Approximate Outage Probability Research Articles

UAV-enabled reliable mobile relaying under the time-varying Rician fading channel

This paper adopts an unmanned aerial vehicle (UAV) relay to forward data from a source sensor to a remote base station (BS). To ensure reliable data transmission, our objective is to minimize the average outage probability along the three-dimensional (3D) UAV trajectory under the UAV mobility and source/relay power allocation constraints. The UAV mobility causes the time-varying Rician fading channel, thus the outage probability function considers both the distance-based large-scale fading and a time-varying Rician factor. To tackle our formulated non-convex problem, we approximate the outage probability by its first-order asymptotic form, based on which we propose a block coordinate descent (BCD) iteration algorithm by alternatively solving the 3D UAV trajectory and power allocation subproblems. The successive convex optimization (SCO) method is applied to deal with the 3D UAV trajectory subproblem. To reveal the advantage by designing the 3D UAV trajectory, we also consider joint optimization of the two-dimensional (2D) UAV trajectory and power allocation to minimize the average outage probability. Extensive simulations verify the accuracy of the approximate outage probability, and the results show that considering the time-varying Rician fading channel, the 3D UAV trajectory helps to obtain a lower link outage probability than the 2D UAV trajectory.

Unsupervised Deep-Learning-Based Reconfigurable Intelligent Surface-Aided Broadcasting Communications in Industrial IoTs

This article presents a general system framework that lays the foundation for reconfigurable intelligent surface (RIS)-enhanced broadcast communications in Industrial Internet of Things (IIoTs). In our system model, we consider multiple sensor clusters co-existing in a smart factory where the direct links between these clusters and a central base station (BS) are blocked completely. In this context, a RIS is utilized to reflect signals broadcast from BS toward cluster heads (CHs) which act as a representative of clusters, where BS only has access to the statistical distribution of the channel state information (CSI). An analytical upper bound of the total ergodic spectral efficiency (SE) and an approximation of outage probability are derived. Based on these analytical results, two algorithms are introduced to control the phase shifts at RIS, which are the Riemannian conjugate gradient (RCG) method and the deep neural network (DNN) method. While the RCG algorithm operates based on the conventional iterative method, and the DNN technique relies on unsupervised deep learning (DL). Our numerical results show that both algorithms achieve satisfactory performance based on only statistical CSI. In addition, compared to the RCG scheme, using DL reduces the computational latency by more than ten times with an almost identical total ergodic SE achieved. These numerical results reveal that while using the conventional RCG method may provide unsatisfactory latency, and the DNN technique shows much promise for enabling RIS in ultrareliable and low-latency communications (URLLC) in the context of IIoTs.

Uplink Multiple Access for Reconfigurable Intelligent Surface-Aided Wireless Systems

The integration of reconfigurable intelligent surface- (RIS-) aided wireless communication and multiple access is an attractive and promising scheme for next-generation wireless networks. In this research work, separate uplink RIS-aided nonorthogonal multiple access (NOMA) and uplink relay-assisted NOMA schemes are studied, where the RIS and relay devices are deployed to enhance the coverage of an obstructed single-antenna far user by assisting it to communicate with a single-antenna base station. In each scenario, both perfect successive interference cancellation (pSIC) and imperfect successive interference cancellation (ipSIC) operations are considered in the proposed multiple access network. To characterize the system performance, the associated residual interference caused by ipSIC and relay loop self-interference is characterized using the Rayleigh fading model; subsequently, new channel statistics are derived based on the Gauss-Laguerre polynomial. Consequently, the closed-form approximate outage probability expressions are derived for each scenario in the high signal-to-noise ratio (SNR) regime. To gain further insight, the system throughput in the delay-limited transmission is also obtained for each scenario. The formulated expressions are validated via Monte-Carlo simulations. Finally, the obtained simulation results demonstrate and validate the superiority of the RIS system over the relay device under several system parameters of interest despite the limitation of ipSIC.

Covert Wireless Communication With Noise Uncertainty in Space-Air-Ground Integrated Vehicular Networks

In this paper, we propose a covert wireless uplink transmission strategy in space-air-ground integrated vehicular networks, where the source vehicle transmits its own message over the channel that being used by the host communication system, to avoid being detected by the warden. It is obvious that the data transmission efficiency of the covert communication system is limited due to the co-channel interference. To improve the data transmission efficiency, we consider that the covert communication system adopts improper Gaussian signaling (IGS). We formulate a joint transmit power and IGS factor optimization problem to minimize the outage probability of the covert communication system. The minimum error detection probability of the warden is first analyzed with noise uncertainty, which is used to measure the system covertness. Under the constraints of the quality of service (QoS) of host communication system and the covertness requirement, the optimal transmit power is first derived with proper Gaussian signaling (PGS) scheme. Then, with the approximate outage probability derived under IGS scheme, the optimization problem is solved by jointly designing the transmit power and IGS factor. Finally, we provide extensive numerical results to validate the proposed covert transmission strategy, and demonstrate that the IGS scheme is beneficial in improving the data transmission efficiency in terms of outage probability compared to PGS scheme.

On the Computation and Approximation of Outage Probability in Satellite Networks With Smart Gateway Diversity

The utilization of extremely high frequency (EHF) bands can achieve very high throughput in satellite networks (SatNets). Nevertheless, the severe rain attenuation at EHF bands imposes strict limitations on the system availability. Smart gateway diversity (SGD) is considered indispensable in order to guarantee the required availability with reasonable cost. In this context, we examine a load-sharing SGD (LS-SGD) architecture, which has been recently proposed in the literature. For this diversity scheme, we define the system outage probability (SOP) using a rigorous probabilistic analysis based on the Poisson binomial distribution (PBD), and taking into consideration the traffic demand as well as the gateway (GW) capacity. Furthermore, we provide several methods for the exact and approximate calculation of SOP. As concerns the exact computation of SOP, a closed-form expression and an efficient algorithm based on a recursive formula are given, both with quadratic worst-case complexity in the number of GWs. Finally, the proposed approximation methods include well-known probability distributions (binomial, Poisson, normal) and a Chernoff bound. According to the numerical results, binomial and Poisson distributions are by far the most accurate approximation methods.

Performance Analysis of IQI Impaired Cooperative NOMA for 5G-Enabled Internet of Things

This paper investigates the joint effects of in-phase and quadrature-phase imbalance (IQI) and imperfect successive interference cancellation (ipSIC) on the cooperative Internet of Things (IoT) nonorthogonal multiple access (NOMA) networks where the Nakagami-m fading channel is taken into account. The closed-form expressions of outage probability for the far and near IoT devices are derived to evaluate the outage behaviors. For deeper insights of the performance of the considered system, the approximate outage probability and diversity order in high signal-to-noise ratio (SNR) regime are obtained. In addition, we also analyze the throughput and energy efficiency to characterize the performance of the considered system. The simulation results demonstrate that, compared with IQI, ipSIC has a greater impact on the outage performance for the near-IoT-device of the considered system. Furthermore, we also find that the outage probabilities of IoT devices can be minimized by selecting a specific power allocation scheme.

Analysis of MRC With $\eta -\mu$ Co-Channel Interference

Approximate outage probability and rate expressions are derived for systems employing maximum ratio combining, when both the desired signal and the interfering signals are subjected to $\eta -\mu$ fading, with the interferers having unequal power. The approximations are in terms of the Gauss hypergeometric function. A close match is observed between the results obtained through the derived analytical expression and the one obtained through Monte-Carlo simulations. Also, the utility of the applications is established in a vehicular application.

Performance Analysis for Multi-Hop Cognitive Radio Networks Over Cascaded Rayleigh Fading Channels With Imperfect Channel State Information

In this letter, we consider a cognitive radio network with imperfect channel state information where secondary users transmit signals using multi-hop relaying. When the channels between secondary users are modeled as cascaded Rayleigh fading, we derive the exact outage probability of the secondary network in an analytic form and the approximate outage probability in a closed form. Then we propose a secondary user selection scheme to minimize the outage probability. The validity of our analysis is verified through simulation.

On the performance of cognitive underlay RF/FSO communication systems with limited feedback

In this work, we consider an underlay cognitive radio (CR) RF/free space optical (FSO) network where the unlicensed secondary user (SU) wishes to communicate with a specific destination node with the aid of an optical path over a selected relay terminal without causing any interference to the primary user (PU). The proposed structure can be viable for metropolitans where an unlicensed user wishes to transfer its information to a specific destination node which is connected to the backbone network over an optical path. For the proposed structure, closed form and approximate outage probability and ergodic capacity expressions are derived for Nakagami-m/ Exponentiated Weibull fading channels. The results show that the transmission capacity of the SU depends on the weather conditions and the number of relays in the system.

Outage Performance Analysis and SWIPT Optimization in Energy-Harvesting Wireless Sensor Network Deploying NOMA.

Thanks to the benefits of non-orthogonal multiple access (NOMA) in wireless communications, we evaluate a wireless sensor network deploying NOMA (WSN-NOMA), where the destination can receive two data symbols in a whole transmission process with two time slots. In this work, two relaying protocols, so-called time-switching-based relaying WSN-NOMA (TSR WSN-NOMA) and power-splitting-based relaying WSN-NOMA (PSR WSN-NOMA) are deployed to study energy-harvesting (EH). Regarding the system performance analysis, we obtain the closed-form expressions for the exact and approximate outage probability (OP) in both protocols, and the delay-limited throughput is also evaluated. We then compare the two protocols theoretically, and two optimization problems are formulated to reduce the impact of OP and optimize the data rate. Our numerical and simulation results are provided to prove the theoretical and analytical analysis. Thanks to these results, a great performance gain can be achieved for both TSR WSN-NOMA and PSR WSN-NOMA if optimal values of TS and PS ratios are found. In addition, the optimized TSR WSN-NOMA outperforms that of PSR WSN-NOMA in terms of OP.

Hop-by-Hop ZF Beamforming for MIMO Full-Duplex Relaying With Co-Channel Interference

In this paper, a comprehensive design and analysis of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment is investigated, where a multi-antenna amplify-and-forward FD relay station serves multiple half-duplex (HD) multi-antenna users. The pivotal obstacles of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when employing FD relaying in cellular networks are addressed. In contrast to the HD relaying mode, the CCI in the FD relaying mode is predicted to double since the uplink and downlink communications are simultaneously scheduled via the same channel. In this paper, the optimal layout of transmit (receive) precoding (decoding) weight vectors which maximizes the overall signal-to-interference-plus-noise ratio is constructed by a suitable optimization problem, and then a closed-form sub-optimal formula based on null space projection is presented. The proposed hop-by-hop rank-1 zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination, i.e., the source and relay perform transmit ZF beamforming, while the relay and destination employ receive ZF combining. To this end, unified accurate expressions for the outage probability and ergodic capacity are derived in closed form. In addition, simpler tight lower bound formulas for the outage probability and ergodic capacity are presented. Moreover, the asymptotic approximations for outage probability are considered to gain insights into system behavior in terms of the diversity order and array gain. Numerical and simulation results show the accuracy of the presented exact analytical expressions and the tightness of the lower bound expressions. The case of hop-by-hop maximum-ratio transmission/maximal-ratio combining beamforming is included for comparison purposes. Furthermore, our results show that while multi-antenna terminals improve the system performance, the detrimental effect of CCI on FD relaying is clearly seen. Therefore, our findings unveil that MIMO FD relaying could significantly improve the system performance compared to its conventional MIMO HD relaying counterpart.

Power Allocation Study for Non-Orthogonal Multiple Access Networks With Multicast-Unicast Transmission

This paper considers a downlink single-cell non-orthogonal multiple access (NOMA) network, where the base station, which has multiple antennas, broadcasts the mixed multicast and unicast messages to multiple users with a single antenna. We propose two types of power allocation schemes for NOMA networks with multicast-unicast transmission to investigate the impact of performance, namely, cognitive radio inspired NOMA with dynamic quality of service (QoS) at multicast users (CR-NOMA-D-M), and CR-NOMA constrains the dynamic QoS at the unicast user (CR-NOMA-D-U). Based on the proposed schemes, we drive the exact/closed-form expressions for the secrecy outage probability, outage probability, as well as the approximate outage probability at high signal-to-noise ratio to study the diversity gain. Compared with existing works, the derived analytical results show that both proposed schemes cannot only significantly improve the outage performance for multicast users, but also remarkably enhance the diversity gain and the secrecy outage probability for the unicast user. Finally, the theoretical results are validated by the numerical results.

Finite Blocklength Communications in Smart Grids for Dynamic Spectrum Access and Locally Licensed Scenarios

This work focuses on the performance analysis of short blocklength communication with application in smart grids. We use stochastic geometry to compute in closed form the success probability of a typical message transmission as a function of its size (i.e. blocklength), the number of information bits and the density of interferers. Two different scenarios are investigated: (i) dynamic spectrum access where the licensed and unlicensed users, share the uplink channel frequency band and (ii) local licensing approach using the so called micro operator, which holds an exclusive license of its own. Approximated outage probability expression is derived for the dynamic spectrum access scenario, while a closed-form solution is attained for the micro-operator. The analysis also incorporates the use of retransmissions when messages are detected in error. Our numerical results show how reliability and delay are related in either scenarios.

A new scheme of dynamic power allocation in wireless powered communication

In this article, we propose a new generalized selection transmit scheme (GSTS) for wireless powered communication (WPC), where data access point (DAP) is powered by energy access point (EAP) to communicate with wireless device (WD). Theoretically speaking, allocating all harvesting energy to the antenna with the best channel gain will achieve the optimal performance. While the harvesting energy is dynamic and may exceed the power limitation of single antenna, we should allocate the harvesting energy to the best antennas subset with the minimum number of antennas. That is GSTS. For GSTS, we derive the new closed-form probability density function (PDF) of signal to noise ratio (SNR). According to the derived PDF, the approximate outage probability is derived. In order to depict the trend of outage probability at high SNR area, the diversity order is derived. It is determined by the minimum one of the transmit antenna number of EAP and that of DAP. Besides, the influence of line-of-sight (LOS) component in wireless power transfer (WPT) is also discussed.

Application of best relay selection approach to cooperative DF IDMA systems over Rayleigh/Weibull fading channels

SummaryThis paper analyzes the performance of cooperative decode‐and‐forward (DF) interleave‐division multiple‐access (IDMA) networks with best relay selection over Rayleigh/Weibull fading environments. In the analysis, approximate outage probability (OP) and bit error probability (BEP) expressions are derived for the considered system. Further, a 2‐hop DF IDMA system is also designed to compare with cooperative one. We propose OP and BEP expression for 2‐hop DF IDMA systems. Numerical results are obtained by changing the number of relays and the value of fading parameter in the proposed expressions. Also, simulations are provided to corroborate the exactness of the derived approximate OP and BEP expressions.

Utility Maximization for Two-Way AF Relaying Under Rate Outage Constraints

In this paper, we focus on maximizing the system utility (e.g., the weighted sum-rate, weighted geometric mean rate, and the harmonic mean rate) of a two-way relay network (TWRN) from the outage probability perspective; a TWRN has multiple relay nodes and two terminal nodes. We assume amplify-and-forward relaying with analog network coding protocol and half-duplex transmission with perfect channel state information at the receiver ends and channel distribution information at the transmitter ends. We derive the approximated closed-form for the outage probability of a TWRN; however, the approximated outage constraints lead to a non-convex structure for the considered problem. Based on the successive convex approximation technique, we obtain near optimal solution for the non-convex problem. Moreover, we derive closed-form solutions for the maximization problem for the weighted sum rate maximization problem for a TWRN with a single relay node and two relay nodes under individual power constraints. Our simulation results demonstrate the accuracy of our outage probability approximation model and the advantages of our algorithm over naive methods of full and uniform power allocation.

Secrecy Outage of Dual-Hop Amplify-and-Forward Relay System with Diversity Combining at the Eavesdropper

In this paper, a dual-hop amplify-and-forward relay system is considered with an eavesdropper where each link undergoes independent, non-identical, flat Rayleigh fading. The eavesdropper is capable of diversity combining the direct and relayed communication from the source using maximal ratio combining (MRC) and selection combining (SC). Closed-form upper and lower bounds on secrecy outage probability are derived. Closed-form approximate secrecy outage probability and ergodic secrecy rate is also obtained when source–relay link average signal-to-noise ratio (SNR) is high. Asymptotic analysis is presented when dual-hop links have equal or unequal average SNR. It is found that SC has both the secrecy outage and ergodic secrecy rate performances are better than MRC. To achieve the same secrecy outage performance of SC, MRC requires relatively higher SNR at lower rate. MRC also requires relatively higher SNR to achieve same secrecy rate performance of SC when eavesdropper link quality degrades. It is observed that lower bound for secrecy outage is tight and tends towards secrecy outage as SNR increases. It is interesting to find that either one of the dual-hop link can limit the performances even if the other link average SNR is infinitely high.

Outage probability of WDM free‐space optical systems affected by turbulence‐accentuated interchannel crosstalk

Massive deployment of free space optical (FSO) communication systems in future optical access networks will use wavelength division multiplexing (WDM) technology to leverage extended reach and enhanced user capacity. An analytical framework for the estimation of outage probability in a turbulence-affected WDM FSO system is presented in this study. The authors derive simplified expressions of the probability of outage in the presence of turbulence-accentuated interchannel crosstalk, and show how design parameters such as the FSO link length, demultiplexer adjacent channel rejection and receiver aperture diameter affect the performance of the system. Numerical results show that the outage probability due to irradiance fluctuation is worsened in WDM FSO systems by the effects of turbulence-affected interchannel crosstalk signals. Specifically, the average crosstalk power and the degree of irradiance fluctuations on the crosstalk set a limit on the outage probability performance of the system which appears in the form of outage floors.

MIMO Full-Duplex Relaying in the Presence of Co-Channel Interference

This paper studies the deployment of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multicell environment, where the source and destination nodes are equipped with a single antenna and communicating via a dual-hop amplify-and-forward (AF) relay station with multiple receive and transmit antennas in the presence of co-channel interference (CCI). This paper addresses the fundamental challenges of loopback self-interference (LI) and CCI when incorporating FD relaying in cellular systems. Due to the higher frequency reuse in FD relaying compared to its half-duplex (HD) relaying counterpart, the CCI is expected to double as the FD relay station simultaneously schedule uplink and downlink transmission on the same channel. The optimal design of relay receive and transmit precoding weight vectors, which maximizes the overall signal-to-interference-plus-noise ratio (SINR) is formulated by a proper optimization problem, and then, a closed-form suboptimal solution based on null space projection is proposed. The proposed precoding vectors are based on the added receive and transmit zero-forcing (ZF) constraints used to suppress the CCI and LI, respectively. To this end, exact closed-form expressions for the outage probability and ergodic capacity are derived, where simpler lower bound expressions are also presented. In addition, the asymptotic high signal-to-noise ratio (SNR) outage probability approximation is also considered, through which the diversity order of the null space projection (ZF/ZF) scheme is found to achieve $\mathrm{min}(N_{R}-M,\, N_{T}-1)$ , where $N_{R}$ and $N_{T}$ are the number of relay receive and transmit antennas, respectively, and $M$ is the number of CCI interferers. Numerical results sustained by Monte Carlo simulations show the exactness of the proposed analytical expressions, as well as the tightness of the proposed lower bound expressions. In addition, simulation results for the minimum mean square error (MMSE)/ZF scheme is also considered for comparison purposes. Our results reveal that MIMO FD relaying could substantially boost the system performance, compared to its conventional MIMO HD relaying counterpart.

Cognitive Multi-Relay Transmission over Asymmetric Fading Channels with Imperfect CSI

Outage performance of a cognitive multi-relay system using imperfect channel state information (CSI) of interfering links is formulated in this paper. In the considered cognitive system, it is assumed that wireless channels in the secondary network (source-to-relay and relay-to-destination links) experience Rician fading whereas interfering channels between primary and secondary networks undergo Rayleigh fading. Under the assumption of asymmetric fading, an outage probability (OP) expression of the secondary network is approximately formulated. Analytical OP values are in good agreement with related empirical ones in low signal-to-noise ratio (SNR) regimes. As a result, the approximate OP expression can be used to quantify the effect of asymmetric fading channels and CSI imperfection on the performance of cognitive multi-relay systems in practical SNR ranges.