communicate with downlink users and probe detection signals to a moving target.  



This is the first paper that applies RSMA in joint communication and radar transmission. The proposed RSMA-based joint communication and radar system is shown to achieve a better tradeoff between weighted sum rate and beam pattern approximation compared with the SDMA-based system.


Visible Light Communication (VLC)


This is the first paper that introduces RSMA to the multi-cell VLC networks. By taking into account the specific constraints of optical signals and the LED effect, 1-layer RSMA is shown to enhance the system spectral efficiency.



This paper provides an overview of the key multiple access techniques used in VLC systems. It also discusses the capabilities and potentials of RSMA in VLC systems. 


Unmanned Aerial Vehicle (UAV)


This paper investigates the energy efficiency of RSMA and NOMA in a millimeter-wave (mmWave) downlink UAV-assisted network. Numerical results indicates that RSMA is superior to NOMA in terms of overall energy efficiency.



This paper studies the joint optimization of UAV placement, RSMA precoding, and message split with the aim of maximizing the weighted sum rate.



This paper gives a comprehensive survey of key multiple access techniques for aerial networks. It also studies RSMA in a two-user MISO BC with UAV serving as an aerial transmitter. 


Coded Caching


This paper proposes a novel scheme to exploit the coded caching gain and leverage the available CSIT, which is shown to achieve a significant gain in terms of delivery time and CSIT quality requirement.



This paper generalizes and expands upon one-shot linear DoF results in the literature by including the parallel no-CSIT (or multicast) channel and by considering decentralization at the receivers.


Multicarrier Transmission


This paper proposes a joint power and muticarrier resource allocation scheme for multi-user multi-carrier RSMA. Random and zero-forcing beamforming are used for common and private messages.



This paper studies joint precoder design and subcarrier allocation for multi-carrier multigroup multicast systems. Rate-splitting is shown to achieve explicit max-min fairness improvement than conventional schemes.


Internet-of-Things 


This paper proposes a novel transmission framework based on RSMA for cellular IoT. The proposed scheme achieves the optimal DoF in the overloaded MISO BC with heterogeneous CSIT.

+ RSMA for 6G


Multiple access (MA) is a crucial part of any wireless system and refers to techniques that make use of the resource dimensions to serve multiple users/devices/machines/services, ideally in the most efficient way. Given the needs of multi-functional wireless networks for integrated communications, sensing, localization, computing, coupled with the surge of machine learning / artificial intelligence (AI) in wireless networks, MA techniques are expected to experience a paradigm shift in 6G and beyond. In this paper, the authors provide a tutorial, survey and outlook of past, emerging and future MA techniques and pay a particular attention to how wireless network intelligence and multi-functionality will lead to a re-thinking of those techniques.

This letter is the first part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part I of the tutorial, the letter presents the basics of RSMA and its applications in light of 6G. The letter delineates the design principle and basic transmission frameworks of downlink and uplink RSMA. The letter then illustrates the applications of RSMA for addressing the challenges of various potential enabling technologies and use cases, consequently making it a promising next generation multiple access (NGMA) scheme for future networks such as 6G and beyond.  


This letter is the second part of a three-part tutorial focusing on rate-splitting multiple access (RSMA) for 6G. As Part II of the tutorial, this letter addresses the interplay between RSMA and integrated radar sensing and communications (ISAC). In particular, the introduces a general RSMA-assisted ISAC architecture, where the ISAC platform has a dual capability to simultaneously communicate with downlink users and probe detection signals to a moving target.  


This letter is the third part of a three-part tutorial that focuses on rate-splitting multiple access (RSMA) for 6G. As Part III of the tutorial, this letter provides an overview of integrating RSMA and reconfigurable intelligent surface (RIS). 

This paper discusses the emerging problems and core services of 5G, KPIs and characteristics of 6G, and how RSMA fits into these standards as an enabling technology.

This paper studies the performance of RSMA in the scenarios related with the important core services of New Radio (NR) and 6G, namely, enhanced Ultra-Reliable and Low-Latency (URLLC) and enhanced Mobile Broadband Communications (eMBB).

In this tutorial, the authors depart from the orthogonal multiple access (OMA) versus non-orthogonal multiple access (NOMA) discussion held in 5G, and the conventional multi-user linear precoding approach used in space-division multiple access (SDMA), multi-user and massive MIMO in 4G and 5G, and show how multi-user communications and multiple access design for 6G and beyond should be intimately related to the fundamental problem of interference management. The authors start from foundational principles of interference management and rate-splitting, and progressively delineate RSMA frameworks for downlink, uplink, and multi-cell networks.  

Rate splitting (RS) and rate splitting multiple access (RSMA) have emerged as a promising and powerful multiple access, interference management, and multi-user strategy for next-generation wireless systems and networks. This Special Issue is entirely dedicated to the theory, design, optimization, and applications of RS and RSMA in various network configurations. It starts with a guest editor-authored tutorial paper that delineates the basic principles and applications of RS and RSMA. The tutorial paper is then followed by 17 technical papers.   

+ RSMA Prototyping and Experimental Results 


For interference-limited multi-user communications, many papers have demonstrated, in theory, the effectiveness of Rate Splitting Multiple Access (RSMA) in suppressing the interference and achieving better outcomes (w.r.t spectral efficiency, fairness etc.) than the conventional Space Division Multiple Access (SDMA) used in present-day standards. However, an experimental demonstration of RSMA's benefits is missing in the literature. In this paper, the authors address this gap by realizing an RSMA prototype using software-defined radios. For the two-user multiple-input single-output (MISO) scenario, the authors measure the throughput performance of SDMA and RSMA in nine different scenarios that vary in terms of the channel pathloss and spatial correlation experienced by the users. Emulating perfect channel state information (CSI) at the transmitter through unquantized CSI feedback, it is observed that RSMA achieves a higher sum throughput (upto 57%) and more fairness than SDMA when the user channels have high spatial correlation. Similarly, emulating imperfect CSI through quantized feedback, RSMA - along with the above trend - also experiences a smaller sum throughput loss, relative to the unquantized case (37%, on average, as opposed to 44% for SDMA). These outcomes are consistent with theoretical predictions, and demonstrate the feasibility and potential of RSMA for next generation wireless networks (e.g., 6G).