Outage Performance Of System Research Articles

Performance Analysis of Reflective Intelligent Surface Assisted Bidirectional Full‐Duplex Communication Systems Over Nakagami‐m$$ m $$ Fading Channels

ABSTRACTIn this paper, a passive reflective intelligent surface (RIS) assisted bidirectional full‐duplex (FD) wireless system in a realistic Nakagami‐ fading with reflective elements and two source nodes is proposed. The source nodes are equipped with dual antennas for FD mode transmission and reception. The primary cause of degradation in the performance of the FD system is self‐interference, which can be reduced by increasing the number of reflective elements on the meta‐surface. Analytical expressions have been derived for the proposed RIS‐aided bidirectional FD wireless systems in terms of outage probability and bit error rate (BER). Numerical results show that doubling the number of reflecting elements considerably improves the outage performance of the proposed system in terms of signal‐to‐noise ratio (SNR) compared with RIS‐assisted half‐duplex (HD) mode. Additionally, different modulation schemes have been employed to evaluate the BER performance of the proposed system. The accuracy of analytical expressions is validated by matching Monte Carlo with analytical simulations.

Modeling Analysis for Downlink RIS-UAV-Assisted NOMA over Air-to-Ground Line-of-Sight Rician Channels

This paper proposes a drone-assisted NOMA communication system equipped with a reconfigurable intelligent surface (RIS). Given the Line-of-Sight nature of the Air-to-Ground link, a more realistic Rician fading environment is chosen for the study of system performance. The user’s outage performance and secrecy outage probability of the RIS-UAV-assisted NOMA downlink communication under the Rician channels are investigated. Jointly considering the Line-of-Sight and Non-Line-of-Sight links, the closed-form expressions of each user’s outage probability are derived by approximating the composite channels as Rician distributions to characterize the channel coefficients of the system’s links. Considering the physical layer security in the presence of the eavesdropper, the secrecy outage probability of two users is further studied. The relationship between the system outage performance and the Rician factor of the channel, the number of RIS elements, and other factors are analyzed. The results of this study show that compared with Rayleigh fading, the Rician fading is more practical with the actual Air-to-Ground links; the user’s outage probability and the secrecy outage probability are lower over the Rician channels. The number of RIS elements and the power allocation factor by the base station for the users are inversely proportional to the user’s outage probability, and RIS element number, path loss index, and distance factor also have a greater impact on the outage probability. Compared with OMA, NOMA has a certain enhancement to the system performance.

Analysis of the outage performance of energy-harvesting cooperative-NOMA system with relay selection methods

Recent years have witnessed the remarkable progress in wireless communication systems due to the escalating demand for higher data rates, improved reliability, and increased energy efficiency. In this regard, Non-Orthogonal Multiple Access (NOMA) has emerged as a promising technology, enhancing spectral efficiency and accommodating multiple users concurrently within the same time and frequency resources. Simultaneously, the energy harvesting has surfaced as a sustainable solution, converting ambient environmental energy into usable electrical power for operating communication nodes. This paper proposes a cooperative NOMA transmission scheme integrating energy harvesting and utilizing Least Squares (LS) channel estimation for precise Channel State Information (CSI) acquisition. The objective is to establish an optimal communication path from source to destination. Relay selection methods: Optimal Relay Selection (ORS) and Max-Min Relay Selection (MMRS), are compared, focusing on their impact on the system performance. The analysis considers the influence of the number of relays and power allocation factor on the system, with a specific emphasis on the outage probability expressions. Comparative analysis between the cooperative-NOMA and the traditional cooperative relaying without NOMA reveals the superior performance of the cooperative-NOMA. Additionally, the ORS scheme outperforms MMRS in terms of the outage performance.

On the Performance of Noma Systems with Different User Grouping Strategies

This paper investigates several critical issues on the ergodic sum capacity and system outage performance of downlink non-orthogonal multiple access (NOMA) systems with different numbers of users per cluster sharing the same resource. The outcomes from this work suggest that NOMA systems with more users per cluster perform better under a low channel gain, while those with fewer users per cluster perform better under a high channel gain. It discloses a fact that a traditional NOMA system with a fixed user grouping scheme may not be a good choice to deal with complex channel conditions with diverse applications. To address the issue, this paper introduces a concept of mixed user grouping NOMA, which outperforms OMA and traditional NOMA significantly. The work in this paper lays a foundation for more further investigations on mixed user grouping NOMA systems.

Joint Power Allocation and Decoding Order Selection for NOMA Systems: Outage-Optimal Strategies

We investigate joint power allocation and decoding order selection (PA-DOS) aimed at enhancing the outage performance of non-orthogonal multiple access (NOMA) systems. By considering the diverse target rates of users, new important properties of NOMA are revealed: When users’ target rates satisfy certain conditions, the channel state information (CSI) is not required by PA-DOS to minimize the system outage probability, and different users’ outage probabilities can be minimized simultaneously; When such conditions are not satisfied, the opposite situation occurs. Following these properties, two PA-DOS strategies are designed regarding distinct user priorities, which ensure the minimization of the system outage probability and the user outage probability of the high-priority user. Especially, these strategies do not require CSI or only require one-bit CSI feedback depending on users’ target rates. Analytical and numerical results are provided to demonstrate that the proposed strategies significantly outperform the existing strategies in terms of both system and user outage performance. Furthermore, the results show that although under some target rates the minimum user outage probabilities cannot be simultaneously achieved, they can be closely approached at the same time in the high-signal-to-noise-ratio regime by the proposed strategies.

System outage probability and diversity analysis of a SWIPT based two-way DF relay network under transceiver hardware impairments

This paper investigates the system outage performance of a simultaneous wireless information and power transfer (SWIPT) based two-way decode-and-forward (DF) relay network, where potential hardware impairments (HIs) in all transceivers are considered. After harvesting energy and decoding messages simultaneously via a power splitting scheme, the energy-limited relay node forwards the decoded information to both terminals. Each terminal combines the signals from the direct and relaying links via selection combining. We derive the system outage probability under independent but non-identically distributed Nakagami-m fading channels. It reveals an overall system ceiling (OSC) effect, i.e., the system falls in outage if the target rate exceeds an OSC threshold that is determined by the levels of HIs. Furthermore, we derive the diversity gain of the considered network. The result reveals that when the transmission rate is below the OSC threshold, the achieved diversity gain equals the sum of the shape parameter of the direct link and the smaller shape parameter of the terminal-to-relay links; otherwise, the diversity gain is zero. This is different from the amplify-and-forward (AF) strategy, under which the relaying links have no contribution to the diversity gain. Simulation results validate the analytical results and reveal that compared with the AF strategy, the SWIPT based two-way relaying links under the DF strategy are more robust to HIs and achieve a lower system outage probability.

An Insight to the Outage Performance of Multi-Hop Mixed RF/FSO/UWOC System

In this paper, we investigate the outage performance of the three-hop mixed system integrating radio frequency (RF), free space optics (FSO), and under water optical communication (UWOC) system. The closed-form analytical expressions for the outage probability of the system are derived. In the considered system, the RF channel follows the Nakagami-m distribution, the FSO channel observes the Gamma-Gamma fading statistics, and the UWOC link experiences a mixture Exponential Generalized Gamma (EGG) fading distribution. To verify the derived analytical expressions, numerical simulations are also carried out, and we present the influence of the various link parameters such as path loss, atmospheric turbulence, pointing errors, angle-of-arrival fluctuations, water salinity, and scintillation on the performance of the decode and forward (DF) relayed multi-hop communication system.

On Secure Uplink Transmissions in Satellite-Aerial Systems

Satellite communication plays an increasingly important role in global wireless systems, which leads to rising concerns about the secure transmission of confidential information. In this paper, we investigate the secrecy outage performance of an uplink satellite-aerial communication system, in which an aerial platform (S) transmits its information over the uplink to a legitimate satellite(D), while an eavesdropping satellite (E) trying to overhear the information delivery between S and D. Specifically, considering the randomness of the positions of D and E and employing the geometric probability theory, a closed-form expression for the lower bound on the secrecy outage probability of the considered system is derived. Finally, Monte-Carlo simulations are conducted to verify our proposed analytical models.

Performance Analysis of Passive Retro-Reflector Based Tracking in Free-Space Optical Communications With Pointing Errors

In this correspondence, we propose a diversity-achieving retroreflector-based fine tracking system for free-space optical (FSO) communications. We show that multiple retroreflectors deployed around the communication telescope at the aerial vehicle save the payload capacity and enhance the outage performance of the fine tracking system. Through the analysis of the joint-pointing loss of the multiple retroreflectors, we derive the ordered moments of the received power. Our analysis can be further utilized for studies on multiple input multiple output (MIMO)-FSO. After the moment-based estimation of the received power distribution, we numerically analyze the outage performance. The greatest challenge of retroreflector-based FSO communication is a significant decrease in power. Still, our selected numerical results show that, from an outage perspective, the proposed method can surpass conventional methods.

Relay Selection for Dual-Hop Cooperative Ambient Backscatter Communication Systems.

Previous works only focus on the optimization design for the dual-hop cooperative ambient backscatter communication (AmBC) system with single-relay selection. The impact of relay selection on the outage performance of dual-hop cooperative AmBC systems is still missing. Motivated by this, in this paper, we investigate the outage performance of a dual-hop cooperative AmBC system with single-relay selection, where the backscatter link shares the receiver with the cellular link and the harmful direct-link interference (DLI) is mitigated by using successive interference cancellation (SIC). In the system considered, the selected relay has dual functions. One is to forward message for the cellular link, and the other is to act as the radio-frequency (RF) source for the backscatter device (BD). Specifically, after proposing two novel single-relay selection schemes (RSSs), namely reactive RSS and proactive RSS, we derive the closed-form outage probability (OP) expressions for both RSSs, which can be performed in a distributed manner. To gain more insights, the asymptotic OPs at high signal-to-noise ratio (SNR) are explored and the outage performance comparison between the reactive RSS and proactive RSS are also provided. Results show that the proposed reactive RSS is outage-optimal among all possible single-relay selection schemes. The theoretical analysis is validated by Monte Carlo simulations. The results also show that the relay selection scheme, the number of relays, the location of BD, and the reflection coefficient of BD have great impact on the outage performance of cooperative AmBC systems.

Physical Layer Security Performance Analysis for Relay-Aided Visible Light Communication System

The risk of information leakage increases when the relay technology is introduced to extend the communication range and improve the quality of communication services of cell-edge users in visible light communication (VLC) systems. To evaluate these security risks, physical layer security (PLS) performance for decode-and-forward (DF) relay-aided VLC system is investigated in this paper. Specifically, the theoretical expressions of the upper and lower bounds of the security outage probability (SOP) for the DF relay-aided VLC system under the amplitude constraint are obtained based on a stochastic geometry analysis method. Monte Carlo simulation validates the correctness of the derived theoretical expressions of the upper and lower bounds of the SOP. Moreover, simulation results show that the security outage performance of the DF relay-aided VLC system is deteriorated compared with the non-relay VLC system. Furthermore, the influences of the eavesdroppers' distribution density, the radiation radius of LED source, the radiation radius and deployment height of the relay on the SOP have been investigated. Last but not least, the optimal deployment height of the relay can be determined for achieving the optimum security outage performance. These parameters can effectively guide the design of the secure relay-aided VLC system.

Accurate Approximation to Channel Distributions of Cascaded RIS-Aided Systems With Phase Errors Over Nakagami-m Channels

Reconfigurable intelligent surfaces (RISs) are a promising technology foreseen to drive the development of beyond-fifth-generation (B5G) wireless networks. This paper proposes a novel accurate approximation to the channel distribution of cascaded RIS-aided wireless networks, with a reasonable assumption of phase errors, over Nakagami-m fading channels. Using the approximation, the probability density function (PDF) and outage probability (OP) expressions are derived for the end-to-end cascaded RIS-aided communication. Obtained PDF and OP formulas are valid for any number of cascaded RISs, n, and reflecting elements per individual RIS, N. The approximation accuracy is validated using the Kolmogorov-Smirnov goodness-of-fit test. Analytical results are verified by Monte Carlo simulations under different system parameters. Finally, derived expressions have been used to illustrate the impact of various important system parameters on the outage performance of the proposed system.

On the outage performance of multi-user NOMA system with adaptive SIC

The performance of non-orthogonal multiple-access (NOMA) is significantly determined by the successive interference cancellation (SIC) technique. However, the interference redundancy can happen during the NOMA receiver performing SIC. To tackle this issue, this paper proposes a novel adaptive successive interference cancellation (ASIC) method. Specifically, the decoding error is considered as interference during the SIC process, and an adaptive filter with various weights is introduced for detection error mitigation. For the multi-user downlink NOMA system, the outage probability is analyzed under conventional and the proposed SIC methods. Simulation results verify our analysis, which also demonstrate the superiority of the proposed ASIC method.

System Outage Performance of SWIPT Enabled Full-Duplex Two-Way Relaying With Residual Hardware Impairments and Self-Interference

This article investigates the joint impact of residual hardware impairments (RHIs) and residual self-interference (RSI) at all transceivers on the system outage performance for a simultaneous wireless information and power transfer (SWIPT) enabled full-duplex two-way decode-and-forward (DF) relay network. Considering a time switching scheme at the relay node, we derive the system outage probability in a closed-form, and further identify the overall system ceiling (OSC) effect caused by only RHIs. More specifically, when the data rate exceeds the OSC threshold determined by the RHIs level, the communication of the entire network ceases no matter what the signal-to-noise ratio is. In addition, we derive the achievable diversity gain of the considered network, and demonstrate that the diversity gain always equals zero due to the existence of RHIs and RSI. Finally, numerical simulations are provided to study the influence of multifarious network parameters on the system outage performance and the performance gap between the DF and amplify-and-forward strategies.

Free-Space Optical Communication Based on Mode Diversity Reception Using a Nonmode Selective Photonic Lantern and Equal Gain Combining

This paper experimentally investigates the perform-ance of free-space optical (FSO) communication based on mode diversity reception (MDR) using nonmode selective photonic lantern (NSPL) and equal gain combining (EGC). By employing a mode demultiplexer and combining technology in the receiver, the bit error rate (BER) and outage performance of FSO communication system can be significantly improved. However, different from diversity system with multiple receive apertures, the branches in mode diversity system are non-independent fading signals, which are influenced by not only atmospheric but also the modal crosstalk of mode demultiplexer. Therefore, we take into consideration the difference of mode demultiplexer and study four schemes for FSO mode diversity reception system: 1) NSPL with equal gain combining (NSPL-EGC), 2) NSPL with maximal ratio combining (NSPL-MRC), 3) mode selective photonic lantern with equal gain combining (MSPL-EGC), and 4) mode selective photonic lantern with equal gain combining (MSPL-MRC). Experimental results show that NSPL-EGC is the most suitable scheme for MDR with low implementation complexity, and the performance difference is less than 1 dB compared with the one using MRC at BER = 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> under turbulence from weak to strong.

Opportunistic Symbiotic Backscatter Communication Systems

This letter proposes an opportunistic commensal mechanism (OppCom) and an opportunistic parasitic mechanism (OppPar) for a pair of backscatter devices (BDs) to strengthen the concurrent transmission of the primary and the backscatter systems. It is shown that the asymptotic outage probability of the OppCom and OppPar mechanisms is not affected by the channel statistics between the two BDs. Also, for the OppPar mechanism, the backscatter efficiency ratio between the two BDs, instead of their individual values, dominates the system outage performance and a larger difference of the backscatter efficiencies leads to a better transmission robustness.

Outage analysis for user selection based downlink cooperative NOMA network over generalized fading channels

Recently, non-orthogonal multiple access (NOMA) scheme is integrated with cooperative communication (C-NOMA) to increase the connectivity and coverage area. In this paper, we analyzed the outage performance of downlink C-NOMA system with the imperfect successive interference cancellation (I-SIC) and imperfect channel state information (I-CSI) aiding multiple users over κ−μ and η−μ independent and identically distributed fading environments. Further, a user selection scheme is adopted for downlink C-NOMA scheme for enhancing the performance of the system. To be precise, the system model considers multiple users at the destination, out of which two users are selected to serve with NOMA standards. The analytical expressions of outage probability (OP) are derived, analyzed, and compared with cooperative-orthogonal multiple access (C-OMA) scheme over generalized fading environments. Moreover, the accuracy of analytical results is validated through Monte Carlo simulation. In addition, the analytical expression of OP for the paired user is also derived, analyzed, and correlated with the C-OMA scheme. Furthermore, through κ−μ and η−μ fading distribution, the outage performance of Rayleigh, Nakagami-m, Rice, Hoyt, and one-sided Gaussian fading environment is also investigated. From the obtained results, it is evident that when compared to C-OMA scheme, the C-NOMA scheme achieves 4.4 and 6.6 percentage gain in terms of SNR for a near user and a far user, respectively at κ=1.0,μ=1.0 to attain outage of 10−1. On the other hand, for the same outage, C-NOMA achieves 4.6 and 6.7 percentage gain in terms of SNR for a near user and a far user, respectively at η=1.0,μ=1.5.

Outage Performance of Multi-relay System with Energy Harvesting and Storage

&lt;p&gt;This paper analyzes the performance of a two-hop half-duplex multi-relay system based on energy harvesting. The relay has energy harvesting and storage functions, and adopts an adaptive AF/DF transmission strategy and PS protocol. Based on three relay selection schemes, namely Energy Optimal Selection (EOS), Channel Gain Optimal Selection (GOS), and Energy and Channel Gain Optimal Selection (EGOS), the outage performance is compared. First, the finite state Markov chain (FSMC) is used to model the energy arrival and use status of each relay, and the energy transfer steady-state matrix is obtained. Then we use the Gauss Chebyshev formula to derive the analytical expression of the communication outage probability (COP). Finally, an optimization model for minimizing the COP for three relay selection schemes is constructed. The EOS and GOS schemes optimize power allocation for energy harvesting and information transmission, and the EGOS scheme jointly optimizes power allocation and energy thresholds. We use a one-dimensional search algorithm based on the golden section and a two-dimensional search algorithm based on iteration to solve these optimization problems. The simulation results show that the EGOS is the best among the three relay selection schemes.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

On the Performance Optimization of Two-Way Hybrid VLC/RF-Based IoT System Over Cellular Spectrum

This paper investigates the system outage performance of a useful architecture of two-way hybrid visible light communication/radio frequency (VLC/RF) communication using overlay mode of cooperative cognitive radio network (CCRN). The demand of high data rate application can be fulfilled using VLC link and communication over a wide area of coverage with high reliability can be achieved through RF link. In the proposed architecture, cooperative communication between two licensed user (LU) nodes is accomplished via an aggregation agent (AA). AA can perform like a relay node and in return, it can access the LU spectrum for two-way communications with Internet-of-Things (IoT) device. First, closed form expressions of outage probability of both LU and IoT communication are established. On the basis of these expressions, optimization problems are formulated to achieve minimum outage probability of both LU and IoT network. The impacts of both VLC and RF system parameters on these systems outage probability and throughput are finally shown in simulation results.

Performance Analysis for DF Relay-Aided Visible Light Communication System With NOMA

Visible light communication (VLC) has been deemed to be one promising technique for the sixth-generation wireless communication network. However, due to the attenuation properties, the VLC ranges are usually limited. To unlock the advantage of multiple light-emitting diodes (LEDs) and extend the coverage of VLC systems, a relay-aided VLC system with non-orthogonal multiple access (NOMA) is proposed in this paper. Specifically, a decode-and-forward (DF) relay protocol is introduced to construct the relay-aided VLC system with NOMA. Moreover, the closed-form expression of the outage probability (OP) in the DF relay-aided VLC system with NOMA is derived to accurately characterize the theoretical performance of the system. Thereafter, the effects of the corresponding parameters on the OP are investigated. Simulation results verify the accuracy of the derived theoretical expression and illustrate that the DF relay-aided VLC system with NOMA can effectively improve system outage performance. Compared to the direct transmission NOMA VLC system without relay link, our scheme can obtain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{15}\,\text{dB}$</tex-math></inline-formula> transmit signal-to-noise ratio gains in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-3}$</tex-math></inline-formula> OP level. Last but not least, the optimal transmit semi-angle and deployment height of the relay can be determined for achieving the optimal system outage performance.