Uplink NOMA Systems Research Articles

Energy Efficiency Maximization for Active IRS-Assisted Uplink NOMA Systems

Energy Efficiency Maximization for Active IRS-Assisted Uplink NOMA Systems

Pairing Inspired Covert Communication in Uplink NOMA Systems Against SIC Warden

Pairing Inspired Covert Communication in Uplink NOMA Systems Against SIC Warden

Max-Min Fairness for Uplink NOMA Systems With Finite Blocklength

Max-Min Fairness for Uplink NOMA Systems With Finite Blocklength

Capacity performance of uplink NOMA system with 2K+1 users over Fisher-Snedecor composite fading channels

In this paper, we study an uplink power-domain non-orthogonal multiple access (PD-NOMA) system, in which 2K+1 users are served. The user clustering process based on High-High/High-Low algorithm precedes the utilization of the data-rate based power allocation algorithm. Channels are characterized by Fisher-Snedecor composite fading model interpreted as model with a high level of generality. The influence of different fading/shadowing channel conditions, number of users and their positions is portrayed through the numerical results of data sum rate of the studied PD-NOMA system.

Resource Allocation in Uplink NOMA Systems: A Hybrid-Decision-Based Multi-Agent Deep Reinforcement Learning Approach

Resource Allocation in Uplink NOMA Systems: A Hybrid-Decision-Based Multi-Agent Deep Reinforcement Learning Approach

Error Performance Analysis of Multiuser Detection in Uplink-NOMA With Adaptive M-QAM

This letter provides a generalized performance analysis for the multi-user uplink-NOMA system with adaptive square quadrature amplitude modulation (QAM) over Rayleigh fading channels. Motivated by the massive IoT connections and unavailability of orthogonal resources for each node, we consider a multi-access scheme where multi-users with single-antenna transmit data to a multiple-antenna base station through the same resource block. By taking advantage of combining diversity paths with the proposed joint maximum-likelihood detector (JMLD), a closed form expression for the upper bound of bit error rate (BER) is obtained. Despite the number of users or the order of modulation, the analytical results endorsed via computer simulations reveal the ability of the MRC-JMLD detector to discard the error floor completely. Moreover, the simulation results show that the MRC-JMLD surpasses its counterparts significantly and ensures a full diversity order.

Achieving Covert Communication in Uplink NOMA Systems via Energy Harvesting Jammer

This letter investigates covert communication in uplink NOMA systems assisted by an energy harvesting jammer (EHJ), where a reliability-required user (RRU) and a covertness-required user (CRU) are paired to perform NOMA to transmit messages to Bob, in the presence of a warden (Willie) who tries to detect CRU’s transmission behavior. In particular, the EHJ with time switching (TS) scheme has been employed for the purpose of confusing Willie and compensating for the energy supply. We derive the closed-form expressions of expected minimum detection error probability (EMDEP) and connection outage probabilities (COPs) at RRU and CRU, then we analyse the maximum effective covert rate (ECR) under the covertness and RRU’s quality of service (QoS) constraints. Our analysis indicates that there exist an optimal transmit power at Bob and time switching factor to maximize the maximum ECR, and RRU’s QoS constraint has a remarkable effect on the maximum ECR as the transmit power at Bob or time switching factor increases.

Performance Analysis of Uplink NOMA Systems With Hardware Impairments and Delay Constraints Over Composite Fading Channels

In this paper, we propose a mixture gamma distribution based analytical framework for NOMA wireless systems over composite fading channels. We analyze the outage probability (OP), delay-limited throughput (TP) and effective capacity (EC) in uplink NOMA with imperfect successive interference cancellation (SIC) due to the presence of residual hardware impairments and delay constraints. A mixture gamma distribution is used to approximate the probability density functions of fading channels. Based on this, we obtain closed-form expressions in terms of Meijer-G functions for the OP, the TP and the EC. We also perform asymptotic analysis of these metrics to characterize system behaviors at the high signal-to-noise ratio regime. Moreover, upper-bounds for the EC is derived. Efficacy of NOMA over orthogonal multiple access is analytically examined. Unlike the existing works, our analytical expressions hold for NOMA systems with an arbitrary number of users per cluster over a wide range of channel models, including lognormal-Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K_G$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\eta -\mu$</tex-math></inline-formula> , Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> (Hoyt), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\kappa -\mu$</tex-math></inline-formula> , Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> (Rician), Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> , and Rayleigh fading channels. This unified analysis facilitates evaluations of impacts of the residual interference, the power allocation among users, the delay quality-of-service exponent as well as the shadowing and small-scale fading parameters on the performance metrics. Simulation results are provided to validate theoretical analysis.

Covert communications with channel inversion power control in uplink NOMA systems

Covert communications with channel inversion power control in uplink NOMA systems

Optimal UAV's Deployment and Transmit Power Design for Two Users Uplink NOMA Systems.

In order to fully utilize the spectrum resources, this work considers a unmanned aerial vehicle (UAV) uplink communication system based on non-orthogonal multiple access technology (NOMA), in which the UAV receives information from the ground users with a certain flying altitude. As an initial study, we consider a simplified setup with two ground users to draw some insightful results. Explicitly, we first formulate an optimization problem that maximizes the sum throughput subject to each user's transmit power constraint and their corresponding minimum transmission rate requirement. Then, both the optimal transmit power and UAV's deployment location are derived with the aid of employing the Karush-Kuhn-Tucher (KKT) conditions. Simulation results show that the proposed UAV's deployment scheme with the users' power allocation can achieve a higher sum throughput compared with two existing benchmark schemes.

Outage Performance of Uplink NOMA Systems with CDF Scheduling

Outage Performance of Uplink NOMA Systems with CDF Scheduling

Energy Harvesting Optimization of Uplink-NOMA System for IoT Networks Based on Channel Capacity Analysis Using the Water Cycle Algorithm

This article presents energy harvesting (EH) in 5G networks for uplink-NOMA systems for Rician and Rayleigh fading channels via optimizing the radio frequency (RF) energy charging period and the data transmission rate for each user. The model aims to maximize the EH system’s efficiency depending on the number of users, time-slot, resource blocks, path loss, and base station power (BS). In this work, a simple, efficient, and multi-objective the Water Cycle Algorithm (WCA) is presented for calculating transmission rate and EH duration. Furthermore, simulation, performance analysis, and complexity results of WCA are shown by comparing its performance to those of the standard well-known Exhaustive Search Algorithm (ESA), Genetic Algorithm (GA), and Particle Swarm Optimization (PSO). According to the optimization results within 6,800,000 possibilities, the WCA provides 11 percent more power allocation for the energy harvesting and more smooth time-sharing per user than the literature.

On the Security Enhancement of Uplink NOMA Systems With Jammer Selection

We investigate physical layer security of an uplink NOMA system consisting of one base station, multiple users and one eavesdropper. During each uplink transmission, two users are paired to perform NOMA and another user is opportunistically selected from the remaining idle users to act as a friendly jammer to emit artificial noise for confusing the eavesdropper. To enhance the transmission security for the system, we propose two friendly jammer selection aided uplink NOMA transmission schemes, namely random jammer selection aided uplink NOMA transmission (RJS-UNT) scheme without knowing the eavesdropper’s channel state information (CSI), and optimal jammer selection aided uplink NOMA transmission (OJS-UNT) scheme where the eavesdropper’s CSI is available. For comparison purpose, a non-jammer selection aided uplink NOMA transmission (NJS-UNT) scheme is also considered. Analytical closed-form expressions for the secrecy outage probability (SOP) are derived to evaluate the secrecy performance achieved by the proposed schemes. Also, the asymptotic SOPs are provided to obtain further insights. The analysis and simulation results indicate that the schemes converge to SOP floors with the increasing SNR, while the floors achieved by the RJS-UNT and OJS-UNT schemes are significantly lower than that achieved by the NJS-UNT scheme, showing the security advantage of the proposed schemes.

Robust Joint Optimization of Transmit Power and Decoding Order in Uplink NOMA Systems

We consider a robust design problem for achieving max-min fairness amongst users in an uplink non-orthogonal multiple access system under imperfect channel state information. Contrary to the conventional approach adopted in the literature, we propose an optimal decoding order-based successive interference cancellation technique by introducing new binary variables, which results in a difficult class of mixed-integer nonconvex optimization problem. For a practical application, we devise an efficient suboptimal solution based on the inner convex approximation framework, which solves a second-order-cone program at each iteration. Simulation results are provided to demonstrate its performance gain over state-of-the-art designs. The proposed design also yields data rates close to those obtained by an exhaustive search method.

Experimental Evaluation of a Novel Up-Link NOMA System for IoT Communication Equipping Repetition Transmission and Receive Diversity

Experimental Evaluation of a Novel Up-Link NOMA System for IoT Communication Equipping Repetition Transmission and Receive Diversity

Variable-Rate Coding With Constant BER for NOMA via Multilevel IRA Coding

In this correspondence paper, a variable-rate coding scheme is proposed for an uplink NOMA system. Specifically, each user employs a multilevel irregular repeat-accumulate (IRA) coding scheme, which consists of multiple common component IRA encoders. The variable-rate coding scheme is realized by flexibly adjusting the number of component IRA encoders allocated to each user. We design this common component IRA encoder based on extrinsic information transfer analysis to achieve an overall good multi-user decoding performance. The advantages of our proposed scheme are as follows: first, simple implementation of rate variation, second, flexible design of multilevel IRA coding, i.e., the well-designed component IRA encoders does not need to be re-designed when any user changes its rate, third, fair decoding convergence of each user, and finally, capacity-approaching performance.

Joint rate and power optimization for SIC in uplink NOMA systems

Joint rate and power optimization for SIC in uplink NOMA systems

Theoretical Analysis of the Dynamic Decode Ordering SIC Receiver for Uplink NOMA Systems

Instead of successive interference cancellation (SIC) for uplink non-orthogonal multiple access systems with fixed decoding order based on the statistical channel state information (CSI), we focus on decoding with the dynamic order according to the instantaneous CSI. After modeling the channel fluctuation of all the users with different transmit powers and different path losses, a dynamic SIC receiver is proposed based on the instantaneous received power of different users. The outage probability of the proposed system is theoretically analyzed and the closed-form expressions for a three-user system are derived. Simulations are performed to validate the accuracy of the theoretical results.