Overall Outage Probability Research Articles

Two-way communications empowered by reconfigurable intelligent surfaces and direct link: Outage analysis under hardware impairments and Nakagami-m fading

In this article, we consider a two-way communication system empowered by a reconfigurable intelligent surface (RIS), consisting of N passive reflective elements, in the presence of transceiver hardware impairments (HIs). To exploit the existence of a direct link between the end communication nodes, we utilize two time slots for their information exchange. We particularly analyze the instantaneous end-to-end signal-to-noise-plus-distortion-ratios (SNDRs) under HIs. The exact distribution of the magnitude of the end-to-end channel coefficients of the studied RIS-empowered communication system is derived under HIs and Nakagami-m fading channels. Using different settings for the level of HIs and the transmit powers at the end nodes, we also deduce novel exact and upper bound analytical expressions for the overall outage probability (OOP). For the high signal-to-noise ratio regime, an asymptotic OOP analysis is derived, which unveils the system’s diversity order. The presented numerical and simulation results corroborate our derived analytical findings, and demonstrate the impact of different system and channel parameters on the system’s OOP performance.

Enhancing the performance of downlink NOMA relaying networks by RF energy harvesting and data buffering at relay

Recently, non-orthogonal multiple access (NOMA) and energy harvesting (EH) from radio frequency (RF) have been considered as promising candidates for next-generation mobile communications. In this paper, we investigate a novel solution to enhance the reliability and the supply stability of a downlink NOMA relaying networks, in which we integrate two techniques: (i) simultaneous wireless information and power transfer, i.e. the relay node can harvest the energy from source signals and use this energy to help forward information from source node to two user nodes; and (ii) data buffer aid at relay node, i.e. the data packets received from the source can be stored in a buffer and then be re-transmitted to the destination nodes only when the channel condition is good. The performance of the proposed system is analyzed rigorously to derive the system outage probability (OP), throughput and the average packet delay. Furthermore, a power allocation optimization problem to minimize the OP is formulated and solution to this problem is also provided. In addition, the optimal transmission rates to maximize the throughput of each user are presented in numerical results. Monte Carlo simulations are conducted to verify the analytical results, which confirms that with data buffer at relay, the overall outage probability (OOP) can be reduced significantly.

Defeating Jamming Using Outage Performance Aware Joint Power Allocation and Access Point Placement in Uplink Pairwise NOMA

In this paper, an uplink pairwise Non-Orthogonal Multiple Access (NOMA) scenario using a mobile access point (AP) or an unmanned aerial vehicle in the presence of a jamming attack is considered. To mitigate the influence of the jamming attack, a joint power allocation and AP placement design is proposed. Accordingly, closed-form expressions of the overall outage probability (OOP) and the individual outage probability (IOP) considering imperfect channel state information for each of the source nodes the AP serves, are derived over Nakagami- $m$ fading channels using dynamic decoding order and fixed pairwise power allocation. We conduct an investigation of the effect of different parameters such as power allocation, source node placements, AP placement, target rates, and jammer location on the OOP and the IOP performance. By adapting the power allocation and the AP placement to the jamming attack, the communication reliability can be increased significantly compared to neglecting the presence of the jammer or treating the jammer as noise. Since the malicious jammer and the AP have conflicting interests in terms of communication reliability, we formulate a non-cooperative game for the two players considering their positions and the power allocation of the NOMA nodes as their strategies and the OOP as utility function. We propose using hybrid simulated annealing - greedy algorithms to address the joint power allocation and AP placement problem for the cases of both a fixed and a mobile jammer. Finally, the Nash equilibrium points are obtained and then the UAV goes directly to this position and keeps staying there to save power consumption.

On the performance of AF full FSO two-way relay networks over exponentiated Weibull fading channels

This work implements free space optical communication (FSO) in an amplify-and-forward (AF) two-way relay network (TWRN) to exploit the advantages of spectral efficiency, full-duplex Gigabit throughput, license-free spectrum, easy installation and to overcome the limitations of free space optical communication due to distance dependent turbulence induced fading. To quantify the performance of the proposed scheme, overall outage probability (OOP) and ergodic sum rate (ESR) expressions are derived over Exponentiated Weibull (EW) fading channels. The simple theoretical results which are validated with the Monte-Carlo simulations show that a system designer can get a quick idea about the FSO TWRN without resorting to complex prototypes or simulations.

Multiuser Full-Duplex IoT Networks With Wireless-Powered Relaying: Performance Analysis and Energy Efficiency Optimization

This paper considers an Internet-of-Things (IoT) network where a multi-antenna access point (AP) and several single-antenna IoT devices (IoDs), operating under the full-duplex (FD) mode, communicate with each other bidirectionally through the help of a wireless-powered FD relay. In particular, the power splitting (PS) protocol is adopted at the amplify-and-forward (AF) relay to implement a simultaneous wireless information and power transfer (SWIPT) receiver. For such a multiuser FD-IoT network assisted by a wireless-powered two-way relay, we derive exact overall outage probability (OOP) expressions and tight closed-form expressions for the ergodic sum rate (ESR) under generalized Nakagami-m fading channels. Furthermore, aiming to maximize the energy efficiency (EE), we obtain optimal power allocation (OPA) under the total power and rate threshold constraints. Finally, extensive numerical and simulation results are presented to corroborate our analytical findings.

Outage Performance of Pairwise NOMA Allowing a Dynamic Decoding Order and Optimal Pairs of Power Levels

In this article, we evaluate the overall outage probability (OOP) of pairwise Non-orthogonal Multiple Access (NOMA) for both uplink and downlink. We also propose a dynamic decoding order (DDO) together with a fixed pairwise power allocation (FPPA) scheme, in which the optimal decoding order is decided based on the instantaneous channel gains, and thereafter, a pair of power levels is assigned in accordance with the selected decoding order. Exact closed-form expressions of the OOPs for both uplink and downlink pairwise NOMA considering all proposed decoding orders over Nakagami-m fading are derived. Further, we find the optimal fixed power levels for different power allocation strategies so that the OOPs are minimized. Moreover, we investigate the influence of the distances between the source nodes and the access point (AP), the target transfer rates and the path-loss exponents on the OOPs for all cases of decoding orders. In addition, we benchmark our proposed DDO against other decoding orders in terms of the OOP. The results show that assigning optimal fixed power levels which takes the instantaneous decoding order into account not only improves the communication reliability, but also reduces the complexity and computational load at the AP.

Performance analysis for interference limited two‐way relay network with antenna selection

This study presents the performance analysis of multiple-antenna two-way amplify-and-forward relay network in an interference-limited environment. To avoid the high feedback overhead and to fully exploit a multiple-antenna diversity, the authors employ transmit and receive antenna selection at the user node and analog network coding at the relaying node. Specifically, they formulate the exact expressions of the generalised signal-to-interference-plus-noise ratio (SINR). On the basis of the derived SINR, the upper-bounded cumulative distribution function is obtained. Subsequently, the outage probability (OP) and symbol error rate (SER) are determined and investigated. To assess the overall performance of the system, they present approximate but simple expressions for the overall OP (OOP) and overall SER. To gain insights, asymptotic expressions of OP and OOP are provided, which enable the characterisation of the achievable coding gain and diversity order of the system. Besides, they derive upper bounds on the achievable rate based on Jensen's inequality. Furthermore, they formulate three optimisation problems to minimise outage, namely optimal relay location under fixed power allocation, optimal power allocation under fixed relay location, and joint ORL and power allocation. Finally, the tightness of their analysis is attested through Monte Carlo simulation.

Outage analysis for multiuser underlay cognitive TWRN with antenna selection and user scheduling

This paper investigates the outage performance of cellular two-way amplify-and-forward (AF) cooperative spectrum sharing systems in the presence of primary user (PU) network and multiple secondary user (SU) destinations. A general Nakagami-m fading environment has been used, where distinct fading parameters, as well as unequal average fading powers between the interference and relaying links, are assumed. Focusing on the cooperation process among the SU nodes and making use of the underlay cognitive approach, an approximate closed-form expression for the overall outage probability (OOP) of the secondary network is derived. In this analysis, an opportunistic scheduling and transmit antenna selection (TAS) algorithm in the secondary network has been employed. Considering the interference constraints due to the presence of PU receiver, power allocation of secondary user is done. The effects of fading severity, secondary network relay placement, the number of PU & SU transmit antenna, and number of SUs on the end-to-end system performance are examined through some representative numerical plots. Moreover, to minimize the secondary network OOP, we investigate the optimization problems of relay position. Monte Carlo simulation results are presented to corroborate the proposed analysis.

Performance Evaluation and Optimization of Traffic-Aware Cellular Multiuser Two-Way Relay Networks Over Nakagami-<italic>m</italic> Fading

We consider a cellular multiuser two-way relay network, where a multiantenna base station communicates with one of the several single-antenna mobile stations via a single-antenna relay terminal. We derive the exact and asymptotic overall outage probability (OOP) expressions of the considered system with asymmetric traffic under Nakagami- m fading. Based on the asymptotic analysis, we formulate three optimization problems, namely, optimal power allocation (OPA) with fixed relay location, optimal relay location with fixed power allocation, and jointly OPA and relay location to minimize the OOP. Specifically, we investigate two OPA schemes, called OPA I and OPA II. To this end, OPA I provides the solutions for individual transmit powers at each terminal, whereas under OPA II, relay terminal is assigned with half of the total power and the remaining power is allocated to the end terminals. The numerical and simulation results corroborate our theoretical findings, and reveal that under highly asymmetric traffic, OPA I can achieve a significant OOP performance than OPA II for different relay locations, except at the relay location where both coincide. Under symmetric traffic, OPA I outperforms OPA II, irrespective of relay locations. The OOP performance can be further improved if the power allocation and relay location are jointly optimized, especially under unbalanced conditions.

Beamforming in Traffic-Aware Two-Way Relay Systems With Channel Estimation Error and Feedback Delay

This paper presents a comprehensive performance analysis of a multi-antenna-based traffic-aware two-way relay system with unavoidable imperfections in channel state information (CSI) under Nakagami-m fading. Herein, we employ transmit/receive beamforming at source nodes and analog network coding (ANC) at the relay node in the presence of CSI imperfections due to channel estimation errors (CEE) and feedback delay. With such a practical setup, we first deduce the pertinent instantaneous end-to-end signal-to-noise ratios (SNRs) after performing partial self-interference cancellation. Then, by imposing asymmetric traffic requirements in two opposite directions, we conduct an accurate analysis of overall outage probability (OOP) of the considered system. We further derive a tight lower bound on OOP that has a simple and compact closed-form representation. Moreover, based on the asymptotic OOP expression at high SNR, we examine the achievable diversity order of the system. In addition, we acquire an upper bound expression of ergodic sum-rate (ESR) and simplify it further in useful compact form for high SNR regime. Besides, we investigate the optimization problems of relay position to minimize the OOP and to maximize the ESR. Numerical and simulation results validate our theoretical analysis and highlight the impact of CEE and feedback delay under various traffic patterns on the overall system performance.

Impact of Outdated Channel Estimates on Opportunistic Two-Way ANC-Based Relaying With Three-Phase Transmissions

In this paper, we investigate the impact of outdated channel estimates on the overall performance of a two-way multirelay system that employs a three-phase (3P) analog network coding (ANC)-based opportunistic relay selection (ORS) scheme under Rayleigh fading. Specifically, considering the imperfect estimation and the time variation of the fading channels, we formulate the 3P ANC-based ORS strategy for the best relay among multiple relays in terms of both outdated and imperfect channel state information (CSI). With such a practical CSI modeling, we derive a tight lower bound expression for the overall outage probability (OOP) and an upper bound expression for the ergodic sum-rate (ESR) of the considered scheme. In addition, by deriving an asymptotic outage behavior in the high signal-to-noise ratio (SNR) regime, we highlight the impact of outdated and imperfect CSI on the achievable diversity order. Moreover, based on the asymptotic analysis, we investigate three optimization problems, namely, optimal relay power allocation for fixed relay location, optimal relay location for fixed power allocation, and jointly optimal relay power allocation and location to minimize the OOP and to maximize the ESR of the considered system. Our results reveal that the optimal relay power allocation has a more significant impact on the performance when the CSI is imperfect, whereas the optimal relay location has a more noticeable impact when the CSI is outdated and unbalanced over the two hops. Furthermore, we show that the imperfect CSI can degrade system performance more severely than the outdated CSI, and it can even reduce the system diversity order to zero. The numerical and simulation results corroborate our theoretical analysis and findings and demonstrate that the 3P ANC-based ORS scheme can achieve better performance than its two-phase counterpart, depending upon the quality of the direct link, particularly in the medium-to-high-SNR regime.

Performance Analysis of Cognitive Spectrum Sharing with Time Division Broadcast Protocol

We investigate the performance of a cognitive spectrum sharing system where a best selected secondary user (SU) assists two-way communication between two primary users (PUs) by employing time division broadcast over Rayleigh channels. We derive tight lower-bound expressions for the overall outage probability (OOP) of both the primary and secondary systems of the considered scheme. We also provide valuable insights into the achievable diversity order, cell coverage, and optimal power allocation factor to ensure spectrum sharing. Numerical and simulation results corroborate the theoretical analysis and illustrate the effectiveness of the considered scheme.

Performance analysis of femtocells network with co-channel interference

In this paper, we will provide the performance analysis of a small cell network employing linear precoding at the base stations. The locations of the base stations are assumed to be Poisson distributed. Exact closed-form expressions for overall outage probability (OOP), symbol error probability (SEP) and capacity are derived, and an asymptotic approximation for both metrics are also investigated. Later numerical results will verify the accuracy of our analysis results. Moreover, we also propose a new access mechanism to maximize the system energy efficiency, and then evaluate the system performance analytically. Both theoretical and numerical results will together show that our proposed mechanism can improve the energy-efficiency of the small cell heterogeneous network effectively.

Performance Analysis of Two-Way AF Cooperative Relay Networks over Weibull Fading Channels

The performance of two-way amplify-and-forward (AF) cooperative relay networks over independent but not necessarily identically distributed Weibull fading channels is studied. Tight closed form approximations for the overall outage probability (OOP) and the average symbol error probability (ASEP) are derived. The analysis is verified by simulation, and the accuracy is shown to be excellent, especially at high signal noise ratio (SNR). According to the analysis, increasing the fading parameter, the power scaling parameter, or the number of relays, can improve the system performance when the best relay is selected.

On the Finite-SNR DMT of Two-Way AF Relaying with Imperfect CSI

A general framework of finite-SNR diversity-multiplexing tradeoff (DMT) is formulated to evaluate the impact of imperfect channel estimation in two-way amplify-and-forward (AF) relaying systems over Nakagami-m fading channels. Imperfect self-interference cancellation and signal detection are performed at both sources due to channel estimation errors. The overall outage probability (OOP) is obtained and then the finite-SNR DMT is derived in the presence of channel estimation errors. Furthermore, the asymptotic and limiting behavior expressions of the finite-SNR DMT are also evaluated adequately. Numerical results verify the theoretical analysis and show that at realistic SNR and channel estimation quality, the DMT is significantly lower than the asymptotic result.

Performance analysis of two-way Amplify-and-Forward relaying system with multiple interferers at the relay

In this paper, we investigate the performance of the two-way Amplify-and-Forward (AF) relaying systems in an interference-limited Rayleigh fading environment. More specifically, assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources, an approximate closed-form expression for the Overall Outage Probability (OOP) and an integral expression for the average Symbol Error Probability (SEP) are derived. The analysis results are verified through comparison with the Monte Carlo simulation results.

Symbol Error Probability of Two-Way Amplify-and-Forward Relaying

The overall outage probability (OOP) and symbol error probability (SEP) of a two-way amplify-and-forward (AF) relaying system are investigated. Tight closed-form expressions for the OOP and average SEP are derived for single-relay two-way AF systems. Further, in the case of multiple-relay two-way relaying, a tight closed-form expression for the OOP and an asymptotic approximation to the average SEP are obtained, respectively. Using these expressions, one can evaluate the outage and SEP performance of a two-way relaying system easily and fast.