Strong User Research Articles

Reducing the Mutual Outage Probability of Cooperative Non-Orthogonal Multiple Access

In this letter, a new power allocation scheme is proposed to improve the reliability of cooperative non-orthogonal multiple access (CO-NOMA). The strong user is allocated the maximum power, whereas the weak user is allocated the minimum power. This power allocation alters the decoding sequence along with the signal-to-interference plus noise ratio (SINR), at the users. The weak user benefits from receiving multiple copies of the signal whereas the strong user benefits from the higher power allocation. Numerical simulation results show that the proposed scheme has a lower mutual outage probability (MOP) and offers better reliability as compared to the conventional power allocation scheme for CO-NOMA. An exact closed-form expression of MOP is derived for the two-user CO-NOMA system and it is shown that each user achieves full diversity. The proposed allocation is able to achieve approximately 30% higher transmission rate at 15 dB as compared to conventional CO-NOMA in a practical non-power balanced scenario.

User Pairing, Link Selection, and Power Allocation for Cooperative NOMA Hybrid VLC/RF Systems

Despite the promising high-data rate features of visible light communications (VLC), they still suffer from unbalanced services due to blockages and channel fluctuation among users. This paper introduces and evaluates a new transmission scheme which adopts cooperative non-orthogonal multiple access (Co-NOMA) in hybrid VLC/radio-frequency (RF) systems, so as to improve both system sum-rate and fairness. Consider a network consisting of one VLC access point (AP) and multiple strong and weak users, where each weak user is paired with a strong user. Each weak user can be served either directly by the VLC AP, or via the strong user which converts light information received through the VLC link, and forwards the information to the weak user via the RF link. The paper then maximizes a network-wide weighted sum-rate, so as to jointly determine the strong-weak user-pairs, the serving link of each weak user (i.e., either direct VLC or hybrid VLC/RF), and the power of each user message, subject to user connectivity and transmit power constraints. The paper tackles such a mixed-integer non-convex optimization problem using an iterative approach. Simulations show that the proposed scheme significantly improves the VLC network performance (i.e., sum-rate and fairness) as compared to the conventional NOMA scheme.

Efficient user pairing algorithm for enhancement of spectral efficiency and interference cancelation in downlink NOMA system

A new subcarrier-user allocation algorithm for the downlink non-orthogonal multiple access system is presented in this paper. The proposed algorithm aims to enhance the spectral efficiency of the system and the successive interference cancelation performance by guaranteeing a high difference in channel-gain between the paired users per subcarrier. To enhance the spectral efficiency, the proposed algorithm provides a higher priority to the subcarrier that has a higher best (maximum) channel gain value rather than that has a lower best channel gain value. Also, it pairs the strong user with the second minimum channel-gain user rather than the minimum channel gain user. Besides, the proposed algorithm divides the subcarriers into two groups according to the standard deviation of the channel gain of each subcarrier. Then, it gives the priority to the group with low standard deviation values during subcarrier-user allocation to guarantee a high difference in channel-gain between the paired users per subcarrier. Later, fractional transmit power allocation is applied to distribute the subcarrier power between the paired users. Simulation results prove that the proposed algorithm improves the spectral efficiency of the system, and guarantees a significantly higher difference in channel-gain between the paired users per subcarrier compared to the conventional algorithms.

IoT-Based Coordinated Direct and Relay Transmission With Non-Orthogonal Multiple Access

This letter studies an Internet-of-Things (IoT)-based coordinated direct and relay transmission (CDRT) adopting non-orthogonal multiple access (NOMA), where an information source directly communicates with a strong user while a weak user needs the help of an IoT master node. Different from traditional NOMA-CDRT systems, in which NOMA protocol is only deployed at the information source to serve users, the proposed novel system, i.e., IoT-assisted NOMA-CDRT, have two stages: (1) information source transmits the information data to users and (2) IoT master node operating as a relay to decode and forward data of the weak user along with IoT-U. Under the considered system setup, we derive exact closed-form expressions for the outage probability of users as well as approximated expressions for the ergodic sum capacity. Our results show that the proposed system may not perform well in terms of outage performance at the strong user during the cooperative transmission phase, but achieves higher ergodic sum capacity in whole communication process, and enhances efficient spectrum usage, compared with conventional CDRT and orthogonal multiple access systems.

NOMA Versus OMA in Finite Blocklength Regime: Link-Layer Rate Performance

In this article, we investigate the latency performance of non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) technologies in finite blocklength regime. In the comparative study, we derive the achievable effective capacity of two-user NOMA and its OMA counterpart under delay quality-of-service constraints. We then obtain closed-form expressions for the achievable effective capacity of the weak and strong users in both scenarios considering transmissions over Rayleigh fading channels. Numerical results are provided. In particular, it is shown that at low signal-to-noise ratios (SNRs), the OMA user with better channel condition outperforms both NOMA users. We also evaluate the impact of fixed power allocation scheme on the achievable effective capacity of two-user NOMA. The comparative analysis of the total link-layer rate shows that at high SNRs, the total link-layer rate of NOMA with finite blocklength outperforms the one of OMA when the delay exponent is loose.

Secure transmission for NOMA systems with imperfect SIC

This paper investigates secure transmission for non-orthogonal multiple access (NOMA) systems where the imperfect successive interference cancellation (SIC) is considered at both legitimate users and eavesdropper (Eve). A power allocation scheme is designed for the legitimate users to mitigate the effect of the SIC error caused by imperfect SIC. For characterizing the secrecy performance of the NOMA system, the closed-form expressions for connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived over Nakagami-m fading channels in both NOMA and benchmark orthogonal multiple access (OMA) systems. We also provide security and reliability trade-off results (SRT) for the users in the NOMA and OMA systems. Simulation results verify our analysis and show that the strong users achieve better secrecy performance but worse reliability performance and NOMA outperforms OMA in terms of SRT.

Throughput optimization of cooperative non orthogonal multiple access

This paper derives the outage and packet error probabilities of Non Orthogonal Multiple Access (NOMA) systems. In the first time slot, the Base Station transmits a combination of two symbols $$s_w$$ and $$s_s$$ dedicated for weak and strong users. This signal is received by the two users and a relay. In the second time slot, the relay amplifies the received signal to the two users. Both users use the signal with the highest Signal to Interference plus Noise Ratio among direct and relayed signals. The weak user detects only its signal. Strong user first detects symbol $$s_w$$ of weak user. After removing the contribution of weak user, strong user detects its own symbol $$s_s$$ . In this article, expressions for outage probability, Packet Error Probability and the throughput of cooperative NOMA are derived. We also optimize the power allocated to weak and strong users to maximize the system throughput.

Power Allocation and Link Selection for Multicell Cooperative NOMA Hybrid VLC/RF Systems

This letter proposes and optimizes a cooperative non-orthogonal multiple-access (Co-NOMA) scheme in the context of multicell visible light communications (VLC) networks to mitigate inter-cell interference. Consider a network where each access-point (AP) serves two users. In each cell, the weak user (cell-edge user) can be served either directly by the VLC AP, or through the strong user that decodes the weak user message and forwards it through the radio-frequency (RF) link. The paper then considers the problem of maximizing the sum-rate under quality-of-service constraints by allocating the powers of the messages and APs, and determining the links serving each weak user. The paper solves this non-convex problem by first finding closed-form solutions of the users' powers and link selection for fixed APs powers. The APs powers are then iteratively solved in an outer loop. Simulation results show that the proposed scheme improves the sum-rate and fairness as compared to non-orthogonal multiple-access (NOMA) scheme.

Joint User Pairing, Subchannel Assignment and Power Allocation in Cooperative Non-Orthogonal Multiple Access Networks

This paper addresses the problem of user pairing, subchannel assignment and power allocation in a downlink cooperative non-orthogonal multiple access (NOMA) network. A joint user pairing and subchannel assignment algorithm is proposed that pairs a user having strong channel conditions with a user having weak channel conditions and assigns them a subchannel simultaneously. Each strong user acts as a relay for the weak user. A Stackelberg game (SG) is employed and a closed-form solution is given to allocate power among the users by the base station (BS) considering the mutual benefits of each user and the BS. Simulation results prove the effectiveness of the proposed scheme in terms of average sum rate of users as compared to that of the cooperative orthogonal multiple access (OMA) scheme and existing NOMA schemes.

Performance analysis of a cooperative D2D communication network with NOMA

The cooperative device-to-device (D2D) network employing non-orthogonal multiple access (NOMA) is expected to play an important role in the next-generation wireless networks. In this work, the authors derive outage probability expressions of a cooperative NOMA D2D network which employs decode-and-forward relaying. A wireless link experiencing Nakagami-m fading is considered which is further assisted in the communication network by a wired link which is a powerline communication link and experiences Rayleigh fading. The outage analysis, shown for both the strong user and the weak user, is derived assuming that at the receiver there is perfect successive interference cancellation. Employing power division NOMA, optimum value for the coefficient of power allocation is obtained corresponding to the minimum probability of outage of the strong user. Furthermore, a range of the NOMA power allocation coefficient is provided for the communication link at the weak user which is between the wireless and the powerline link. Symbol error probability expressions are also derived for the strong and the weak users for the scenario when: i) both the wireless and the wired links are available for communication and ii) only the wireless link is available for communication.

Virtual MIMO Beamforming for Opportunistic Cooperative Time Division Multiple Access

The conventional studies on virtual multiple-input multiple-output based cooperative time division multiple access (TDMA) have been focused on the cooperative retransmission of failed data. In this paper, we propose an opportunistic cooperative TDMA (OC-TDMA) scheme where a source user transmits its own data and the cooperative users opportunistically transmit low-data-rate users’ data. To do this, time slots are divided into non-cooperative and cooperative time slots. The non-cooperative time slots are located at earlier time slots, in which weak users, who cannot satisfy the required signal-to-interference-plus-noise ratio (SINR), are scheduled. The cooperative time slots are located at later time slots, in which strong users, who can satisfy the required SINR, are scheduled. In the cooperative time slots, the source user transmits its own data and the other users (i.e., cooperative users) assist to transmit the weak users’ data which was transmitted at the non-cooperative time slots. The optimal and sub-optimal OC-TDMA algorithms are analyzed and evaluated in terms of the required excess capacity , which indicates the capacity additionally required to satisfy the SINR constraints of all the users after all the transmission is finished. Throughout the simulation and numerical results, it is demonstrated that OC-TDMA schemes outperform conventional TDMA schemes.

Use of an Indoor Navigation System by Sighted and Blind Travelers

This article first reviews the pros and cons of current accessible indoor navigation systems and then describes a study using commercial smart devices to navigate routes through a complex building. Our interest was in comparing performance when using real-time narrative descriptions (system-aided condition) vs. a memory-based condition where the same narrative information was only provided to users from the route's origin. We tested two groups of blind and visually impaired (BVI) users, including people above and below 60 years of age, as well as a third sighted control group. Evaluating older BVI participants is important, as the majority of vision loss is age-related, yet navigation performance using access technology is rarely studied with this demographic. Behavioral results demonstrated that access to real-time (system-aided) information led to better navigation accuracy and greater confidence by blind users compared to the information-matched memory condition. Performance for blind participants over 60 years old was nearly identical with their younger peers—an important outcome supporting the efficacy of using navigational technologies by this fast-growing population. Route completion accuracy and requests for assistance did not reliably differ between blind and sighted participants when using the system, suggesting that access to narrative route information led to functionally equivalent navigation behavior, irrespective of visual status. Survey results revealed strong user support for real-time information and provided important guidance for future interface refinements.

Developing web-based character value integration in school culture

This study aims at developing web-based character value integration in school culture for elementary school students in Jakarta in Indonesia. The research method used is Research and Development. The research product of web-based character value integration in school culture built with wix.com consist of home, introduction, concept, application of character value integration in school culture at elementary school, video, and contact pages. The result of validation of expert, limited, and extensive field test related to usage of web-based character value integration in school culture including organization, content utility, navigation, graphical representation, purpose, simplicity, credibility, consistency, accuracy, loading speed, security, interactive, strong user control capabilities, readability, efficiency, and learnability attained 3.78, 3.82, and 3.85 from maximum score 4 pointing out that this product has already been valid, practical, and effective. This study comes to the conclusion that web-based character value integration in school culture is effective to be implemented at elementary schools in Jakarta in Indonesia.

Coverage Analysis of Downlink NOMA-Enabled Dense Networks With ISP-Based User Ordering

In the existing non-orthogonal multiple access (NOMA) works, ordering users depending on their distances is widely used, which can provide tractable results. However, it is not accurate in dense networks with considering the line-of-sight (LoS)/non-line-of-sight (NLoS) propagation and multipath fading. Hence, the received instantaneous signal power (ISP)-based ordering is investigated in this letter. We derive the probability of the near user in distance-based ordering being the strong user in ISP-based ordering, which is termed as the accuracy probability, and also analyze the respective coverage probabilities. The analytical and simulation results show that the accuracy probability varies with base station (BS) density and the gap between the distance and ISP-based ordering highly depends on the BS density and power allocation coefficient.

Large System Analysis of Downlink MISO-NOMA System via Regularized Zero-Forcing Precoding With Imperfect CSIT

This letter studies the multiple-input single-output (MISO) non-orthogonal multiple-access (NOMA) downlink using regularized zero-forcing (RZF) precoding with imperfect channel state information (CSI). We first propose a new user scheduling scheme based on imperfect CSI and a model to characterize the channel correlation between the weak and strong users. Then we derive an approximate expression of the ergodic sum-rate using large-system random matrix theory. This approximation permits us to derive the optimal power allocation scheme that satisfies the rate requirement of the weak users. Simulation results are presented to confirm the accuracy of the approximation and reveal the relationships between the ergodic sum-rate, the channel correlation, and other system parameters.

Energy-Efficient Power Allocation and User Selection for mmWave-NOMA Transmission in M2M Communications Underlaying Cellular Heterogeneous Networks

Non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) communication are two important technologies considered for the fifth generation (5G) of mobile networks. In this paper, we propose a machine-to-machine (M2M) communication underlaying heterogeneous network (HetNet) with mmWave-NOMA transmission, where small cell users (SCUs) and machine type communication (MTC) devices share the same resource block (RB) to increase the network capacity. We formulate an optimization problem to select efficient users and allocate transmission powers to SCUs and MTC devices. The object of optimization is to maximize the energy efficiency (EE) subject to the minimum spectral efficiency (SE) requirements and maximum transmission powers. We present a low computational complexity sub-optimum solution based on the non-cooperative game. An iterative algorithm with fast convergence speed and a reduced complexity search-based algorithm are respectively presented to solve the power control and user selection problems. The comparison between the proposed solution and optimum solution for different number of transmit antennas indicate that there is a small gap between SEs and EEs of the proposed and optimum solutions. Further, the results of user selection scheme demonstrate that the location of strong user affects the performance. We also derive analytical expressions for the outage probability which confirm Monte Carlo simulations.

SAPIUM: A Generic Framework for a Practical and Transparent Quantification of Thermal-Hydraulic Code Model Input Uncertainty

Uncertainty analysis is a key element in nuclear power plant deterministic safety analysis using best-estimate thermal-hydraulic codes and best-estimate-plus-uncertainty methodologies. If forward uncertainty propagation methods have now become mature for industrial applications, the input uncertainty quantification (IUQ) on the physical models still requires further investigations. The Organisation for Economic Co-operation and Development/Nuclear Energy Agency PREMIUM project attempted to benchmark the available IUQ methods, but observed a strong user effect due to the lack of best practices guidance. The SAPIUM project has been proposed toward the construction of a clear and shared systematic approach for IUQ. The main outcome of the project is a first “good-practices” document that can be exploited for safety study in order to reach consensus among experts on recommended practices as well as to identify remaining open issues for further developments. This paper describes the systematic approach that consists of five elements in a step-by-step approach to perform a meaningful model IUQ and validation as well as some good-practice guideline recommendations for each step.

Joint Beamforming and Phase Shift Design in Downlink UAV Networks with IRS-Assisted NOMA

This paper investigates a simple design of intelligent reflecting surface (IRS) based unmanned aerial vehicles (UAV) assisted multiple-input single-output nonorthogonal multiple access (NOMA) downlink network. The aim of this paper is to maximize the rate of the strong user while guaranteeing the target rate of the weak user given by the optimized UAV horizontal position. We first optimize the location of IRS-UAV. Then we propose an iterative algorithm to optimize the transmit beamforming and phase shift of IRS alternatively. For the beamforming optimization, the closed-form expressions of the optimal beamforming vectors are derived. Then, given by the obtained beamforming, we propose two methods to obtain the optimal phase shifting of IRS. One is the semidefinite relaxation based iteration algorithm which provides high data rate and the other one is based on successive convex approximation technique which has low complexity. Finally, simulation results are provided to show that the performance of the two proposed algorithms are significantly better than using random phase shifting scenario and IRS based UAV-assisted orthogonal frequency-division multiple access scheme.

Performance Analysis of Uplink NOMA-Relevant Strategy Under Statistical Delay QoS Constraints

A new multiple access (MA) strategy, referred to as non orthogonal multiple access - Relevant (NOMA-R), allows selecting NOMA when this increases all individual rates, i.e., it is beneficial for both strong(er) and weak(er) individual users. This letter provides a performance analysis of the NOMA-R strategy in uplink networks with statistical delay constraints. Closed-form expressions of the effective capacity (EC) are provided in two-users networks, showing that the strong user always achieves a higher EC with NOMA-R. Regarding the network's sum EC, there are distinctive gains with NOMA-R, particularly under stringent delay constraints.

A Novel Multiserver Authentication Scheme Using Proxy Resignature With Scalability and Strong User Anonymity

As the indispensable part of the security demand in a distributed system, a variety of online services need to be protected from unauthorized access. Multiserver authentication (MA) is one of the most effective and promising approaches to guarantee one party the authenticity of its partner in the distributed system. In this article, we first elaborate the problem of scalability for MA protocol. After that, a two-level framework for multiserver environment is proposed to convert single-server authentication to MA with provable security and perfect scalability. Also, we give an instance of our novel infrastructure by adopting the idea of proxy resignature to achieve strong anonymity. Furthermore, the security analysis and performance evaluation show that our protocol is secure and practical.