Multiple User Access Research Articles

Opca: Enabling Optimistic Concurrent Access for Multiple Users in Oblivious Data Storage

Opca: Enabling Optimistic Concurrent Access for Multiple Users in Oblivious Data Storage

STAR-RIS aided NOMA Networks: A Signal Enhancement Algorithm

In order to overcome the reflecting-only issue of the conventional reconfigurable intelligent surface (RIS), simultaneous-transmitting-and-reflecting reconfigurable intelligent surface (STAR-RIS) stands as a potential solution for providing access services to the users located at the full space. By utilizing the omnidirectional properties of STAR-RIS, non-orthogonal multiple access (NOMA) users on both sides can be served simultaneously. By making the signal reflected by STAR-RIS coherent superposition with the direct signal, using the Riemannian optimization algorithm (ROA), the proposed signal enhancement algorithm can greatly enhance the signal power of NOMA users, reduce the outage probability, and improve the ergodic rate performance. According to the simulation results, the random phase STAR-RIS can improve the spectral efficiency of 3.6bit/s/Hz compared without STAR-RIS. After using the proposed ROA, the spectral efficiency can be extra increased by 1.8bit/s/Hz, which verifies the superiority of the proposed algorithm.

QoS-Oriented uplink OFDMA random access for the next-gen WLAN

Abstract OFDMA, introduced by the IEEE 802.11ax standard, divides the channel into multiple resource units (RUs), enabling parallel access for multiple users. On this basis, we propose a QoS-oriented double arbitration random access (Q-DARA) scheme. This scheme ensures high-priority priority access through priority arbitration in the first phase and random code arbitration in the second phase. It can also greatly reduce collisions and effectively guarantee the QoS of high-priority traffic. Simulation shows that our proposed scheme has better performance on throughput and latency. Compared to the traditional EDCA, the throughput and latency increase by more than 70%. Compared to the PATB scheme, the throughput increases by about 20%, and the latency increases by about 23%. Moreover, our proposed scheme has almost no changes to the protocol and is suitable for 802.11ax and beyond.

Joint task offloading and resource allocation for secure OFDMA-based mobile edge computing systems

With the advent of the fifth generation (5G) era, Mobile edge computing (MEC) has become a promising technology. In order to increase the spectrum utilization efficiency and mitigate interference between users, Orthogonal Frequency-Division Multiple Access (OFDMA) technology is introduced into MEC systems. However, uplink offloading signals from users to servers are vulnerable to malicious eavesdropping. We utilize physical layer security, specifically, jamming caused by servers and co-frequency interference provided by users in non-orthogonal multiple access (NOMA) groups to address this issue. This paper investigates an OFDMA based MEC system which consists of multiple users, multiple servers and an eavesdropper. For this system, an innovative algorithm is designed to minimize latency of the system through optimizing resource allocation and task offloading policy which has lower computation complexity while ensuring its security. The proposed scheme can decrease system latency and ensure secure communication according to experimental results.

Modelling and Compensation of SIC Imperfection in IRS-NOMA based 5G-System

This article considers the impairments in the application of successive interference cancellation (SIC) at the detection phase of non-orthogonal multiple access (NOMA) users. A practical approach is proposed to model the SIC impairment which takes into account the number of multiplexed users in NOMA’s power domain, in addition to the overall number of shared radio resources. In such case the imperfection of the SIC varies in accordance with the number of users. This strategy is closer to the situation in practice than the case where the SIC is modeled with fixed error factor as in the previous research articles that already considered the matter. A channel estimation approach is also proposed, which depends on the user’s channel gain variations to predict the change in its peers’ channel so as to compensate for the error resulting from SIC imperfection. The outcome of the proposed compensation strategy is promising as the simulation results reflect significant improvement in the achievable rate and energy efficiency.

Performance Study of Downlink Users in Non-Orthogonal Multiple Access (NOMA) for 5G Communications

An outline of NOMA principles is provided in this article. Furthermore, this page discusses cooperative NOMA and its variations, explains power allocation in detail as a technique of resource allocation for NOMA, and gives an overview of the research challenges related to NOMA. We then, use a two-case scenario, to suggest a dynamic power allocation (DPA) plan for the downlink NOMA users, albeit it can also be expanded to many use cases. The DPA relies on channel state information (CSI) to guarantee the quality of service (QOS) for cell center customers (user c). The Outage probability (OP) as a critical performance criterion simulation data is also provided, and they demonstrate a notable performance improvement when DPA is employed compared to fixed power allocation.

Hierarchical Multiple Access for Spectrum-Energy Opportunistic Ambient Backscatter Wireless Networks

Recently, ambient backscatter communication has become a promising technology to support the low-power and low-cost Internet-of-Things (IoT). However, the nondeterministic and sporadic nature of ambient signals makes it a great challenge when designing multiple access in spectrum opportunistic ambient backscatter wireless networks (AmBWNs). Moreover, the stringent energy supply and ultra-low-cost design of the backscatter transmitter make most multiple access schemes no longer suitable for AmBWNs. To effectively share carrier frequency resources for backscattering, we propose a hierarchical multiple access scheme, which allows beamforming based spatial division multiple access among groups, and non-orthogonal multiple access (NOMA) for multiple users access within a group. Consequently, we formulate a multi-objective optimization problem to balance the sum rate and the fairness by exploiting grouping, beamforming, and reflection coefficients. To solve this problem, we employ the matching theory to tackle the grouping problem and achieve the corresponding beamforming. We then reformulate the non-convex reflection coefficient optimization and solve it with successive convex approximation and geometric programming. Our extensive evaluation results demonstrate that the spectrum and energy efficiency, latency, and fairness can be significantly improved with minimal overhead at the transmitter.

A Novel Authentication Scheme Supporting Multiple User Access for 5G and Beyond

A Novel Authentication Scheme Supporting Multiple User Access for 5G and Beyond

Dynamic Power Allocation as a Way of Improving the Performance of Users in Non-Orthogonal Multiple Access (NOMA) for 5G Communications

Dynamic Power Allocation as a Way of Improving the Performance of Users in Non-Orthogonal Multiple Access (NOMA) for 5G Communications

Dynamic Power Allocation as a Way of Improving the Performance of Users in Non-Orthogonal Multiple Access (NOMA) for 5G Communications

Dynamic Power Allocation as a Way of Improving the Performance of Users in Non-Orthogonal Multiple Access (NOMA) for 5G Communications

The iMHere 2.0 System for Family Caregivers of Older Adults: A Focus Group.

Family caregivers with continuous caregiving responsibilities are at increased risk for adverse physical and mental health outcomes. In response to the challenges of caregiving, a mobile health system (iMHere 2.0) was developed to support caregivers. The study's objective was to gather feedback from family caregivers of older adults on the current features of iMHere 2.0 and to formulate design criteria for future iterations of the system. An exploratory qualitative study with thematic analyses of focus group feedback. A total of 10 caregivers of older adults participated in a focus group. Five themes emerged: (1) Monitoring health data, (2) Setting up customized reminders, (3) Supporting care coordination, (4) Balancing security and multiple user access, and (5) Disseminating iMHere 2.0 into the community, along with some potential barriers to implementation. Design criteria were developed to provide a framework for iterative design and development of the iMHere system to support caregivers of older adults.

Green NOMA based MU-MIMO transmission for MEC in 6G Networks

Mobile edge computing (MEC) is a distributed computing paradigm that brings computing and data storage closer to the network’s edge. This paper considers a multiple-input multiple-output (MIMO) uplink scenario where non-orthogonal multiple access (NOMA) users partially offload their data to a MEC server. The objective of this study is to minimize the total energy consumption during local computing, task offloading, and MEC computing. To this end, the base station optimizes power allocation vectors and task assignment coefficients under time and power constraints. The generalized singular value decomposition-based linear beamforming method integrates NOMA, MIMO, and MEC technologies. Due to the non-convex nature of the problem, a successive convex optimization (SCA) and alternation optimization (AO) based low-complex solution is proposed. The impact of the delay tolerance, the size of the offloaded task, and the distance of the users are investigated concerning energy consumption. The simulation results show that the proposed method achieves better energy performance than the orthogonal multiple access (OMA) schemes. More importantly, the performance gap increases when the data size is large, and the delay requirement is stringent, as 6G networks require.

An optimal algorithm for energy harvesting in optical networks

Optical fiber cables, which make up the majority of the world's telecommunications infrastructure, now carry the vast majority of digital data. However, because to the Internet's exponential expansion and a slew of bandwidth-hungry new services like online gaming, 3D or high-definition television, and cloud computing, this infrastructure will soon run out of capacity. The growing need for faster transmission speeds by clients has led to the development of heterogeneous optical networks. High throughput, portability, and future information interconnects may all be accommodated by such a system. Delivering such high-capacity connections to a mobile client should need heterogeneous optical networks. Different multiple access user technologies have been suggested to meet the needs of a group of future heterogeneous optical network users. In order to address the high energy consumption, poor QoS and low resource utilization in cloud radio access network, this paper proposed a novel algorithm. The main idea is to allocate virtual resources with energy-awareness and hybrid energy supply. Then, the energy arrival and consumption models were established based on different network devices. Simulation results show that the proposed algorithm effectively improved the energy consumption performance and QoS as compared with existing methods.

A Powerful Joint Modulation and STBC Identification Algorithm for Multiuser Uplink SC-FDMA Transmissions

Owing to the rapid development and broad adoption of multiple antenna communication systems over the past few years, space-time block coding (STBC) identification has emerged as a crucial responsibility for smart radios. The majority of previous analysis of STBC identification assumed that the utilized modulation schemes for single-user and uncoded broadcasts were known. This paper investigates the challenge of joint STBC and modulation identification for uplink transmissions with numerous users in single-carrier frequency division multiple access (SC-FDMA) systems using coded transmissions. Multi-user channel estimation brings us one step closer to implementing the proposed design in real-world systems. We additionally employ the channel decoder’s deliverables, which are common in many real-world systems, to enhance the identifying and estimating procedures. Mathematical findings prove that a recursive approach can be utilized to tackle the maximum likelihood (ML) problem of simultaneous STBC and modulation identification with channel estimation. Distinguishing the superimposed signals that originate at the base-station (BS) is accomplished with the use of the space-alternating generalized expectation-maximization (SAGE) algorithm. After that, an expectation-maximization (EM) engine is deployed to make the necessary adjustments to the parameters being considered for each user. The success of the above-mentioned architecture for usage in practical applications is demonstrated by the simulation results obtained under various conditions.

Анализ безопасности систем NOMA

Existing Physical Layer Security (PLS) schemes for NOMA are either based on cryptography-based approaches or are limited to approaches that require high processing complexity and key sharing. The conventional NOMA system suffers from security risks and weaknesses, such as being prone to external or internal eavesdropping. By sending NOMA messages to multiple users at the same time on the same resources, there is a risk that an unauthorized user could eavesdrop on or access multiple users' information if the NOMA transmission is successfully intercepted. The NOMA system is susceptible to internal interception when protecting confidential data in cases where untrusted users are present. Therefore, traditional methods of data exchange cannot provide the required level of secrecy for NOMA systems. The results. The work uses non-orthogonal access (NOMA) technology and security assessment of various wireless communication systems using NOMA, such as cognitive radio networks, systems with support for relaying the IoT mode, as well as the D2D mode. The results of the analysis of security characteristics and operation of the NOMA system in different modes are presented.

Outage Probability of Aerial Base Station NOMA MIMO Wireless Communication With RF Energy Harvesting

In this work, we consider a base station (BS) mounted on an unmanned aerial vehicle (UAV) called as an aerial BS (ABS). The ABS is equipped with multiple antennas to assist two pairs of users in nonorthogonal multiple access (NOMA) scheme, and it serves as a relay station to forward the data from the uplink to the downlink of ground IoT users in half-duplex mode. Moreover, the communication power of ABS is harvested from ambient radio-frequency (RF) sources, such as television (TV) and radio signals via the time switching mechanism. In order to improve the efficiency of harvested energy, multiple antennas at the TV/radio tower and the maximal-ratio transmission (MRT) scheme are applied. The proposed ABS RF energy harvesting system overcomes the problem of connectivity of ground IoT users and the energy limitation of devices. The system performance is evaluated in terms of the outage probability of each pair of IoT users in various urban communication environments. Monte Carlo simulation results are provided to validate the accuracy of the developed analytical results and also demonstrate the performance of the proposed system. The results show that the proposed system achieves better performance than that of benchmark systems and the performance can be improved significantly by adjusting the UAV’s altitude.

BER performance analysis of asynchronous NOMA with arbitrary phase offset

An asynchronous transmission scenario for non-orthogonal multiple access (NOMA) user signals with arbitrary phase offset is investigated in this paper. To improve the system performance in the user power-balanced conditions, we adopt a synthetic detection method at the receiver, i.e., the jointly optimal maximal likelihood detection aided triangular successive interference cancellation (JO ML-TSIC) method. Analytical bit error rate (BER) solutions are obtained for a two-user case with the optimal, intentional one-half symbol period time delay implemented between the user signals. Furthermore, closed-form BER solutions for the case using the triangular successive interference cancellation (TSIC) detection method are also derived for comparisons. Numerical results show that the JO ML-TSIC receiver for the asynchronous system outperforms the TSIC receiver as well as the synchronous successive interference cancellation (SIC) receiver in all the conditions concerned. The results also show that the superiority of the JO ML-TSIC receiver is strengthened when the signals experience flat Rayleigh fading channels compared to the TSIC and the synchronous SIC receivers.

Physical random access signal design for 5G mobile satellite communication systems

In view of the distinctive characteristics of satellite communication, the physical random access signals used in the terrestrial mobile communication system have to be modified or redesigned for the satellite communication system. In this paper, we boost the random access signal energy by repeating the short Zadoff–Chu (ZC) sequence based preamble signal used in the terrestrial system. Different long ZC sequences are used to scramble this cascaded sequence to distinguish different random access signals for multiple random access user equipments. For correlation performance optimization, properties of the roots for both the short and long ZC sequences are mathematically analyzed and derived. Finally, we illustrate how to construct a root set for these different long ZC sequences based on the obtained propositions in a practical way. This analytical framework provides a useful insight into ZC sequence-based random access signal design and performance analysis in mobile satellite communication systems.

On performance of full-duplex UAV system with multiple NOMA users and millimeter-wave communications

This article considers millimeter-wave (mmWave) communications in a full-duplex (FD) unmanned aerial vehicle (UAV) system with multiple non-orthogonal multiple access (NOMA) users. In particular, a UAV operates in an FD transmission mode and acts as a decode-and-forward (DF) relay to aid communications between a ground base station and multiple ground users. Unlike previous works on the UAV-aided NOMA systems, where the specific carrier frequencies are often ignored, this work investigates the effect of a specific carrier frequency in the mmWave band and the channel model proposed for the fifth and beyond generations (5G and B5G) of mobile communications. The closed-form expressions of outage probability (OP) and achievable data rate (ADR) of the FD-UAV-NOMA system with mmWave communications (called as the MW-FD-UAV-NOMA system) are successfully derived over Nakagami-m fading channels. Numerical results clearly indicate the strong effects of the residual self-interference (RSI), high frequency, far distances between transmitters and receivers, wide bandwidth, and the altitude of the UAV on the OP and ADR of the MW-FD-UAV-NOMA system. Since the mmWave communications are used, an increase in the frequency, distances, bandwidth, and/or altitude of the UAV will significantly reduce the performance of the MW-FD-UAV-NOMA system. Importantly, when the UAV flies nearer the base station, the performance of the MW-FD-UAV-NOMA system can be better than when the UAV flies nearer the users. Finally, the exactness of the obtained expressions is confirmed via Monte-Carlo simulations.

Ergodic capacity analysis of multiple IRS‐aided dual‐hop DF relaying system

Intelligent reflecting surface (IRS) is regarded as a promising emerging technology, which has shown enormous potentials for performance enhancement. This paper investigates the multiple IRS-aided dual-hop DF relaying system for both single-user and multi-user scenarios over Nakagami-m fading. Based on a scenario with non-orthogonal multiple access users, tight upper bounds for the ergodic capacity in perfect channel state information(pCSI) scenario are first derived, and then approximate expressions are obtained in imperfect CSI (ipCSI) mode. Moreover, the performance of multiple IRS-aided DF relaying system are compared with multi-IRSs-only system and DF relaying-only system. Finally, all the analytical results are verified using Monte Carlo simulations.