Non-orthogonal Multiple Access Protocol Research Articles

On the outage performance analysis of α − κ − µ fading channels with non-orthogonal multiple access protocol

In this paper, we consider effective performance transmission under generalized α − κ − µ the fading distribution. The source-user links are assumed to be non-orthogonal multiple access (NOMA) channels through a downlink power do-main. Two users are selected to service in a situation with perfect channel state information (CSI) in accordance with the NOMA protocol. The closed-form ex-pressions of outage probability (OP) and bit error rate (BER) are derived with the effect of power allocation coefficient, target rate, and channel fading param-eters. In addition, we calculate numerical results to demonstrate the asymptotic expansion in the high signal-to-noise ratio (SNR) analysis. Finally, Monte Carlo simulations are provided to validate and assess the accuracy of the analytical framework proposed.

Hybrid NOMA Protocol with Relay Adaptive AF/DF Collaboration and Its Modeling Analysis in NB-IoT

In order to meet the demand for large-scale device access in Narrowband Internet of Things (NB-IoT) and to overcome the problem that some resources are wasted due to the use of single decode-and-forward (DF) or amplify-and-forward (AF) collaboration in traditional collaborative communication, this paper introduces a non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) hybrid access method into the NB-IoT and proposes a new Hybrid NOMA transmission protocol with relay adaptively selectable collaboration, which is represented as an algorithm. Based on this protocol, we classify the whole transmission process into five states after deriving the outage probability of each link. We then consider the system as a discrete-time Markov model, the closed expressions of the system outage probability and throughput are derived based on the system steady-state probability. In order to improve the system’s reliability, we further optimize the above protocol by allowing the source node to retransmit the unsuccessful received superimposed signals a limited number of times. Numerical results and simulations show that the outage probability is lower when multiple retransmissions are possible. The proposed relay adaptive collaborative hybrid NOMA transmission protocol has advantages over the pure OMA transmission mode.

UAV-Assisted Secure Communication for Coordinated Satellite-Terrestrial Networks

This letter investigates an unmanned aerial vehicle (UAV)-assisted satellite-terrestrial communication network. Specifically, a three-dimensional mobile UAV helps to enhance coverage and simultaneously enable secure communication between the satellite and ground users with the internal eavesdropper. Moreover, non-orthogonal multiple access protocol is adopted, such that the spectral efficiency can be further improved. Aiming to maximize the secrecy rate, a joint cooperative jamming, transmit power, and UAV trajectory optimization problem is proposed. To deal with its non-convexity, we propose an iterative optimization algorithm that first optimally addresses the jamming and transmit power optimization in close forms and then uses an iterative relaxation technique to design the UAV trajectory for the given power. Simulation results highlight the critical role of the mobile UAV and significantly confirm the effectiveness of the proposed algorithm over the benchmark schemes.

Markov chain modelling of ordered Rayleigh fading channels in non‐orthogonal multiple access wireless networks

AbstractA first‐order finite‐state Markov chain (FSMC) typically models the Rayleigh fading channel in the open literature because the first‐order FSMC is analytically tractable and can derive closed‐form results. Non‐orthogonal multiple access (NOMA) has been recognised as a novel wireless technology that addresses challenges in the next generation of mobile communications. According to the power‐domain NOMA protocol, channels in the NOMA wireless network are sorted by the channel gain. Then considering NOMA, there is insufficient information on how to further form a suitable model for ordered Rayleigh fading channels based on the first‐order FSMC. Given the mathematical statement on how to model the order statistics of multidimensional Markov chains for ordered Rayleigh fading channels, the authors consider these order statistics as a Markov chain, and propose specific processes of representing the state space and constructing the transition probability matrix accordingly. Numerical and simulation results validate the mathematical correctness and accuracy of these novel processes. In addition, for ordered Rayleigh fading channels, the performances of various methods of partitioning the entire signal‐to‐noise ratio range are compared. The performance comparison results are the same as those obtained for the individual unordered Rayleigh fading channel.

Strategy for Non-Orthogonal Multiple Access and Performance in 5G and 6G Networks.

The purpose of this paper is to provide a high-level overview of the most important non-orthogonal multiple access (NOMA) protocols in 5G and 6G networks that incorporate code division within the context of 3GPP standardization. The article's objective is also to look into and compare the various strategies that have been proposed as a solution to the issue of resource distribution to achieve high performance. Many different NOMA plans for 5G and 6G systems have been suggested by a multitude of businesses. NOMA is currently developing in two primary directions: one of them is with power division, and the other is with code division. During the process of standardization carried out by the 3GPP, the attention of the developers was concentrated in the second direction for the application of NOMA schemes in 5G and 6G systems. Hardware communication, also known as D2D communication, performs a significant role in the process of communication between devices. This will increase the efficiency with which network resources are utilized. Devices are now able to interact directly with one another, avoiding the need for transmission nodes. It also serves as one of the approaches to the problem of limited network coverage, which can be improved by utilizing D2D, and as a result fees and energy can be reduced. Increasing the size of the network is one way to achieve this goal, the explained of NOMA technology as well as its primary benefits in wireless technology. The most common variants of code division NOMA and the characteristics of those variants are discussed, as well as the opportunities and challenges associated with implementing those variants. NOMA protocols allow continuous expansion of wireless communication networks, i.e., 5G and 6G, which leads to enhanced performance of the networks.

Performance Analysis of Cognitive-Inspired Wireless Powered NOMA Systems With Joint Collaboration

This paper investigates the performance analysis of cognitive-inspired wireless-powered non-orthogonal multiple access (NOMA) systems, where two collaborative schemes are jointly proposed to enhance the quality-of-signal at the primary cell-edge (CE) user in dead zones. In particular, the first scheme, namely internal collaborative schemes, is developed based on the availability of primary cell-near users (CU), while the rest, called external collaborative schemes, comes from the help of a secondary source (SS). For the second scheme, SS’ operation is considered with two relaying-encoding NOMA protocols, namely decode-and-forward (DF) and amplifier-and-forward (AF). In order to enable CE’s communications in short execution times, the power-splitting mechanism is considered at both CU and SS. To capture the system’s performance trend accurately, closed-form approximate expressions for the outage probability of users are derived. Moreover, we also carry out the respective asymptotic expression at high transmit power regimes to show some useful insight, such as diversity order and coding gain. Finally, extensive Monte-Carlo simulations are presented to collaborate the accuracy of the theoretical analysis and numerical results show that the proposed collaborative scheme provides CE’s performance enhancement better than using only one collaborative scheme.

Outage performance for wireless-Powered relaying satellite-Terrestrial NOMA systems

This study investigates the outage performance for a wireless-powered relaying satellite-terrestrial system, which consists of a satellite source, a relay, a power beacon, and two users. In particular, the satellite source transmits its information to the relay, which uses up all the harvested energy from the power beacon with a nonlinear energy harvesting mode to forward a superimposed signal of the source and its own information under a non-orthogonal multiple access protocol. Assuming the satellite link experiences Shadowed-Rician fading and the terrestrial links undergo Nakagami-m fading distribution, the analytical expressions of outage probability for both users are presented in the presence of imperfect successive interference cancellation. In addition, the optimal power allocation factor, which can result in the best outage performance, is also obtained. Finally, Monte-Carlo simulations are used to verify the accuracy of the analytical expressions.

Physical layer secrecy analysis of HS-UAV NOMA network with spatially random eavesdroppers

This work investigates the physical layer secrecy performance of a hybrid satellite/unmanned aerial vehicle (HS-UAV) terrestrial non-orthogonal multiple access (NOMA) network, where one satellite source intends to make communication with destination users via a UAV relay using NOMA protocol in the existence of spatially random eavesdroppers. All the destination users randomly distributed on the ground comply with a homogeneous Poisson point process in the basis of stochastic geometry. Adopting Shadowed-Rician fading in satellite-to-UAV and satellite-to-eavesdroppers links while Rayleigh fading in both UAV-to-users and UAV-to-eavesdroppers links, the theoretical expressions for the secrecy outage probability (SOP) of the paired NOMA users are obtained based on the distance-determined path-loss. Also, the asymptotic behaviors of SOP expressions at high signal-to-noise ratio (SNR) regime are analyzed and the system throughputs of the paired NOMA users are examined for gaining further realization of the network. Moreover, numerical results are contrasted with simulation to validate the theoretical analysis. Investigation of this work shows the comparison of SOP performance for the far and near user, pointing out the SOP performance of the network depends on the channel fading, UAV coverage airspace, distribution of eavesdroppers and some other key parameters.

Performance analysis of SWIPT‐assisted adaptive NOMA/OMA system with hardware impairments and imperfect CSI

AbstractThis paper investigates the effect of hardware impairments (HIs) and imperfect channel state information (ICSI) on a SWIPT‐assisted adaptive nonorthogonal multiple access (NOMA)/orthogonal multiple access (OMA) system over independent and nonidentical Rayleigh fading channels. In the NOMA mode, the energy‐constrained near users act as a relay to improve the performance for the far users. The OMA transmission mode is adopted to avoid a complete outage when NOMA is infeasible. The best user selection scheme is considered to maximize the energy harvested and avoid error propagation. To characterize the performance of the proposed systems, closed‐form and asymptotic expressions of the outage probability for both near and far users are studied. Moreover, exact and approximate expressions of the ergodic rate for near and far users are investigated. Simulation results are provided to verify our theoretical analysis and confirm the superiority of the proposed NOMA/OMA scheme in comparison with the conventional NOMA and OMA protocol with/without HIs and ICSI.

Outage Analysis of Coordinated NOMA Transmission for LEO Satellite Constellations

This work investigates the performance of a downlink non-orthogonal multiple access (NOMA) based coordinated low-earth orbit (LEO) satellite system. Two LEO satellites are assumed to coordinate their transmissions to serve three users simultaneously using NOMA protocol, where only one user lies in the intersection of the footprints of the two satellites. We investigate the reliability of the proposed architecture, which is expressed in terms of the outage probability (OP). We derive closed-form expressions of the users’ OPs taking into considerations different realistic losses effects on the link budget including receiver antenna gain, satellite antenna gain, antennas pointing errors, shadowing, small-scale fading, and large-scale free space path loss. The channels between satellites and the three users are assumed to follow shadowed-Rician (SR) fading. The mathematical analysis is verified by the extensive representative Monto-Carlo simulations. Finally, we demonstrate the impact of the system parameters on the considered system as well as the superiority of the NOMA scheme over conventional OMA system.

On secrecy performance for IoT enabled SWIPT multi-relaying NOMA systems

In this paper, we evaluate the secrecy performance in terms of secrecy outage probability (SOP) for Internet of things (IoT) enabled multi-relaying non-orthogonal multiple access (NOMA) networks with energy harvesting over Nakagami-m fading channels. Specifically, we consider the scenario that a power-constrained source and N(N⩾1) IoT relays first harvest energy from a dedicated power beacon under a time switching mode, and then the source sends a confidential information to a legitimate user via a selected IoT relay, which forwards the decoded signal together with its own information data under a NOMA protocol to two legitimate users in the presence of an eavesdropper. Moreover, a two-stage relay selection criterion is also adopted to enhance the system’s secrecy performance. As a benchmark, we also adopt a random relay selection scheme to analyze the secrecy performance. To clearly reveal the benefits of our proposed schemes, the analytical expressions for SOP under those two schemes have been obtained and validated through Monte-Carlo simulations.

Heterogeneous Non-Orthogonal Multiple Access With Distributed Alamouti Space-Time Coding

Full frequency reuse with nonorthogonal multiple access (NOMA) in heterogeneous networks (HetNets) can promisingly satisfy the fast-growing wireless transmission requirements, as the data of different users can be simultaneously delivered over the same frequency band. In HetNets, the transmissions from a micro base station (BS) to its cell-edge users often suffer from strong interference from the macro BS, which severely degrades the communication quality. The macro BS and the micro BS can transmit simultaneously to a common far-user using the distributed Alamouti coding technique to improve the communication robustness. Meanwhile, each BS also transmits data to a near-user using the NOMA protocol. The common far-user adopts the maximal ratio combining (MRC) technique to decode its desired data by treating the data of near users as interference. Each near-user decodes the data of far-user using the MRC technique and cancels it to decode its own data by treating the remaining undesired data as interference. Numerical results show that the Alamouti coding based NOMA transmission can greatly improve the throughput of HetNets.

Resource Allocation in Virtualized CoMP-NOMA HetNets: Multi-Connectivity for Joint Transmission

In this work, we design a generalized joint transmission coordinated multi-point (JT-CoMP)-non-orthogonal multiple access (NOMA) model for a virtualized multi-infrastructure network. In this model, all users benefit from multiple joint transmissions of CoMP thanks to the multi-connectivity opportunity provided by wireless network virtualization (WNV) in multi-infrastructure networks. The NOMA protocol in CoMP results in an unlimited NOMA clustering (UNC) scheme, where the order of each NOMA cluster is the maximum possible value. We show that UNC results in maximum successful interference cancellation (SIC) complexity at users. In this regard, we propose a limited NOMA clustering (LNC) scheme, where the SIC is performed to only a subset of users. We formulate the problem of joint power allocation and user association for the UNC and LNC schemes. Then, one globally and one locally optimal solution are proposed for each problem based on mixed-integer monotonic optimization and sequential programming, respectively. Numerical assessments reveal that WNV and LNC improves users sum-rate and reduces users SIC complexity by up to 35% and 46% compared to the non-virtualized CoMP-NOMA system and UNC model, respectively. Therefore, the proposed algorithms are suitable candidates for the implementation on open and intelligent radio access networks.

Performance Evaluation of Power-Beacon-Assisted Wireless-Powered NOMA IoT-Based Systems

In this article, we investigate power beacon (PB)-assisted wireless-powered nonorthogonal multiple access (NOMA) Internet-of-Things (IoT)-based systems, where all transmitters harvest energy from a PB to transmit their signals to a destination by employing a time-splitting mechanism. In order to utilize spectral efficiency and enhance the quality of service of an edge user (EU), a cellular base station can communicate with the EU thank to the help of one IoT node in a cellular network by employing the NOMA protocol. To characterize the performance of the proposed systems, we derive the exact closed-form expression for the outage probability, throughput, energy efficiency, and the approximate closed-form expression for the ergodic capacity. To further improving the system performance, we present two algorithms that are to minimize the outage performance of users by optimizing the time-splitting factor and to maximize sum throughput via jointly optimal power allocation and time-spitting factor. Our numerical results show that the proposed system has outstanding performance in comparison with simultaneous wireless information and power transfer NOMA systems under time switching mechanism based on the IoT relay.

Optimizing Computation Efficiency for NOMA-Assisted Mobile Edge Computing With User Cooperation

In this article, we investigate the application of user cooperation (UC) and non-orthogonal multiple access (NOMA) schemes for a wireless powered mobile edge computing (MEC) system under the non-linear energy harvesting model, in which two single-antenna mobile users first harvest energy from a multi-antenna access point (AP) integrated with an MEC server. Then, during the computation offloading phase, both mobile users simultaneously offload tasks to the MEC server with the harvested energy, by performing NOMA protocol. To better enhance the system performance, UC scheme is carried out, where the near user acts as a relay to help the far user offload computation tasks to the AP. To obtain energy efficient MEC design, our objective is to maximize the computation efficiency (i.e., the total computation bits divided by the consumed energy) by jointly designing the energy beamforming, time and power allocations, which yields a challenging nonconvex optimization problem. To deal with it, the original problem is first transformed into a more tractable formulation by applying the semidefinite relaxation (SDR) technique and then solved by utilizing the sequential convex approximation (SCA) method. Numerical results demonstrate that UC has a great impact when two users are close, while NOMA makes effect when two users are relatively far. Combining both NOMA and UC, the proposed scheme, named NOMA-UC MEC, yields better system performance than the benchmark schemes.

Iterative Collision Resolution for Slotted ALOHA With NOMA for Heterogeneous Devices

In this paper, the problem of using uncoordinated multiple access (UMA) to serve a massive amount of heterogeneous users is investigated. Leveraging the heterogeneity, we propose a novel UMA protocol, called iterative collision resolution for slotted ALOHA (IRSA) with non-orthogonal multiple access (NOMA), to improve the conventional IRSA. In addition to the inter-slot successive interference cancellation (SIC) technique used in existing IRSA-based schemes, the proposed protocol further employs the intra-slot SIC technique that enables collision resolution for certain configurations of collided packets. A novel multi-dimensional density evolution is then proposed to analyze and to optimize the proposed protocol. Simulation results show that the proposed IRSA with NOMA protocol can efficiently exploit the heterogeneity among users and the multi-dimensional density evolution can accurately predict the throughput performance. Last, an extension of the proposed IRSA with NOMA protocol to the frame-asynchronous setting is investigated, where a boundary effect similar to that in spatially-coupled low-density parity check codes can be observed to bootstrap the decoding process.

Sub-Channel Scheduling, Task Assignment, and Power Allocation for OMA-Based and NOMA-Based MEC Systems

In this paper, sub-channel scheduling, task assignment and power allocation are investigated for orthogonal multiple access (OMA)-based and non-orthogonal multiple access (NOMA)-based mobile edge computing (MEC) systems. Based on different channel conditions and computational capacities, computational tasks are partially offloaded to the MEC server via OMA or NOMA protocols. In order to minimize the total energy consumption, an optimization problem under the task execution latency constraint is formulated and divided into two sub-problems. By utilizing matching theory, the formulated sub-channel allocation problem is solved by a proposed low-complexity algorithm, where the joint optimization of task assignment and power allocation is performed at each iteration. Based on the delay constraint, some insights are obtained, and the closed-form solutions of task assignment coefficients and transmit power are derived. Furthermore, the offloading strategy in both OMA and NOMA schemes is analyzed, which shows that the optimal task assignment coefficient is decided by the energy consumption efficiency (ECE). Simulation results indicate that: i) the proposed sub-channel allocation algorithm and derived closed-form solutions can significantly improve the MEC system in terms of the energy consumption; ii) the provided offloading strategy can be dynamically and efficiently employed with different channel conditions and computational capacities.

On secrecy analysis of UAV-enabled relaying NOMA systems

In this paper, we analyze the secrecy outage performance for an unmanned aerial vehicle (UAV) -enabled relaying non-orthogonal multiple access (NOMA) system, in which a source transmits a superimposed signal under the NOMA protocol to two users via a UAV-enabled decode-and-forward relay in the presence of an eavesdropper. Assuming the channels experience Nakagami-m fading and both hops are wiretapped, the probability density function (PDF) and cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio are first characterized, and then based on those PDF and CDF expressions, the analytical expressions for secrecy outage probability of two users are derived. Finally, Monte Carlo simulations are used to verify the accuracy of the derived expressions.

Secrecy Outage Probability of Relay Selection Based Cooperative NOMA for IoT Networks

As an important partner of fifth generation (5G) communication, the internet of things (IoT) is widely used in many fields with its characteristics of massive terminals, intelligent processing, and remote control. In this paper, we analyze security performance for the cooperative non-orthogonal multiple access (NOMA) networks for IoT, where the multi-relay Wyner model with direct link between the base station and the eavesdropper is considered. In particular, secrecy outage probability (SOP) for two kinds of relay selection (RS) schemes (i.e., single-phase RS (SRS) and two-phase RS (TRS)) is developed in the form of closed solution. As a benchmark for comparison, the SOP for random RS (RRS) is also obtained. To gain more meaningful insights, approximate derivations of SOP under the high signal-to-noise ratio (SNR) region are provided. Results of statistical simulation confirm the theoretical analysis and testify that: i) Compared with RRS scheme, SRS and TRS may improve secure performance because of obtaining smaller SOPs; ii) There exists secrecy performance floor for the SOP in strong SNR regime, which is dominated by NOMA protocol; iii) The security performance can be enhanced by augmenting the quantity of relays for SRS and TRS strategies. The purpose of this work is to provide theoretical basis for the analysis and design of anti-eavesdropping for NOMA systems in IoT.

Height Optimization and Resource Allocation for NOMA Enhanced UAV-Aided Relay Networks

In this paper, we investigate the application of the non-orthogonal multiple access (NOMA) technique into the unmanned aerial vehicle (UAV) aided relay networks. Specifically, we first incorporate the NOMA protocol with the decode-and-forward (DF) relay protocol to enhance the performance of the cell edge users in a macrocell network. Theoretical analysis indicates that the NOMA-DF-relay protocol outperforms the conventional orthogonal multiple access (OMA) based DF-relay protocol in terms of data rate. To fully exploit the advantages of the proposed protocol, we formulate a joint UAV height optimization, channel allocation, and power allocation problem with the objective to maximize the total data rate of the cell edge users under the coverage of the UAV. For solving the formulated problem effectively, we first analyze its property and employ the golden section method to propose a general framework to obtain the optimal height of the UAV. Then, we design a low-complexity iterative algorithm to solve the joint channel-and-power allocation problem based on the matching theory and the Lagrangian dual decomposition technique. Finally, simulation results demonstrate that the NOMA-DF-relay protocol is superior to the OMA-DF-relay protocol even when the system parameters are not optimized, and the proposed algorithms can further significantly improve the network performance in comparison with the other schemes.