Tutorials

Duration: 1 hours 7 minutes

Speaker: Prof. Bruno Clerckx

Abstract: In the past few years, a large body of literature has been created on downlink Non-Orthogonal Multiple Access (NOMA), employing superposition coding and Successive Interference Cancellation (SIC), in multi-antenna wireless networks. Furthermore, the benefits of NOMA over Orthogonal Multiple Access (OMA) have been highlighted. In this paper, we take a critical and fresh look at the downlink Next Generation Multiple Access (NGMA) literature. Instead of contrasting NOMA with OMA, we contrast NOMA with two other multiple access baselines. The first is conventional Multi-User Linear Precoding (MU–LP), as used in Space-Division Multiple Access (SDMA) and multi-user Multiple-Input Multiple-Output (MIMO) in 4G and 5G. The second, called Rate-Splitting Multiple Access (RSMA), is based on multi-antenna Rate-Splitting (RS). It is also a non-orthogonal transmission strategy relying on SIC developed in the past few years in parallel and independently from NOMA. We show that there is some confusion about the benefits of NOMA, and we dispel the associated misconceptions. First, we highlight why NOMA is inefficient in multi-antenna settings based on basic multiplexing gain analysis. We stress that the issue lies in how the NOMA literature, originally developed for single-antenna setups, has been hastily applied to multi-antenna setups, resulting in a misuse of spatial dimensions and therefore loss in multiplexing gains and rate. Second, we show that NOMA incurs a severe multiplexing gain loss despite an increased receiver complexity due to an inefficient use of SIC receivers. Third, we emphasize that much of the merits of NOMA are due to the constant comparison to OMA instead of comparing it to MU–LP and RS baselines. We then expose the pivotal design constraint that multi-antenna NOMA requires one user to fully decode the messages of the other users. This design constraint is responsible for the multiplexing gain erosion, rate and spectral efficiency loss, ineffectiveness to serve a large number of users, and inefficient use of SIC receivers in multi-antenna settings. Our analysis and simulation results confirm that NOMA should not be applied blindly to multi-antenna settings, highlight the scenarios where MU–LP outperforms NOMA and vice versa, and demonstrate the inefficiency, performance loss, and complexity disadvantages of NOMA compared to RSMA. The first takeaway message is that, while NOMA is suited for single-antenna settings (as originally intended), it is not efficient in most multi-antenna deployments. The second takeaway message is that another non-orthogonal transmission framework, based on RSMA, exists which fully exploits the multiplexing gain and the benefits of SIC to boost the rate and the number of users to serve in multi-antenna settings and outperforms both NOMA and MU–LP. Indeed, RSMA achieves higher multiplexing gains and rates, serves a larger number of users, is more robust to user deployments, network loads and inaccurate channel state information and has a lower receiver complexity than NOMA. Consequently, RSMA is a promising technology for NGMA and future networks such as 6G and beyond. 

More details in B. Clerckx, Y. Mao, R. Schober, E. Jorswieck, D. J. Love, J. Yuan, L. Hanzo, G. Y. Li, E. G. Larsson, and G. Caire., "Is NOMA efficient in multi-antenna networks? A critical look at next generation multiple access techniques," in IEEE Open Journal of the Communications Society, vol. 2, pp. 1310-1343, 2021.

Abstract: This is the latest tutorial of RSMA on 14 Jun, 2021. More up-to-date works on RSMA have been added. The tutorial gives the audience a comprehensive introduction of the state-of-the-art development in RSMA theory and applications in wireless systems.

Duration: 1 hours 15 minutes

Speaker: Prof. Bruno Clerckx

Abstract: This is the WTC seminar on Nov. 10, 2020. This talk shares key principles of RSMA, recent developments, and emerging applications and opportunities of RSMA for beyond 5G networks.

Presentation Slide: [find here]

Presentation Record: [find here] (Password for the recording: WTCseminar2020!)

Duration: 3 hours 40 minutes

Speaker: Prof. Bruno Clerckx

Abstract: This tutorial is dedicated to the theory, design, optimization and applications of rate-splitting and demonstrates the significant benefits in terms of spectral/energy efficiencies, reliability and robustness to Channel State Information imperfections over conventional strategies used in 5G (multi-user MIMO, massive MIMO, CoMP, mmwave MIMO) and NOMA, in a wide range of deployments, network loads (underloaded, overloaded), services (unicast, multicast) and systems (terrestrial and satellite).

Duration: 35 minutes

Speaker: Prof. Bruno Clerckx

Abstract: This tutorial is a shorter version of the above tutorial. It is a brief introduction of the fundamentals of rate-splitting and its state-of-the-art applications. 

Duration: 14 minutes

Speaker: Dr. Onur Dizdar

Abstract: This is a brief introduction of the paper "Rate-splitting multiple access: A new frontier for the PHY layer of 6G". In this paper, we discussed the emerging problems and core services of 5G and KPIs and characteristics of 6G and how RSMA fits into these standards as an enabling technology. The literature and results so far imply that RSMA is a promising candidate in numerous application areas and use cases, and that RSMA can be used as a fundamental building block of the physical layer and lower MAC of 6G communications. There are still numerous open research topics for RSMA and addressing them will provide a better picture on the role and benefits of RSMA in 6G.

Duration: 13 minutes

Speaker: Dr. Onur Dizdar

Abstract: This is a brief introduction of the paper "Rate-splitting multiple access for downlink multi-antenna communications: Physical layer design and link-level simulations". In this work, we analyse the performances of RSMA, SDMA and NOMA by link-level simulations (LLS) under imperfect CSIT. We design basic transmitter and receiver architectures for RSMA with finite constellation modulation schemes, polar codes and an AMC algorithm. Using the proposed architectures and our LLS platform, we demonstrate that RSMA is more robust and achieves significantly higher throughput than SDMA and NOMA with and without QoS constraints in the considered imperfect CSIT settings.