Power-domain Non-orthogonal Multiple Access Research Articles

Profit Maximization in 5G+ Networks with Heterogeneous Aerial and Ground Base Stations

In this paper, we propose a novel framework for 5G and beyond (5G+) heterogeneous wireless networks consisting of macro aerial base stations (MABSs), small aerial base stations (SABSs), and ground base stations (GBSs) with two types of access technologies: power domain non-orthogonal multiple access (PD-NOMA) and orthogonal frequency-division multiple access (OFDMA). We aim to maximize the total network profit under some practical network constraints, e.g., NOMA and OFDMA limitations, transmit power (TP) maximum limits, and isolation of the virtualized wireless network. We formulate the resource allocation problem encompassing joint TP allocation, ABS altitude determination, user association, and sub-carrier allocation parameters. Our optimization problem is mixed integer non-linear programming (MINLP) with high computational complexity. To propose a practical approach with reduced computational complexity, we use an alternate method where the main optimization is broken down into three sub-problems with lower computational complexity. We do this by adopting successive convex approximation (SCA), geometric programming (GP), and mesh adaptive direct search (MADS) to solve each of the resulting problems, and find power allocation, altitudes of ABSs, and assignment parameters, respectively. Simulation results reveal that our proposed scenario can improve the overall network profit by up to 47 percent compared to the case where the TPs and ABS altitudes are fixed. Besides, finding the ABS altitude with fixed TPs can improve the network profit by 20 percent compared to the power allocation case with fixed ABS altitudes. Our proposed heterogeneous approach improves the network profit by up to 18, 16, 15, and 10 percent in suburban, urban, dense urban, and high-rise urban environments, respectively, compared to the cases with homogeneous ABSs.

Uplink Power-Domain Non-Orthogonal Multiple Access (NOMA)

Non-orthogonal multiple access (NOMA) has been proposed as a promising multiple access (MA) technique in order to meet the requirements for fifth generation (5G) communications and to enhance the performance in internet of things (IoT) networks by enabling massive connectivity, high throughput, and low latency. This paper investigates the bit error rate (BER) performance of two-user uplink power-domain NOMA with a successive interference cancellation (SIC) receiver and taking into account channel estimation errors. The analysis considers two scenarios: perfect (ideal) channel estimation and a channel with estimation errors for various modulations schemes, BPSK, QPSK, and 16-QAM. The simulation results show that, as expected, increasing of the modulation level increases the SIC receiver BER. For example, at a signal-to-noise ratio (SNR) of 5 dB for perfect channel estimation and QPSK modulation, the user that is detected first has a BER of 0.005 compared to 0.14 for the user that is detected with the aid of the SIC receiver. Similarly, the BER of QPSK, assuming 0.25 channel estimation error of user 1, is equal to 0.06 at SNR = 15 dB compared to 0.017 for perfect estimation.

A Novel Rate Improvement Technique of Power Domain NOMA in Wireless 5G

Error performance (EP) and capacity improvement (CI) are two important aspects essentially addressed using NOMA in the future cellular networks. In a dense user environment, transmit antenna selection NOMA (TAS-NOMA) algorithm if often employed to save the power. Apart from this antenna selection scheme, it is significant to manage sum rate calculation (i.e., spatial diversity) and delay (latency). In this paper, we propose ensemble average sum rate (EASR) algorithm which is capable of controlling the sum rate while minimizing the latency. However, it is significant to note that the system suffers non-linearity when the number of antennas enhanced in the transmitting side. The proposed technique produced better results in terms of enhanced power allocation than the conventional selection algorithm.

Color-Domain SCMA NOMA for Visible Light Communication

Visible light communications (VLC) has emerged as a promising technology for the next-generation communication systems. For VLC, several non-orthogonal multiple access (NOMA) techniques have emerged, among which sparse-code multiple access (SCMA) is particularly viable due to promised shaping and coding gain, and typically minimal/no error propagation as compared to power-domain NOMA (PD-NOMA). In this work, we introduce using polychromatic light emitting diodes (LEDs) as transmitters, where several users are overlapped on each color using SCMA; consequently, the SCMA codewords on each color are overlapped in the color-domain before transmission. At the receiver, after color-filtering, the residual color-coupling is removed by inverting the coupling matrix. Finally, the users’ signals over each color-channel are recovered using the message passing algorithm. Further, asymptotic error-rate expressions are derived for the proposed color-domain SCMA. These expressions are validated by simulations assuming VLC channel-models for random waypoint user-mobility. The analytical results promise a potential gain in the sum-rate while supporting a larger number of users as compared to a monochromatic white-LED based SCMA system.

Covert Communications in D2D Underlaying Cellular Networks With Power Domain NOMA

A device-to-device (D2D) communication link is vulnerable because it is relatively easy to be compromised by adversaries due to the fact that D2D terminals are power limited nodes. This article proposes a covert communication scheme that allows D2D communication links to transmit covert signals (e.g., privacy sensitive data) to ensure a low probability of detection. We allocate transmit powers of cellular and D2D noncovert signals following a fading D2D channel to add the uncertainty in adversary's background noises. With the help of base station, cooperative power domain nonorthogonal multiple access and successive interference cancellation are used to decode covert signal. Depending on whether a D2D transmitter has the knowledge of adversary's detection threshold, we derive minimum error probability to measure the covertness performance. Furthermore, we evaluate covert throughput, which is defined as a maximum average transmission rate of covert signal, subject to a given covertness performance.

NOMA With Zero-Forcing V-BLAST

In this study, power-domain non-orthogonal multiple access (NOMA) is combined with zero-forcing (ZF) vertical Bell Labs layered space-time (V-BLAST) technique. Motivated by the fact that the successive interference cancellation (SIC) is a pivotal element in either technique, we thoroughly investigate the impact of SIC on inter-user and inter-layer interference. A two-user downlink scenario is investigated where a multi-antenna base station with no instantaneous channel state information simultaneously communicates with two users each with multiple antennas. The average sum rate of the considered system is analytically derived in an exact form. Correspondingly, the power allocation value on each substream is optimized such that the average sum rate is maximized. We show that when the classical power-domain NOMA idea is incorporated into the ZF V-BLAST algorithm, the far user cannot completely cancel inter-layer interference. Nonetheless, the proposed approach turns out to yield an average sum rate performance near to that of a higher-complexity method based on maximum likelihood detection.

Advanced NOMA Receivers From a Unified Variational Inference Perspective

Non-orthogonal multiple access (NOMA) on shared resources has been identified as a promising technology in 5G to improve resource efficiency and support massive access in all kinds of transmission modes. Power domain and code domain NOMA have been extensively studied and evaluated in both literatures and 3GPP standardization, especially for the uplink where large number of users would like to send their messages to the base station. Though different in the transmitter side design, power domain NOMA and code domain NOMA share the same need of the advanced multi-user detection (MUD) design at the receiver side. Various multi-user detection algorithms have been proposed, balancing performance and complexity in different ways, which is important for the implementation of NOMA in practical networks. In this paper, we introduce a unified variational inference (VI) perspective on various universal NOMA MUD algorithms such as belief propagation (BP), expectation propagation (EP), vector EP (VEP), approximate message passing (AMP) and vector AMP (VAMP), demonstrating how they could be derived from and adapted to each other within the VI framework. Moreover, we unveil and prove that conventional elementary signal estimator (ESE) and linear minimum mean square error (LMMSE) receivers are special cases of EP and VEP, respectively, thus bridging the gap between classic linear receivers and message passing based nonlinear receivers. Such a unified perspective would not only help the design and adaptation of NOMA receivers, but also open a door for the systematic design of joint active user detection and multi-user decoding for sporadic grant-free transmission.

Mathematical evaluation of spectrum sharing in cognitive radio networks for 5G systems using Markov processes

Nowadays, efficient spectrum usage is one of the most important design principles to take into account in wireless communications due to the exponential growth of mobile devices. In that sense, solutions such as non-orthogonal multiple access (NOMA) and cognitive radio (CR), investigated separately, have been proposed to overcome the spectrum scarcity issue. However, it is important to quantify the benefits of the link of both technologies to improve spectrum utilization. In this work, a novel mathematical model of teletraffic for resource allocation using power-domain NOMA (PD-NOMA) in a cognitive radio (CR) environment, specifically in the interweave spectrum sharing scheme, calculating the birth-death process by teletraffic analysis, is developed. This new methodology involves a mathematical model where users can be born or die as primary or secondary users and are represented by a two-dimensional Markovian process. Mathematical results are validated through simulations considering three different scenarios. In these scenarios, a comparison between PD-NOMA and orthogonal multiple access (OMA) schemes is presented considering the blocking probability and the average number of users. The proposed mathematical model shows convergence to the performed simulations. The outcomes indicate that PD-NOMA increases the blocking probability, however, if this parameter is less than 0.03, the average number of active users is at least 90% higher compared to the OMA case.

Performance analysis of Power-Domain NOMA and NOMA-2000 on AWGN and Rayleigh fading channels

Non-Orthogonal Multiple Access (NOMA) has been a hot research topic over the past years, because it is widely viewed as a promising technology for 5G cellular networks and beyond. The NOMA literature today is heavily based on the so-called Power-Domain NOMA (PD-NOMA), which consists of superposing user signals with different powers. Also, the focus in the literature has been on the derivation of achievable rates and other information theoretic measures. In contrast, the performance degradation that is caused by multi-user interference at practical bit error rate (BER) values has not attracted much attention thus far. Taking a major deviation from the current trend, some of the present authors recently revived an early NOMA concept, which had been rather overlooked in the literature. This concept, which we refer to as NOMA-2000 due to its year of introduction, consists of superposing the signals of two user groups instead of superposing the signals of two single users. In subsequent papers, performance of NOMA-2000 has been investigated in different scenarios, but no comparisons with PD-NOMA have been provided. The purpose of this paper is to fill this gap and compare the BER performances of the two schemes using different channel models, channel overload factors, and power imbalance levels between users. For the Rayleigh fading channel, we consider both static user grouping and dynamic user grouping. Our results give a clear insight into the practical performance limitations of PD-NOMA and the improvements that can be achieved with NOMA-2000 in most cases.

A Novel Spectrally-Efficient Uplink Hybrid-Domain NOMA System

This paper proposes a novel hybrid-domain (HD) non-orthogonal multiple access (NOMA) approach to support a larger number of uplink users than the recently proposed code-domain NOMA approach, i.e., sparse code multiple access (SCMA). HD-NOMA combines the code-domain and power-domain NOMA schemes by clustering the users in small path loss (strong) and large path loss (weak) groups. The two groups are decoded using successive interference cancellation while within the group users are decoded using the message passing algorithm. To further improve the performance of the system, a spectral-efficiency maximization problem is formulated under a user quality-of-service constraint, which dynamically assigns power and subcarrier to the users. The problem is non-convex and has sparsity constraints. The alternating optimization procedure is used to solve it iteratively. We apply successive convex approximation and reweighted $\ell_1$ minimization approaches to deal with the non-convexity and sparsity constraints, respectively. The performance of the proposed HD-NOMA is evaluated and compared with the conventional SCMA scheme through numerical simulation. The results show the potential of HD-NOMA in increasing the number of uplink users.

Reliable uplink transmissions for NOMA-based Industrial Wireless Networks with guaranteed real-time performance

Reliability is vital for ultra-reliability low-latency transmission applications in Industrial Wireless Networks (IWNs). The power-domain Non-Orthogonal Multiple Access (NOMA) technology can support multiple parallel transmissions, and has been thought of as one of the most powerful candidate radio access technology for the next-generation IWNs. However, it suffers from low transmission reliability because of the high interferences caused by parallel transmissions in power-domain NOMA. In this paper, given the real-time performance requirements, we consider a single-hop network supporting 2-Successive Interference Cancellation, and study how to maximize the reliabilities of uplink transmissions by the joint user pairing and power allocation. We show that the problem is solvable in polynomial time by an optimal algorithm with complexity of O(nlogn), where n is the number of users. The performance evaluations reveal that the transmission reliabilities will increase exponentially with the linear degradation of the guaranteed real-time performance.

Demonstration of Pattern Division Multiple Access With Message Passing Algorithm for Multi-Channel mmWave Uplinks via RoF Mobile Fronthaul

Orthogonal multiple access (OMA) such as orthogonal frequency division multiple access (OFDMA) has been the predominant access technology adopted by the current generation of mobile communication. Representing an evolutionary step in radio access networks, non-orthogonal multiple access (NOMA) is considered to be a promising technology to meet the goals of increased capacity, enhanced flexibility, and reduced latency. Pattern division multiple access (PDMA) is a NOMA scheme using resource-element mapping as the multiple-access signature in the symbol level. This article introduces PDMA in a millimeter-wave (mmWave) radio access system with systematic experimental demonstration. One key advantage of PDMA is that it can facilitate advanced parallel interference cancellation (PIC) in the decoding process. A message passing algorithm (MPA) is developed and implemented in this article to enhance the decoding performance of PDMA. A novel PDMA system integrated with MPA is experimentally demonstrated in a multi-user mmWave radio access system that uses radio-over-fiber (RoF) mobile fronthaul, achieving reduced sensitivity penalty and improved modulation spectral efficiency compared to conventional power-domain NOMA (PD-NOMA) with successive interference cancellation (SIC). Experimental results show that PDMA is capable of supporting disparate channel conditions, adapting to various patterns, and providing improved system flexibility.

Cross-Layer Interference Management Scheme for D2D Mobile Users Using NOMA

Device-to-device (D2D) communication is a promising technology in which the spectrum resources are reused efficiently with cellular mobile users (CMUs) in an underlay of the fifth generation network. Using it, network capacity and spectral efficiency increase but it introduces the cochannel interference. Moreover, massive connectivity has not been fully exploited for efficient spectral efficiency usage in the existing solutions. Therefore, to address the aforementioned challenges, we integrate power domain nonorthogonal multiple access (PD-NOMA) technique with the D2D mobile groups (DMGs) to maximize their sum rate and to maintain the signal-to-interference noise ratio provided by CMUs. We formulate the problem of spectrum reuse as mixed-integer nonlinear programming and then converted it into two subproblems. First, the DMGs are formed between the D2D transmitter and D2D mobile users to reduce the intrauser interference using successive interference cancellation technique. Second, the resource allocation scheme for both the CMUs and DMGs is designed to mitigate the cross and cochannel interference using many-to-many mapping scheme. Also, to fully exploit the potential benefits of DMGs, the group rate selection criterion based resource block reuse algorithm among DMGs is designed. Finally, for power optimization, we use the difference of two convex functions programming approach based on a successive convex approximation low complexity. To simulate the proposed scheme, the 3GPP urban path loss model based on release 15 and RAN1 is used. Numerical results demonstrated that the proposed scheme has superior sum rate as compared to the existing NOMA and orthogonal frequency-division multiple access schemes.

An experimental study of NOMA in underwater visible light communication system

In this paper, power domain non-orthogonal multiple access (NOMA) is introduced in underwater visible light communication (UVLC) to improve the spectrum efficiency and the sum transmission rate. A NOMA-UVLC system employing two LEDs with different colors is designed to improve the propagation efficiency, by bearing different information on different carriers. We experimentally investigate the BER performance of the system in air and water environment, respectively. The results demonstrate that the proposed NOMA system works better in underwater environment than in air environment. The total transmission rate in underwater environment achieves 117.4 Mb/s when employing red/blue LEDs in the proposed system, and 93.9 Mb/s when employing red/green LEDs in the proposed system, with a transmission distance of 1 m.

Security performance analysis for power domain NOMA employing in cognitive radio networks

The power domain non-orthogonal multiple access (NOMA) technique introduces one of the fundamental characteristics and it exhibits the possibility of users to decode the messages of the other paired users on the same resources. In cognitive radio inspired NOMA (CR-NOMA), the base station (BS) has to serve untrusted users or users with different security clearance. This phenomenon raises a security threat particularly in such CR-NOMA. This paper develops a tractable analysis framework to evaluate the security performance of cooperative non-orthogonal multiple access (NOMA) in cognitive networks, where relay is able to serve two far NOMA users in the presence of external eavesdropper. In particular, we study the secrecy outage probability in a two-user NOMA system. This situation happens in practical the BS is pairing a legitimate user with another untrusted user. Main reason is that the non-uniform distribution in terms of trusted and untrusted users in the cell. By performing numerical results demonstrate the performance improvements of the proposed NOMA scheme in comparison to that of several situations in terms of different parameters. Furthermore, the security performance of NOMA is shown to verify the derived expressions.

Repetition-Based NOMA Transmission and Its Outage Probability Analysis

In this paper, we discuss a non-orthogonal multiple access (NOMA) scheme to exploit a high diversity gain using repetition, namely repetition-based NOMA. Unlike conventional power-domain NOMA, all the users can have the same transmit power, but different number of repetitions. Thanks to a high diversity gain, a low outage probability can be achieved without instantaneous channel state information (CSI) feedback for power allocation. A closed-form expression for an upper-bound on the outage probability is derived so that the values of key parameters can be decided to maintain the outage probability below a target value. We also consider the average error probability for finite-length codes. Simulation results are compared with the derived bounds and it is shown that the bounds are reasonably tight and can be used to decide key parameters (e.g., code rates) to guarantee target error probabilities.

Secrecy performance of an uplink-downlink cooperative PD-NOMA DF network in PLS

ABSTRACT In this paper, we investigate the secrecy performance of an uplink-downlink power domain non-orthogonal multiple access (PD-NOMA) system with imperfect successive interference cancellation (SIC) in physical layer security (PLS). In the proposed system, two source users (SUs) communicate with two destination users (DUs) with the help of a cluster of multi-relay nodes using the decode-and-forward (DF) protocol in the presence of multi-eavesdroppers. These eavesdroppers try to overhear the wireless signal around the DUs. In our system, the selected DF-relay node also works as a jammer to improve security and protect confidential information from multi-eavesdroppers. In this role, the DF-relay node generates a jamming signal, creating artificial interference to reduce the quality of the eavesdropping channels. To evaluate the secrecy performance of the system, we derived the analytical expressions of the secrecy outage probability (SOP) for both DUs using three relay selection strategies over Rayleigh fading channels and used Monte Carlo simulations to confirm the accuracy of our calculations. Furthermore, we examined the effects of system parameters such as the number of eavesdroppers and DF relaying nodes, the power allocation, SIC performance, the position of eavesdropper on the SOP of the two DUs. We compared the performance of our proposed NOMA system with those of conventional orthogonal multiple access (OMA) schemes.

Mean-Field Transmission Power Control in Dense Networks

We consider uplink power control in wireless communication when a large number of users compete over the channel resources. The CDMA protocol, as a supporting technology of 3G networks accommodating signal from different sources over the code domain, represents the orthogonal multiple access (OMA) techniques. With the development of 5G wireless networks, non-orthogonal multiple access (NOMA) is introduced to improve the efficiency of channel allocation. Our goal is to investigate whether the power-domain NOMA protocol can introduce performance improvement when the users interact with each other in a non-cooperative manner. It is compared with the CDMA protocol, where the fierce competition among users jeopardizes the efficiency of channel usage. In this work, we conduct analysis with an aggregative game model, and show the existence and uniqueness of an equilibrium strategy. Next, we adopt the social welfare of the population as the performance metric, which is the average utility achieved by the user population. It is shown that under the corresponding equilibrium strategies, NOMA outperforms CDMA by higher efficiency of channel access for uplink communications.

Quadrature NOMA: A Low-Complexity Multiple Access Technique With Coordinate Interleaving

In this letter, we offer a low-complexity multiple access method based on coordinate interleaving coined as quadrature non-orthogonal multiple access (NOMA). It is shown that by properly utilizing two quadrature carriers, both error performance enhancement and reduction in the number of successive interference cancellation (SIC) operations can be attained as compared to the standard power-domain NOMA approach. Specifically, in a $K$ -user network with single-antenna nodes, the reduction in the number of SIC operations is more than 50% as compared to the original NOMA scheme. When $K=2$ , the power gain obtained by the inspected technique can be as large as 2.5 dB without resorting to any SIC process at all. Further, as compared to the original NOMA idea, the considered approach requires fewer number of SIC stability conditions on power allocation and functions for any power allocation strategy (without an error floor) when $K=2$ . Some similar gains are also applicable for $K>2$ . The decrease in the number of SIC operations manifests itself by boosting the immunity of the system against possible failures during the SIC process.

MULTIPLE ACCESS TECHNIQUES FOR 5G NETWORKS

Fifth generation (5G) wireless networks face various challenges in order to support largescale heterogeneous traffic and users, therefore new modulation and multiple access (MA) schemes are being developed to meet the changing demands. As this research space is ever increasing, it becomes more important to analyze the various approaches, therefore, in this article we present a comprehensive overview of the most promising Multiple Access schemes for 5G networks. Our article focuses on various types of non-orthogonal multiple access (NOMA) techniques. Specifically, we first introduce different types of modulation schemes, potential for OMA. We then pay close attention to various types of NOMA candidates, including power-domain NOMA, code-domain NOMA, and NOMA multiplexing in multiple domains. From this exploration, we can identify the opportunities and challenges that will have the most significant impacts on modulation and MA designs for 5G networks.