NOMA-based Scheme Research Articles

Performance analysis and optimization for cellular two-way relay networks with cooperative NOMA transmission

This paper proposes a cooperative non-orthogonal multiple access (NOMA) based two-way transmission scheme for a two-user cellular system, in which a base station (BS) exchanges information with a directlink user and an indirect link user. With superimposition coding, physical-layer network coding (PLNC) and successive interference cancellation, the BS and the two users are able to exchange messages within three time slots. We derive the sum-rate upper bound of the proposed scheme and investigate the optimal time and power allocations to maximize the sum-rate bound. Numerical results demonstrate that the derived bound is tight and the proposed scheme can improve the sum-rates significantly as compared with existing NOMA-based schemes.

IRS-Assisted Wireless Powered IoT Network With Multiple Resource Blocks

In this paper, we investigate an intelligent reflecting surface (IRS)-assisted wireless powered Internet of Things (WP-IoT) network that operates in multiple resource blocks (RBs). Particularly, the IRS helps in both downlink wireless energy transfer (WET) and uplink wireless information transfer (WIT), in a way that it improves energy reflection in WET from a power station (PS) to various IoT devices and boosts information delivery in WIT from the IoT devices to an access point (AP). Those IoT devices are capable of utilizing the collected energy, and adopting the time-division multiple access (TDMA) or non-orthogonal multiple access (NOMA) scheme in the uplink WIT. Aiming to maximize the average throughput as the overall performance indicator of the considered network, we jointly optimize the transmit power allocation of the PS, the time scheduling, and the IRS phase shifts. These coupled variables lead to the non-convexity of this optimization problem, which cannot be solved directly. To address this problem, we first design the optimal PS’s transmit power allocation for each RB. For the TDMA-based scheme, we design the closed-form IRS beam pattern of the uplink WIT. Then, the closed-form downlink and uplink time allocations are derived by the Lagrange dual method and the Karush-Kuhn-Tucker (KKT) conditions. In addition, the quadratic transformation (QT)-based Alternating Direction Method of Multipliers (ADMM) approach is proposed to iteratively derive the sub-optimal IRS beam pattern of the downlink WET in an alternated fashion. For the NOMA-based scheme, we propose to apply an alternating optimization (AO) algorithm to iteratively optimize the IRS phase shifts, where the uplink IRS beam pattern is iteratively designed by the Riemannian Manifold Optimization (RMO) approach, and the QT-based ADMM method is adopted to alternately derive the sub-optimal downlink IRS phase shifts. Finally, numerical results demonstrate the improved performance of the proposed solution approaches compared to the benchmark schemes, also highlight advantages of the application of IRS in multiple RB scenarios.

Active IRS Aided Multiple Access for Energy-Constrained IoT Systems

In this paper, we investigate the fundamental multiple access (MA) scheme in an active intelligent reflecting surface (IRS) aided energy-constrained Internet-of-Things (IoT) system, where an active IRS is deployed to assist the uplink transmission from multiple IoT devices to an access point (AP). Our goal is to maximize the sum throughput by optimizing the IRS beamforming vectors across time and resource allocation. To this end, we first study two typical active IRS aided MA schemes, namely time division multiple access (TDMA) and non-orthogonal multiple access (NOMA), by analytically comparing their achievable sum throughput and proposing corresponding algorithms. Interestingly, we prove that given only one available IRS beamforming vector, the NOMA-based scheme generally achieves a larger throughput than the TDMA-based scheme, whereas the latter can potentially outperform the former if multiple IRS beamforming vectors are available to harness the favorable time selectivity of the IRS. To strike a flexible balance between the system performance and the associated signaling overhead incurred by more IRS beamforming vectors, we then propose a general hybrid TDMA-NOMA scheme with device grouping, where the devices in the same group transmit simultaneously via NOMA while devices in different groups occupy orthogonal time slots. By controlling the number of groups, the hybrid TDMA-NOMA scheme is applicable for any given number of IRS beamforming vectors available. Despite of the non-convexity of the considered optimization problem, we propose an efficient algorithm based on alternating optimization, where each subproblem is solved optimally. Simulation results illustrate the practical superiorities of the active IRS over the passive IRS in terms of the coverage extension and supporting multiple energy-limited devices, and demonstrate the effectiveness of our proposed hybrid MA scheme for flexibly balancing the performance-cost tradeoff.

Fairness-Oriented Transmission Schemes for Multiuser MISO Broadcast Channels

With the increasing number of Internet of Things (IoT), Industry 4.0 (I4.0), and mobile devices, it can be expected that base stations will have to serve more and more clients with a limited number of antennas. For their broadcast channels, nonorthogonal multiple access (NOMA) and blind interference alignment (BIA) are two efficient and commonly adopted transmission schemes. This paper conducts a comparison study on these techniques on a 3-user 2 × 1 multiple-input single-output (MISO) broadcast channel with a limited number of transmit antennas. Specifically, space-time block coding based NOMA (STBC-NOMA) and NOMA-assisted beamforming (NOMA-BF) are compared with BIA. Both perfect and imperfect successive interference cancellation (SIC) have been considered for NOMA-based schemes, and the theoretical achievable rates of all schemes have been derived. Furthermore, with a given fairness constraint among end users, the power allocation (PA) problems have been solved for cases when accurate channel state information is available at the transmitter (CSIT) as well as when only path loss information is available. Numerical results show the following: (1) none of the schemes under this study can always outperform the others under different SNR regions. (2) With imperfect SIC, NOMA-BF, and STBC-NOMA both suffer from a significant performance loss under a high SNR condition. (3) Fairness PA with only path loss information provides similar performance as that with perfect CSIT, thus partial CSIT is adequate for system or scheme designs in practice.

IRS-Assisted Downlink and Uplink NOMA in Wireless Powered Communication Networks

This paper studies the integration of the newly-emerged intelligent reflecting surface (IRS) technology into non-orthogonal multiple access (NOMA)-based wireless powered communication networks (WPCNs). We consider two WPCNs which communicate with a common hybrid access point (HAP), where there exists two types of devices in each WPCN, namely information receiving device (IRD) and harvest-then-transmit device (HTTD). Downlink communication from the HAP to IRDs, downlink energy transfer (ET) from the HAP to HTTDs, and uplink information transmission (IT) from the HTTDs to the HAP are assisted by two IRSs, one in each WPCN. Under this setup, we propose efficient algorithms to optimize reflection coefficients, beamforming vectors, and resource allocation for the sake of uplink sum-rate maximization, taking into account the minimum rate requirement at the IRDs. Numerical results show the considerable performance gain of the proposed NOMA-based scheme as compared to the conventional orthogonal multiple access (OMA)-based counterpart.

Performance analysis for wireless-powered IoT networks with hybrid non-orthogonal multiple access

Aim: In this paper, we study a wireless-powered Internet of Things (IoT) network, where a hybrid access point (HAP) charges IoT devices with wireless energy transfer technology (WET) and collects their data by wireless information transfer (WIT). Methods: To improve spectral efficiency, we propose a hybrid non-orthogonal multiple access (NOMA)-based transmission scheme. On the one hand, NOMA technology is applied for WIT. On the other hand, when some devices transmit data, the HAP can simultaneously charge the other devices, namely concurrent WET and WIT, such that the other devices can harvest more energy to achieve a better rate with some rate loss of these devices due to interference. %During the transmission of some devices, the WET is simultaneously conducted, such that other devices can harvest more energy to achieve a better rate with a rate loss of these devices due to the interference. How to divide devices into the interference and non-interference groups, namely device grouping, and how to pair devices, e.g., device pairing, becomes critical issues in terms of the achieved network throughput and fairness. Results: We first formulate the network throughput maximization problem by optimizing the pairing and grouping policies. To simplify the analysis, we then investigate two specific hybrid NOMA-based transmission schemes. In the former, all devices are firstly paired based on the max-min criterion, where the "best" device is paired with the "worst" one, and then grouped in either ascending or descending order; this is referred to as the first-pairing-then-grouping (FPTG) scheme. In the latter, devices are first grouped and then paired; this is referred to as the first-grouping-then-pairing (FGTP) scheme. By applying the order statistics theory, we theoretically analyze the achieved network throughput and derive the corresponding pairing and grouping policies. Furthermore, we study the max-min fairness of the proposed hybrid NOMA-based scheme. Conclusion: Simulation results validate the significant improvement of the proposed hybrid NOMA-based scheme in terms of network throughput and fairness.

NOMA-Based Spectrum Leasing in Cognitive Radio Network: Power Optimization and Performance Analysis

In this paper, we design a NOMA-based spectrum leasing scheme by considering the following three assumptions for the successive interference cancellation (SIC): (i) the primary network performs the SIC (PSIC), (ii) the secondary network performs the SIC (SSIC), (iii) either the primary or secondary network adaptively performs the SIC depending on the channel conditions (ASIC). We first analyze the achievable rate regions of these schemes. Then, we optimize the power allocation to different layers of the superimposed signal by maximizing the achievable rate of the secondary network under a QoS constraint for the primary network. Finally, we analyze these schemes in terms of the outage probability. The analysis shows that: (i) In terms of the primary network, the PSIC and ASIC schemes perform the same and these schemes outperform the SSIC scheme. (ii) In terms of the secondary network, the ASIC scheme outperforms the other two schemes. (iii) In terms of the primary network, the NOMA-based and OMA-based schemes perform the same, provided that the SIC is performed either adaptively or in a fixed manner at the primary network. (iv) In terms of the secondary network, the NOMA-based scheme outperforms the OMA-based scheme, provided that the SIC is performed adaptively.

Secrecy capacity results for a secure NOMA-based cognitive radio network with an external eavesdropper

In this paper, we investigate a secure cognitive radio network (CRN), which deploys non-orthogonal multiple access (NOMA) to deliver a mixed multicast and unicast traffic to the intended receivers, while keeping them secret from the eavesdroppers. This model represents a cognitive interference channel with an external eavesdropper (CIC-EE). In this model, there are one pair of primary nodes, one pair of secondary nodes, and an external eavesdropper. The primary transmitter multicasts a confidential message to both primary and secondary receivers, while trying to keep it secret from the eavesdropper. The secondary transmitter helps the primary user to deliver its message in exchange of transmission opportunity. The secondary message is unicasted to the secondary receiver, while concealing it from both primary receiver and the eavesdropper. This scenario models a NOMA-based overlay cognitive radio paradigm with an external eavesdropper. For this scenario, the achievable rate-equivocation region is obtained and its optimality is shown for a class of degraded channels. Then, the results obtained for the discrete memoryless channel are extended to the Gaussian channel model. Furthermore, by deploying numerical examples, a comparison is made between the proposed secure NOMA-based scheme, its orthogonal multiple access (OMA) based counterpart, and a cognitive interference channel without an external eavesdropper. It is shown that the NOMA-based method achieves significantly higher rates than its OMA based counterpart.

Sum Rate Maximization for IRS-Assisted Uplink NOMA

An intelligent reflecting surface (IRS) consists of a large number of low-cost reflecting elements, which can steer the incident signal collaboratively by passive beamforming. This way, IRS reconfigures the wireless environment to boost the system performance. In this paper, we consider an IRS-assisted uplink non-orthogonal multiple access (NOMA) system. The objective is to maximize the sum rate of all users under individual power constraint. The considered problem requires a joint power control at the users and beamforming design at the IRS, and is nonconvex. To handle it, semidefinite relaxation is employed, which provides a near-optimal solution. Presented numerical results show that the proposed NOMA-based scheme achieves a larger sum rate than orthogonal multiple access (OMA)-based one. Moreover, the impact of the number of reflecting elements on the sum rate is revealed.

DIYA: Tactile Internet Driven Delay Assessment NOMA-Based Scheme for D2D Communication

Device-to-device (D2D) two-hop cooperative communication improves the network coverage and throughput to provide the quality of service and quality of experience to the end users. Nonorthogonal multiple access (NOMA) can be used at the D2D transmitter to improve the spectral efficiency of the network. But, two-hop transmission with NOMA suffers from delay and interference from the neighboring nodes. To resolve the aforementioned issues, in this paper, we propose Tactile Internet (TI) driven delay assessment for D2D communication (DIYA) scheme, which works in two phases. In the first phase, a full duplex communication at relays (intermediate nodes) is used to have the first- and second-hop transmission simultaneously in the same time slot. Then, TI-based communication is used at D2D transmitter to increase the speed of transmission. In the second phase, pricing-based three-dimensional (3-D) matching is proposed to improve the throughput of the cell edge users along with the mitigation of cochannel interference. Also, the power of the D2D transmitter is optimized using successive convex approximation with low complexity, which converts the nonconvex optimization problem of subchannel allocation and power control into convex problem. Numerical results demonstrate that DIYA achieves higher throughput with reduced delay in comparison to other existing orthogonal multiple access (OMA) and NOMA-based schemes.

V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G-Enabled Vehicular Networks

Benefiting from widely deployed infrastructure, the LTE network has recently been considered as a promising candidate to support vehicle-to-everything (V2X) services. However, with a massive number of devices accessing the V2X network in the future, the conventional OFDM-based LTE network faces congestion issues due to its low efficiency of orthogonal access, resulting in significant access delay and posing a great challenge especially to safety-critical applications. The non-orthogonal multiple access (NOMA) technique has been well recognized as an effective solution for the future 5G cellular networks to provide broadband communications and massive connectivity. In this article, we investigate the applicability of NOMA in supporting cellular V2X services to achieve low latency and high reliability. Starting with a basic V2X unicast system, a novel NOMAbased scheme is proposed to tackle the technical hurdles in designing high spectrally efficient scheduling and resource allocation schemes in the ultra-dense topology. We then extend it to a more general V2X broadcasting system. Other NOMA-based extended V2X applications and some open issues are also discussed.