Showing papers on "Noma published in 2018"
TL;DR: A comprehensive survey of the original birth, the most recent development, and the future research directions of non-orthogonal multiple access, along with a range of challenging open problems that should be solved for NOMA.
Abstract: In the fifth generation (5G) of wireless communication systems, hitherto unprecedented requirements are expected to be satisfied. As one of the promising techniques of addressing these challenges, non-orthogonal multiple access (NOMA) has been actively investigated in recent years. In contrast to the family of conventional orthogonal multiple access (OMA) schemes, the key distinguishing feature of NOMA is to support a higher number of users than the number of orthogonal resource slots with the aid of non-orthogonal resource allocation. This may be realized by the sophisticated inter-user interference cancellation at the cost of an increased receiver complexity. In this paper, we provide a comprehensive survey of the original birth, the most recent development, and the future research directions of NOMA. Specifically, the basic principle of NOMA will be introduced at first, with the comparison between NOMA and OMA especially from the perspective of information theory. Then, the prominent NOMA schemes are discussed by dividing them into two categories, namely, power-domain and code-domain NOMA. Their design principles and key features will be discussed in detail, and a systematic comparison of these NOMA schemes will be summarized in terms of their spectral efficiency, system performance, receiver complexity, etc. Finally, we will highlight a range of challenging open problems that should be solved for NOMA, along with corresponding opportunities and future research trends to address these challenges.
787 citations
TL;DR: A novel and effective deep learning (DL)-aided NOMA system, in which several N OMA users with random deployment are served by one base station, and a long short-term memory (LSTM) network based on DL is incorporated into a typical NOMa system, enabling the proposed scheme to detect the channel characteristics automatically.
Abstract: Nonorthogonal multiple access (NOMA) has been considered as an essential multiple access technique for enhancing system capacity and spectral efficiency in future communication scenarios. However, the existing NOMA systems have a fundamental limit: high computational complexity and a sharply changing wireless channel make exploiting the characteristics of the channel and deriving the ideal allocation methods very difficult tasks. To break this fundamental limit, in this paper, we propose a novel and effective deep learning (DL)-aided NOMA system, in which several NOMA users with random deployment are served by one base station. Since DL is advantageous in that it allows training the input signals and detecting sharply changing channel conditions, we exploit it to address wireless NOMA channels in an end-to-end manner. Specifically, it is employed in the proposed NOMA system to learn a completely unknown channel environment. A long short-term memory (LSTM) network based on DL is incorporated into a typical NOMA system, enabling the proposed scheme to detect the channel characteristics automatically. In the proposed strategy, the LSTM is first trained by simulated data under different channel conditions via offline learning, and then the corresponding output data can be obtained based on the current input data used during the online learning process. In general, we build, train and test the proposed cooperative framework to realize automatic encoding, decoding and channel detection in an additive white Gaussian noise channel. Furthermore, we regard one conventional user activity and data detection scheme as an unknown nonlinear mapping operation and use LSTM to approximate it to evaluate the data detection capacity of DL based on NOMA. Simulation results demonstrate that the proposed scheme is robust and efficient compared with conventional approaches. In addition, the accuracy of the LSTM -aided NOMA scheme is studied by introducing the well-known tenfold cross-validation procedure.
418 citations
TL;DR: In this paper, a comprehensive overview of the most promising modulation and multiple access (MA) schemes for 5G networks is presented, including modulation techniques in orthogonal MA (OMA) and various types of non-OMA (NOMA).
Abstract: Fifth generation (5G) wireless networks face various challenges in order to support large-scale 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 paper we present a comprehensive overview of the most promising modulation and MA schemes for 5G networks. Unlike other surreys of 5G networks, this paper focuses on multiplexing techniques, including modulation techniques in orthogonal MA (OMA) and various types of non-OMA (NOMA) techniques. Specifically, we first introduce different types of modulation schemes, potential for OMA, and compare their performance in terms of spectral efficiency, out-of-band leakage, and bit-error rate. 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.
371 citations
TL;DR: In this paper, the authors proposed a divide-and-next-largest-difference-based user pairing algorithm to distribute the capacity gain among the NOMA clusters in a controlled manner.
Abstract: This article presents advances in resource allocation for downlink non-orthogonal multiple access (NOMA) systems, focusing on user pairing and power allocation algorithms. The former pairs the users to obtain high capacity gain by exploiting the channel gain difference between the users, while the latter allocates power to users in each cluster to balance system throughput and user fairness. Additionally, the article introduces the concept of cluster fairness and proposes the divide-and-next-largest-difference-based user pairing algorithm to distribute the capacity gain among the NOMA clusters in a controlled manner. Furthermore, performance comparison between multiple-input multiple-output NOMA (MIMO-NOMA) and MIMO orthogonal multiple access (MIMO-OMA) is conducted when users have pre-defined quality of service. Simulation results are presented, which validate the advantages of NOMA over OMA. Finally, the article provides avenues for further research on resource allocation for downlink NOMA.
295 citations
TL;DR: It is confirmed that the use of direct link overcomes zero diversity order of far NOMA user inherent to FD relaying and new closed-form expressions for asymptotic ergodic rates are derived.
Abstract: In this paper, a novel cooperative non-orthogonal multiple access (NOMA) system is proposed, where one near user is employed as decode-and-forward relaying switching between full-duplex (FD) and half-duplex (HD) mode to help a far user. Two representative cooperative relaying scenarios are investigated insightfully. The first scenario is that no direct link exists between the base station (BS) and far user. The second scenario is that the direct link exists between the BS and far user. To characterize the performance of potential gains brought by the FD NOMA in two considered scenarios, three performance metrics outage probability, ergodic rate, and energy efficiency are discussed. More particularly, we derive new closed-form expressions for both exact and asymptotic outage probabilities as well as delay-limited throughput for two NOMA users. Based on the derived results, the diversity orders achieved by users are obtained. We confirm that the use of direct link overcomes zero diversity order of far NOMA user inherent to FD relaying. In addition, we derive new closed-form expressions for asymptotic ergodic rates. Based on these, the high signal-to-noise ratio (SNR) slopes of two users for FD NOMA are obtained. Simulation results demonstrate that: 1) the FD NOMA is superior to the HD NOMA in terms of outage probability and ergodic sum rate in the low SNR region; and 2) in delay-limited transmission mode, the FD NOMA has higher energy efficiency than the HD NOMA in the low SNR region; However, in delay-tolerant transmission mode, the system energy efficiency of the HD NOMA exceeds the FD NOMA in the high SNR region.
289 citations
Abstract: With the fast development of Internet of Things (IoT), the fifth generation (5G) wireless networks need to provide massive connectivity of IoT devices and meet the demand for low latency. To satisfy these requirements, nonorthogonal multiple access (NOMA) has been recognized as a promising solution for 5G networks to significantly improve the network capacity. In parallel with the development of NOMA techniques, mobile edge computing (MEC) is becoming one of the key emerging technologies to reduce the latency and improve the quality of service (QoS) for 5G networks. In order to capture the potential gains of NOMA in the context of MEC, this paper proposes an edge computing aware NOMA technique which can enjoy the benefits of uplink NOMA in reducing MEC users’ uplink energy consumption. To this end, we formulate an NOMA-based optimization framework which minimizes the energy consumption of MEC users via optimizing the user clustering, computing and communication resource allocation, and transmit powers. In particular, similar to frequency resource blocks (RBs), we divide the computing capacity available at the cloudlet to computing RBs. Accordingly, we explore the joint allocation of the frequency and computing RBs to the users that are assigned to different order indices within the NOMA clusters. We also design an efficient heuristic algorithm for user clustering and RBs allocation, and formulate a convex optimization problem for the power control to be solved independently per NOMA cluster. The performance of the proposed NOMA scheme is evaluated via simulations.
232 citations
TL;DR: It is demonstrated that NomA with NGDPA achieves a sum rate improvement of up to 29.1% compared with NOMA with the gain ratio power allocation method in the $2\times 2$ MIMO-VLC system with three users.
Abstract: In this letter, we apply the non-orthogonal multiple access (NOMA) technique to improve the achievable sum rate of multiple-input multiple-output (MIMO)-based multi-user visible light communication (VLC) systems. To ensure efficient and low-complexity power allocation in indoor MIMO-NOMA-based VLC systems, a normalized gain difference power allocation (NGDPA) method is first proposed by exploiting users’ channel conditions. We investigate the performance of an indoor $2\times 2$ MIMO-NOMA-based multi-user VLC system through numerical simulations. The obtained results show that the achievable sum rate of the $2\times 2$ MIMO-VLC system can be significantly improved by employing NOMA with the proposed NGDPA method. It is demonstrated that NOMA with NGDPA achieves a sum rate improvement of up to 29.1% compared with NOMA with the gain ratio power allocation method in the $2\times 2$ MIMO-VLC system with three users.
215 citations
TL;DR: In this article, the authors investigated the integration of NOMA with CR into a holistic system, namely a cognitive nOMA network, for more intelligent spectrum sharing and proposed cooperative relaying strategies to address inter-network and intra-network interference.
Abstract: Two emerging technologies toward 5G wireless networks, namely non-orthogonal multiple access (NOMA) and cognitive radio (CR), will provide more efficient utilization of wireless spectrum in the future. In this article, we investigate the integration of NOMA with CR into a holistic system, namely a cognitive NOMA network, for more intelligent spectrum sharing. Design principles of cognitive NOMA networks are perfectly aligned to functionality requirements of 5G wireless networks, such as high spectrum efficiency, massive connectivity, low latency, and better fairness. Three different cognitive NOMA architectures are presented, including underlay NOMA networks, overlay NOMA networks, and CR-inspired NOMA networks. To address inter-network and intra-network interference, which largely degrade the performance of cognitive NOMA networks, cooperative relaying strategies are proposed. For each cognitive NOMA architecture, our proposed cooperative relaying strategy shows its potential to significantly lower outage probabilities. We discuss open challenges and future research directions on implementation of cognitive NOMA networks.
205 citations
TL;DR: For the first time in the literature, an exact closed-form bit error rate (BER) expressions under SIC error for downlink NOMA over Rayleigh fading channels are derived and validated by simulations.
Abstract: Non-orthogonal multiple access (NOMA) is a strong candidate for next generation radio access networks due to its ability of serving multiple users using the same time and frequency resources. Therefore, researchers in academia and industry have been recently investigating the error performances and capacity of NOMA schemes. The main drawback of NOMA techniques is the interference among users due to the its non-orthogonal access nature, that is usually solved by interference cancellation techniques such as successive interference cancellation (SIC) at the receivers. On the other hand, the interference among users may not be completely eliminated in the SIC process due to the erroneous decisions in the receivers usually caused by channels. In this study, for the first time in the literature, the authors derive an exact closed-form bit error rate (BER) expressions under SIC error for downlink NOMA over Rayleigh fading channels. Besides, they derive one-degree integral form exact BER expressions and closed-form approximate expressions for uplink NOMA. Then, the derived expressions are validated by simulations. The numerical results are depicted to reveal the effects of error during SIC process on the performance for various cases such as power allocation for downlink and channel quality difference for uplink.
197 citations
TL;DR: In this article, the optimal time allocation for maximizing the system spectral efficiency of a TDMA-based WPCN (T-WPCN) and a non-orthogonal multiple access (NOMA)-based wireless powered communication networks (WPCNs) was derived for the uplink of WPCNs based IoT networks with a massive number of devices.
Abstract: Wireless powered communication networks (WPCNs), where multiple energy-limited devices first harvest energy in the downlink and then transmit information in the uplink, have been envisioned as a promising solution for the future Internet-of-Things (IoT). Meanwhile, nonorthogonal multiple access (NOMA) has been proposed to improve the system spectral efficiency (SE) of the fifth-generation (5G) networks by allowing concurrent transmissions of multiple users in the same spectrum. As such, NOMA has been recently considered for the uplink of WPCNs based IoT networks with a massive number of devices. However, simultaneous transmissions in NOMA may also incur more transmit energy consumption as well as circuit energy consumption in practice which is critical for energy constrained IoT devices. As a result, compared to orthogonal multiple access schemes such as time-division multiple access (TDMA), whether the SE can be improved and/or the total energy consumption can be reduced with NOMA in such a scenario still remains unknown. To answer this question, we first derive the optimal time allocations for maximizing the SE of a TDMA-based WPCN (T-WPCN) and a NOMA-based WPCN (N-WPCN), respectively. Subsequently, we analyze the total energy consumption as well as the maximum SE achieved by these two networks. Surprisingly, it is found that N-WPCN not only consumes more energy, but also is less spectral efficient than T-WPCN. Simulation results verify our theoretical findings and unveil the fundamental performance bottleneck, i.e., “worst user bottleneck problem”, in multiuser NOMA systems.
193 citations
TL;DR: Simulation results show that the proposed reinforcement learning-based power control scheme for the downlink NOMA transmission can significantly increase the sum data rates of users, and thus, the utilities compared with the standard Q-learning-based strategy.
Abstract: Nonorthogonal multiple access (NOMA) systems are vulnerable to jamming attacks, especially smart jammers who apply programmable and smart radio devices such as software-defined radios to flexibly control their jamming strategy according to the ongoing NOMA transmission and radio environment. In this paper, the power allocation of a base station in a NOMA system equipped with multiple antennas contending with a smart jammer is formulated as a zero-sum game, in which the base station as the leader first chooses the transmit power on multiple antennas, while a jammer as the follower selects the jamming power to interrupt the transmission of the users. A Stackelberg equilibrium of the antijamming NOMA transmission game is derived and conditions assuring its existence are provided to disclose the impact of multiple antennas and radio channel states. A reinforcement learning-based power control scheme is proposed for the downlink NOMA transmission without being aware of the jamming and radio channel parameters. The Dyna architecture that formulates a learned world model from the real antijamming transmission experience and the hotbooting technique that exploits experiences in similar scenarios to initialize the quality values are used to accelerate the learning speed of the Q-learning-based power allocation, and thus, improve the communication efficiency of the NOMA transmission in the presence of smart jammers. Simulation results show that the proposed scheme can significantly increase the sum data rates of users, and thus, the utilities compared with the standard Q-learning-based strategy.
TL;DR: This article demonstrates that a 30° beamwdith, as opposed to a typical 120?
Abstract: Millimeter-wave (mm-wave) communications and nonorthogonal multiple access (NOMA) are two important techniques to achieve high data rates in fifth-generation (5G) ultradense networks (UDNs). Due to interference that is intentionally added during the superpositioned transmissions with NOMA, an additional power budget is required to maintain the target block error rate (BLER). This necessitates the consideration of new approaches to ensure the power efficiency of NOMA systems. In this article, we show that this additional required power can be implemented using the directional transmission capabilities offered by mm-wave antenna arrays. Through the use of our small cells cluster simulations, we investigate the performance of NOMA in mm-wave frequency bands with consideration to the total system capacity, hybrid resource allocation, pairing probability, and power requirements. We demonstrate that a 30d beamwdith, as opposed to a typical 120? beamwidth, can result in a 20% system-capacity gain without requiring any extra transmission power. Our results indicate novel tradeoffs between system capacity, pairing probability, and transmission power in mm-wave NOMA networks owing to the effect of beamwidth variations. We conclude by summarizing the future challenges of NOMA in mm-wave bands.
TL;DR: In this article, a taxonomy is devised to categorize the literature based on operation paradigms, enabling techniques, design objectives, and optimization characteristics, and the key challenges for the domain researchers and designers to realize CRNs with NOMA.
Abstract: The explosive growth of mobile devices and the rapid increase of wideband wireless services call for advanced communication techniques that can achieve high spectral efficiency and meet the massive connectivity requirement. CR and NOMA are envisioned to be important solutions for fifth generation wireless networks. Integrating NOMA techniques into CRNs has tremendous potential to improve spectral efficiency and increase system capacity. However, there are many technical challenges due to the severe interference caused by using NOMA. Many efforts have been made to facilitate the application of NOMA into CRNs and to investigate the performance of CRNs with NOMA. This article aims to survey the latest research results along this direction. A taxonomy is devised to categorize the literature based on operation paradigms, enabling techniques, design objectives, and optimization characteristics. Moreover, the key challenges are outlined to provide guidelines for the domain researchers and designers to realize CRNs with NOMA. Finally, open issues are discussed.
TL;DR: Numerical results validate the theoretical analysis and demonstrate the superior performance of NOMA in reducing transmission latency, and obtain the near-optimal power allocation coefficients and blocklength to ensure certain reliability.
Abstract: This letter investigates the performance of non-orthogonal multiple access (NOMA) in short-packet communications. We aim to answer a fundamental question–for given reliability requirements of users: how much physical-layer transmission latency can NOMA reduce when compared with orthogonal multiple access in the finite blocklength regime? We derive closed-form expressions for the block error rates of users in NOMA. Further, we obtain the near-optimal power allocation coefficients and blocklength to ensure certain reliability. Numerical results validate our theoretical analysis and demonstrate the superior performance of NOMA in reducing transmission latency.
TL;DR: Non-orthogonal multiple access (NOMA) is investigated for aerial base station (BS) and results are presented for various environment settings to conclude NOMA manifesting better performance in terms of sum-rate, coverage, and energy efficiency.
Abstract: The future wireless networks promise to provide ubiquitous connectivity to a multitude of devices with diversified traffic patterns wherever and whenever needed. For the sake of boosting resilience against faults, natural disasters, and unexpected traffic, the unmanned aerial vehicle (UAV)-assisted wireless communication systems can provide a unique opportunity to cater for such demands in a timely fashion without relying on the overly engineered cellular network. However, for UAV-assisted communication, issues of capacity, coverage, and energy efficiency are considered of paramount importance. The case of non-orthogonal multiple access (NOMA) is investigated for aerial base station (BS). NOMA’s viability is established by formulating the sum-rate problem constituting a function of power allocation and UAV altitude. The optimization problem is constrained to meet individual user-rates arisen by orthogonal multiple access (OMA) bringing it at par with NOMA. The relationship between energy efficiency and altitude of a UAV inspires the solution to the aforementioned problem considering two cases, namely, altitude fixed NOMA and altitude optimized NOMA. The latter allows exploiting the extra degrees of freedom of UAV-BS mobility to enhance the spectral efficiency and the energy efficiency. Hence, it saves joules in the operational cost of the UAV. Finally, a constrained coverage expansion methodology, facilitated by NOMA user rate gain is also proposed. Results are presented for various environment settings to conclude NOMA manifesting better performance in terms of sum-rate, coverage, and energy efficiency.
TL;DR: This article investigates the NOMA-based cooperative relay network by classifying them into three categories: uplink, downlink, and composite architectures, and provides a comprehensive comparison from the perspective of spectral efficiency, energy efficiency, and total transmit power.
Abstract: NOMA is a promising radio access technique for next-generation wireless networks. In this article, we investigate the NOMA-based cooperative relay network. We begin with an introduction of the existing relay-assisted NOMA systems by classifying them into three categories: uplink, downlink, and composite architectures. Then we discuss their principles and key features, and provide a comprehensive comparison from the perspective of spectral efficiency, energy efficiency, and total transmit power. A novel strategy called hybrid power allocation is further discussed for the composite architecture, which can reduce the computational complexity and signaling overhead at the expense of marginal sum rate degradation. Finally, major challenges, opportunities, and future research trends for the design of NOMA-based cooperative relay systems with other techniques are also highlighted to provide insights for researchers in this field.
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TL;DR: This work provides a comprehensive overview of the state-of-the-art in power-domain multiplexing aided NOMA, with a focus on the theoretical N OMA principles, multiple antenna aided NomA design, on the interplay between NOM a and cooperative transmission, onthe resource control of NOMa, onThe co-existence of Noma with other emerging potential 5G techniques and on the comparison with other NOMC variants.
Abstract: Driven by the rapid escalation of the wireless capacity requirements imposed by advanced multimedia applications (e.g., ultra-high-definition video, virtual reality etc.), as well as the dramatically increasing demand for user access required for the Internet of Things (IoT), the fifth generation (5G) networks face challenges in terms of supporting large-scale heterogeneous data traffic. Non-orthogonal multiple access (NOMA), which has been recently proposed for the 3rd generation partnership projects long-term evolution advanced (3GPP-LTE-A), constitutes a promising technology of addressing the above-mentioned challenges in 5G networks by accommodating several users within the same orthogonal resource block. By doing so, significant bandwidth efficiency enhancement can be attained over conventional orthogonal multiple access (OMA) techniques. This motivated numerous researchers to dedicate substantial research contributions to this field. In this context, we provide a comprehensive overview of the state-of-the-art in power-domain multiplexing aided NOMA, with a focus on the theoretical NOMA principles, multiple antenna aided NOMA design, on the interplay between NOMA and cooperative transmission, on the resource control of NOMA, on the co-existence of NOMA with other emerging potential 5G techniques and on the comparison with other NOMA variants. We highlight the main advantages of power-domain multiplexing NOMA compared to other existing NOMA techniques. We summarize the challenges of existing research contributions of NOMA and provide potential solutions. Finally, we offer some design guidelines for NOMA systems and identify promising research opportunities for the future.
TL;DR: A comprehensive study and comparison on current NOMA technologies that many mainstream companies have proposed for the fifth generation (5G) wireless communication standard and some promising schemes and directions are suggested for the future 5G N OMA development.
Abstract: Compared to the traditional orthogonal multiple access, non-orthogonal multiple access (NOMA) technology can achieve higher spectrum efficiency and support more massive connectivity. In this paper, we conduct comprehensive study and comparison on current NOMA technologies that many mainstream companies have proposed for the fifth generation (5G) wireless communication standard. According to the characteristics of the NOMA schemes, we classify these schemes into four categories: scrambling-based NOMA, spreading-based NOMA, coding-based NOMA, and interleaving-based NOMA. We systematically summarize the transceiver block diagram of each category, and detail basic principles, key features, and transmission-reception algorithms of all NOMA schemes. Furthermore, the theoretical analysis based on average mutual information is given to evaluate the achievable sum-rate performance of the NOMA systems and their potential performance gains as compared with OMA. Comprehensive simulations are carried out for the block-error-rate performance evaluation of these NOMA schemes as well, which coincide with the theoretical analysis. By comparing the performance of these technologies, some promising schemes and directions are suggested for the future 5G NOMA development.
TL;DR: This article is focused on exploiting multiple antenna techniques in NOMA networks, with an emphasis on investigating the rate region of MIMO-NOMA, while reviewing two popular multiple antennas aided NomA structures, as well as underlining resource management problems of both single-carrier and multi- carrier MIMo-NomA networks.
Abstract: Non-orthogonal multiple access (NOMA) is potentially capable of circumventing the limitations of the classic orthogonal multiple access schemes. Hence, it has recently received significant research attention in both industry and academia. This article is focused on exploiting multiple antenna techniques in NOMA networks, with an emphasis on investigating the rate region of MIMO-NOMA, while reviewing two popular multiple antennas aided NOMA structures, as well as underlining resource management problems of both single-carrier and multi-carrier MIMO-NOMA networks. This article also points out several effective methods of tackling the practical implementation constraints of multiple-antenna NOMA networks. Finally, some promising open research directions are provided in the context of multiple- antenna-aided NOMA.
TL;DR: Numerical results demonstrate that the proposed hybrid relaying scheme can achieve a significant performance improvement with respect to the conventional NOMA, HD-CN OMA, and FD-CNOMA scheme.
Abstract: Power allocation is an important issue in order to optimize the performance of non-orthogonal multiple access (NOMA) systems. However, the power allocation problem for cooperative NOMA systems has not been well investigated. In this paper, we investigate the power allocation problems for half-duplex cooperative NOMA (HD-CNOMA) and full-duplex cooperative NOMA (FD-CNOMA) systems, respectively. From the fairness standpoint, the optimization problem for each system is formulated to maximize the minimum achievable user rate in a NOMA user pair. Even though both of the formulated problems are neither concave nor quasi-concave, the optimal closed-form solutions of both cases are still obtained with the proposed two-step method. First, we transform the initial problem into a quasi-concave problem by treating the relay transmit power, namely $P_{R}$ , as a constant, and then solve the obtained quasi-concave problem. Second, we convert the original problem into a univariate problem of $P_{R}$ based on the results of the first step, and eventually obtain the optimal power allocation. In addition, a hybrid half/full-duplex cooperative NOMA scheme, which dynamically switches between the HD-CNOMA and FD-CNOMA mode, is proposed. After that, a relay selection scheme is also investigated to extend the hybrid scheme into general networks with multiple users. Numerical results demonstrate that the proposed hybrid relaying scheme can achieve a significant performance improvement with respect to the conventional NOMA, HD-CNOMA, and FD-CNOMA scheme.
TL;DR: In this paper, the authors studied the trade-off between data rate performance and energy consumption in NOMA heterogeneous networks and proposed energy-efficient user scheduling and power allocation schemes.
Abstract: Non-orthogonal multiple access has attracted much recent attention due to its capability of improving the system spectral efficiency in wireless communications. Deploying NOMA in a heterogeneous network can satisfy users' explosive data traffic requirements, and NOMA will likely play an important role in the next generation mobile communication networks. However, NOMA brings new technical challenges on resource allocation due to the mutual cross-tier interference in heterogeneous networks. In this article, to study the trade-off between data rate performance and energy consumption in NOMA, we examine the problem of energy-efficient user scheduling and power optimization in NOMA heterogeneous networks. The energy-efficient user scheduling and power allocation schemes are introduced for the downlink NOMA heterogeneous network for perfect and imperfect CSI, respectively. Simulation results show that the resource allocation schemes can significantly increase the energy efficiency of NOMA heterogeneous networks for cases of both perfect CSI and imperfect CSI.
TL;DR: This paper reveals that the NOMA techniques have evolved from single-carrier NomA (SC-NOMA) into multi- carrier NOMa (MC-N OMA), and comprehensively investigated on the basic principles, enabling schemes and evaluations of the two most promising MC-NomA techniques, namely sparse code multiple access (SCMA) and pattern division multiple access(PDMA).
Abstract: Non-orthogonal multiple access (NOMA) is one promising technology, which provides high system capacity, low latency, and massive connectivity, to address several challenges in the fifth-generation wireless systems. In this paper, we first reveal that the NOMA techniques have evolved from single-carrier NOMA (SC-NOMA) into multi-carrier NOMA (MC-NOMA). Then, we comprehensively investigated on the basic principles, enabling schemes and evaluations of the two most promising MC-NOMA techniques, namely sparse code multiple access (SCMA) and pattern division multiple access (PDMA). Meanwhile, we consider that the research challenges of SCMA and PDMA might be addressed with the stimulation of the advanced and matured progress in SC-NOMA. Finally, yet importantly, we investigate the emerging applications, and point out the future research trends of the MC-NOMA techniques, which could be straightforwardly inspired by the various deployments of SC-NOMA.
TL;DR: In this paper, the authors introduce the basic concepts of MIMO-NOMA and summarize the key technical problems in the NOMA-MIMO systems, and explore the problem formulation, beamforming, user clustering, and power allocation of single/multi-cluster NOMAs along with their limitations.
Abstract: NOMA, as the newest member of the multiple access family, is envisioned to be an essential component of 5G mobile networks. The combination of NOMA and multi-antenna MIMO technologies exhibits significant potential in improving spectral efficiency and providing better wireless services to more users. In this article, we introduce the basic concepts of MIMO-NOMA and summarize the key technical problems in MIMO-NOMA systems. Then we explore the problem formulation, beamforming, user clustering, and power allocation of single/multi-cluster MIMO-NOMA in the literature along with their limitations. Furthermore, we point out an important issue of the stability of successive interference cancellation that arises using achievable rates as performance metrics in practical NOMA/MIMO-NOMA systems. Finally, we discuss incorporating NOMA with massive/millimeter- wave MIMO, and identify the main challenges and possible future research directions in this area.
TL;DR: This letter investigates the outage probability (OP) of amplify-and-forward hybrid satellite-terrestrial relay networks with a nonorthogonal multiple access (NOMA) scheme and derives closed-form OP expressions for each NOMA user.
Abstract: In this letter, we investigate the outage probability (OP) of amplify-and-forward hybrid satellite-terrestrial relay networks with a nonorthogonal multiple access (NOMA) scheme. By assuming that a single antenna satellite communicates with multiple multiantenna users simultaneously through the help of a single antenna relay and the NOMA scheme, we first derive the closed-form OP expressions for each NOMA user. Then, asymptotic OP expressions at the high signal-to-noise ratio regime are also obtained to evaluate the achievable diversity order and coding gain. Finally, simulations are provided to the validity of theoretical results, the superiority of introducing the NOMA scheme in satellite-terrestrial relay networks, and the effect of key parameters on the performance of NOMA users.
TL;DR: The application of NOMA techniques in HUDNs to support massive connectivity in 5G systems is investigated, with particular focus on user association and resource allocation.
Abstract: Heterogeneous ultra dense networks (HUDNs) and non-orthogonal multiple access (NOMA) have been identified as two proposing techniques for 5G mobile communication systems due to their great capabilities to enhance spectrum efficiency. This article investigates the application of NOMA techniques in HUDNs to support massive connectivity in 5G systems. In particular, a unified NOMA framework is proposed, including power-domain NOMA and code-domain NOMA, which can be configured flexibly to serve different application scenarios. As a further advance, unified NOMA framework enabled HUDNs are further investigated, with particular focus on user association and resource allocation. Two case studies are provided for demonstrating the effectiveness of unified NOMA enabled HUDNs. Finally, some main challenges and promising research directions in NOMA enabled HUDNs are identified.
TL;DR: The achievable sum rate of NOMA can be lower than that of OMA even in the regime of low number of users due to intra-cluster pilot contamination and error propagation of imperfect SIC.
Abstract: A cell-free massive multiple-input multiple-output system with non-orthogonal multiple-access (NOMA) is investigated. An achievable sum rate is derived and compared against the orthogonal multiple access (OMA) counterpart. Thereby, the detrimental effects of intra-cluster pilot contamination, inter-cluster interference and imperfect successive interference cancellation (SIC) are investigated. The number of users served simultaneously by NOMA can be significantly higher than that of OMA. Nevertheless, the achievable sum rate of NOMA can be lower than that of OMA even in the regime of low number of users due to intra-cluster pilot contamination and error propagation of imperfect SIC.
TL;DR: A unified framework for NOMA is provided and the current understanding of the N OMA principle is generalized from the conventional code and power domains to the spatial domain as well as to their hybrids and to the networking domain.
Abstract: Non-orthogonal multiple access (NOMA) is a promising technique for future mobile communication systems, which can approach multiuser channel capacity by sharing the same time-frequency resources with multiple users. In this article, we provide a unified framework for NOMA and review the principles of various NOMA schemes in different domains with the objective of creating a unified framework. A systematic performance comparison of different NOMA schemes regarding their peak-to-average power ratio, receiver complexity, latency, grant-free access, user load, and peak throughput is also provided for different application scenarios. Relying on our unified framework, we generalize the current understanding of the NOMA principle from the conventional code and power domains to the spatial domain as well as to their hybrids and to the networking domain. Finally, the challenges in terms of resource allocation, channel estimation, security, system flexibility, and implementation issues are also discussed.
TL;DR: Monte Carlo simulations are presented to verify the analytical results: 1) when the number of subcarriers becomes lager, the NOMA users are capable of achieving more steep slope in terms of outage probability and 2) the outage behavior of CD-NOMA is superior to that of PD-NomA.
Abstract: This paper proposes a unified framework of non-orthogonal multiple access (NOMA) networks. Stochastic geometry is employed to model the locations of spatially NOMA users. The proposed unified NOMA framework is capable of being applied to both code-domain NOMA (CD-NOMA) and power-domain NOMA (PD-NOMA). Since the detection of NOMA users mainly depend on efficient successive interference cancelation (SIC) schemes, both imperfect SIC (ipSIC) and perfect SIC (pSIC) are taken into account. To characterize the performance of the proposed unified NOMA framework, the exact and asymptotic expressions of outage probabilities as well as delay-limited throughput for CD/PD-NOMA with ipSIC/pSIC are derived. In order to obtain more insights, the diversity analysis of a pair of NOMA users (i.e., the n th user and m th user) is provided. Our analytical results reveal that: 1) the diversity orders of m th and n th user with pSIC for CD-NOMA are mK and nK , respectively; 2) due to the influence of residual interference, the n th user with ipSIC obtains a zero diversity order; and 3) the diversity order is determined by the user who has the poorer channel conditions out of the pair. Finally, Monte Carlo simulations are presented to verify the analytical results: 1) when the number of subcarriers becomes lager, the NOMA users are capable of achieving more steep slope in terms of outage probability and 2) the outage behavior of CD-NOMA is superior to that of PD-NOMA.
TL;DR: It is proved that for the user with the stronger channel condition in a two-user network, NOMA prevails over OMA when the transmit signal-to-noise ratio (SNR) is large, and for the users with the weaker channel condition, NomA outperforms OMAWhen the transmit SNR is small.
Abstract: In this paper, we study the achievable link-layer rate, namely, effective capacity (EC), under the per-user statistical delay quality-of-service (QoS) requirements, for a downlink non-orthogonal multiple access (NOMA) network with $M$ users. Specifically, the $M$ users are assumed to be divided into multiple NOMA pairs. Conventional orthogonal multiple access (OMA) then is applied for inter-NOMA-pairs multiple access. Focusing on the total link-layer rate for a downlink $M$ -user network, we prove that OMA outperforms NOMA when the transmit signal-to-noise ratio (SNR) is small. On the contrary, simulation results show that NOMA prevails over OMA at high values of SNR. Aware of the importance of a two-user NOMA network, we also theoretically investigate the impact of the transmit SNR and the delay QoS requirement on the individual EC performance and the total link-layer rate for a two-user network. Specifically, for delay-constrained and delay-unconstrained users, we prove that for the user with the stronger channel condition in a two-user network, NOMA prevails over OMA when the transmit SNR is large. On the other hand, for the user with the weaker channel condition in a two-user network, it is proved that NOMA outperforms OMA when the transmit SNR is small. Furthermore, for the user with the weaker channel condition, the individual EC in NOMA is limited to a maximum value, even if the transmit SNR goes to infinity. To confirm these insightful conclusions, the closed-form expressions for the individual EC in a two-user network, by applying NOMA or OMA, are derived for both users and then confirmed using Monte Carlo simulations.
TL;DR: Analytical and simulation results are provided to demonstrate that FD-NOMA can offer significant performance gains over half-duplex NOMA and orthogonal multiple access, provided that co-channel interference is sufficiently suppressed.
Abstract: The purpose of this letter is to investigate the feasibility of full-duplex non-orthogonal multiple access (FD-NOMA), where uplink and downlink NOMA transmissions are carried out at the same time. Analytical and simulation results are provided to demonstrate that FD-NOMA can offer significant performance gains over half-duplex NOMA and orthogonal multiple access, provided that co-channel interference is sufficiently suppressed.