Outage Performance of Cognitive AF Relay Networks with Imperfect CSI Based on Geometrical Analysis

This paper studies the outage performance of a cognitive Amplify-and-forward (AF) relay network subject to Rayleigh fading.Under the condition of imperfect Channel state information (CSI) estimations of the links from the secondary system to the Primary user (PU),the closed-form upper and lower bounds of the outage probability are derived through a geometrical analysis method.An asymptotic analysis of the outage probability is also derived in the high Signal-to-noise ratio (SNR) regime to gain additional insights on the system.The simulation results corroborate our theoretical analysis,and the effectiveness of the geometrical analysis method is verified with the conventional approach as a benchmark.The asymptotic results are very tight with the analytical lower bound in the high SNR regime.It also can be observed from the simulation results that the impact of the number of relays as well as the imperfect CSI on the outage probability and the diversity order.     

Performance analysis of opportunistic amplify-and-forward two-way relaying in two-wave with diffuse power fading channels

This paper considers cooperative amplify-and-forwards(AF) two-way relay networks(TWRNs) with opportunistic relay selection(ORS) in two-wave with diffuse power(TWDP) fading channels. To investigate the system performance, we first derive an easy-to-computer approximated expression for the exact outage probability to reduce computational cost. Furthermore, we presented compact expressions for the asymptotic outage probability and asymptotic symbol error rate, which characterizes two factors governing the network performance at high signal-to-noise ratio(SNR) in terms of diversity order and coding gain. Additionally, based on the asymptotic outage probability, we determine the optimal power allocation solution between the relay and the sources to minimize the overall outage probability under the assumption that both the sources have identical transmit power. The correctness of the analysis is validated through Monte Carlo simulations. Our derived results can be applied to general operating scenarios with distinct TWDP fading parameters which encompass Rayleigh and Rician fading as special cases and arbitrary number of relays.     

Power allocation of cooperative amplify-and-forward communications with multiple relays

Cooperative diversity is one of the most effective ways to mitigate the fading effect of wireless channels and obtain the spatial gain in wireless networks.In this paper,an optimal power allocation(OPA)scheme for a cooperative communication system using the amplify-and-forward(AF)transmit strategy with multiple relay users is proposed by minimizing the bit-error-rate(BER)at the destination under the constraint of the total transmit power of both the source user and the relay users.Simulation results indicate that the proposed power allocation method can achieve significant BER performance improvement than using the equal power allocation(EPA)scheme,while still attains low complexity.The system performance is improved significantly with the increasing of the number of relay users at high signal-noise ratio(SNR).However,at low SNR,the system performance decreases when the relay number increases.Thus,an adaptive relay selection scheme may be used to choose the appropriate relay numbers in different transmission scenarios to provide system performance improvement and keep the power allocation scheme with low complexity.     

Joint power allocation and multi-relay selection scheme based on system outage probability

An amplify-and-forward （AF） based multi-relay network is studied. In order to minimize the system outage probability with a required transmission rate, a joint power allocation （PA） and multi-relay selection scheme is proposed under both total and individual power constraints （TIPC）. In the proposed scheme, the idea of ordering is adopted to avoid exhaustive search without losing much system performance. Besides the channel quantity, the ordering algorithm proposed in this article also takes relays＇ maximal output ability into consideration, which is usually ignored in traditional relay ordering algorithms. In addition, simple power reallocation method is provided to avoid repetitive PA operation during the process of searching all possible relay subsets. By Adopting the idea of ordering and using the proposed power reallocation method lead to remarkable decrease of the computation complexity, making the scheme easier and more feasible to implement in practical communication scenarios. Simulations show that the proposed multi-relay selection scheme provides similar performance compared to the optimal scheme with optimal PA and exhaustive search （OPAES） but with much lower complexity.     

Antenna Selection in Energy Harvesting Relaying Networks Using Q-Learning Algorithm

In this paper,a novel opportunistic scheduling(OS)scheme with antenna selection(AS)for the energy harvesting(EH)cooperative communication system where the relay can harvest energy from the source transmission is proposed.In this considered scheme,we take into both traditional mathematical analysis and reinforcement learning(RL)scenarios with the power splitting(PS)factor constraint.For the case of traditional mathematical analysis of a fixed-PS factor,we derive an exact closed-form expressions for the ergodic capacity and outage probability in general signal-to-noise ratio(SNR)regime.Then,we combine the optimal PS factor with performance metrics to achieve the optimal transmission performance.Subsequently,based on the optimized PS factor,a RL technique called as Q-learning(QL)algorithm is proposed to derive the optimal antenna selection strategy.To highlight the performance advantage of the proposed QL with training the received SNR at the destination,we also examine the scenario of QL scheme with training channel between the relay and the destination.The results illustrate that,the optimized scheme is always superior to the fixed-PS factor scheme.In addition,a better system parameter setting with QL significantly outperforms the traditional mathematical analysis scheme.     

Greedy Algorithm Applied to Relay Selection for Cooperative Communication Systems in Amplify-and-Forward Mode

Using a relaying system to provide spatial diversity and improve the system performance is a tendency in the wireless cooperative communications. Amplify-and-forward(AF) mode with a low complexity is easy to be implemented. Under the consideration of cooperative communication systems, the scenario includes one information source, M relay stations and N destinations. This work proposes a relay selection algorithm in the Raleigh fading channel. Based on the exhaustive search method, easily to realize, the optimal selection scheme can be found with a highly complicated calculation. In order to reduce the computational complexity, an approximate optimal solution with a greedy algorithm applied for the relay station selection is proposed. With different situations of the communication systems, the performance evaluation obtained by both the proposed algorithm and the exhaustive search algorithm are given for comparison. It shows the proposed algorithm could provide a solution approach to the optimal one.     

Performance Analysis of a Novel Cooperative Diversity Scheme

The traditional cooperative diversity could improve the system performance enormously, which has already widely been investigated by researchers. How-ever, it didn＇t exploit channel code and Distributed space-time block code （DSTBC） together to achieve both diversity gain and coding gain. Therefore, in order to further improve system performance, a novel cooperative diver-sity scheme based on concatenating the channel code and DSTBC is proposed in this paper. The closed-form expres-sions of channel capacity, outage probability and Bit error rate （BER） are derived to evaluate the performance of the proposed scheme. Also, computer simulations are conducted to validate our scheme, showing that, even though the interuser channel is noisy, the proposed scheme out-performs the traditional cooperative diversity in terms of channel capacity, outage probability and BER with distinct system gains.     

High throughput relay policy in wireless cooperative relaying networks based on stochastic control theory

This paper proposes a distributed relay and modulation and coding scheme (MCS) selection in wireless cooperative relaying networks where the adaptive modulation and coding (AMC) scheme is applied. First-order finite-state Markov channels (FSMCs) are used to model the wireless channels and make prediction. The objective of the relay policy is to select one relay and MCS among different alternatives in each time-slot according to their channel state information (CSI) with the goal of maximizing the throughput of the whole transmission period. The procedure of relay and MCS selection can be formulated as a discounted Markov decision chain, and the relay policy can be obtained with recent advances in stochastic control algorithms. Simulation results are presented to show the effectiveness of the proposed scheme.     

Outage Probability Analysis of Relay Systems over K-μ Fading Channels

This paper provides an analytical framework for the outage probability evaluation of dual-hop decode-and-forward relay systems operating over K-μfading channels in the presence of co-channel interference. The interferers are independent non-identically distributed K-μfading. An accurate analytical-form expression for the cumulative distribution function of the received signal power to interference and noise ratio is derived. Various numerical results are compared with Monte Carlo simulation results in order to corroborate the accuracy of the proposed expressions. Our results show that increasing the value of kappa of main links will decrease the outage probability of relay systems. Furthermore, the system performance degrades with the number of interferences.     

Secure Transmission in Cognitive Radio Networks Using Full-Duplex Technique with Outdated CSI

This paper investigates the effects of the outdated channel state information(CSI) on the secrecy performance of an underlay spectrum sharing cognitive radio networks(CRNs), where the secondary user(SU) source node(Alice) aims to transmit the trusted messages to the full-duplex(FD) aided SU receiver(Bob) with the assistance of cooperative relay(Relay). Considering the impact of feedback delay, outdated CSI will aggravate the system performance. To tackle such challenge, the collaborative zero-fo...     

过时信道状态信息下的机会式中继选择系统的安全性能分析

在 Nakagami m衰落信道下,目的端和窃听者采用最大比合并策略,本文研究了在机会式自适应解码转发中继选择安全协作系统中的安全性能。由于实际信道中的反馈延迟,最优的合法中继选择基于合法信道反馈的过时信道状态信息。为了评价机会式中继选择在改善安全性能上的表现,分别推导了准确的正安全容量概率和准确的安全中断概率闭合表达式。此外,针对两种不同情况, 推导了形式简单的渐近表达式,并明确给出安全分集阶数和安全阵列增益。理论分析和数值仿真表明,增加中继个数和目的节点的天线数能够改善安全中断概率的性能表现,且在信道状态信息过时的条件下,系统的安全分集阶数与中继数无关。      

基于过时信道状态信息的机会协作性能研究

机会中继是协作通信系统中提高频谱效率和节省功率消耗的常用方法.在通信过程中,信道估计时刻和实际中继传输信息时刻存在一定的延时,其产生的过时信道状态信息（Outdated CSI）会严重地影响协作通信系统的性能.分别从考虑直传链路和不考虑直传链路两方面,分析了过时信道状态信息对机会协作分集系统中断概率的影响.仿真结果表明,系统性能随着相关系数ρ的减小而变差,并且随着中继节点数目的增加而提高.     

过时CSI下全双工中继辅助D2D网络的物理层安全

中继辅助终端直通（devicetodevice,D2D）网络通过与蜂窝网络共享频谱提高D2D用户的频谱效率和蜂窝用户（cellular user,CU）的物理层安全性。为进一步改善其性能,可以在基站和D2D链路的中继节点采用天线选择以及在中继节点采用全双工技术。然而,由于存在反馈时延和移动性,用于蜂窝链路和所有D2D链路天线选择的信道状态信息（channelstateinformation,CSI）均可能是过时的,针对该场景下的物理层安全性和可靠性问题,提出一种主动窃听和过时CSI场景下基站和中继节点均采用发射天线选择的全双工中继辅助D2D网络安全模型,推导CU的中断概率、遍历容量、非零安全容量概率、安全中断概率、渐近安全中断概率的解析表达式。数值计算与仿真结果均表明,基站发射天线数、中继干扰天线数越多,CU的安全性能越好;过时的CSI会降低CU的中断性能和安全性能。     

Outage Probability Analysis for Energy Harvesting Cooperative Relays in a Clustered Environment

This paper presents the outage probability analysis of the energy harvesting (EH) decode and forward (DF) cooperative relay network when more than one relays are available to assist the communication between source and destination in the presence of the direct connection. The relays use power splitting (PS) protocol with adaptive PS ratio for EH. As wireless EH can be more beneficial over smaller distances therefore a clustered environment is considered in which the source, destination and relays are located in a small area. First, we analyze the performance of selection cooperation (SC) which requires channel state information (CSI) at the source. High signal to noise ratio approximation of the outage probability is provided for this case. Secondly, we present the performance of all relays cooperation (ARC) scheme which requires no CSI at the source. Lower and upper bounds of the outage probability are presented for smaller number of relays in ARC scheme whereas high signal to noise ratio approximation is provided for higher number of relays. Simulation results validate the analytical results and show that SC scheme outperforms ARC scheme at the expense of CSI requirement.     

Cognitive relay network with several primary receivers and outdated CSI: a new spectrum sharing constraint

This paper introduces a new spectrum sharing constraint which facilitates outage analysis for the cognitive relay networks with multiple primary receivers (PR)s and under outdated channel state information (CSI). The pivotal idea in spectrum sharing paradigm is controlling the interference generated due to the coexistence of primary and secondary users. In a realistic scenario, interference management is hampered by several parameters. In this context, this paper targets the influence of the CSI accuracy and the number of PRs. In a cognitive network with multiple PRs, the best approach to shielding the receivers from intolerable interference is to limit the maximum inflicted interference. Although being effective, this strategy has two drawbacks. First: it measurably affects mathematical tractability of the outage analysis. Second: it requires substantial resources to find the strongest interference channel which may be unaffordable in certain applications, especially when there are many PRs. In this paper, we propose the total interference (TI) constraint as the spectrum sharing criterion and investigate the outage behavior of the secondary network. A simple back-off power control method is adopted so as to mitigate the harmful effect of the outdated CSI. Considering decode-and-forward relays and partial relay selection strategy, we derive exact expressions for the end-to-end outage probability. Monte-Carlo simulations are made and results corroborate correctness of the mathematical derivations. The findings suggest that: first, outage assessment under the TI constraint is more tractable than under the maximum interference (MI) constraint as it leads to simple closed-form expressions. Second, the secondary network under the TI constraint is more resilient against the outdated CSI because the interference probability arising from the outdated CSI is smaller under the TI constraint than MI.     

分布式环境中协作分集的移动中继动态选择和切换策略研究

在协作无线通信系统中,中继节点的移动会大大降低系统的性能,目前该方面的结果很少。本文探讨分布式环境中协作分集的移动中继选择算法,在放大转发（AF）协作通信模式下,给出了基于信道统计状态信息的功率分配和中继的动态选择策略。针对单中继情况提出了中继切换方案,针对多中继情况提出了动态剔除、补充中继的方案,并导出了分集增益及系统容量的计算公式。通过模拟仿真分析,该方案能有效的降低中断概率,提高系统分集增益,扩大系统容量,实现良好的整体性能。      

Predictive relay‐selection cooperative diversity in land mobile satellite systems

Cooperative diversity protocols promise a new dimension of diversity that provides better communication by engaging nearby relays in forming a ‘virtual’ array of antennas for combined signal transmission. The current incremental cooperative diversity algorithms incrementally select best relay(s) to cooperate based on the channel quality reported by the relays. However, the algorithms do not take into consideration the fact that the chosen best relay(s) at estimation may not always be the best at the time of communication. This is due to the time delay between the relay selection and its transmission of signal (problem of outdated channel quality information (CQI)). To solve this problem, the concept of channel prediction is introduced and employed whereby each relay determines a predicted value of its CQI based on its past measurements. The paper therefore develops a novel predictive relay‐selection (PRS) cooperative diversity model that seeks to improve land mobile satellite communication through prediction protocols. In the model, the chosen best relay is the one with the best predicted CQI value instead of the traditional outdated one. Performance analysis of outage probability and average bit error probability for the newly developed PRS cooperation shows that the PRS cooperation is better than direct and outdated CQI relay communication. Copyright © 2015 John Wiley & Sons, Ltd.     

On the performance of cooperative cognitive networks with proactive relay selection

This paper provides a general outage analysis framework for cooperative cognitive networks with proactive relay selection over non-identical Rayleigh fading channels and under both maximum transmit power and interference power constraints. We firstly propose an exact closed-form outage probability expression, which is then exploited for determining the diversity order and coding gain for proactive relay selection scenarios as well as deriving system performance limits at either large maximum transmit power or large maximum interference power. The derived performance metrics bring several insights into system performance behavior without the need of time-consuming Monte-Carlo simulations. Various results confirm the validity of the proposed derivations and show that cooperative cognitive networks with proactive relay selection incur performance saturation and their performance depends considerably on the number of involved relays. In addition, cooperative cognitive networks are significantly better than dual-hop counterparts without any cost of system resources.     

PHY-layer Fairness in Amplify and Forward Cooperative Diversity Systems

We deal with the concept of physical-layer fairness in amplify and forward cooperative diversity systems, which reflects the need for equally allocating the consumed power among the relays. To this end, we propose a method which utilizes knowledge on both the instantaneous and average channel conditions in order to encompass this concept, by attributing a weight coefficient to each relay depending on its average channel state and then selecting the relay with the best instantaneous "weighted" channel conditions. We also provide a performance analysis of the proposed scheme that includes an analytical expression for the outage probability, together with a closed form one in the high signal-to-noise-ratio (SNR) regime. Through the latter expression, the average symbol error probability (ASEP) for high SNRs is also derived. Numerical results demonstrate that, for small number of available relays or for high SNRs, the performance of the proposed scheme resembles that of the "best relay selection" scheme, in terms of outage probability and ASEP, despite maintaining the average power consumptions equal.     

一种新型多协作中继选择协议研究

机会中继选择协议是一种基于即时信道状态的单协作中继选择方法。文章将机会中继的思想推广到多中继选择场景,提出一种新的中继选择协议。协议通过采用目的节点确认协作中继及加入延时等机制,有效地降低了中继选择的冲突概率,并能控制中继选择的数目,保证中继选择的公平性。协议还修正了原协议中继定时器参数选择问题。仿真表明该协议能够极大地提升系统误码率性能。