Conventional Non-orthogonal Multiple Access Research Articles

Enhancing wireless communication systems through large intelligent surfaces: a performance analysis of LIS-assisted NOMA networks

The integration of large intelligent surfaces (LIS) with non-orthogonal multiple access (NOMA) networks has emerged as a promising solution to enhance the capacity and coverage of wireless communication systems. In this study, we analyse the performance of a NOMA network with the assistance of LIS. We propose a system model where a base station (BS) equipped with a LIS serves multiple users. The LIS consists of many passive elements that can influence the wireless channel by adjusting the reflection coefficients. We consider a downlink scenario where the BS transmits to multiple users simultaneously using NOMA, and the LIS helps to improve the signal quality and coverage. We additionally evaluate the efficiency of the suggested LIS-assisted NOMA network. In addition, we evaluate the efficiency of the LIS-assisted NOMA network in comparison to conventional NOMA systems that do not utilize LISs. The findings indicate that the LIS has a notable impact on enhancing the system's performance in terms of diversity gain, probability of error, and pairwise error probability (PEP). Moreover, the suggested LIS-assisted NOMA network is shown to be superior to conventional NOMA systems through comparison. These findings offer useful insights into the performance analysis of LIS-assisted NOMA networks. They also serve as inspiration and motivation for future research and development in this new subject, with the potential to revolutionize wireless communication systems.

IRS-aided NOMA-based communication architecture for 6G wireless networks: An enhanced error-control and reliable data transmission

Intelligent reflecting surface (IRS) is a key technology for sixth-generation (6G) wireless communication to obtain high energy and spectral efficiency with a minimum cost. On the other hand, non orthogonal multiple access (NOMA) enhances the spectrum efficiency of the network. The combining schemes are implemented to obtain error-free data at the receiver. This paper proposes an IRS-aided NOMA-based packet combining (PC) and aggressive packet combining (APC) schemes-assisted communication architecture to enhance service quality and achieve sustainable and resilient connectivity among users for 6G wireless networks. In this paper, the mathematical model has been derived for the instantaneous achievable data rate, bit error rate, outage probability, and packet correction capability. The derived analytical expressions are validated through detailed Monte Carlo simulations. The obtained results show that the proposed schemes outperform the conventional NOMA with PC and NOMA with APC schemes and facilitate enhanced error control and reliable data transmission capabilities. Moreover, the proposed schemes have been compared with the IRS-aided orthogonal multiple access (OMA) schemes, where IRS-aided OMA schemes are considered benchmarks of the proposed schemes. It is presented that the proposed schemes are superior to the conventional OMA with PC and APC schemes and IRS-aided OMA with PC and APC schemes.

Secure transmission design in cooperative NOMA networks: Orienting toward user requirements

AbstractThis paper presents a full‐duplex and multi‐antenna relay‐aided transmission scheme for the user‐oriented perspective in cooperative non‐orthogonal multiple access (NOMA) systems. Relying on the service requirements, two legitimate users with security demands (SU) and quality of service (QoS) demands (QU) are paired for NOMA execution. The security of SU is enhanced through inverse power allocation of the conventional NOMA. The QoS requirements for QU are guaranteed, simultaneously. Then, the precoding design at the multi‐antenna relay has been exploited to improve the reliability demands of SU. Closed‐form expressions for SU's outage probability (OP) and intercepted probability, as well as QU's OP, are derived. The security–reliability trade‐off is also presented. Additionally, performance analysis under the half‐duplex and multi‐antenna scheme is provided as a benchmark for comparison. Finally, numerical simulations are performed to confirm the accuracy of the theoretical derivations under different schemes. Results demonstrate the superiority of the proposed scheme over benchmark schemes in terms of improving the security and reliability of SU, as well as saving power consumption of the system.

Reducing peak‐to‐average power ratio of filtered non‐orthogonal multiple access and new radio 5g waveforms using hybrid partial transmit sequence‐companding technique

AbstractFor fifth‐generation (5G) and beyond 5G communications, filtered nonorthogonal multiple access (F‐NOMA) can be used as a waveform contender. Filtering‐based waveform frameworks provide suppression of out‐of‐band emission (OOBE) and asynchronous transmission. For new types of waveforms, a high peak‐to‐average power ratio (PAPR) remains a challenge. A high PAPR in multicarrier systems can be efficiently mitigated by applying partial transmit sequence (PTS). Combining PAPR reduction techniques can improve the transmission efficiency by nonlinearly scaling the signal amplitudes before transmission and inversely scaling them at the receiver. We propose a hybrid technique that combines PTS and companding to reduce the PAPR in an F‐NOMA system. Conventional nonorthogonal multiple access (NOMA) is compared with F‐NOMA, and systems with and without the hybrid technique are examined regarding metrics including the power spectral density, bit error rate (BER), and computational complexity. Compared with NOMA, simulation results show that F‐NOMA using the proposed technique improves the PAPR and OOBE while preserving the BER performance of F‐NOMA.

Quantum aided efficient resource control for connected support in IRS assisted networks

Context:To achieve the vision of all connected world with uninterrupted communication support, 6G technology plays an important role. But the scarce radio spectrum and limited network resources is the main challenge in delivering its promised performance. Objectives:This paper presents an IRS-aided cell free NOMA network model that aims to provide uniform network coverage. The future 6G technology envisions for serving billions of interconnected devices with seamless communication support, data handling capabilities and computational accuracy. But the scarcity of network resources is the main limitation. Thus, the need is to design quantum enabled intelligent and dynamic networks capable of offering extended network capabilities. Proposed work is on intelligent network framework that provides uniform network coverage through efficient resource management for a 6G enabled expanded IoT network. Methods:To enable efficient resource management, a quantum enabled resource control algorithm is proposed that creates user clusters and associates each AP-IRS pair to each cluster. Each AP transmits the superimposed signals of its intended cluster against all the user clusters as in conventional NOMA system. The nodes in each cluster have been assigned unique pilots so as to avoid intracluster interference. The use of IRS enables desired NOMA beamforming such that the effect of unfavourable wireless environment is mitigated. Results:The performance of the IRS-aided cell-free NOMA network is evaluated for average sum rate with different AP transmit power, cluster sizes, IRS reflecting elements and IRS phase shifts. It is shown that at transmit power per AP of 30dBm, the average sum rate of the system improves by 7.52% with the proposed algorithm using equal power allocation scheme. Further, the comparative performance analysis of three different communication systems is carried out to validate the proposed communication model. Conclusion:It is observed that with more number of users per cluster, the average sum rate of the system initially increases for small cluster sizes and then it becomes constant for large cluster sizes. The proposed clustering method outperforms the random clustering approach achieving sum rate of 12.9 bits/s/Hz with N =300 and M= 8. The comparison of different communication scenarios reveals that the maximum sum rate of 12.2 bits/s/Hz is achieved with the proposed model incorporating proposed clustering mechanism. Further, the energy efficiency analysis suggests that energy efficiency improves with N and Pc with proposed clustering approach. The use case scenarios for the integration of quantum computing with IRS technology are also presented.

Computation offloading in NOMA-MEC-enabled aerial-vehicular networks exploiting mmWave capabilities

In recent years, there has been a significant interest in ubiquitous coverage, high data rate connectivity, and mobile edge computing (MEC) as crucial services within the future sixth-generation (6G) wireless networks. These services are regarded as essential components, exemplifying the advancements anticipated in 6G technology. Nevertheless, the successful implementation of these services in MEC-enabled vehicular networks significantly relies on the availability of robust network coverage and telecommunication framework. Unfortunately, in far-flung and isolated regions, such framework is often lacking, posing significant challenges in achieving uninterrupted connectivity, comprehensive coverage, and efficient computation offloading. Targeting the aforementioned horizon, in this paper, an uplink non-orthogonal multiple access (NOMA)-MEC-enabled aerial-vehicular network operating at millimeter wave (mmWave) is proposed in which the ground vehicles are provided edge computing services by an aerial autonomous vehicle, i.e., a high-altitude platform (HAP). We present a system model in which a HAP equipped with MEC servers offers computation offloading capabilities to a vehicular network. Our main objective is to minimize the transaction time of a NOMA cluster offloading its data to MEC servers located at the HAP. We devise a dual-layer optimization scheme for optimizing the transmission power and computational resource allocation by using the Lagrange multipliers method and then attain convergence by implementing a sub-gradient approach. We further extend our work by proposing a data-aware NOMA clustering scheme. The simulation results demonstrate the efficacy of our proposed approach, showing a notable reduction in the transaction time in comparison to the baseline scheme. The optimal power allocation enhances the data rates which subsequently reduces the transmission time, and the optimal cores assignment effectively minimizes the computation time. Additionally, the data-aware NOMA clustering scheme shows promising results by enhancing the system effective throughput and the spectral efficiency in comparison to the conventional NOMA clustering.

Performance analysis of power-efficient IRS-Assisted full duplex NOMA systems

In this paper, we utilize intelligent reflecting surfaces (IRSs) in full-duplex (FD) systems to enhance diversity gain and system performance. The issue of self-interference in FD systems causing an outage floor is addressed. We propose a beamforming (BF) method that mitigates this effect, even when there is no direct channel between the source and the far user in non-orthogonal multiple access (NOMA) systems. We examine two designs, named fixed antenna mode (FAM) and adaptive antenna mode (AAM), for K decode-and-forward (DF) FD near users in a Rayleigh fading environment. To improve system performance, we employ joint antenna mode and near user selection techniques in IRS-NOMA systems. We evaluate the performance of the proposed schemes and derive closed-form expressions for outage probability and ergodic capacity, which are validated through simulations. The results demonstrate that the proposed scheme achieves additional spatial diversity gain through the use of the IRS structure and antenna mode selection at the relay nodes. Furthermore, the new BF technique improves power efficiency compared to conventional FD NOMA structures, and the analysis can be extended to 6G Massive MIMO systems using machine learning algorithms, which are applicable for millimeter wave channels.

A streamlined user grouping in downlink NOMA systems

AbstractReducing SIC operations and interference while maintaining the same radio resources for users in a cluster is a potential research direction in non‐orthogonal multiple access (NOMA) systems. In order to reach this goal, a streamlined user grouping is proposed for a four‐user cluster in downlink NOMA systems, which is carried out based on the in‐phase and quadrature components of a constellation. In terms of bit error rate performance, the proposed scheme is superior in comparison with the conventional NOMA without user grouping and phase rotation‐based user grouping. This improvement is achieved in light of the three positive points of pulse amplitude modulation, the Gray mapping rule, and the joint maximum‐likelihood detector.

Performance Analysis of Cooperative NOMA for Different Power Allocation Strategies

Cooperative None Orthogonal Multiple Access (C-NOMA) is a promising approach for 5G and beyond communication networks. Users will benefit from the full bandwidth of the channel without time constraints. NOMA’s features are incomplete without efficient power allocation that ensures power distribution among users fairly. Integrating power management (allocation) with Cooperative-NOMA (C-NOMA) may improve the system metrics. In addition, a physical layer security (PLS) is added to make the process of sending and receiving safe, and the system works in an integrated manner, preventing any interrupting or eavesdropping inside or outside the network. This paper demonstrates the user and channel performance of C-NOMA with Amplify-and-forward (AF) and Decode-and-forward (DF) approaches. The analysis is performed by varying the power allocation techniques to derive the best system configurations. The simulation results confirmed the analytic findings and showed that the proposed system outperforms orthogonal multiple access (OMA), conventional NOMA, and conventional cooperative NOMA, enhancing the performance metrics in terms of throughput, sum rate, and outage probability. The bit-error-rate (BER) of the far user can be identical to that of the near user if power allocation is properly set. All techniques excelled except for the fixed power allocation, which had the same BER. The Channel capacity and outage probability were also considered. A slight variation in the channel capacity in all the experiments for different numbers of users was found. The generalized power allocation for AF and DF models had the optimum channel capacity close to 14 bps/Hz. Moreover, far users always had a higher outage probability than near users and channels, and generalized power allocation was the highest outage probability technique when the transmit power was close to (4 dB).

Impact of Power Consumption Models on the Energy Efficiency of Downlink NOMA Systems

While non-orthogonal multiple access (NOMA) improves spectral efficiency, it adds complexity to the receivers due to successive interference cancellation (SIC). Prior studies on the energy efficiency of NOMA overlook the SIC overhead and rely on simplistic power consumption models (PCM). To fill this gap, we first introduce PCM-κ that accounts for SIC-related power expenditure. Then, to investigate the energy efficiency of NOMA and joint transmission (JT)-coordinated multipoint (CoMP) NOMA, we formulate a power allocation problem for maximizing the energy efficiency and propose a global approach running at a centralized entity and a local algorithm running at a base station. We evaluate the energy efficiency using PCM-κ and two PCMs commonly used in the literature. Numerical analysis suggests that using simplistic PCMs leads to a few orders of magnitude overestimation of energy efficiency, especially when the receivers have low rate requirements. Despite the superiority of JT-CoMP NOMA over conventional NOMA in finding a feasible power allocation, the difference in their energy efficiency is only marginal when users have identical rate requirements and more significant in more heterogeneous settings with users having different rate requirements. Moreover, when conventional NOMA is feasible, the optimal solution for JT-CoMP NOMA converges to conventional NOMA.

Provably Energy Efficiency and Lower Power Consumption Based on HOA in 5G MIMO-NOMA Systems

The rapid expansion of 5G communication networks necessitates improved energy efficiency and reduced power consumption. This article explores the integration of Hybrid Optimization Algorithms (HOA) in 5G MIMO-NOMA systems, aiming to enhance energy efficiency and minimize power usage. The proposed methodology leverages MIMO technology and Non-Orthogonal Multiple Access (NOMA). We introduce a new power consumption model based on HOA, recognizing MIMO-NOMA as pivotal in future wireless communication systems. HOA allows simultaneous service for more users, leading to heightened energy efficiency and reduced power consumption compared to conventional MIMO or NOMA systems. A streamlined user admission scheme is presented, admitting users based on ascending power requirements to meet Quality of Service criteria. Numerical results demonstrate the efficacy of HOA and the power allocation strategy in enhancing energy efficiency and user admission. Comparative analysis shows lower power consumption and approximately a 10% increase in energy efficiency compared to traditional methods and other algorithms like GA, PSO, SPPA, and the water-filling algorithm.

Energy Efficiency Optimization for Backscatter Enhanced NOMA Cooperative V2X Communications Under Imperfect CSI

Automotive-Industry 5.0 will use beyond fifth-generation (B5G) technologies to provide robust, computationally intelligent, and energy-efficient data sharing among various onboard sensors, vehicles, and other devices. Recently, ambient backscatter communications (AmBC) have gained significant interest in the research community for providing battery-free communications. AmBC can modulate useful data and reflect it towards near devices using the energy and frequency of existing RF signals. However, obtaining channel state information (CSI) for AmBC systems would be very challenging due to no pilot sequences and limited power. As one of the latest members of multiple access technology, non-orthogonal multiple access (NOMA) has emerged as a promising solution for connecting large-scale devices over the same spectral resources in B5G wireless networks. Under imperfect CSI, this paper provides a new optimization framework for energy-efficient transmission in AmBC enhanced NOMA cooperative vehicle-to-everything (V2X) networks. We simultaneously minimize the total transmit power of the V2X network by optimizing the power allocation at BS and reflection coefficient at backscatter sensors while guaranteeing the individual quality of services. The problem of total power minimization is formulated as non-convex optimization and coupled on multiple variables, making it complex and challenging. Therefore, we first decouple the original problem into two sub-problems and convert the nonlinear rate constraints into linear constraints. Then, we adopt the iterative sub-gradient method to obtain an efficient solution. For comparison, we also present a conventional NOMA cooperative V2X network without AmBC. Simulation results show the benefits of our proposed AmBC enhanced NOMA cooperative V2X network in terms of total achievable energy efficiency.

Analysis on Fairness and Efficiency of the 3-PLP LDM System Using a Normalized Channel Capacity

This article presents a novel approach to investigate efficient resource allocation in the layered division multiplexing (LDM) system, a key technology in next-generation broadcasting systems. The LDM system provides diverse services, resulting in different channel capacities for each service, unlike the conventional non-orthogonal multiple access scheme that aims for equal channel capacity among users. To achieve efficient resource allocation among services, we proposed a new method that normalizes the channel capacities allocated to different services while maintaining high fairness. Our proposed method involves normalizing the channel capacities of each service and finding the point where the sum of normalized channel capacities is maximized. This point can be obtained using the Lagrange multiplier method, ensuring a high normalized fairness index. Through simulations, we confirmed that the proposed approach maintains high fairness in the LDM system and achieves the highest normalized channel capacities compared to other transmission techniques. These findings provide valuable insights into resource allocation strategies for the LDM system, enabling a fair comparison of efficiency and performance within a multi-service environment.

Non-Orthogonal Multiple Access Based on Orthogonal Space-Time Block Codes for Mobile Communications

Non-orthogonal multiple access (NOMA), which combines multiple user signals and transmits the combined signal over one channel, can achieve high spectral efficiency for mobile communications. However, combining the multiple signals can lead to degradation of bit error rates (BERs) of NOMA under severe channel conditions. In order to improve the BER performance of NOMA, this paper proposes a new NOMA scheme based on orthogonal space-time block codes (OSTBCs). The proposed scheme transmits several multiplexed signals over their respective orthogonal time-frequency channels, and can gain diversity effects due to the orthogonality of OSTBC. Furthermore, the new scheme can detect the user signals using low-complexity linear detection in contrast with the conventional NOMA. The paper focuses on the Alamouti code, which can be considered the simplest OSTBC, and theoretically analyzes the performance of the linear detection. Computer simulations under the condition of the same bit rate per channel show that the Alamouti code based scheme using two channels is superior to the conventional NOMA using one channel in terms of BER performance. As shown by both the theoretical and simulation analyses, the linear detection for the proposed scheme can maintain the same BER performance as that of the maximum likelihood detection, when the two channels have the same frequency response and do not bring about any diversity effects, which can be regarded as the worst case.

Partial-NOMA Based PLS: Following NOMA Decoding Principle or Enhanced Decoding Design?

In the insecure transmission environment, compared with the passive eavesdropper (Eve), the active Eve plays a more threatening role in the physical layer security (PLS), since it can wiretap and jam the signals. To simultaneously decrease the wiretap massage for Eve and improve secrecy outage probability (SOP) for the legitimate users, an enhanced decoding protocol in PLS is proposed for the device-to-device (D2D) non-orthogonal multiple access (NOMA) system under an active Eve attack. In addition, the partial NOMA (P-NOMA) is firstly introduced into PLS to further enhance the performance of the proposed system. The provided closed-forms of SOPs are verified via simulations, whose results show the superiority of our proposed schemes over the conventional NOMA schemes.

Bit-Interleaved Multiple Access: Improved Fairness, Reliability, and Latency for Massive IoT Networks

Internet-of-Things (IoT) networks require massive connections in dense areas. Therefore, a resource efficient multiple access scheme seems inevitable to enable immense connectivity where multiple devices have to share the same resource block. Non-orthogonal multiple access (NOMA) has been considered as the strongest candidate in recent years. However, in this paper, by considering the practical implementation, we first provide a true power allocation (PA) constraint with finite alphabet inputs for conventional downlink NOMA and demonstrate that it cannot support massive connections in practical systems. To this end, we propose bit-interleaved multiple access (BIMA) scheme in downlink IoT networks. The proposed BIMA scheme implements bitwise multiaccess interleaving and deinterleaving at the transceiver ends and there are no strict PA constraints, unlike conventional NOMA, thus allowing a high number of devices in the same resource block. We provide a comprehensive analytical framework for BIMA by investigating all key performance indicators (KPIs) to present both information-theoretic (i.e., ergodic capacity EC and outage probability OP) and finite alphabet inputs (i.e., bit error rate BER) performance metrics with both instantaneous and statistical channel ordering. In addition, we define Jain’s fairness index and proportional fairness index in terms of all KPIs. Based on the extensive computer simulations, we reveal that BIMA outperforms conventional NOMA significantly, with a performance gain of up to 20-30 dB in terms of KPIs in some scenarios. In other words, compared to conventional NOMA schemes, the same KPIs are met in BIMA with 20-30 dB less transmit power, which is quite promising for energy-limited use cases. Moreover, this performance gain becomes greater when more IoT devices are supported. BIMA provides a full diversity order for all IoT devices and enables the implementation of an arbitrary number of devices and modulation orders, which is crucial for IoT networks where a huge number of devices should be supported in a single resource block in dense areas. In addition to the overall performance gain, BIMA guarantees a fairness system where none of the devices gets a severely degraded performance and the sum-rate is shared in a fair manner among devices. It guarantees QoS satisfaction for all devices. Finally, we provide an intense complexity and latency analysis for BIMA and demonstrate that it provides lower latency compared to conventional NOMA receivers, since it allows parallel computation at the receivers and no iterative operations are required. We show that compared to conventional NOMA receivers, BIMA reduces latency by up to 350% for specific IoT devices and 170% on average.

IRS-enabled NOMA communication systems: A network architecture primer with future trends and challenges

Non-Orthogonal Multiple Access (NOMA) has already proven to be an effective multiple access scheme for 5th Generation (5G) wireless networks. It provides improved performance in terms of system throughput, spectral efficiency, fairness, and energy efficiency (EE). However, in conventional NOMA networks, performance degradation still exists because of the stochastic behavior of wireless channels. To combat this challenge, the concept of Intelligent Reflecting Surface (IRS) has risen to prominence as a low-cost intelligent solution for Beyond 5G (B5G) networks. In this paper, a modeling primer based on the integration of these two cutting-edge technologies, i.e., IRS and NOMA, for B5G wireless networks is presented. An in-depth comparative analyses of IRS-assisted Power Domain (PD)-NOMA networks is provided through 3-fold investigations. First, a primer is presented on the system architecture of IRS-enabled multiple-configuration PD-NOMA systems, and parallels are drawn with conventional network configurations, i.e., conventional NOMA, Orthogonal Multiple Access (OMA), and IRS-assisted OMA networks. Followed by this, a comparative analysis of these network configurations is showcased in terms of significant performance metrics, namely, individual users' achievable rate, sum rate, ergodic rate, EE, and outage probability. Moreover, for multi-antenna IRS-enabled NOMA networks, we exploit the active Beamforming (BF) technique by employing a greedy algorithm using a state-of-the-art branch-reduce-and-bound (BRB) method. The optimality of the BRB algorithm is presented by comparing it with benchmark BF techniques, i.e., minimum-mean-square-error, zero-forcing-BF, and maximum-ratio-transmission. Furthermore, we present an outlook on future envisioned NOMA networks, aided by IRSs, i.e., with a variety of potential applications for 6G wireless networks. This work presents a generic performance assessment toolkit for wireless networks, focusing on IRS-assisted NOMA networks. This comparative analysis provides a solid foundation for the development of future IRS-enabled, energy-efficient wireless communication systems.

Performance Analysis of Selective DF Cooperative NOMA in Presence of Practical Impairments

In this article, we investigate a selective decode-and-forward (DF)-aided cooperative nonorthogonal multiple access (NOMA) system performance in the presence of practical impairments using imperfect successive interference cancellation (SIC) and channel estimation error (CEE). The base station communicates directly and via a relay with the two NOMA users in two-time phases. In particular, the selective DF with synchronized direct and relay transmission relaying protocol is proposed for the considered downlink NOMA system to offer enhanced quality of service and improved data reliability compared with the conventional NOMA and DF NOMA systems. The closed-form of exact and asymptotic expressions of the average bit error rate (ABER) at both NOMA users are derived considering the impact of imperfect SIC and CEE. Furthermore, the outage probability is also obtained. Finally, the improvement in the system performance acquired by the proposed scheme over the existing methods is corroborated by Monte Carlo simulations.

A Low-Complexity Coding Scheme for NOMA

This work focuses on exploiting the constructive interference among different users' data waveforms to introduce new coding and decoding techniques, which are specifically designed for nonorthogonal multiple access (NOMA) systems. In this article, a structured coding scheme is devised. In essence, the proposed technique focuses on finding a relationship between the sent users' data waveforms and then uses this relationship in the decoding process at the receiving destination. It is worth pointing out that the proposed coding and decoding techniques exhibit better performance and reduced the complexity compared with the conventional uncoded NOMA. The complexity order evaluation shows that the proposed scheme attains a reduction in the required number of the floating point operations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{5}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{6}\,N$</tex-math></inline-formula> at the second and third users, respectively, compared with that of the uncoded NOMA. Moreover, we have derived a closed-form expression for the bit error rate, which is verified using the Monte Carlo simulation. To demonstrate the practicality of the proposed system, the obtained results are compared with those of the uncoded and convolutional coding NOMA systems. Finally, the performance of the proposed system outperformed the conventional systems by an average of 5 dB in the case of two users and an average of 15 dB in the case of three users in the same work environment.

Exploiting Semantic Communication for Non-Orthogonal Multiple Access

A novel semantics-empowered two-user uplink non-orthogonal multiple access (NOMA) framework is proposed for resource efficiency enhancement. More particularly, a secondary far user (F-user) employs the semantic communication (SemCom) while a primary near user (N-user) employs the conventional bit-based communication (BitCom). The fundamental performance limit, namely <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">semantic-versus-bit (SvB) rate region</i> , of the proposed semantics-empowered NOMA framework is characterized. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">equivalent</i> SvB rate region achieved by the conventional BitCom-based NOMA is provided as the baseline scheme. It unveils that, compared to BitCom, SemCom can significantly improve the F-user’s performance when its permitted transmit power is strictly capped, but may perform worse when its permitted transmit power is high. Guided by this result, the proposed semantics-empowered NOMA framework is investigated over fading channels. An <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opportunistic</i> SemCom and BitCom scheme is proposed, which enables the secondary F-user to participate in NOMA via the most suitable communication method at each fading state, thus striking a good tradeoff between its own achieved performance and the interference imposed on the primary N-user. Two scenarios are considered for employing the opportunistic scheme, namely on-off resource management and continuous resource management. For each scenario, the optimal communication policy over fading channels is derived for maximizing the ergodic semantic rate achieved at the secondary F-user, subject to the minimum ergodic bit rate constraint of the primary N-user. Numerical results show that: 1) The proposed opportunistic scheme in both scenarios can achieve higher communication performance for NOMA than the baseline schemes merely employing SemCom or BitCom; 2) SemCom can better guarantee the performance of the F-user admitted in NOMA than BitCom when the communication requirement of the primary N-user is high; and 3) The continuous power control at the F-user is necessary for ensuring high performance over fading channels, while the on-off time scheduling is sufficient.