Conventional Orthogonal Multiple Access Scheme Research Articles

Joint User Patterning and Power Control Optimization of MIMO–NOMA Systems

This paper illustrates the application of non-orthogonal multiple access (NOMA) scheme in multiple-input multiple-output (MIMO) communication system by use of joint user patterning and power allocation optimization. For the proposed MIMO–NOMA system, a non-convex optimization problem is formulated to improve the channel capacity. Then, the tight bound optimization problem is relaxed by a moderate convex approximation algorithmic approach to improve the channel capacity of the network. Further, a matching theory technique is applied to improve the user patterning and resource utilization of the whole system. Finally, the simulation results demonstrate that the proposed MIMO–NOMA framework with joint optimization can achieve convincing performance improvement in comparison to the conventional orthogonal multiple access schemes and other established NOMA schemes.

Two-Way Relaying Non-Orthogonal Multiple Access With Imperfect Successive Interference Cancellation in Power Line Communications

In this article, we study the application of cooperative non-orthogonal multiple access (NOMA) in power line communication (PLC) where two users exchange information using a two-way relay (TWR). Under the assumption of perfect and imperfect successive interference cancellation (SIC), we analyze key performance metrics for PLC log-normal channels impaired by impulsive noise. In particular, for delay-limited (DL) and delay-tolerant (DT) modes, approximate closed-form expressions are derived for the user outage probability and user ergodic rate. The analytic results are verified via Monte Carlo simulations. Compared with the conventional orthogonal multiple access (OMA) scheme, the simulation results show that our proposed NOMA TWR enhances the user outage probability and the user ergodic rate performance in the low signal-to-noise ratio (SNR) region. However, this gain diminishes as the imperfect SIC error increases and is non-existent beyond a certain level of imperfect SIC. Furthermore, the system performance is maximized by optimizing the power allocation coefficients where the system throughput and ergodic sum-rate of the NOMA TWR network in DL and DT operation, respectively, are shown to approach a ceiling in the presence of imperfect SIC. The energy efficiency (EE) of the proposed system is also analyzed for DL and DT modes.

Joint Relay Selection, Full-Duplex and Device-to-Device Transmission in Wireless Powered NOMA Networks

This paper investigates non-orthogonal multiple access (NOMA), cooperative relaying, and energy harvesting to support device-to-device (D2D) transmission. In particular, we deploy multiple relay nodes and a cell-center D2D device which can operate in full-duplex (FD) or half-duplex (HD) mode to communicate with a cell-edge D2D device. In this context, there are two possible signal transmission paths from the base station (BS) to the far D2D user either through multiple decode-and-forward (DF) relay nodes or through a near D2D user. Consequently, we propose three schemes to support D2D-NOMA systems, namely non-energy harvesting relaying (Non-EHR), energy harvesting relaying (EHR) and quantize-map-forward relaying (QMFR) schemes. For each of the proposed schemes, closed-form expressions of the outage probabilities of both D2D users are derived. Extensive Monte-Carlo simulation results are provided to validate the derived analytical expressions. The study results show that the proposed schemes can improve the outage performance compared to conventional orthogonal multiple access (OMA) schemes. Moreover, it is shown that the Non-EHR scheme achieves the best outage performance among the three considered schemes.

A Conditional Clustering Scheme for Hybrid NOMA in Millimeter Wave Communication System

Millimeter-wave (mmWave) and Non-orthogonal multiple access (NOMA) are expected to be the major techniques that lead to the next generation wireless communication. NOMA provides a high spectrum efficiency by sharing of spatial resources among users in the same frequency band. Meanwhile, millimeter-wave gives a huge underutilized bandwidth at extremely high frequency band (EHF) which covers 30GHz to 300GHz. These techniques have been proven in several recent literatures to achieve high data rates. The combination of NOMA and millimeter-wave techniques further improves average sum capacities, as well as reduces the interference compared to conventional wireless communication systems. In this paper, we focus on hybrid NOMA system working in millimeter-wave frequency. We propose a clustering algorithm used for a hybrid NOMA scheme to optimize the usage of wireless resources. The proposed clustering algorithm adds several conditions in grouping users and defining clusters to increase the probability of the successful superposition decoding process. The performance of the proposed clustering algorithm is investigated in hybrid NOMA system and compared with the conventional orthogonal multiple access (OMA) scheme.

Performance analysis at far and near user in NOMA based system in presence of SIC error

Non-orthogonal multiple access (NOMA) scheme is an emerging 5G technology to improve upon the spectral efficiency. It can support more users than the number of available frequency-,time-, and code-domain resources. The innovation behind NOMA technology is to exploit non-orthogonal resource allocation at the cost of receiver complexity to mitigate the inter-user interference arising due to non-orthogonal signals. In this paper, we present performance analysis of downlink NOMA (DL-NOMA) system in presence of successive interference cancellation (SIC) error over Rayleigh fading channels. In particular, we derive the exact closed-form expressions of bit error rate (BER) at near-user (U1) and far-user (U2) for the considered DL-NOMA system. Besides, we also present the achievable rate analysis of the considered NOMA system and it is observed that its achievable rate is higher as compared to conventional orthogonal multiple access (OMA) schemes. Further, we also determine the optimized power allocation coefficient for the NOMA system. The analytical results are corroborated with the Monte-Carlo simulations. The simulation results are presented for different modulation schemes and for different NOMA scenarios. A close argument between the analytical and simulation results validate our analysis.

Cooperative Non-Orthogonal Multiple Access over Log-Normal Power Line Communication Channels

In this paper, we analyze the performance of cooperative power domain non-orthogonal multiple access (NOMA) in power line communication (PLC) networks. Due to the high signal attenuation of the source to user links, a relay aids communication from the source to two users. With half-duplex transmission, the source transmits a superimposed symbol in the first phase. The relay utilizes amplify-and-forward (AF) and decode-and-forward (DF) protocol on the received superimposed signal and forwards it to the users in the second phase. We derive analytic expressions for the outage probability and the system throughput of the proposed system under a PLC log-normal channel with impulsive noise. Based on the results for AF NOMA relaying case, we analyze the system performance at high signal-to-noise ratio (SNR) and derive closed-form lower and upper bounds for the outage probability. Simulation results show an improvement in the outage probability and the system throughput performance of the AF and DF NOMA schemes compared to the NOMA without relaying transmission and conventional orthogonal multiple access scheme. Furthermore, the impact of the channel variance is highlighted in the results. It is shown that the DF NOMA has a better outage probability than the AF NOMA scheme for low channel variance scenarios (i.e., less branches and connected loads in the PLC network). However, as the channel variance increases, AF NOMA scheme has similar outage probability performance as the DF NOMA scheme. In addition, it is shown that the system throughput is enhanced when the relay employs DF relaying compared to AF relaying.

Outage analysis of underlay cognitive NOMA system with cooperative full duplex relaying

AbstractThis paper investigates the outage performance of secondary users (SUs) in underlay cognitive radio–based nonorthogonal multiple access (CR‐NOMA) networks. We consider down link scenario for the secondary network, which consists of a secondary transmitter (ST) and two SUs, ie, a near user and far user. The ST uses NOMA signaling to transfer the information to the down link SUs. A dedicated node is used as the full‐duplex decode‐and‐forward (DF) relay for delivering the message to the far‐user. We derive exact expressions for the outage probabilities experienced by the SUs for full duplex (FD)/half duplex (HD)–based CR‐NOMA networks, in independent, nonidentically distributed Rayleigh fading channels. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. We compare the performance of the proposed FD/HD‐based CR‐NOMA networks against that of a CR network, which use conventional orthogonal multiple access (OMA) scheme. We establish that the performance of CR‐NOMA network is better as compared to CR‐OMA networks. We then consider finding the optimal location for the FD relay node that minimizes the outage probability of far‐user. We formulate an optimization problem that is solved using genetic algorithm. Numerical results show that optimized relay location significantly improves the outage performance of the far‐user. The analytical results are validated by extensive simulation studies.

Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

SummaryThis paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies.

Energy harvesting relay-antenna selection in cooperative MIMO/NOMA network over Rayleigh fading

In this paper, a combination system of multi-antenna multiple input multiple output (MIMO) and non-orthogonal multiple access (NOMA) technologies is investigated, in which the source communicates with users using a multiple amplify-and-forward (AF) relaying network. These relay nodes are equipped with a single antenna and employ a power-splitting protocol to harvest energy from received signals, whereas the source and users are multiple-antenna nodes. In addition, two antenna-relay selection methods are considered to enhance the harvested energy at the relay including the maximum ratio transmission (MRT) and transmit antenna selection (TAS) at the source, with maximal-ratio combining at the users, these methods are compared to the performance of the random selection (RS) scheme. To evaluate the performance of the proposed system, we derive analytical expressions of the outage probability and throughput for the MRT and TAS schemes over Rayleigh fading channels, and use a Monte Carlo simulation to verify the accuracy of the analytical results. The results demonstrate the benefit of using MRT and TAS schemes, which provide a better performance than RS schemes, in a MIMO/NOMA system. Moreover, these results characterize the effects of various system parameters, such as power allocation factors, the numbers of antenna and relay nodes, power-splitting ratio, successive interference cancellation and energy-harvesting efficiency, on the system performance of two users of MIMO/NOMA. This is further compared with multiple-antenna conventional orthogonal multiple access (MIMO/OMA) schemes.

NOMA for Hybrid mmWave Communication Systems With Beamwidth Control

In this paper, we propose a novel non-orthogonal multiple access (NOMA) scheme with beamwidth control for hybrid millimeter wave communication systems and study the resource allocation design to maximize the system energy efficiency. In particular, NOMA transmission allows more than one user to share a single radio frequency chain, which is beneficial to enhance the system energy efficiency. More importantly, the proposed beamwidth control can increase the number of served NOMA groups by widening the beamwidth that can further exploit the energy efficiency gain brought by NOMA. To this end, two beamwidth control methods, based on the conventional beamforming and the Dolph–Chebyshev beamforming, respectively, are proposed. We first characterize the main lobe power losses due to the two beamwidth control methods and propose an effective analog beamformer design to minimize the power loss. Then, we formulate the energy-efficient resource allocation design as a non-convex optimization problem, which takes into account the minimum required user data rate. A NOMA user grouping algorithm based on the coalition formation game theory is developed and a low-complexity iterative digital precoder design is proposed to achieve a locally optimal solution utilizing the quadratic transformation. Simulation results verify the fast convergence and effectiveness of our proposed algorithms. In addition, our results demonstrate the superior energy efficiency achieved by our proposed beamwidth controlling NOMA scheme compared to the conventional orthogonal multiple access and NOMA schemes without beamwidth control.

Energy-Efficient Power Allocation in Uplink mmWave Massive MIMO With NOMA

In this paper, we study the energy efficiency (EE) maximization problem for an uplink millimeter wave massive multiple-input multiple-output system with non-orthogonal multiple access (NOMA). Multiple two-user clusters are formed according to their channel correlation and gain difference, and NOMA is applied within each cluster. Then, a hybrid analog-digital beamforming scheme is designed to lower the number of radio frequency chains at the base station (BS). On this basis, we formulate a power allocation (PA) problem to maximize the EE under users' quality of service requirements. An iterative algorithm is proposed to obtain the PA. Moreover, an enhanced NOMA scheme is also proposed, by exploiting the global information at the BS. Numerical results show that the proposed NOMA schemes achieve superior EE when compared with the conventional orthogonal multiple access scheme.

Radio-Frequency Front-End Impairments: Performance Degradation in Nonorthogonal Multiple Access Communication Systems

The explosive growth of connected devices poses key challenges on the effective design and deployment of future wireless systems and networks. Nonorthogonal multiple access (NOMA) has been recently proposed as a viable solution to such related challenges because it has been shown to be capable of enabling increased spectral efficiency, massive connectivity, and low latency. NOMA allows multiple users to share the same frequency bands and time slots through power-domain or code-domain multiplexing, while successive interference cancelation (SIC) eliminates the resulting multiuser interference. However, transceiver architectures inevitably suffer from radio-frequency (RF) front-end-associated impairments, such as in-phase (I)/quadrature-phase (Q) imbalances, dc offsets, and power amplifier (PA) nonlinearities. This article addresses the main RF impairments that degrade the performance of communication systems in the context of NOMA-based communication scenarios. In addition, it provides useful insights into the potential opportunities and challenges that are envisioned to enable efficient design and implementation of NOMA in future wireless networks. Extensive computer simulations assuming such impairments reveal that NOMA communication systems experience significant performance degradation compared to conventional orthogonal multiple access (OMA) schemes. Furthermore, the different users in NOMA inevitably experience different levels of degradation, which highlights the importance for accurate modeling and dynamic compensation of the incurred impairments to ensure successful deployment of NOMA in critical applications, such as vehicle-to-vehicle communications.

Performance Analysis of NOMA-Based Cooperative Spectrum Sharing in Hybrid Satellite-Terrestrial Networks

In this paper, the performance of non-orthogonal multiple access (NOMA) based cooperative spectrum sharing in hybrid satellite-terrestrial networks (HSTNs) is investigated, where the primary satellite network recruits the secondary terrestrial network as a cooperative relay. To improve the fairness and spectrum utilization under cooperative spectrum sharing (i.e. overlay paradigm of cognitive radio), the NOMA power allocation profile is determined by instantaneous channel conditioning at the second temporal phase. The closed-form outage probability and approximated ergodic capacity expressions for the primary user (PU) and the secondary user (SU) are derived by decode-and-forward (DF) relay protocols, where the generalized Shadowed-Rician fading and Nakagami-m fading are considered for satellite links and terrestrial links, respectively. Simulation results are conducted for validation of the theoretical derivation and analysis of the impact of key parameters, and prove the superiority of NOMA comparing to conventional orthogonal multiple access (OMA) schemes on cooperative spectrum sharing in HSTNs. Besides, the fairness analysis between the PU and the SU is introduced by Jain's fairness index (JFI).

Resource Allocation for Energy Harvesting-Powered D2D Communications Underlaying NOMA-Based Networks

This paper investigates the resource allocation problem in device-to-device (D2D) communications underlaying a non-orthogonal multiple access (NOMA)-based cellular network with energy harvesting, where the energy harvesting-powered D2D communications share the downlink resources of the cellular network. To fully exploit the high-data-rate D2D links in this system, a two-phase framework is proposed for D2D users. In particular, the D2D users harvest energy from the base station (BS) in the first phase and then transmit their own information using the harvested energy in the second one. Meanwhile, the D2D communications could cause severe interference to cellular users (CUs) and hence probably ruin the SIC decoding order of the CUs. To deal with this issue, joint power allocation and time scheduling scheme is proposed to maximize the throughput of the D2D links while guaranteeing the quality of service (QoS) for each CU. Through rigorous derivation, the optimal power control and time scheduling parameters are analyzed to simplify the optimization problem formulation. The closed-form optimal solution is derived in some cases. In other cases, a gradient-based algorithm is employed to find an appropriate sub-optimal solution. The simulation results are demonstrated to validate the superiority of the proposed scheme over the conventional orthogonal multiple access (OMA) scheme.

Energy and spectrum efficient power allocation with NOMA in downlink HetNets

This paper investigates the tradeoff between energy efficiency (EE) and spectrum efficiency (SE) in a downlink non-orthogonal multiple access (NOMA)-based heterogeneous networks (HetNets). The tradeoff problem is formulated as a multi-objective optimization problem (MOP). Under the constraints of maximum transmit power of small cell users (SUEs) and minimum rate requirements, both EE and SE are maximized. In order to make the MOP tractable, a weighted sum method is used to transform it into a single-objective optimization problem (SOP), which enables the network providers to dynamically tune the weight factor to adapt to different EE and SE design requirements. To solve the transformed SOP, a SUE allocation algorithm is proposed to determine the multiple SUEs for each sub-channel, based on which a power proportional factor determination algorithm for SUEs and a novel power allocation algorithm for sub-channels are proposed. Numerical results show the fast convergence property, and demonstrate that the EE and SE obtained by our algorithms are Pareto optimal solutions and superior to the conventional orthogonal multiple access scheme.

What Role can NOMA Play in Massive MIMO?

This paper seeks to answer a simple but fundamental question: What role can NOMA play in massive MIMO? It is well-established that power-domain non-orthogonal multiple access (NOMA) schemes can outperform conventional orthogonal multiple access (OMA) schemes in cellular networks. However, this fact does not imply that NOMA is the most efficient way to communicate in massive MIMO setups, where the base stations have many more antennas than there are users in the cell. These setups are becoming the norm in future networks and are usually studied by assuming spatial multiplexing of the users using linear multi-user beamforming. To answer the above question, we analyze and compare the performance achieved by NOMA and multi-user beamforming in both NLOS and LOS scenarios. We reveal that the latter scheme gives the highest average sum rate in massive MIMO setups. We also identify specific cases where NOMA is the better choice in massive MIMO and explain how NOMA plays an essential role in creating a hybrid of NOMA and multi-user beamforming that is shown to perform better than two standalone schemes do.

A downlink non-orthogonal multiple access scheme having physical layer security

In recent years, the standardization for the fifth generation (5G) mobile communication systems has been actively discussed, and it is expected that a large number of wireless communication terminals, and beyond, in the current systems are accommodated in 5G systems. One of the steps in establishing this system is an advanced multiple access technology. In this paper, we propose a chaos non-orthogonal multiple access (C-NOMA) scheme for downlink transmission that offers high capacity allocation and secure wireless multiple access with physical layer security. In 5G systems where many terminals concurrently communicate, it is also important to ensure communication integrity for each user while maintaining large capacity communication. As a secure wireless channel-coded communication scheme, we have proposed a chaos multiple-input multiple-output (C-MIMO) scheme using the principle of chaos communication. By applying C-MIMO into a power-domain non-orthogonal multiple access transmission, we were able to demonstrate the operation and suitability of the C-NOMA configuration for handling both large capacity and physical layer security against eavesdroppers. We also demonstrated its improved performances through numerical simulations, and provided comparisons with those of conventional NOMA and chaos orthogonal frequency division multiple access schemes. In addition, we evaluated the security capability of the proposed technique based on the channel capacity of eavesdroppers and showed that secure transmission can be achieved using floating-point calculations.

Energy-Efficient Joint Power and Bandwidth Allocation for NOMA Systems

In this letter, we consider a downlink non-orthogonal multiple access (NOMA) system where a base station (BS) simultaneously communicates with multiple users. These users are grouped on multiple unequal-bandwidth subchannels. The power and bandwidth allocation are jointly optimized in order to maximize the system energy efficiency (EE) under transmit power constraint at the BS and minimum rate constraints for individual users. The optimization problem is nonconvex because of the fractional objective function and the nonconvex constraints. To deal with the original problem, it is first converted into an equivalent DC (difference of two convex functions) program by introducing slack variables, and then an iterative algorithm based on the constrained concave-convex procedure is proposed to solve it. Our numerical results demonstrate that the proposed algorithm has better EE performance compared to the NOMA scheme with equal-bandwidth allocation and conventional orthogonal multiple access scheme.

Pattern Division Multiple Access: A New Multiple Access Technology for 5G

The anticipated 1000-fold increase in mobile data traffic over the next decade and the explosion of new services and applications pose great challenges for the current orthogonal multiple access (OMA)-based 4G systems. A promising solution to address these challenges is to shift from the currently predominant OMA to non-orthogonal multiple access (NOMA). This article first introduces the principle of the complexity-constrained capacity-achieving NOMA design. Then a non-orthogonal pattern division multiple access (PDMA) scheme is proposed to meet the exponentially growing demand of mobile users for computing and information application services. The key feature of the PDMA scheme is a joint design of transmitter and receiver, which allows low-complexity successive interference cancellation (SIC)-based multi-user detection with substantially improved performance over conventional OMA schemes. More specifically, the patterns of multiple users are judiciously designed so that the data symbols of different users are of appropriate diversity disparity at the symbol level and power disparity at the resource element level. The appropriate disparity in diversity and power can be effectively exploited by the low-complexity SICbased detector to realize the near-perfect cancellation of multi-user interference. Moreover, the PDMA system parameters can be flexibly adjusted to provide different levels of overload, rendering it suitable to meet the diverse traffic requirements in future 5G systems. Link-level simulations illustrate that PDMA is capable of accommodating a 300 percent overload, while it still enjoys transmission reliability close to conventional OMA schemes. The results demonstrated in this article indicate that PDMA can be a promising multiple access technology with low signaling overhead, low latency, and massive connectivity support for 5G.

Dynamic resource allocation for uplink non‐orthogonal multiple access systems

This study investigates a problem of resource allocation for an uplink multi-carrier non-orthogonal multiple access (NOMA) system. To provide a general resource allocation problem, the order of successive interference cancellation (SIC), subcarrier assignment and power allocation are all considered as the optimisation variables of interest, with the objective of maximising the weighted sum rate under the transmit power constraint of each user equipment (UE). Firstly, a novel optimal SIC order is proposed based on the inherent structure of the uplink NOMA system. Then, with the optimal SIC order, the Lagrange dual method is employed to solve the joint subcarrier assignment and power allocation problem in an asymptotically optimal manner. In addition, an optimal solution of power allocation with a fixed subcarrier assignment is presented. In light of the optimal power allocation, a tight upper bound of the uplink NOMA system is developed by relaxing the number of multiplexed UEs on each subcarrier. Simulation results show that the proposed algorithm outperforms conventional orthogonal multiple access schemes and other static NOMA schemes, and as a benchmark, the upper bound reveals that multiplexing at most two UEs on each subcarrier is sufficient for the performance improvement.