Outage Performance Of System Research Articles

On the Performance of Cognitive Underlay SIMO Networks over Equally Correlated Rayleigh Fading Channels

The performance of single-input multiple-output (SIMO) cognitive spectrum sharing networks with the presence of equally correlated Rayleigh fading channels is investigated. In particular, based on the truncated infinitive series of cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end signal-to-noise ratios (SNRs), close-form expressions are provided for the system outage performance, bit error rate and ergodic capacity. It is shown that the system performance merely depends on the correlation coefficient between antennas. Monte-Carlo simulations are also contributed to confirm the accuracy of our analysis.

Outage Analysis of Mixed FSO/WiMAX Link

In this paper, we study the outage performance of a complex system consisting of a free-space optical (FSO)/radio-frequency (RF) link. Using radio over free-space optics technology, the FSO link carries Worldwide Interoperability for Microwave Access (WiMAX) signals from a core network to a WiMAX base station, delivering traffic to multiple end RF users. A novel closed-form analytical expression for overall outage probability is derived when $M$ -ary phase-shift keying ( $M$ -PSK) and $M$ -ary quadrature amplitude modulation ( $M$ -QAM) are applied. The analysis is performed when the FSO link is under the influence of the Gamma–Gamma turbulence, path loss, and misalignment between the transmitter and receiver apertures, and the RF part is influenced by the Gamma-shadowed Nakagami- $m$ multipath fading. To illustrate the usefulness of the derived expressions, we present some numerical results that enable us to estimate the effects of different transceiver and channel parameters on the outage probability. The results are used for optimizing the transmitter laser beam radius at the waist to achieve the minimal overall outage probability in the case of different conditions over the RF part. The numerical and simulation results show that multipath fading severity and shadowing spread over the RF part have a significant effect on the optimal value of the laser beam waist and can decrease the overall outage probability for several orders of magnitude.

Cooperative spectrum sharing MIMO systems with successive decoding

A spectrum sharing system with primary and secondary nodes, each equipped with an arbitrary number of antennas, is investigated. Particularly, the outage performance of an underlay cognitive system is analytically studied, in the case when the end-to-end (e2e) communication is established via an intermediate relay node. To better enhance the e2e communication, successive interference cancellation (SIC) is adopted, which compensates for both the transmission power constraint and the presence of interference from primary nodes. Both the relay and secondary receiver perform unordered SIC to successively decode the multiple streams, whereas the decode-and-forward relaying protocol is used for the e2e communication. New closed-form expressions for the e2e outage performance of each transmitted stream are derived in terms of finite sum series of the Tricomi confluent hypergeometric function. In addition, simplified yet tight approximations for the asymptotic outage performance are obtained. Useful engineering insights are manifested, such as the diversity order of the considered system and the impact of interference from the primary nodes in conjunction with the constrained transmission power of the secondary nodes.

Outage Balancing in Downlink Non-Orthogonal Multiple Access With Statistical Channel State Information

This paper considers a downlink non-orthogonal multiple access (NOMA) system where the source intends to transmit independent information to the users at targeted data rates under statistical channel state information at the transmitter. The problem of outage balancing among the users is studied with the issues of power allocation, decoding order selection, and user grouping being taken into account. Specifically, with regard to the max-min fairness criterion, we derive the optimal power allocation in closed-form and prove the corresponding optimal decoding order for the elementary downlink NOMA system. By assigning a weighting factor for each user, the analytical results can be used to evaluate the outage performance of the downlink NOMA system under various fairness constraints. Further, we investigate the case with user grouping, in which each user group can be treated as an elementary downlink NOMA system. The associated problems of power and resource allocation among different user groups are solved. The implementation complexity issue of NOMA is also considered with focus on that caused by successive interference cancellation and user grouping. The complexity and performance tradeoff is analyzed by simulations, which provides fruitful insights for the practical application of NOMA. The simulation results substantiate our analysis and show considerable performance gain of NOMA when compared with orthogonal multiple access.

An Equivalence Principle for OFDM-Based Combined Bulk/Per-Subcarrier Relay Selection over Equally Spatially Correlated Channels

In this paper, we propose a novel relay selection scheme for orthogonal frequency-division multiplexing systems by combining conventional bulk and per-subcarrier selection schemes and analyze its outage performance over equally spatially correlated channels. Specifically, the combined selection scheme selects only two relays at the first attempt and performs per-subcarrier selection over these two relays. We analyze the asymptotic outage performance of the combined selection scheme in the high signal-to-noise ratio (SNR) region and prove a generalized theorem. This theorem states that the combined selection can achieve an optimal outage probability equivalent to the per-subcarrier selection at a high SNR without using the full set of available relays for selection. This unique property is termed the equivalence principle , and it holds for all correlation conditions. To explore this principle, we consider three examples: decode-and-forward, fixed-gain amplify-and-forward (AF), and variable-gain AF relay systems. Furthermore, two extended applications, i.e., antenna selection and branch selection, are also considered to reveal the feasibility and the expandability of the equivalence principle. Our analysis is verified by Monte Carlo simulations. The proposed combined selection and the proved theorem provide a general and feasible solution to the tradeoff between system complexity and outage performance when relay selection is applied.

Non-Orthogonal Multiple Access for Multiple-Antenna Relaying Networks

In this letter, we design non-orthogonal multiple access (NOMA) for multiple-antenna relaying networks. The receive antennas at the mobile users are assumed to adopt maximal ratio combining (MRC), whereas the transmit antenna that maximizes the instantaneous signal-to-noise ratio (SNR) at the relay is selected. The system outage performance is investigated and closed-form expressions for the exact outage probability are derived. Furthermore, we obtain the lower bound of the outage probability. Finally, simulation results are presented to show the correctness of the theoretical analysis and the superiority of NOMA.

Enhancing Cooperative Diversity Gains in Dual-Hop One-Way/Two-Way AF Relaying Systems: A Fully Opportunistic Role Selection Strategy

In this paper, we establish a three-node cooperative framework, where three nodes compete to transmit their own information to other nodes in an adaptive manner. Motivated by Darwin's “natural selection law” whose essence is “adaptation,” a new opportunistic ROle SElection (ROSE) mechanism is presented, and the cooperative role for each node can be adaptively adjusted based on the instantaneous channel fading environment. We refer to this fully dynamic role selection rule as full-ROSE. Then, the proposed full-ROSE strategy is incorporated into classical one-way and two-way dual-hop amplify-and-forward (AF) relaying systems, and analytic lower and upper bound expressions are derived for the system outage probability. Furthermore, an asymptotic analysis is performed to characterize the system outage behavior at a high signal-to-noise ratio (SNR), which manifests that under both one-way and two-way relaying scenarios, the proposed full-ROSE strategy can boost the system diversity gain relative to a traditional fixed-role configuration, and a higher diversity gain, as well as a superior diversity–multiplexing tradeoff (DMT), can be achieved. In addition, a new measure, namely, the ROSE gain, is defined to describe the performance improvement of the full-ROSE strategy relative to the fixed-role configuration. Finally, the impacts of node placement and transmit SNR on the system outage performance and ROSE gain are investigated, and insightful discussions are drawn.

Outage Analysis of Practical FSO/RF Hybrid System With Adaptive Combining

Hybrid free-space optical (FSO)/radio-frequency (RF) systems have emerged as a promising solution for high-data-rate wireless transmission. We present and analyze a transmission scheme for the hybrid FSO/RF communication system based on adaptive combining. Specifically, only FSO link is active as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is above a certain threshold level. When it falls below this threshold level, the RF link is activated along with the FSO link and the signals from the two links are combined at the receiver using a dual-branch maximal ratio combiner. Novel analytical expression for the cumulative distribution function (CDF) of the received SNR for the proposed hybrid system is obtained. This CDF expression is used to study the system outage performance. Numerical examples are presented to compare the outage performance of the proposed hybrid FSO/RF system with that of the FSO-only and RF-only systems.

Performance Analysis of Cooperative Wireless Networks With Unreliable Backhaul Links

A cooperative wireless network, where a cluster of $K$ single-antenna transmitters jointly serve a single-antenna receiver, is considered. Each transmitter is connected to the control unit (CU) via independent but unreliable backhaul links. The CU sends a common message to each transmitter over backhaul links, which upon successful reception, jointly transmit this message to the intended receiver. To facilitate analysis, a general expression is derived for the complementary cumulative distribution function of a sum of $K$ independent random variables, where each random variable is a product of an exponential and a Bernoulli random variable. This result is applied to find a simple closed-form expression that characterizes the system outage performance as a function of network parameters and node geometry. The analytical model is validated using numerical simulations. As an application, the derived expression is also used for investigating the impact of backhaul assignment on the system performance.

Outage Analysis of Transmit Beamforming and Relay Selection with Outdated Channel Estimates over Nakagami-m Fading Channels

We investigate the joint effects of feedback delay and channel estimation errors (CEE) over Nakagami- m fading channels for two-hop amplify-and-forward (AF) relaying systems with transmit beamforming (TB) and relay selection (RS). We derive new closed-form expressions for the system outage performance including the exact analysis and informative high SNR asymptotic approximations, which indicate that TB feedback delay reduces the achievable diversity order to one, regardless of Nakagami- m fading parameters. Whereas RS delay reduces the diversity order to a case without relay selection and CEE merely result in coding gain loss, numerical results verify the theoretical analysis and illustrate that the outage performance is more sensitive to the TB feedback delay.

Exact Outage Analysis in Cognitive Two-Way Relay Networks With Opportunistic Relay Selection Under Primary User's Interference

In the current study of cognitive relay networks, most related works focus on the effect of interference from secondary users (SUs) to primary receivers (PRs), while neglecting the links from primary transmitters (PTs) to SUs. In this paper, the interference both from SUs to PRs and from PTs to SUs is considered in the analysis of cognitive two-way relay networks with opportunistic relay selection. The exact closed-form expression for the outage probability of the secondary system is derived over Rayleigh fading channels, which is verified through various Monte Carlo simulations. Meanwhile, an asymptotic expression and diversity order are also derived to reveal additional insights into the effect of the mutual interference between the primary and secondary systems on the diversity. Above all, based on the analysis, the effects of the positions of the PT, the PR, and secondary relays on the outage performance of the secondary system are studied. Our results reveal that network placement planning is desperately necessary to achieve a better outage performance. It is shown that the position of relays has a strong impact on the performance, particularly when the number of relays is large. However, when the relative position between the primary system and secondary systems is fixed, the positions of the PT have a very slight impact on the outage performance, which can be neglected. Hence, in practical deployment, when performing cognitive two-way relaying with opportunistic relay selection, proper network placement planning should be carefully addressed.

Outage performance of relay-assisted transmissions in cognitive full-duplex relay networks

Abstract Relay cooperation can enhance coverage, throughput, and reliability of wireless communication systems, thus attracting intense research interest in the past decade. However, most of them focused on half-duplex relay systems, which encounter loss of resource efficiency. With the progress of self-interference cancellation technologies, full-duplex relay systems come into sight. In this paper, outage performances of the primary system and the secondary system in a cognitive full-duplex relay network are analyzed, under the adverse effect of self-interference caused by the signals at the transmitting and receiving antennas of the relay. The full-duplex decode-and-forward relay assists the transmissions of the primary system and the secondary system where there is no direct link between the secondary transmitter and the secondary receiver. Simulation results show that better outage performance of the primary system is achieved compared with the cognitive relay network adopting half-duplex relaying. Moreover, communication of the secondary system is realized on the condition that the secondary transmission link is non-ideal.

Outage Analysis and Optimization for Four-Phase Two-Way Transmission with Energy Harvesting Relay

This paper investigates the outage performance and optimization for the four-phase two-way transmission network with an energy harvesting (EH) relay. To enable the simultaneous information processing and energy harvesting at the relay, we firstly propose a power splitting-based two-way relaying protocol (PSTWR). Then, we discuss its outage performance theoretically and derive an explicit expression for the system outage probability. In order to find the optimal system configuration parameters such as the optimal power splitting ratio and the optimal transmit power redistribution factor, we formulate an outage-minimized optimization problem. As the problem is difficult to solve, we design a genetic algorithm (GA) based algorithm for it. Besides, we also investigate the effects of the power splitting ratio, the power redistribution factor at the relay, and the source to relay distance on the system outage performance. Finally, extensive simulation results are provided to demonstrate the accuracy of the analytical results and the effectiveness of the GA-based algorithm. Moreover, it is also shown that, the relay position greatly affects the system performance, where relatively worse outage performance is achieved when the EH relay is placed in the middle of the two sources.

Relay selection for two‐way opportunistic relaying with outdated Nakagami‐m estimates

AbstractOpportunistic relay selection (RS) is an efficient method to obtain diversity gain in two‐way relaying protocol with multiple relays. However, in practical wireless networks, the channel state information (CSI) used in the RS procedure becomes outdated because of the feedback delay, which severely deteriorates the system performance. In this paper, we study the RS strategies that aim to optimise the system outage performance of two‐phase two‐way opportunistic relaying protocol in Nakagami‐m channels. RS schemes for two different cases are designed, that is, (i) the scheme with only the outdated CSI during the RS procedure and (ii) the scheme with both the outdated CSI and the statistical knowledge of channels during the RS procedure. The system outage performance and the achievable diversity for the proposed schemes are analysed theoretically. It is shown that the RS schemes that use the statistical knowledge of channels can not only provide improvement in outage probability but also harvest diversity gain. Simulation results are presented to evaluate the performances while validating the theoretical analyses for the proposed schemes. Copyright © 2014 John Wiley & Sons, Ltd.

Performance analysis for free‐space optical communications using parallel all‐optical relays over composite channels

In the last 2 years, all-optical relaying techniques for free-space optical (FSO) communications have drawn considerable attention. In this study, the outage performance of an FSO communication system with parallel all-optical relays is investigated. A composite channel is established, which includes atmospheric loss, pointing error and atmospheric turbulence. To show the impact of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. After that, the theoretical expressions of the outage probabilities for different scenarios are derived. Numerical results show that the derived expressions are quite accurate to evaluate the system performance. Moreover, the derived results demonstrate that the systems with semi-blind CSI relaying can provide comparable performance to systems with full CSI relaying, and also indicate that the performance over strong turbulence channels with clear weather outperforms that over weak turbulence channels with light fog.

Analysis of spectrally efficient two‐way relay assisted free space optical systems in atmospheric turbulence with path loss

SummaryIn this paper, we investigate the performance of two‐way relay assisted free space optical systems over atmospheric turbulence‐induced fading channels affected by molecular absorbtion‐induced path losses. A three node, dual‐hop, bi‐directional, half‐duplex relaying system with independent but not necessarily identically distributed channels is considered. Spectral efficiency is achieved by employing network coding to complete data transmission in two‐time phases. Closed form expression for system outage performance is derived considering decode‐and‐forward protocol. Additionally, the error performance in terms of average symbol error rate for M‐ary phase shift keying is evaluated. Further, the net achievable capacity of the system is also calculated. Copyright © 2014 John Wiley & Sons, Ltd.

Outage performance of relay-assisted primary and secondary transmissions in cognitive relay networks

Abstract In this paper, a two-phase protocol for relay-assisted spectrum sharing in cognitive relay network is proposed. The primary system comprises a transmitter-receiver pair (PT-PR) and a decode-and-forward relay (Relay), while the secondary system comprises a transmitter-receiver pair (ST-SR). In the proposed protocol, the Relay assists the transmissions of the primary users as well as the secondary users where there is no direct link between the ST and the SR. Outage probabilities of the primary system and the secondary system are derived and verified through simulations. Compared with the protocol without cooperation, better outage performance of the primary system is achieved. Meanwhile, though the ST causes interference to the PR, the interference is compensated by the cooperation of the Relay. Moreover, the proposed protocol realizes the communications of the secondary users on the condition that the secondary transmission link is not ideal.

Balancing outage performance of primary user and secondary user by relay-assisted primary transmission

In this paper, a cooperative transmission protocol for cognitive radio systems is proposed. In this protocol, the primary system comprises a transmitter (PT), a receiver (PR), and a decode-and-forward relay (Relay), while the secondary system comprises a transmitter (ST) and a receiver (SR). Both the ST and the Relay assist the transmissions of the primary users together. The outage probabilities of the primary system and the secondary system are analyzed and verified through simulations. In order to decrease outage probability of the secondary system, power allocation is performed at the ST. However, it will lead to deterioration of outage performance of the primary system. In order to guarantee outage performance of the primary system, a Relay is employed. Compared with two existing protocols, one without cooperation and the other with cooperation of the secondary system only, the proposed protocol is able to better balance outage performances of the primary system and the secondary system.

Outage Performance of Two-Way Fixed Gain Amplify-and-Forward Relaying Systems with Asymmetric Traffic Requirements

In this letter, we investigate the outage performance of two-way relaying system based on the fixed gain amplify-and-forward protocol and asymmetric traffic requirements. At first, we propose a three-step scheme to obtain the channel state information with a low-complexity relay. Then, the exact expression of system outage performance is derived and we further investigate the asymptotic performance at high signal-to-noise ratio. Finally, numerical results are given to verify the analytical results.

Outage performance of multi-hop cooperative diversity system

An approximate outage probability formulation and diversity order were derived for multi-hop diversity system employing Decode-and-Forward(DF) relaying in high Signal-to-Noise Ratio(SNR).And a modified multi-hop Selective Decode-and-Forward(SDF) protocol was proposed to overcome the limitation of space full diversity system unemploying DF relaying,the source node resended the information when the relay could not decode information correctly.An approximate outage probability formulation and diversity order were deduced for SDF protocol in high SNR.The theoretical analysis and simulation results show that the SDF protocol can improve transmission performance and achieve the full space diversity contrasted with DF protocol.