Outage Performance Of System Research Articles

Wireless-Powered Full-Duplex UAV Relay Networks Over FTR Channels

A thorough understanding of fundamental limits of wireless-powered unmanned aerial vehicle (UAV) relay networks in millimeter waves is still missing. We narrow this gap by investigating the outage performance of a UAV-assisted wireless network over fluctuating two-ray (FTR) channels. The FTR fading model is particularly appealing since well characterizes the wireless propagation in a wide range of frequencies, including those in millimeter waves. The proposed setup consists of a source-destination pair communicating with the assistance of a UAV, which is a wireless-powered relay station operating in full-duplex mode under the amplify-and-forward protocol. For the wireless energy harvesting at the UAV, wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT), and self-recycling energy techniques are employed together. To characterize the system outage probability, we obtain an integral-form expression derived from an approximate analysis and a simple closed-form expression derived from an asymptotic analysis at the high signal-to-noise ratio (SNR) regime. Monte Carlo simulations are provided to validate the correctness of our theoretical results and provide insights on the network performance in terms of key system parameters. Interestingly, obtained results show that the FTR fading parameters corresponding to the first hop and second hop play no role on the system outage performance at high SNR. Instead, it is mainly governed by the effect of the residual self-interference at the UAV, leading to outage floors.

Performance Analysis of NOMA-Based AF Cooperative Overlay System With Imperfect CSI and SIC

This paper studies a new amplify-and-forward cooperative overlay cognitive radio (CR) non-orthogonal multiple access (AFCO-NOMA) system, where a primary network shares its license spectrum with a secondary network by using NOMA principles. An approximate closed-form expression for the outage probability of the proposed system is analyzed. Asymptotic expressions for the outage probability in high signal-to-noise ratio (SNR) regime of both secondary and primary destinations are derived assuming channel estimation error (CEE) and imperfect successive interference cancellation (SIC). Further, the optimal power allocation coefficients to maximize the system throughput for different target rates are determined to ensure priority to the primary user. The diversity order at the primary and secondary destinations are also derived. Moreover, the AFCO-NOMA system is compared with the OMA-based cooperative overlay system in terms of outage probability. The paper also studies the impact of various parameters such as power allocation coefficients, CEE, and detection threshold, on the outage performance of the proposed system. Monte Carlo simulations are used to confirm the correctness of the derived analytical results.

Joint Effects of Imperfect CSI and SIC on NOMA Based Satellite-Terrestrial Systems

This paper investigates a satellite-terrestrial system employing the non-orthogonal multiple access (NOMA) scheme over Shadowed-Rician fading channels. The effects of both imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) on the NOMA based satellite-terrestrial system are taken into account. First, the outage performance of the proposed system is evaluated, and the closed-form expressions for the exact and asymptotic outage probabilities are obtained. Next, the expressions of the ergodic sum rate and system throughput are derived in the presence of channel estimation errors and residual interference. Moreover, we analyze the impacts of different residual interference levels on the energy efficiency. Finally, the numerical simulation results are conducted to verify the correctness of theoretical analysis and the advantages of the proposed NOMA scheme. At medium-high SNR region, the NOMA users are capable of outperforming orthogonal multiple access (OMA) users in terms of outage behaviors and system throughput with imperfect CSI and imperfect SIC. The ergodic sum rate decreases as the level of residual interference $\varpi $ increases, and is even lower than that of OMA once $\varpi $ goes beyond a certain value. Additionally, the energy efficiency of NOMA scheme is sensitive to the imperfect SIC.

CR‐NOMA Networks over Nakagami‐m Fading: CSI Imperfection Perspective

There are high demands on both massive connections and high spectrum efficiency, and the cognitive radio‐based nonorthogonal multiple access (CR‐NOMA) system is developed to satisfy such demand. The unreal situation of CR‐NOMA is considering the perfect channel state information (CSI) in receivers. This paper indicates impacts of imperfect CSI on outage and throughput performance. In particular, we focus on performance of the secondary network related to the imperfect CSI, and we derive closed‐form expressions of outage probability and throughput for the downlink in such a CR‐NOMA system. Particularly, a general form of Nakagami‐m fading channel is adopted to examine the impact of fading on the performance of the CR‐NOMA system. As the main achievement, we conduct extensive simulations and provide analyses to demonstrate the outage performance of the CR‐NOMA system with CSI imperfections.

Outage performance analysis of full-duplex assisted non-orthogonal multiple access with bidirectional relaying mode

The fifth-generation (5G) wireless network needs massive connectivity to allow large number of users access to network in the same time. Non-orthogonal multiple access (NOMA) and full-duplex (FD) are two promising techniques recommended for the 5G wireless network. This work combines these approaches to improve system outage performance in the situation of bidirectional cooperative relaying. The main metric to evaluate system performance relying on outage probability. Notably, the outage expression for such a system under the Nakagami-m fading environment is derived for exact and approximate computation. The simulation results demonstrated the effectiveness of NOMA and FD in low transmit power compared to conventional half-duplex (HD) and orthogonal multiple access (OMA) schemes.

Outage Performance of Full‐Duplex Relay Networks Powered by RF Power Station in Ubiquitous Electric Internet of Things

This paper investigates a full‐duplex relay network assisted by radio frequency (RF) power station in ubiquitous electric Internet of Things (UEIoT), where a wireless sensor on high voltage transmission line collects electric data and then transmits data to a destination via a full‐duplex decode‐and‐forward relay. The destination receives and processes the data to inspect the state of high voltage transmission line. Both the sensor and relay do not have fixed energy source; so, they first have to harvest energy from a RF power station and then complete information transmission by using the harvested energy. As the line‐of‐sight (LOS) propagations often exist in outdoor application scenarios of UEIoT, the Rician fading channel is adopted in the network. To explore the system outage performance, the explicit expressions of the outage probability and throughput of the system are derived by using mathematical analysis. Simulation results validate the correctness of our theoretical analysis and also evaluate the effects of system parameters and deployment position of power station on the outage performance.

Outage Performance Analysis of Full-Duplex Assisted Non-Orthogonal Multiple Access with Bidirectional Relaying Mode

The fifth-generation (5G) wireless network needs massive connectivity to allow large number of users access to network in the same time. Non-orthogonal multiple access (NOMA) and full-duplex (FD) are two promising techniques recommended for the 5G wireless network. This work combines these approaches to improve system outage performance in the situation of bidirectional cooperative relaying. The main metric to evaluate system performance relying on outage probability. Notably, the outage expression for such a system under the Nakagami-m fading environment is derived for exact and approximate computation. The simulation results demonstrated the effectiveness of NOMA and FD in low transmit power compared to conventional half-duplex (HD) and orthogonal multiple access (OMA) schemes.

System Outage Probability of PS-SWIPT Enabled Two-Way AF Relaying With Hardware Impairments

In this paper, we investigate the system outage probability of a simultaneous wireless information, and power transfer (SWIPT) based two-way amplify-and-forward (AF) relay network, where transceiver hardware impairments (HIs) are considered. The energy-constrained relay node processes the received signals based on a power splitting protocol, and the two terminals employ a selection combining (SC) scheme to exploit the signals from the direct and relaying links. Assuming independent but non-identically distributed Nakagami-m fading channels, we derive the system outage probability in a closed-form, which enables us to identify two crucial ceiling effects on the system outage probability caused by HIs in the high data rate regions, i.e., relay cooperation ceiling (RCC) and overall system ceiling (OSC). Specifically, the RCC prevents the relaying link from participating in cooperative communications, while the OSC leaves the overall system in outage. Furthermore, we derive the achievable diversity gain of the considered network, which shows that the diversity gain equals either the shape parameter of the direct link or zero. Computer simulations are provided to validate the correctness of our analytical results, and study the effects of various system parameters on the system outage performance and the optimal power splitting ratio, as well as the energy efficiency.

Outage analysis of NOMA-based cooperative relay systems with imperfect SIC

In fifth-generation (5G) wireless communication systems, non-orthogonal multiple access (NOMA) has been considered as a promising multiple access technique. In this paper, a NOMA-based cooperative relay system (CRS) is proposed and analyzed. In contrast to the conventional cooperative relay NOMA system (system model in Kim and Lee (2015)), the proposed NOMA-based CRS allows a source and a relay to transmit a superimposed signal in the first and second time slots, respectively. The proposed scheme gives more reliable communication by fully leveraging the concepts of NOMA and cooperative relaying. The exact closed-form expressions for the outage probability are derived in a Rayleigh fading environment with imperfect successive interference cancellation (SIC) at the relay and destination. The outage performance of the proposed scheme is compared with the existing CRS-NOMA schemes. The paper also investigates the impact of various parameters on the outage performance of the proposed system. The accuracy of the analytical results is verified through simulations.

Performance study of wavelength diversity serial relay OFDM FSO system over exponentiated Weibull channels

This paper proposes a wavelength diversity decode-and-forward (DF) serial relay orthogonal frequency division multiplexing (OFDM) free-space optical (FSO) communication system. The proposed system performance is evaluated by the quadrature phase-shift keying (QPSK) as an OFDM signal subcarrier mapping method, considering the maximum ratio combining (MRC) and equal gain combining (EGC) schemes, over exponentiated Weibull (EW) channels. The Monte Carlo (MC) method is used to simulate the system performance. The closed-form expressions of outage probability and average symbol error rate (SER) are also derived considering the joint effect of atmospheric turbulence, path loss, and pointing errors. In addition, the effects of the number of operating wavelength, receiving aperture diameter, number of relay hops, and link length between relays on the outage performance of an FSO communication system, and the effect of the MRC and EGC schemes the average SER are analyzed through simulations. The MC simulations verify the correctness of the numerical results. The results show that the proposed system can concurrently expand the communication range and improve system performance.

Performance Optimization of Hybrid Satellite-Terrestrial Relay Network Based on CR-NOMA

The non-orthogonal multiple access (NOMA) scheme realizes the transmission of multiple user signals at the same time and frequency resource block through power domain multiplexing, which improves the system transmission rate and user fairness. In this paper, we propose a joint relay-and-antenna selection scheme based on the cognitive radio scenario. This scheme can achieve the maximum communication rate of the secondary user when the primary user maintains the optimal outage performance. In the considered system both terrestrial relays and users are deployed with multi-antenna configurations and the terrestrial relays adopt the decode-and-forward (DF) strategy to achieve communication between satellites and users. Then, we derive the exact outage probability expression of each user in the system and the asymptotic probability expression under high signal-to-noise ratio (SNR). Numeric results demonstrate that increasing the number of relays and antennas on the terrestrial nodes can both improve system outage performance. Moreover, the number of relays imposes a more obvious effect on the achievable system performance.

Combined Relay Selection in Spatially Random Networks

In deterministic networks where relay nodes are stationary, combined relay selection is an efficient relay selection scheme, which is capable of achieving the near-optimal outage performance with much lower system complexity. However, the efficiency of combined relay selection is only validated upon fixed topological settings. To investigate the performance of combined relay selection in spatially random networks (SRNs), we employ the Poisson point process to model the dynamical nature of cooperative networks and study the outage performance of the proposed system. It is surprising that the equivalence principle of combined relay selection appearing in deterministic networks does not hold in SRNs.

Analysis and outage performance evaluation of a fair scheduling for independent non‐identically distributed users in a cognitive radio using OSTBC with equally correlated transmit antennas

In this study, a fair user-scheduling method is considered for an underlay cognitive radio system, in which the secondary users (SUs) are sharing the licenced frequency spectrum of a single primary user (PU), where the PU and SUs utilise Alamouti orthogonal space-time block coding (OSTBC). The impacts of some important practical issues are investigated in the system. First, it is assumed that the signal-to-noise-ratios of the SUs are independent non-identically distributed. Second, the transmit antennas for OSTBC corresponding to the SUs are assumed to be equally correlated. Third, the interference from the PU to SUs as well as the interferences from SUs to the PU are taken into consideration. To investigate the outage performance of the SUs, a closed-form expression for the cumulative distribution function of the SUs signal-to-interference-noise-ratio is obtained and then used to derive an expression for evaluating the secondary system outage performance. The numerically evaluated results, validated by computer simulations, provide insights about system outage performance under various practical situations on the impacts of the spatial antennas correlation and the PU interference on to SUs.

Outage Performance Analysis of Two-Way Full-Duplex DF Relaying Networks With Beamforming

In this paper, we investigate the system outage performance of full-duplex (FD) two-way relay networks where all nodes are equipped with FD multiple-input multiple-output (MIMO) capability and two sources exchange information via decode-and-forward (DF) relay protocol in two consecutive time slots. In order to completely separate the desired signal and interference, we consider a finite size of buffer at the relay. We propose zero-forcing based beamforming schemes for two different cases of the buffer-aided relay and non-buffer-aided relay. We derive exact closed-form expression and lower bound of the outage probability for those two-way relay system, respectively. Numerical results show that the proposed buffer-aided relay scheme significantly improves the system performance over the conventional scheme in terms of outage probability.

On Secure Mixed RF-FSO Systems With TAS and Imperfect CSI

In this work, we analyze the secrecy outage performance of a dual-hop relay system composed of multiple-input-multiple-output radio-frequency (RF) links and a free-space optical (FSO) link while a multiple-antenna eavesdropper wiretaps the confidential information by decoding the received signals from the resource node. The channel state information (CSI) of the RF and FSO links is considered to be outdated. We propose three transmit antenna selection (TAS) schemes to enhance the secrecy performance of the considered systems. The secrecy outage performance with different TAS schemes is analyzed and the effects of misalignment and detection technology on the secrecy outage performance of mixed systems are studied. We derive the closed-form expressions for probability density function (PDF) and cumulative distribution function (CDF) over M\'alaga channel with imperfect CSI. Then the closed-form expressions for the CDF and PDF of the equivalent signal-to-noise ratio (SNR) at the legitimate receiver over Nakagami-$m$ and M\'alaga channels are derived. Furthermore, the lower bound of the secrecy outage probability (SOP) with different TAS schemes are derived. Besides, the asymptotic results for SOP are investigated by exploiting the unfolding of Meijer's $G$-function when the electrical SNR of FSO link approaches infinity. Finally, Monte-Carlo simulation results are presented to testify the correctness of the proposed analysis. The results illustrate that the outdated CSI shows a strong effect on the secrecy outage performance. In addition, increasing the number of antennas at the source cannot significantly enhance the secrecy performance of the considered systems.

Outage Performance of Uplink NOMA in Land Mobile Satellite Communications

Non-orthogonal multiple access (NOMA) can be efficiently used in land mobile satellite (LMS) communications in order to increase link availability, coverage and reliability. In this letter, we study -for first time in the literature- the outage performance of an uplink LMS system consisting of two terrestrial user nodes which perform NOMA in the uplink, with either successive interference cancellation or joint decoding at the satellite receiver. Closed-form expressions for the outage probability are derived for both cases assuming composite shadowed-Rician fading channels. Finally, numerical results and simulations validate the theoretical analysis.

Performance Analysis of Overlay Cognitive NOMA Systems With Imperfect Successive Interference Cancellation

Non-orthogonal multiple access (NOMA) and cognitive radio (CR) are envisioned as promising solutions to achieve high spectral efficiency for future wireless networks. This work investigates the outage performance of an overlay cognitive NOMA system with imperfect successive interference cancellation (SIC). The outage probability of primary user and secondary user are derived in closed forms. To obtain further insights, asymptotic expressions of outage probability and system throughput are evaluated when the transmit signal-to-noise ratio approaches infinity. An optimal power allocation coefficient is provided to maximize the system throughput. Moreover, the overlay cognitive NOMA system is compared with the underlay CR system and the overlay cognitive orthogonal multiple access (OMA) system in terms of outage probability. Finally, the performance analysis is validated by simulations. The simulation results demonstrate that the outage performance and system throughput of overlay cognitive NOMA system are superior to those of overlay cognitive OMA system and underlay CR system when the imperfect SIC satisfies certain conditions.

Performance of Opportunistic Receiver Beam Selection in Multiaperture OWC Systems Over Foggy Channels

The atmospheric foggy condition is a major bottleneck for the deployment of optical wireless communication (OWC) systems in outdoor environments. Although the attenuation coefficient in the foggy channel follows the simple Gamma distribution, the distribution of its channel state is quite complicated similar to the well-studied Gamma–Gamma turbulence channel. Furthermore, existing literature suggested schemes that require feedback of the channel state information (CSI) to improve the outage performance of the OWC system under foggy conditions. In this article, we study the average signal-to-noise ratio (SNR), ergodic rate, and energy consumption performance of OWC systems under foggy conditions. First, we show that a single-aperture OWC system suffers significantly from the fog attenuation by deriving analytical expressions on the ergodic rate and energy consumption. Then, we consider a multiaperture OWC system equipped with an opportunistic receiver beam selection (RBS) scheme. The RBS scheme is based on the simple selection combining diversity algorithm, which does not require the knowledge of CSI. We analyze the proposed scheme by deriving computable bounds on the average SNR, ergodic rate, and energy consumption using system parameters and show the performance improvement of the RBS scheme comparing the single-aperture system. We demonstrate the performance of the considered scheme and validate derived expressions using computer simulations.

Non-orthogonal multiple access in full-duplex-based coordinated direct and relay transmission (CDRT) system: performance analysis and optimization

This paper considers non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the nearby users while it requires the help of a dedicated relay to communicate with the cell-edge users. We derive exact closed form expression for the outage probabilities experienced by the downlink users and the system outage probability of the considered CDRT network with full-duplex relaying (FDR) technique. Further, we derive approximate closed form expressions for the ergodic rates achieved by the users. The channel of all the links experience Nakagami fading distribution and the analysis takes into account the residual interference generated due to the imperfect successive interference cancelation (I-SIC) technique. We provide numerical and simulation results to identify the impact of key system parameters on the outage and ergodic rate performance of the users and the system outage performance. The outage and ergodic rate performance of users in the considered FDR-based NOMA-CDRT system has been observed to be significantly improved compared to a FDR-based OMA (orthogonal multiple access)-CDRT system. It is observed that random selection of NOMA power allocation coefficients at the BS leads to higher outage for the near users compared to the far users. We determine numerical results for the NOMA power allocation coefficient that leads to equal outage performance for both the users. Finally, we derive analytical expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability. Through extensive numerical and simulation studies, we establish that OPA can lead to significant reduction of system outage probability compared to random selection of power allocation coefficients at the BS.

Two-Way Transmission for Low-Latency and High-Reliability 5G Cellular V2X Communications.

As one of key technologies of future networks, vehicle-to-everything (V2X) communication has recently been proposed to improve conventional vehicle systems in terms of traffic and communications. Main benefits of using V2X are efficient and safe traffic as well as low-latency communications and reliable massive connections. Non-orthogonal multiple access (NOMA) scheme was introduced as a promising solution in the fifth-generation (5G) mobile communications, by which quality-of-service (QoS) requirements of many 5G-enabled applications are satisfied as a result of improved network throughput and lower accessing and transmission latency. In this paper, we study NOMA-based communications between vehicles equipped with multiple antennas over Nakagami-m fading channels in V2X networks, in which uplink and downlink transmission between two vehicles with upper controller are supported by a road side unit (RSU) to increase the capacity rather than simply be connected to the base station. In the NOMA-V2X system under study, the outage probability depends on the power allocation factor of RSU transmission and the operation of successive interference cancellation (SIC) at vehicles. Analyses and simulations verify that the outage performance of NOMA-V2X system are mainly affected by fading parameters, levels of imperfect SIC, and power allocation factors.