Uplink Non-orthogonal Multiple Access Research Articles

A New Design of Hybrid SIC for Improving Transmission Robustness in Uplink NOMA

Conventionally, it was thought that outage probability error floors are unavoidable in uplink non-orthogonal multiple access (NOMA) regardless which type of successive interference cancellation (SIC) is adopted. However, a recent work breaks such myths by introducing the concept of hybrid SIC, which dynamically chooses the decoding order according to the users' channel conditions and quality of service requirements. However, there is still a limitation in this existing work that the error floors can only be avoidable under a stringent condition on users' target rates. To this end, this letter proposes a new hybrid SIC scheme by exploiting the benefit of power control, which guarantees no error floor without any conditions on users' target rates.

Performance Analysis of Filtered OFDM Based Downlink and Uplink NOMA System over Nakagami-m Fading Channel

Efficient consumption of available resources and fulfillment of increasing demands are the two main challenges which are addressed by exploring advanced multiple access schemes along with efficient modulation techniques. To this end, non-orthogonal multiple access (NOMA) is discussed as a promising scheme for future 5G traffic. NOMA enables the users to share same resource block, permitting certain level of interference. In this paper, we propose filtered OFDM (F-OFDM) as a transmission waveform for NOMA systems, as it offers all the advantages of OFDM with the additional provision of sub-band filtering to satisfy the diverse services of the users. We examine F-OFDM in both downlink and uplink NOMA systems. Error-related performances of both downlink and uplink F-OFDM NOMA systems are analyzed and compared with conventional OFDM NOMA system over Nakagami-m fading channel. The results show that the error performance of F-OFDM NOMA is better than that of OFDM NOMA. An improvement of about 2 dB and 1 dB in bit error rate is achieved in downlink and uplink F-OFDM NOMA, respectively. Monte Carlo simulations are conducted for different values of fading parameter m, supporting the obtained analytical results

Performance Study of Cognitive Relay NOMA Networks With Dynamic Power Transmission

The cooperative non-orthogonal multiple access (NOMA) networks with one pair primary user and one pair cognitive user share the same spectrum resource via a common relay is considered in this paper. We propose a dynamic power transmission scheme for both uplink and downlink NOMA transmission in cognitive relay networks, which preserves the quality of service for the primary user. The closed-form expressions of overall outage probability and average sum rate for the proposed dynamic power transmission scheme of cognitive relay NOMA networks are derived. Both developed analytical results and Monte Carlo simulations show that the proposed dynamic power control scheme can dramatically enhance performance gain for the proposed networks, compared to other existing NOMA power allocation schemes.

Asynchronous Transmission for Multiple Access Channels: Rate-Region Analysis and System Design for Uplink NOMA

In this work, we thoroughly analyze the rate-region provided by the asynchronous transmission in multiple access channels (MACs). We derive the corresponding capacity-regions, applicable to a wide range of pulse shaping methods. We analytically prove that asynchronous transmission enlarges the capacity-region of MACs. Although successive interference cancellation (SIC) can achieve the optimal sum-rate for the conventional uplink non-orthogonal multiple access (NOMA) methods, it is unable to achieve the boundary of the capacity-region for the asynchronous transmission. We demonstrate that for the asynchronous transmission, the optimal SIC decoding order to achieve the maximum sum-rate is based on the users' channel strengths. This optimal ordering is in contrast to the conventional uplink NOMA, where various decoding orders can result in the maximum sum-rate. Furthermore, we provide practical transceiver designs to approach the capacity-region. The memory induced by asynchronous transmission enables the use of the trellis-based detection methods which improves the performance. In addition, we propose a transceiver design, based on channel diagonalization to exploit the frequency-selectivity introduced by timing offsets. The proposed transceiver design, joint with the turbo principle, enables us to achieve a rate pair that is not achievable by the synchronous transmission.

DeepMuD: Multi-User Detection for Uplink Grant-Free NOMA IoT Networks via Deep Learning

In this letter, we propose a deep learning-aided multi-user detection (DeepMuD) in uplink non-orthogonal multiple access (NOMA) to empower the massive machine-type communication where an offline-trained Long Short-Term Memory (LSTM)-based network is used for multi-user detection. In the proposed DeepMuD, a perfect channel state information (CSI) is also not required since it is able to perform a joint channel estimation and multi-user detection with the pilot responses, where the pilot-to-frame ratio is very low. The proposed DeepMuD improves the error performance of the uplink NOMA significantly and outperforms the conventional detectors (even with perfect CSI). Moreover, this gain becomes superb with the increase in the number of Internet of Things (IoT) devices. Furthermore, the proposed DeepMuD has a flexible detection and regardless of the number of IoT devices, the multi-user detection can be performed. Thus, an arbitrary number of IoT devices can be served without a signaling overhead, which enables the grant-free communication.

OTFS Signaling for Uplink NOMA of Heterogeneous Mobility Users

We investigate a coded uplink non-orthogonal multiple access (NOMA) configuration in which groups of co-channel users are modulated in accordance with orthogonal time frequency space (OTFS). We take advantage of OTFS characteristics to achieve NOMA spectrum sharing in the delay-Doppler domain between stationary and mobile users. We develop an efficient iterative turbo receiver based on the principle of successive interference cancellation (SIC) to overcome the co-channel interference (CCI). We propose two turbo detector algorithms: orthogonal approximate message passing with linear minimum mean squared error (OAMP-LMMSE) and Gaussian approximate message passing with expectation propagation (GAMP-EP). The interactive OAMP-LMMSE detector and GAMP-EP detector are respectively assigned for the reception of the stationary and mobile users. We analyze the convergence performance of our proposed iterative SIC turbo receiver by utilizing a customized extrinsic information transfer (EXIT) chart and simplify the corresponding detector algorithms to further reduce receiver complexity. Our proposed iterative SIC turbo receiver demonstrates performance improvement over existing receivers and robustness against imperfect SIC process and channel state information uncertainty.

CS-Based Near-Optimal MUD for Uplink Grant-Free NOMA

In order to furnish connectivity to an incredible number of devices and to satisfy the capacity demands, non-orthogonal multiple access (NOMA) is considered as a hopeful solution for future 5G. Moreover, grant-free transmission is substantially expected in the uplink NOMA to minimize the latency time and detection overhead. However, multi-user detection (MUD) without user-activity information in uplink grant-free NOMA is hard in practice. In this paper, by benefit from the user-activity sparsity existing in uplink grant-free NOMA, the multipath matching pursuit (MMP) is used for user-activity detection, and then message passing algorithm (MPA) can be efficiently applied for active users’ data detection. Simulation results show that the proposed MMP-MAP MUD with acceptable complexity can achieve better performance than conventional solutions. Also, the MMP-MAP detector reaches the performance obtained by the MPA detector with perfect user-activity information once the level of signal-to-noise ratio exceed 11 dB.

Multiuser Detection Schemes Based on Families of OMP and MUSIC Algorithms for Uplink Grant Free NOMA Wireless Communications Systems

Background and Objective: The Non-Orthogonal Multiple Access (NOMA) technology is a multi-access scheme that overcomes most of the disadvantages of its predecessor, the OMA technology. Specifically, NOMA technology supports massive connectivity of multiple users by employing the same non-orthogonal spectrum resource. In an uplink NOMA system with grant-free transmission mode, the Base Station (BS) is unaware of which users are active in the networks at a given time. Consequently, there is a need for mechanism to ensure successful recovery of users’ transmitted signals. This paper presents some new Multiuser Detector (MUD) schemes for uplink grant-free NOMA wireless communication networks with system’s model involving Multiple Measurement Vectors (MMV) rather than the Single Measurement Vector (SMV) that many previous works have considered. These MUDs include those that are based on differential Orthogonal Matching Pursuit (OMP), adaptive Simultaneous OMP (SOMP), compressive- multiple signal classification (MUSIC), and sequential compressive-MUSIC algorithms. Methods: The MUDs are employed in the detection of users’ signals in the uplink NOMA systems. Results and Discussion: Comparative performances of these MUDs with another one that is also based on the MMV system model, the SOMP-based MUD are presented for the scenarios when the system is under-loaded, fully loaded and over-loaded. Conclusion: The results suggest that the sequential compressive-MUSIC-based MUD, though shows weak performance at lower range of SNR, outperforms all the other MUDs including the SOMP-based MUD at higher SNR. Its performance is quite outstanding during the over-loaded scenarios, especially at higher SNR. However, its computational complexity is higher that the closely performing compressive-MUSIC-based MUD and SOMP-based MUD.

SCMA System Design With Index Modulation via Codebook Assignment

Sparse code multiple access (SCMA) is a promising non-orthogonal multiple access (NOMA) scheme for massive machine-type communications for 5G-and-beyond communication systems. Innovative use of orthogonal frequency division multiplexing with index modulation (OFDM-IM) takes advantage of using tone indices in data transmission. In this study, we propose a novel multiplexing and multiple access scheme, namely SCMA based on OFDM-IM (SCMA-IM). SCMA-IM method can be implemented in uplink NOMA systems in an efficient way with similar computational complexity as SCMA. In this method constellation differences and diversity are obtained via SCMA codebooks (CBs) and the employment of CBs is transferred to index modulation (IM). Performance improvement is achieved via CBs so that the number of data bits carried by indices increases more than one bit with different constellations, and also with the number of CBs assigned. In order to determine the indices used in IM, the receiver structure is simplified by the message passing algorithm and log-likelihood ratio detection process used in SCMA receivers without indexing the receiver. Thus, a new NOMA scheme is obtained by coding with IM. Bit error rate performance of the system is studied for 150% and 200% overloading factors.

Hybrid NOMA/OMA Broadcasting-and-Buffer-State-Based Relay Selection

In this paper, we propose a novel buffer-aided relay selection scheme that is capable of amalgamating the concepts of non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) in the context of two-hop cooperative networks supporting multiple relays. This is enabled by allowing relay nodes to share a common information packet in their buffers with the aid of a source-to-relay broadcasting mode. Hence, the proposed relay selection scheme switches between diverse modes of uplink NOMA, downlink NOMA, unicast, source broadcasting, and cooperative beamforming. The theoretical bounds of the outage probability, throughput, average delay, and diversity order are derived for the proposed scheme, based on a Markov chain model. Through our analytical and numerical results, it is demonstrated that the proposed scheme is capable of switching to one of the best modes in an adaptive manner while outperforming the conventional buffer-aided cooperative schemes.

Multiple Unmanned-Aerial-Vehicles Deployment and User Pairing for Nonorthogonal Multiple Access Schemes

Nonorthogonal multiple access (NOMA) significantly improves the connectivity opportunities and enhances the spectrum efficiency (SE) in the fifth generation and beyond (B5G) wireless communications. Meanwhile, emerging B5G services demand for higher SE in the NOMA-based wireless communications. However, traditional ground-to-ground (G2G) communications are hard to satisfy these demands, especially for the cellular uplinks. To solve these challenges, this article proposes a multiple unmanned-aerial-vehicles (UAVs)-aided uplink NOMA method. In detail, multiple hovering UAVs relay data for a half of ground users (GUs) and share the spectrums with the other GUs that communicate with the base station (BS) directly. Furthermore, this article proposes a K-means clustering-based UAV deployment scheme and location-based user pairing (UP) scheme to optimize the transceiver association for the multiple UAVs-aided NOMA uplinks. Finally, a sum power minimization-based resource allocation problem is formulated with the lowest Quality-of-Service (QoS) constraints. We solve it with the message-passing algorithm and evaluate the superior performances of the proposed scheduling and paring schemes on SE and energy efficiency (EE). Extensive simulations are conducted to compare the performances of the proposed schemes with those of the single UAV-aided NOMA uplinks, G2G-based NOMA uplinks, and the proposed multiple UAVs-aided uplinks with a facility location framework-based UAV deployment. Simulation results demonstrate that the proposed multiple UAVs deployment and UP-based NOMA scheme significantly improves the EE and the SE of the cellular uplinks at the cost of only a little relaying power consumption of UAVs.

Enabling Full-duplex in MEC Networks Using Uplink NOMA in Presence of Hardware Impairments

To satisfy the fast growth of Internet of Things (IoT) or development of applications in the fifth generation (5G) wireless networks, the expected systems need two main functions such as massive connectivity of IoT devices and the low latency. Fortunately, non-orthogonal multiple access (NOMA) has been recommended as a promising approach for 5G networks to satisfy concerned requirements and to significantly improve the network capacity. Together with advances of NOMA scheme, mobile edge computing (MEC) is recognized as one of the key emerging approaches to improve the quality of service and reduce the latency for 5G networks. In order to capture the potential gains of NOMA-aided MEC systems, this paper proposes design of multiple antennas and full-duplex for an edge computing aware NOMA architecture. As expected, such NOMA-aided MEC systems can enjoy the benefits of uplink NOMA in reducing MEC users’ uplink outage probability. To this end, we derive expression of outage probability for signals corresponding two-user model at uplink. Especially, degraded performance might happens in practice under impact of hardware impairment.

ISHU: Interference Reduction Scheme for D2D Mobile Groups Using Uplink NOMA

In this paper, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Interference Reduction Scheme for Device-to-Device (D2D) Mobile Groups Using Uplink NOMA (ISHU)</i> is proposed to maximize the throughput of the network. To achieve this goal, we integrated uplink non-orthogonal multiple access (NOMA) in the D2D mobile groups (DMGs). DMGs improve the spectral efficiency by sharing the resources with cellular mobile users (CMUs) whereas, uplink NOMA in DMGs associate the large number of D2D mobile users (DMUs) with the D2D transmitter (DDT). ISHU jointly optimizes the user group association and resource allocation in the uplink NOMA-enabled DMGs. The problem of joint user association and resource allocation is formulated as a mixed integer non-linear programming. To address this problem, we divided the problem of interference mitigation in two sub-problems and solved it independently. First, for joint user group association and sub-carrier assignment, a 3-D matching game is designed between the DMUs, DDT, and sub-carriers, respectively. Second, to optimize the power of DMUs across each sub-carriers, the branch and bound (BB) technique is used. Also, to reduce the complexity of ISHU scheme, the successive convex approximation low complexity (SCALE) technique is used across each sub-carrier. Simulated results demonstrated that ISHU provides 3.846 and 26.92 percent superior throughout as compared to the existing uplink conventional NOMA and OFDMA schemes.

Sum-Throughput Maximization in NOMA-Based WPCN: A Cluster-Specific Beamforming Approach

Wireless power transfer is a promising solution for wireless networks composed of Internet-of-Things (IoT) devices that may suffer from insufficient battery capacity. A wireless powered communication network (WPCN) is a framework to design energy-constrained networks such as IoT networks. In this article, we consider WPCNs consisting of a hybrid access point (H-AP) and energy harvesting users, all equipped with multiple antennas. A H-AP transfers energy to the users using energy beamforming in the downlink, and the users transmit information using the harvested energy in the uplink, where nonorthogonal multiple access (NOMA) transmission is employed. For the uplink NOMA transmission, users are grouped into multiple clusters by cluster-specific beamforming. In particular, signal alignment is exploited for the beamforming so that the channels of users in a cluster are aligned in the same direction. By signal alignment, the number of messages decoded by successive interference cancellation (SIC) is reduced, which can be effective at lowering the decoding complexity and SIC error propagation. Due to the difficulty of jointly optimizing cluster-specific beamforming and time/energy resources for sum-throughput maximization, we determine the beamforming relying on signal alignment first, and then the resources are optimized for given beamforming. To be more specific, we propose a novel iterative algorithm for cluster-specific beamforming design followed by the sum-throughput maximization algorithm. Numerical results show the sum-throughput performance of the proposed scheme and its robustness toward SIC error propagation compared to existing schemes.

Uplink NOMA-based long-term throughput maximization scheme for cognitive radio networks: an actor–critic reinforcement learning approach

Non-orthogonal multiple access (NOMA) is one of the promising techniques for spectrum efficiency in wireless networks. In this paper, we consider an uplink NOMA cognitive system, where the secondary users (SUs) can jointly transmit data to the cognitive base station (CBS) over the same spectrum resources. Thereafter, successive interference cancellation is applied at the CBS to retrieve signals transmitted by the SUs. In addition, the energy-constrained problem in wireless networks is taken into account. Therefore, we assume that the SUs are powered by a wireless energy harvester to prolong their operations; meanwhile, the CBS is equipped with a traditional electrical supply. Herein, we propose an actor–critic reinforcement learning approach to maximize the long-term throughput of the cognitive network. In particular, by interacting and learning directly from the environment over several time slots, the CBS can optimally assign the amount of transmission energy for each SU according to the remaining energy of the SUs and the availability of the primary channel. As a consequence, the simulation results verify that the proposed scheme outperforms other conventional approaches (such as Myopic NOMA and OMA), so the system reward is always maximized in the current time slot, in terms of overall throughput and energy efficiency.

Uplink Non-Orthogonal Multiple Access With Golden Codeword Constellation

Non-orthogonal multiple access (NOMA) is a technique to improve spectral efficiency. In uplink NOMA (UL-NOMA) systems, mobile multiusers are globally synchronized to share the same time and frequency resources, and transmit their own independent symbols to the base station (BS). This paper proposes an UL-NOMA system with Golden codeword constellation (GCC). In the proposed UL-NOMA system, two users, the center user and the edge user, transmit their own independent Golden codewords to the BS. Compared to the conventional UL-NOMA systems, the proposed UL-NOMA system not only preserves the spectral efficiency, but also improves error performance. The fast essentially maximum likelihood (FE-ML) detection with dynamic signal detection subset (DSDS) is proposed to decode the Golden codewords. A lower bound on error performance for both the center user and edge user is further derived. Simulation results show that the derived lower bound well predicts the error performance of UL-NOMA with GCC. Simulation results also show that the proposed UL-NOMA system outperforms the conventional UL-NOMA system by at least 2 dB signal-to-noise ratio (SNR) for both the center user and edge user at a bit error rate of $2 \times 10^{-5}$ . Finally, both complexity analysis and simulation results show that the proposed FE-ML with DSDS result in a 68% complexity reduction compared to the FE-ML with SDS at an SNR of 23 dB for the center user transmitting 64QAM and the edge user transmitting 16QAM.

ECF-Based Estimator for the LOS Power in Uplink NOMA System With Unknown Impulsive Noise

In this paper, an empirical characteristic function (ECF) based estimator of the line-of-sight (LOS) power for the near user in an uplink non-orthogonal multiple access (NOMA) system with unknown impulsive noise is proposed. The channels between the users and the base station (BS) are assumed to have Rician fading. The performance of the proposed estimator is analytically evaluated, which demonstrates the asymptotic unbiasedness and consistency of the estimator. Furthermore, the approximate expression derived for the variance is confirmed through computer simulations. Numerical results show that the proposed estimator outperforms the previous estimator for the LOS power in the mixture of Gaussian and $\alpha$ -stable noise.

PSO‐Based UAV Deployment and Dynamic Power Allocation for UAV‐Enabled Uplink NOMA Network

Recently, unmanned aerial vehicles (UAVs) have been used as flying base stations (BSs) to take advantage of line‐of‐sight (LOS) connectivity and efficiently enable fifth‐generation (5G) and cellular network coverage and data rates. On the other hand, nonorthogonal multiple access (NOMA) is a promising technique to help achieve unprecedented requirements by simultaneously allowing multiple users to send data over the same resource block. In this paper, we study a UAV‐enabled uplink NOMA network, where the UAV collects data from ground users while flying at a certain altitude. Unlike all existing work on this topic, this study consists of two stages. In the first stage, we use the well‐known Particle Swarm Optimization (PSO) algorithm, which is a metaheuristic algorithm, to deploy the UAV in 3D space, so that the users’ sum pathlosses are minimized. In the second stage, we investigate the user pairing problem and propose a dynamic power allocation technique for determining the user’s power allocation coefficients, as well as a closed‐form equation for the ergodic sum‐rate. Results show our PSO‐based algorithm prevailing over the Genetic Algorithm (GA) and random deployment methods. The proposed dynamic power allocation strategy maximizes the network’s ergodic sum‐rate and outperforms the fixed power allocation strategy. Additionally, the results reveal that the best pairing scheme is the one that keeps uniform channel gain difference in the same pair.

Control Efficient Power Allocation of Uplink NOMA in UAV-Aided Vehicular Platooning

Power allocation in non-orthogonal multiple access (NOMA) systems is essential to avoid multi-user detection failure. However, controlling the uplink transmission power brings extra signaling overhead, especially in dynamic environments. In this paper, we investigate the uplink transmission power allocation problem in an unmanned aerial vehicle (UAV)-aided platooning NOMA system, where the UAV acts as a relay to assist inter-vehicle communications. Platoon vehicles are admitted to the same vehicle-to-UAV (V2U) channel via our proposed sequence-based power allocation (SPA) strategy. Instead of achieving the optimal energy efficiency, our goal is to design a simple yet effective power control scheme. Specially, in SPA strategy, vehicles determine their transmission power according to their positions in the platoon. Considering platoon dynamics due to vehicle mobility, a power-reserved mechanism is further incorporated in the proposed strategy to pre-allocate power resources for newly joined vehicles. In addition, a power-moving mechanism is further employed to guarantee the uplink signal-to-interference-plus-noise ratio (SINR) of vehicles by changing vehicle transmission power into higher levels during vehicle leaving a platoon. As the system only needs to update vehicle positions for the SPA strategy, only a small amount of signaling is required in our power allocation strategy. Extensive simulation results are provided to demonstrate that the proposed SPA strategy ensures the required SINR of platoon communication in different dynamic scenarios.

Exploiting Secrecy Performance of Uplink NOMA in Cellular Networks

We study the secrecy transmission of uplink non-orthogonal multiple access (NOMA) with single antenna and multi-antenna users in presence of an eavesdropper. Two phases are required for communications during each time frame between the users and the base station in cellular networks. We study the case where an eavesdropper overhears the relay and direct links from the users to the base stations. In terms of the secure performance analysis, we focus on two main metrics including secrecy outage probability (SOP) and strictly positive secrecy capacity (SPSC) with the assumption that the eavesdropper is able to detect the signals. Analytical closed-form expressions for the SOP and SPSC are derived to evaluate the system secure performance achieved by the proposed schemes. Furthermore, the asymptotic analysis is presented to gain further insights. The analytical and numerical results indicate that the proposed schemes can realize better secrecy performance once we improve the channel condition and signal-to-noise ratio (SNR) at the base station. Our results confirms that the secrecy performance gaps exist among the two users since different power allocation factors are assigned to these users.