Proposed Non-orthogonal Multiple Access Scheme Research Articles

Performance Analysis of Multiple-RIS-Based NOMA Systems

In this paper, we present a study on a model of multirelay radio network system that utilizes reconfigurable intelligent surfaces (RISs). We investigate the use of nonorthogonal multiple access (NOMA) combined with cooperative RIS systems, using partial RIS selection (PRISs). Specifically, the RISs act as relays to forward data from the base station to the two users. The focus of this paper is to analyze the outage probabilities and throughput for the two users. Based on the results, we examine how PRISs affect the performance of the proposed NOMA scheme. The derived asymptotic expressions show that the proposed model can improve user fairness. Finally, we compare the analysis results with the simulation results and find good agreement.

Performance analysis and optimization of multiple IIoT devices radio frequency energy harvesting NOMA mobile edge computing networks

In this day and age, the Industrial Internet of Things (IIoT) has been considered to revolutionize industrial manufacturing by capturing and accessing massive data sources with incredible speed and efficiency than before. Combined with it, Mobile Edge Computing (MEC) is a comprehensive Digital Transformation tendency to solve the problems Cloud computing faces. However, the fundamental challenges of energy and latency make deploying IIoT MEC networks difficult. Accordingly, this paper considers the efficient design of time allocation for successful computation probability (SCP) maximization for multiple energy-constrained mobile devices (MD) and multiple antennas access point (AP) in uplink radio frequency energy harvesting (RF EH) non-orthogonal multiple access (NOMA) IIoT network. Specifically, multiple MDs need to receive the energy and compute support of a MEC server placed in a multiple antenna wireless AP to complete the task immediately. Accordingly, a four-phase communication protocol is proposed to ensure system performance. The system follows the cluster head (CH) scheme based on the channel state information (CSI) to harvest RF energy from the AP. To ensure the highest system performance, we propose two algorithms for determining the optimal EH time for two CHs: SCPM-GSS and SCPM-GA. In addition, we derive the closed-form expressions for the SCP of the system and each CH. Monte Carlo simulations are used to verify the results of the analysis. The numerical results demonstrate the effects of crucial system parameters of our proposed NOMA scheme with those of conventional orthogonal multiple access (OMA) schemes. Furthermore, the proposed optimization algorithms allow the system to avoid outages like the random parameters setting approach and improve the SCP by 3 to 30% compared to the fixed parameters set when the transmit power is low and medium.

Reliability analysis for NOMA‐based UAV assisted short packet communication

AbstractThis paper introduces the short packet transmission in non‐orthogonal multiple access (NOMA)‐based unmanned aerial vehicle (UAV) assisted relay communication system. Short packet transmission has considerable potential to decrease the transmission latency of UAV communication, and NOMA can effectively enhance the spectrum efficiency and fairness. To improve the reliability of the system, an effective packet error rate (PER) minimization problem within short packet transmission is proposed by jointly optimizing the packet length, UAV placement, and power allocation under the reliability requirement and total power constraints. To address the intricate PER minimization problem, the optimization problem is firstly decomposed into three sub‐problems, and the corresponding monotonicity and convexity are analyzed, respectively. Then, an overall iterative optimization algorithm for PER minimization based on alternating direction method of multipliers algorithm and optimal solution algorithm is formulated by solving the three sub‐problems in an iterative manner. Simulation results validate the effectiveness and convergence of the proposed NOMA scheme and overall iterative optimization algorithm, respectively.

Cooperative non-orthogonal multiple access with D2D communication and opportunistic relaying in large-scale cellular networks

In order to improve the spectrum efficiency and communication robustness, we propose a cooperative non-orthogonal multiple access (NOMA) scheme in large-scale cellular networks with Device-to-Device (D2D) communication and opportunistic relaying. The distribution of base stations (BSs) is assumed to follow homogeneous Poisson Point Process (PPP). Each BS communicates to both a near-user (CU1) and a far-user (CU2) in its coverage area. A collaborative region is defined between each BS and CU2, wherein there are multiple D2D transmitters (DTs) uniformly distributed and intending to communicate with a common D2D receiver (DR). Among all the DTs that has correctly decoded the data of CU2, one is selected to perform the single-hop decode-and-forward relaying. The selected DT superimposes its own data onto CU2’s data, and broadcasts the composite signal. If there is no DT available to forward the cellular data, the DT with the best channel quality towards DR will be selected to transmit the pure D2D data. Through properly modeling the aggregate interference, we analyze the throughput of each terminal. Numerical results show that with specific parameter settings, the NOMA scheme with optimal relay selection can greatly outperform random relay selection in terms of the far-user’s throughput and the system throughput. With optimal relay selection, the proposed NOMA scheme can achieve much higher throughput than the orthogonal multiple access scheme.

Multitype Services Coexistence in Uplink NOMA for Dual-Layer LEO Satellite Constellation

The upcoming mega low-earth orbit (LEO) high-throughput satellite constellation is regarded as an emerging paradigm shift in the fifth-generation-advance (5GA) networks. In this article, we propose a multitype services coexistence handover (MSCH) nonorthogonal multiple access (NOMA) scheme for a dual-layer mega LEO satellite constellation, which can simultaneously and efficiently provide uplink NOMA for three types of fifth-generation user equipments (UEs): 1) mission-critical communications (MCCs) UEs (CUs); 2) massive machine-type communications (mMTCs) UEs (MUs); and 3) enhanced mobile broadband (eMBB) UEs (EUs). The EUs are mainly served in the higher layer satellites for longer service duration and may handover to the lower layer satellites to coexist with CUs or MUs. Moreover, the CUs and MUs perform grant-based (GB) and grant-free (GF) NOMA on resource blocks (RBs) in the lower layer satellites, respectively. Then, we derive the closed-form expressions of three specific key performance indicators (KPIs), i.e., outage probability (OP), system throughput (ST), and ergodic capacity (EC) in the MSCH NOMA scheme, and design five corresponding NOMA algorithms. Simulation results verify the accuracy of our theoretical derivations and show that the proposed NOMA schemes can achieve a better KPI performance than the state-of-the-art ones.

Cognitive radio-inspired NOMA in short-packet communications

Short-packet communication is an important feature of the internet of things (IoT). For allowing massive IoT devices to connect to a network through short packets, this paper designs a cognitive radio-inspired non-orthogonal multiple access (NOMA) scheme, where the IoT users will not necessarily occupy an exclusive spectrum. To further improve the connections in an IoT network, we propose a general NOMA scheme that serves multi- ple IoT users. Since the IoT devices are generally homogeneous, a user fairness-oriented power allocation scheme is designed for the proposed NOMA scheme. Besides, for comparison purposes, the benchmark orthogonal multiple access (OMA) scheme and its corresponding user fairness transmission scheme are also proposed. The closed-form expressions of average block error rates for secondary users are derived over Nakagami-m channels in both NOMA and benchmark OMA scheme. Simulation and analysis results show that a faraway primary network will benefit the spectrum sharing. In addition, shorter packets and more different channel conditions improve the NOMA gains over OMA. Besides, power allocation factors are found to be capable of achieving user fairness and the fairness transmission is achieved by the proposed scheme. Interestingly, when the channel differences are bigger enough, paring an extra NOMA user nearly does not affect the previous system performance.

On the Power-Splitting Relaying Protocol for SWIPT with Multiple UAVs in Downlink NOMA-IoT Networks

Unmanned aerial vehicle (UAV) communication and non-orthogonal multiple access (NOMA) are two promising technologies for wireless 5G networks and beyond. The UAVs can be used as flying base stations to form line-of-sight communication links to the Internet of things devices (IDs) and to enhance the performance of usual terrestrial cellular networks. Moreover, the UAVs can also be deployed as flying relay nodes for forwarding data from a base station (BS) to the IDs. On the other hand, non-orthogonal resource sharing for many concurrent users is exploited in NOMA, thus improving spectrum efficiency (SE) and supporting massive connections. The NOMA combined with energy harvesting (EH) in an amplify-and-forward (AF) with cooperative UAV systems is researched. Specifically, the UAVs act as rotary-wing relays to forward data from the BSs to two IDs. This paper focuses on the analysis of outage probabilities (OPs), system throughput, and energy efficiency (EE) for two IDs. Besides, we also do the asymptotic analysis of OPs at high signal-to-noise ratios (SNRs). Furthermore, this paper also inspects the impacts of the UAV-based relaying on the OP, system throughput, and EE of the proposed NOMA scheme. The derived asymptotic expansions show that the suggested model can enhance user fairness and the analytical results match the simulation results.

Capacity Optimization of Next-Generation UAV Communication Involving Non-Orthogonal Multiple Access

Unmanned air vehicle communication (UAV) systems have recently emerged as a quick, low-cost, and adaptable solution to numerous challenges in the next-generation wireless network. In particular, UAV systems have shown to be very useful in wireless communication applications with sudden traffic demands, network recovery, aerial relays, and edge computing. Meanwhile, non-orthogonal multiple access (NOMA) has been able to maximize the number of served users with the highest traffic capacity for future aerial systems in the literature. However, the study of joint optimization of UAV altitude, user pairing, and power allocation for the problem of capacity maximization requires further investigation. Thus, a capacity optimization problem for the NOMA aerial system is evaluated in this paper, considering the combination of convex and heuristic optimization techniques. The proposed algorithm is evaluated by using multiple heuristic techniques and deployment scenarios. The results prove the efficiency of the proposed NOMA scheme in comparison to the benchmark technique of orthogonal multiple access (OMA). Moreover, a comparative analysis of heuristic techniques for capacity optimization is also presented.

Active device detection and performance analysis of massive non-orthogonal transmissions in cellular Internet of Things

This paper investigates multiple access schemes for uplink and downlink transmissions in cellular networks with massive Internet of Things (IoT) devices. Recall that single-carrier frequency division multiple access and orthogonal frequency division multiple access, which are orthogonal multiple access (OMA) schemes, have been conventionally adopted for uplink and downlink transmissions in narrow-band IoT, respectively. Unlike these OMA schemes, we propose two non-orthogonal multiple access (NOMA) schemes for cellular IoT with short-packet transmissions. Especially, a generalized expectation consistent signal recovery-based algorithm is proposed to estimate active devices, channel state information and data in uplink transmission, where all of the active devices are allowed to transmit their pilots and data through the same resource block without authorization. On the other hand, the active devices estimated during uplink transmission are grouped for downlink transmission with a trade-off between performance and detection complexity. Additionally, the data error rates are analysed for both uplink and downlink transmissions with low-resolution analog-to-digital converters (ADCs), where the effects of critical parameters such as the estimation error, ADC bits, packet length, and message bits are revealed. Both simulation and analytical results are provided to demonstrate the excellent performance of the proposed NOMA schemes and algorithms, especially for active device, channel, and data estimations. More importantly, the obtained results show that the data error rate performance of downlink NOMA is superior to that of OMA when the message bits of devices in one group are selected following the proposed strategy.

Stochastic analysis of urban V2X communications: Orthogonality versus non-orthogonality

In this paper, we study the broadcasting performance of urban Vehicle-to-everything (V2X) communications at road intersections. In such environments, dense buildings obstruct the radio channel between vehicles in adjacent road segments and Non-Line-Of-Sight (NLOS) signal propagation reduces the received power level. Therefore, messages that originate from adjacent roads traveling in a non-parallel direction usually have weaker signals than those from the road segment traveling in parallel opposite direction. Besides, the high vehicular density leads to insufficient orthogonal channel resources and high level of interference. We propose to apply Non-Orthogonal Multiple Access (NOMA) to V2X communications at urban road intersections to enhance the spectrum efficiency and improve the Package Delivery Ratio (PDR) performance. With NOMA, signals from multiple transmitters are decoded together and the interference from undesired users can be canceled if these messages are retrieved. Specifically, we study two NOMA-based V2X communication schemes, namely, NOMA-V2X decoded by Successive Interference Cancellation (SIC-V2X) and NOMA-V2X decoded by Joint Decoding (JD-V2X). Based on the tools developed in stochastic geometry, we derive and compare the PDR expressions for both NOMA schemes and the Orthogonal Multiple Access (OMA) scheme. Our results indicate that 1) both NOMA schemes outperform the conventional OMA scheme and the PDR of LOS/NLOS communications with two-user access increases by 51%/369%; 2) for four-user access, the proposed NOMA scheme shows 375% goodput enhancement as compared with the OMA scheme; and 3) JD-V2X provides significant PDR enhancement compared with SIC-V2X in the high data rate regime. Finally, we also demonstrate that the random access based NOMA schemes can achieve lower transmission latency than collision-free scheduling schemes when the road is over 56% jammed.

Effective Throughput Maximization of NOMA With Practical Modulations

Non-orthogonal multiple access (NOMA) has been considered as a promising technology for future wireless communications. In most of the existing NOMA schemes, the ideal information rate based on Shannon capacity is used as the performance metric, assuming perfect successive interference cancellation (SIC) and Gaussian transmit signals without considering practical modulations. The implicit assumptions and the resulting schemes may lead to suboptimal performance in practical NOMA systems. In this paper, we consider multi-user multi-channel NOMA systems using practical quadrature amplitude modulation (QAM) with imperfect SIC. We aim to maximize a more practical performance metric, namely the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">effective throughput</i> , which takes into account the data rate and error performance. To achieve this goal, we derive both the exact and approximate expressions of the effective throughput. We also formulate a joint resource optimization problem of the power allocation, channel assignment, and modulation selection to maximize the effective throughput. We develop an efficient power allocation solution by proposing a closed-form power allocation within channels and a waterfilling-form power budget allocation among channels. We also develop efficient channel assignment and modulation selection methods with the aid of matching theory and machine learning, respectively. Consequently, we provide an efficient joint resource allocation algorithm via iterative optimization to maximize the effective throughput. Numerical results are presented to verify the superiority of the proposed NOMA scheme over orthogonal multiple access (OMA) and other NOMA schemes.

Spectrum Sharing in Cognitive-Radio-Inspired NOMA Systems Under Imperfect SIC and Cochannel Interference

In this article, we investigate the performance of spectrum sharing inunderlay cognitive radio (CR)-inspired nonorthogonal multiple access (NOMA) systems, at which a primary transmitter with a weak channel shares its spectrum with a secondary transmitter (ST) with a strong channel to promote the network spectrum efficiency. In this article, we derive closed-form expressions of the outage probabilities (OPs), in terms of elementary functions, and the ergodic capacities (ECs) of the two transmissions, in terms of exponential integral function, assuming imperfect successive interference cancellation (SIC) and cochannel interference. Moreover, the feasible range for the power-allocation factor to achieve a NOMA instantaneous data-rate gain for both nodes is investigated. The results reveal the degradation effects of imperfect SIC on the OP and EC of the ST. Additionally, the simulation shows a better sum EC of the proposed NOMA scheme compared with two reference schemes, namely the orthogonal multiple access and the underlay CR with interference temperature constraint scheme. Finally, the accuracy of the analytical results is verified with representative numerical simulations.

User Fairness Aware Power Allocation for NOMA-Assisted Video Transmission With Adaptive Quality Adjustment

In this paper, we investigate the user fairness power allocation (PA) for video transmission in a non-orthogonal multiple access (NOMA)-assisted wireless system with a pair of users. Considering that video transmission is usually delay-sensitive, the video quality can be adaptively adjusted based on the network conditions. First, a new performance metric, called the average video quality degradation probability, is proposed to describe the adaptive video quality. Then, based on the principles of NOMA and user queue model, the average video quality degradation probability of both users is derived. Next, a bisection search based power allocation (PA) algorithm is proposed to balance the video quality between the NOMA pair. Simulation results demonstrate that the proposed NOMA scheme is more effective to achieve the user fairness compared with the fixed NOMA scheme, the fractional transmit power allocation (FTPA) based NOMA scheme, the achievable rate fairness (ARF) NOMA scheme, and the optimized time division multiple access (TDMA) scheme.

On the Comparison of Optimal NOMA and OMA in a Paradigm Shift of Emerging Technologies

Non-orthogonal multiple access (NOMA) is a better multiple access technique than orthogonal multiple access (OMA), precisely orthogonal frequency division multiple access (OFDMA) scheme, at the conceptual level for fifth-generation (5G) networks and beyond 5G (B5G) networks. We investigate the potentials of the schemes by comparing the proposed NOMA scheme with the traditional cooperative communication NOMA (CCNOMA) scheme, rather than the comparison between NOMA and OMA only. To probe the effectiveness of NOMA as a multiple access technique, we propose a novel NOMA scheme considering two adjacent BSs with a special design of the transceiver architecture. The proposed scheme provides a reasonable data rate to both near user (NU) and far user (FU) without compromising the quality of service (QoS) to anyone of them. The conclusive analyses on the optimization framework of multi-user sum rate, capacity, transmit power, spectral efficiency (SE), and energy efficiency (EE) trade-off for NOMA and OFDMA schemes have been established to a succession of derivations. Under the analytical optimization framework, we also prove quite a few properties for them. Simulation results confirm the theoretical findings and show that the two schemes can efficiently approach the optimal power allocation, minimization of power consumption, and optimal SE-EE trade-off, and the proposed NOMA scheme provides comparatively better data sum rates than the baseline OMA scheme.

A Novel User Grouping in Phase Rotation Based Downlink NOMA

Non-orthogonal multiple access (NOMA) is a promising candidate beyond 5G and 6G to improve spectral efficiency by sharing the same resource block with other users. However, as the number of users increases in a single NOMA cluster, not only the spectral efficiency but also the interference increases. Therefore, to ensure a trade-off between capacity and error performance in NOMA systems, this study introduces a novel downlink NOMA scheme using the phase rotation. In the system, four users can create a single NOMA cluster and are grouped into two subgroups by exploiting conventional NOMA. Within each subgroup, the symbols of two users, near user and far user, are rotated and multiplexed by the power domain. Subsequently, the final transmitted signal is obtained by multiplexing the in-phase and quadrature components of the first and second subgroups, respectively. By superposing signals from two independent subgroups, the number of successive interference cancellation (SIC) operations are reduced compared to the existing NOMA. Moreover, the analytical bit error rate (BER) for a four-user scenario is derived, and the optimal rotation angle and power allocation are proposed to minimize the BER performance. Numerical results demonstrate the improved performance of the proposed NOMA scheme over several existing schemes, such as conventional NOMA and orthogonal multiple access (OMA).

Joint NOMA for Improved SER of Cell-Edge Users in Multi-Cell Indoor VLC

In this letter, we propose a non-orthogonal multiple access (NOMA) based scheme for multi-cell indoor visible light communications (VLC), where cell-edge user is jointly served by multiple cells. Unlike the typical designs in NOMA-VLC literature, the proposed scheme doesn’t involve complex domain and direct current bias addition, which makes the design simple and feasible for real time implementation in indoor VLC. The symbol error rate (SER) of the proposed NOMA scheme is analysed using simulation results, and is compared with orthogonal multiple access (OMA). It is observed that the average SER of the users with the proposed NOMA is marginally degraded as compared to OMA. However, the SER of cell-edge user with the proposed NOMA is significantly improved with joint maximum likelihood decoding, and outperforms successive interference cancellation based decoding and OMA, with trade-off on computational complexity.

A NOMA Scheme Using Oblique Projection for HetNet Uplink Under Perfect and Imperfect CSIR

The emerging non-orthogonal multiple access (NOMA) technique for fifth-generation (5G) heterogeneous network (HetNet) yields performance improvement specifically by boosting the network capacity and spectral efficiency. This paper proposes a new NOMA scheme for the uplink HetNet using oblique projection (OP) under perfect and imperfect channel state information at the receiver (CSIR). In this scheme, the OP operation performed at the femtocell base station (FBS) recovers the desired NOMA users’ signal from the composite received signal. Unlike the existing successive interference cancellation (SIC) based NOMA schemes, the proposed scheme does not demand any power control or user clustering techniques for decoding NOMA users’ data at the receiver side. Further, it does not need information exchange between users for decoding and hence the computational complexity and the signaling overhead of the system gets reduced significantly. To evaluate the performance of the proposed scheme under perfect CSIR analytically, we derive the closed-form expression for the probability of error and outage probability at the FBS receiver. We also derive the diversity order, sum-rate, and perform the computational complexity analysis of the NOMA-HetNet system employing the proposed scheme. Simulation results illustrate that the derived analytical results accurately describe the proposed NOMA scheme. We compare the performance of the proposed technique with a prevailing SIC based NOMA scheme and establish its superiority. Performance of the proposed NOMA scheme under imperfect CSIR is also studied and established that the scheme works well under this scenario also.

Joint Effects of Imperfect CSI and SIC on NOMA Based Satellite-Terrestrial Systems

This paper investigates a satellite-terrestrial system employing the non-orthogonal multiple access (NOMA) scheme over Shadowed-Rician fading channels. The effects of both imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) on the NOMA based satellite-terrestrial system are taken into account. First, the outage performance of the proposed system is evaluated, and the closed-form expressions for the exact and asymptotic outage probabilities are obtained. Next, the expressions of the ergodic sum rate and system throughput are derived in the presence of channel estimation errors and residual interference. Moreover, we analyze the impacts of different residual interference levels on the energy efficiency. Finally, the numerical simulation results are conducted to verify the correctness of theoretical analysis and the advantages of the proposed NOMA scheme. At medium-high SNR region, the NOMA users are capable of outperforming orthogonal multiple access (OMA) users in terms of outage behaviors and system throughput with imperfect CSI and imperfect SIC. The ergodic sum rate decreases as the level of residual interference $\varpi $ increases, and is even lower than that of OMA once $\varpi $ goes beyond a certain value. Additionally, the energy efficiency of NOMA scheme is sensitive to the imperfect SIC.

Application-Based Coexistence of Different Waveforms on Non-Orthogonal Multiple Access

In the study, the coexistence of different waveform structures on the same resource element is studied under the theory of non-orthogonal multiple access (NOMA). This study introduces a paradigm-shift on NOMA towards the application-centric waveform coexistence. Throughout this article, the coexistence of different waveforms is explained with two specific use cases, which are power-balanced NOMA and joint radar-sensing and communication with NOMA. For the first use case, block error rate (BLER) performance in the power-balanced regime for two user is improved compared to conventional NOMA transmission with the same waveform. For the joint radar-sensing and communication aspect, the superiority of proposed NOMA scheme over orthogonal frequency division multiplexing (OFDM) joint radar-communication (JRC) scheme is demonstrated regarding radar ambiguity, channel estimation mean-square error (MSE) and bit-error rate (BER) performances. In addition, some of the previous works in the literature are reviewed regarding waveform coexistence in a non-orthogonal manner. However, the concept is not limited to these use cases. With the rapid development of wireless technology, next-generation wireless systems are proposed to be flexible and hybrid, having different kinds of capabilities such as sensing, security, intelligence, control, and computing. Therefore, the concept of different waveforms’ coexistence to meet these concerns are becoming impressive for researchers.

NOMA-Based Pervasive Edge Computing: Secure Power Allocation for IoV

Nowadays, intelligent transportation industry is becoming a hot spot in Internet of vehicles (IoV). However, owing to the existence of numerous intelligent terminals, communication security becomes a pressing problem. On the other hand, pervasive edge computing (PEC), as a pivotal technology, can significantly improve the performance of the system compared to the traditional cloud computing. In this article, we propose a nonorthogonal multiple access (NOMA)-based PEC power allocation framework in IoV, aiming at minimizing the system latency in the presence of eavesdroppers. Besides, queuing models, imperfect channel state information, and vehicles' speeds are all considered. Since the formulated problem is complicated, we consider its lower bound and derive the suboptimal closed-form expressions of the power allocation coefficients. Furthermore, a Frank-and-Wold algorithm is proposed to achieve the optimum total power. Simulation results illustrate the superior performance of the proposed NOMA scheme.