Performance Enhancement Using NOMA-MIMO for 5G Networks

The integration of MIMO and NOMA technologies addresses key challenges in 5G and beyond, such as connectivity, latency, and dependability. However, resolving these issues, especially in MIMO-enabled 5G networks, required additional research. This involved optimizing parameters like bit error rate, downlink spectrum efficiency, average capacity rate, and uplink transmission outage probability. The model employed Quadrature Phase Shift Keying modulation on selected frequency channels, accommodating diverse user characteristics. Evaluation showed that MIMO-NOMA significantly improved bit error rate and transmitting power for the best user in download transmission. For uplink transmission, there was an increase in the average capacity rate and a decrease in outage probability for the best user. Closed-form formulas for various parameters in both downlink and uplink NOMA, with and without MIMO, were derived. Overall, adopting MIMO-NOMA led to a remarkable performance improvement for all users, even in challenging conditions like interference or fading channels

Signal Processing and Learning for Next Generation Multiple Access in 6G

Wireless communication systems to date primarily rely on the orthogonality of resources to facilitate the design and implementation, from user access to data transmission. Emerging applications and scenarios in the sixth generation (6G) wireless systems will require massive connectivity and transmission of a deluge of data, which calls for more flexibility in the design concept that goes beyond orthogonality. Furthermore, recent advances in signal processing and learning have attracted considerable attention, as they provide promising approaches to various complex and previously intractable problems of signal processing in many fields. This article provides an overview of research efforts to date in the field of signal processing and learning for next-generation multiple access, with an emphasis on massive random access and non-orthogonal multiple access. The promising interplay with new technologies and the challenges in learning-based NGMA are discussed

Tangential Power Allocation NOMA scheme for Visible Light Communications

Proceeding of: IEEE Conference on Standards for Communications and Networking (CSCN 2022), 28-30 November 2022, Thessaloniki, GreeceNon-orthogonal multiple access (NOMA) has been proposed in both radio-frequency (RF) and visible light communications (VLC) to both improve the achievable rate and overcome the constrains in the number of users of orthogonal multiple access (OMA) schemes. Despite the advantages of NOMA, there still exist some issues that require more investigation such as power allocation schemes. This is issue is more remarkable in VLC due to the small and confined coverage footprint of each optical access point. In this poster, we propose a novel methodology denoted by tangential power allocation (TPA) for NOMA in VLC. Basically, the power allocation coefficients are calculated based on the tangential point on the NOMA rate region that is parallel to the OMA region. It is shown that TPA achieves greater performance in terms of achievable rate and fairness in comparison with conventional NOMA schemes.This work was funded by the European Union(EU) Horizon 2020 research and innovation program under the Marie Sklodowska-Curie ETN TeamUp5G, grant agreement No. 813391

A Generalized Cluster-Free NOMA Framework Towards Next-Generation Multiple Access

A generalized downlink multi-antenna non-orthogonal multiple access (NOMA) transmission framework is proposed with the novel concept of cluster-free successive interference cancellation (SIC). In contrast to conventional NOMA approaches, where SIC is successively carried out within the same cluster, the key idea is that the SIC can be flexibly implemented between any arbitrary users to achieve efficient interference elimination. Based on the proposed framework, a sum rate maximization problem is formulated for jointly optimizing the transmit beamforming and the SIC operations between users, subject to the SIC decoding conditions and users' minimal data rate requirements. To tackle this highly-coupled mixed-integer nonlinear programming problem, an alternating direction method of multipliers-successive convex approximation (ADMM-SCA) algorithm is developed. The original problem is first reformulated into a tractable biconvex augmented Lagrangian (AL) problem by handling the non-convex terms via SCA. Then, this AL problem is decomposed into two subproblems that are iteratively solved by the ADMM to obtain the stationary solution. Moreover, to reduce the computational complexity and alleviate the parameter initialization sensitivity of ADMM-SCA, a Matching-SCA algorithm is proposed. The intractable binary SIC operations are solved through an extended many-to-many matching, which is jointly combined with an SCA process to optimize the transmit beamforming. The proposed Matching-SCA can converge to an enhanced exchange-stable matching that guarantees the local optimality. Numerical results demonstrate that: i) the proposed Matching-SCA algorithm achieves comparable performance and a faster convergence compared to ADMM-SCA; ii) the proposed generalized framework realizes scenario-adaptive communications and outperforms traditional multi-antenna NOMA approaches in various communication regimes.Comment: 30 pages, 9 figures, submitted to IEEE TW

Fundamental Limits on the Uplink Performance of the Dynamic-Ordered SIC Receiver

Due to the rapid and widespread growth of the Internet-of-Things (IoT) paradigm, present days witness an exponential increase in the number of connected devices. In this regard, the orthogonal transmission techniques featured by conventional 4G and 5G systems can only support a limited number of simultaneously active users, due to their low spectral efficiency and poorly flexible resource allocation. To overcome such limitations, the 6G framework will include novel Next Generation Multiple Access (NGMA) solutions that will efficiently and flexibly connect a significantly larger number of devices over the same portion of spectrum. Under the NGMA umbrella, the Power-Domain Non-Orthogonal Multiple Access (PD-NOMA) technology is able to accommodate multiple users on the same frequencies by carefully assigning different power levels to the active users and employing Successive Interference Cancellation (SIC) receivers. In this work, we put forth a novel analytical approach to evaluate the performance that PD-NOMA achieves on the uplink of a single cell when a dynamic-ordered SIC receiver is considered. With respect to other existing works, the fundamental limits on the system performance are assessed analytically for an arbitrary number = of simultaneously transmitting users, and both the case of Rayleigh and lognormal-shadowed Rayleigh fading are examined. The closed-form expressions presented in this work, whose correctness and excellent accuracy are validated through Monte Carlo simulations, disclose the impact of lognormal shadowing and an increasingly larger number of active users on the PD-NOMA performance

Non-Orthogonal Multiple Access For Near-Field Communications

The novel concept of near-field non-orthogonal multiple access (NF-NOMA) communications is proposed. The near-filed beamfocusing enables NOMA to be carried out in both angular and distance domains. Two novel frameworks are proposed, namely, single-location-beamfocusing NF-NOMA (SLB-NF-NOMA) and multiple-location-beamfocusing NF-NOMA (MLB-NF-NOMA). 1) For SLB-NF-NOMA, two NOMA users in the same angular direction with distinct quality of service (QoS) requirements can be grouped into one cluster. The hybrid beamformer design and power allocation problem is formulated to maximize the sum rate of the users with higher QoS (H-QoS) requirements. To solve this problem, the analog beamformer is first designed to focus the energy on the H-QoS users and the zero-forcing (ZF) digital beamformer is employed. Then, the optimal power allocation is obtained. 2) For MLB-NF-NOMA, the two NOMA users in the same cluster can have different angular directions. The analog beamformer is first designed to focus the energy on both two NOMA users. Then, a singular value decomposition (SVD) based ZF (SVD-ZF) digital beamformer is designed. Furthermore, a novel antenna allocation algorithm is proposed. Finally, a suboptimal power allocation algorithm is proposed. Numerical results demonstrate that the NF-NOMA can achieve a higher spectral efficiency and provide a higher flexibility than conventional far-field NOMA

Resource Allocation for Sum-Rate Maximization in Multi-UAV SCMA Networks

This work investigates a sparse code multiple access (SCMA) assisted multiple unmanned aerial vehicles (UAVs) downlink communication network for improved data services to multiple ground users. Our objective is to maximize the sum-rate of the multi-UAV SCMA network by optimizing the SCMA factor graph matrix used for resource allocation, considering the inter-UAV and intra-UAV interference components. The formulated problem is non-convex in nature and is subject to the SCMA codebook constraints. We propose a factor graph matrix assignment algorithm to solve this optimization problem. Our simulation results demonstrate the superiority of the proposed scheme in terms of rate performance over the benchmark schemes. Thus, compared with orthogonal multiple access strategies, SCMA emerge as a promising candidate for next generation multiple access (NGMA) techniques

Non-orthogonal multiple access for machine-type communications toward 6G

Abstract. Massive machine-type communications (mMTC) is one of the main focus areas in the fifth generation of wireless communications. It is also the fastest-growing field in terms of the number of devices. The massive increase in devices connected to the internet and global data traffic creates unprecedented requirements for future generations of wireless communications. One of the key technologies for the performance of the system is the utilized multiple access (MA) scheme. The conventional orthogonal MA (OMA) schemes from the earlier generations fail to satisfy the increasing demands for connectivity and spectral efficiency. On the contrary, non-orthogonal MA (NOMA) schemes offer the connectivity and spectral efficiency needed to enable mMTC. NOMA does this by allowing multiple users to transmit their data through the same resource blocks (RBs) simultaneously. NOMA is generally divided into two categories, namely power domain (PD-) NOMA and code domain (CD-) NOMA. PD-NOMA utilizes the power domain for the multiplexing, whereas CD-NOMA uses the code domain. This thesis focuses on the fundamentals of NOMA, MTC, and what NOMA can offer to MTC. We will also discuss the challenges and open problems that need to be solved. Finally, the thesis includes some simulations that demonstrate NOMA in practice.Ei-ortogonaalinen monikäyttö kone-tyyppisessä kommunikaatiossa kohti 6G:tä. Tiivistelmä. Massiivinen kone-tyyppinen kommunikaatio (mMTC) on yksi viidennen sukupolven langattoman viestinnän pääpainopisteistä. Se on myös nopeimmin kasvava osa-alue, kun katsotaan laitteiden lukumäärää. Internetiin yhdistettyjen laitteiden ja globaalin tietoliikenteen valtava kasvu luo ennennäkemättömiä vaatimuksia tuleville langattoman viestinnän sukupolville. Yksi avainteknologioista järjestelmän suorituskyvyn kannalta on käytetty monikäyttömenetelmä (MA). Tavanomaiset ortogonaaliset MA (OMA) -järjestelmät eivät saavuta yhdistettävyyden ja spektritehokkuuden kasvavia vaatimuksia. Sitä vastoin ei-ortogonaaliset MA (NOMA) -järjestelmät tarjoavat mMTC:n mahdollistamiseen tarvitun yhdistettävyyden ja spektritehokkuuden. NOMA saavuttaa tämän sallimalla usean käyttäjän lähettää dataa saman resurssilohkon kautta samanaikaisesti. NOMA voidaan yleisesti jakaa kahteen kategoriaan, tehoalueen NOMA:an ja koodialueen NOMA:an. Tämä työ keskittyy NOMA:n ja MTC:n perusteisiin ja siihen, mitä NOMA voi tarjota MTC-käyttökohteille. Työssä käydään myös läpi ratkaisuja vaativat haasteet ja avoimet ongelmat. Lopuksi työ sisältää simulaatioita, jotka mallintavat NOMA:n toimintaa käytännössä