A distributed method for relay selection in cooperative cognitive radio networks

We analyze the performance of a fully decentralized relay-selection method for the relay-assisted Cognitive Radio (CR) systems. The method requires no explicit communication among relay, assumes no prior knowledge of geometry. In particular, we assume that the frequencies chosen by the relay-assisted CR network overlapped with an active primary link. The proposed relay-selection scheme decreases the outage probability by considering both the channel scenario and the interference to the primary link compared with the non-cooperative transmission. Benefits of cooperative diversity are increased with the increased number of relays.     

能量收集多跳D2D无线传感网络中的中继选择算法

针对无线功率传输技术的能量收集效率有限造成信噪比下降进而引发通信中断率增加的问题,在能量收集多跳D2D(Device to Device)无线传感网络中,提出一种基于改进K-means聚类的中继选择方法。首先,推导得到能量收集下的信噪比因子,使其作为K-means聚类特征。然后,利用最小欧氏距离原则得到距离聚类中心最近的实际节点的位置。最后,根据距离重排序得到中继节点,形成从源节点到目的节点的通信链路。仿真实验结果表明,相比最短路径算法和随机中继协作方案,所提出的改进算法链路信噪比更大,能够减小通信中断率,具有更好的中继性能。     

Optimization of energy efficiency for cognitive radio with partial RF energy harvesting

The cognitive radio (CR) with energy harvesting is a potential technology to improve both the spectrum efficiency (SE) and the energy efficiency (EE). In this letter, we consider that the secondary users can harvest radio frequency (RF) energy from primary signal and its own signal. The goal is to maximize the energy efficiency of the CR system subject to sufficient protection to the primary user and the power constraint. An efficient algorithm is proposed to optimize the sensing time and the power of the secondary transmitter. Simulation results show that the EE is further improved by using the proposed mechanism.     

Power allocation,relay selection and energy cooperation strategies in energy harvesting cooperative wireless networks

In this paper, optimal power allocation and relay selection strategies in energy harvesting cooperative wireless networks are studied. In particular, signal‐to‐noise ratio (SNR)‐maximizing based power allocation and relay selection without and with energy cooperation—via wireless energy transfer—are considered. Moreover, total relay power minimization subject to target end‐to‐end SNR is investigated. The different optimal strategies are formulated as optimization problems, which are non‐convex. Thus, intelligent transformations are applied to transform non‐convex problems into convex ones, and polynomial‐time solution procedures are proposed. Simulation results illustrate that power allocation strategies achieve higher end‐to‐end SNR than relay selection ones. Finally, energy cooperation is shown to be effective in improving end‐to‐end SNR, while total relay power minimization balances end‐to‐end SNR, transmit power consumption, and harvested energy. Copyright © 2016 John Wiley & Sons, Ltd.     

Learning AP in wireless powered communication networks

In a wireless powered communication network (WPCN), sensor nodes harvest energy to transmit information. By a harvest‐then‐transmit (HT) protocol, nodes can be classified into either energy receiving (ER) or data transmitting (DT) nodes depending on the current level of the harvested energy. Since nodes may join or leave a network any time and energy levels vary, the distribution of ER and DT nodes changes over time. As the number of contending DT nodes is highly dynamic, a quick learning mechanism is required for an access point (AP). We propose a learning AP that learns from experience and adapts the frame size according to the changes in the number of DT nodes. The proposed learning AP is also shown to learn well and react to the situation. We compare the performances of the proposed learning mechanism with a WPCN and conventional HT FSA schemes. The proposed RL scheme outperforms the comparative schemes in terms of success rate and delay.     

能量收集双向中继网络的中继选择和功率分配

结合能量收集技术,研究了放大转发双向中继网络的系统性能。基于双向中继系统中的两个端到端信噪比平衡准则,推导出了单中继选择情况下信源最优的功率分配方案和中继最优的能量收集比例。仿真结果证明所提方法能够实现最好的系统性能。通过比较发现,能量收集双向中继网络比传统双向中继网络能够实现更高的传输速率。     

On the outage probability of large scale decode-and-forward relay wireless networks

This paper considers a wireless network consisting of large number of clusters, wherein each cluster represents a decode-and-forward (DF) relay network. Two main scenarios according to the distances among the nodes in the network are investigated. In the case of deterministic distances, the outage probability is obtained in a closed-form expression. Whereas for the case when these distances are independent random variables, the framework of Stochastic Geometry (SG) is exploited for deriving the closed-form of the outage probability in case of Rayleigh fading channel. Furthermore, a lower and upper bound for the outage probability in case of general fading channel have been also provided. Numerical simulations are carried out to validate the derived analytical expressions, and to illustrate how the obtained results can be utilized in interference management of such networks.     

Performance evaluation of a two-way relay network with energy harvesting and hardware noises

In this paper, we propose a Two-Way Cognitive Relay Network (TWCRN) where the secondary users operate on an underlay mode to access the licensed bands. In the proposed protocols, two secondary sources transmit their data to a relay in the first time slot, and then the relay would forward the received information to both sources in the remaining time. Moreover, the relay is self-powered by harvesting energy from ambient Radio Frequency (RF) signals, using the Time Switching (TS) and the Power Switching (PS) method. This paper concentrates on evaluating the performance of the secondary networks under the impact of hardware impairments and co-channel interference from the primary networks. In particular, based on the secondary transmitters’ constraint power, we derive the closed-form expressions of the outage probability and the throughput over Rayleigh fading channels in two cases: TS and PS. We also investigate the energy efficiency issue and the locally optimal position of the relay to maximize the system throughput, which provides much information to install the relay location. Finally, our derivations are verified by Monte Carlo simulation.     

Secure wireless powered relaying networks: Energy harvesting policies and performance analysis

In this paper, we investigate the problem of secure communication for a scenario, which consists of one pair of source‐destination nodes and one untrusted relay. The source communicates with the destination via the help of energy harvesting–aware untrusted relay, which acts as the helper to forward the source information to the destination; however, the relay also acts as the unintended user to eavesdrop the source information. To keep the source information confidential from untrusted relay, the destination‐assisted jamming technique is deployed. We evaluate the impact of energy harvesting protocols on such a secure communication scenario through the proposed energy transfer protocols, namely, source‐based energy harvesting protocol and maximum energy harvesting protocol. To evaluate the secrecy performance of these proposed schemes, we derive analytical expressions for two important performance metrics including intercept probability and strictly positive secrecy capacity. The numerical analysis reveals the different trade‐off between secure performance and relevant system parameters (i.e., power splitting ratio, time switching ratio, energy conversion efficiency, transmit signal‐to‐noise ratio, and relay location). Simulation results are also provided to demonstrate the accuracy of the developed analytical expression.     

User-centric energy efficiency fairness in backscatter-assisted wireless powered communication network

In order to address the unfair user-centric energy efficiency (EE) problem caused by channel difference in the backscatter-assisted wireless powered communication network,a resource allocation scheme was proposed.Firstly,a mixed integer nonconvex fractional programming problem was formulated to maximize the minimum user-centric EE,subject to the quality of service and energy-causality constraints.Based on the generalized fractional programming theory,the original problem was transformed into a mixed integer nonconvex subtraction problem.With the aid of the slack variable,the proof by contradiction,the auxiliary variable and the mixed integer nonconvex subtraction problem were further transformed into an equivalent convex problem.Finally,an iterative algorithm was proposed to obtain the optimal solutions.Computer simulations validated the quick convergence of the proposed iterative algorithm,and that the developed resource allocation scheme efficiently guarantees the fairness among users in terms of EE.     

Analyzing lifetime of energy harvesting underwater wireless sensor nodes

Underwater Wireless Sensor Networks (UWSNs) are utilized to monitor underwater environments that pose many challenges to researchers. One of the key complications of UWSNs is the difficulty of changing node batteries after their energy is depleted. This study aims to diminish the issues related to battery replacement by improving node lifetime. For this goal, three energy harvesting devices (turbine harvester, piezoelectric harvester, and hydrophone harvester) are analyzed to quantitate their impacts on node lifetime. In addition, two different power management schemes (schedule‐driven and event‐driven power management schemes) are combined with energy harvesters for further lifetime improvement. Performance evaluations via simulations show that energy harvesting methods joined by power management schemes can improve node lifetime substantially when actual conditions of Istanbul Bosporus Strait are considered. In this respect, turbine harvester makes the biggest impact and provides lifetime beyond 2000 days for most cases, while piezoelectric harvester can perform the same only for low duty cycle or event arrival values at short transmission ranges.     

Power allocation algorithm of full duplex cognitive relay network based on energy harvesting

To alleviate the shortage of spectrum resources and improve the power utilization of cognitive radio networks,a resource allocation algorithm of full duplex cognitive relay networks with energy harvesting was proposed.In the algorithm,the coefficient for power splitting of the relay and the transmit power of the secondary users were jointly optimized to maximize the throughput of the secondary users under the interference to primary users and energy harvesting constraints.Since the optimization of the algorithm was non-convex,it was transformed into two sub-optimizations,the sub-optimization of the coefficient for power splitting and the sub-optimization of the power transmitted of secondary users,which were the solvable convex sub-optimizations.Then,the final solution of the original optimization was obtained with the iterative algorithm.Simulation results show that the throughput of the proposed algorithm,can obtain 2 times throughput of the networks with half-duplex power splitting algorithm and 1.5 times throughput of the networks with full-duplex time switching algorithm.     

Impact of fixed power allocation in wireless energy harvesting NOMA networks

The time switching‐based relaying (TSR) scheme is considered in energy harvesting protocol to implement with its advantage to nonorthogonal multiple access (NOMA) system. In particular, decode‐and‐forward (DF) mode is proposed to employ in relay to forward signal to serve two far NOMA users. There are two main metrics including outage probability and ergodic rate, which are derived in exact expressions with respect to varying performance under impacts of energy harvesting fractions. To evaluate system performance, outage event and related capacity are illustrated, and we tailor performance gap among two NOMA users and such gap can be controlled by selecting of appropriate power allocation factors assigned for each user to obtain optimal performance. By examining node arrangement, target rates and varying transmit signal to noise ratio (SNR), it can be further achieved performance in several situations of such NOMA. As important result, the considered NOMA system outperforms than the conventional multiple access scheme, and this expected result is confirmed in numerical result and theoretical results. We also explore impacts of transmit power at source, noise power, the other key parameters of energy harvesting scheme to exhibit outage, and ergodic performance. Simulation results are presented to corroborate the proposed methodology.     

能量收集认知多跳中继网络中断性能分析及优化

针对能量收集认知无线网络中的多跳中继传输问题,该文构建了一种新的具有主网络干扰的功率信标(PB)辅助能量收集认知多跳中继网络模型,并提出单向传输方案。在干扰链路统计信道状态信息场景下,推导了次网络精确和渐近总中断概率闭合式。针对精确总中断概率表达式的复杂性和非凸性,采用自适应混沌粒子群优化(ACPSO)算法对次网络总中断性能进行优化。仿真结果表明,PB功率、干扰约束、次网络跳数、能量收集比率、主接收端数目和信道容量阈值等参数对中断性能影响显著,所提算法能快速和有效地对网络中断性能进行优化。     

A rendezvous reservation protocol for energy constrained wireless infrastructure networks

This paper considers a low power wireless infrastructure network that uses multi-hop communications to provide end user connectivity. A generalized Rendezvous Reservation Protocol (RRP) is proposed which permits multi-hop infrastructure nodes to adapt their power consumption in a dynamic fashion. When nodes have a long-term association, power consumption can be reduced by having them periodically rendezvous for the purpose of exchanging data packets. In order to support certain applications, the system invokes a connection set up process to establish the end-to-end path and selects node rendezvous rates along the intermediate nodes to meet the application’s quality of service (QoS) needs. Thus, the design challenge is to dynamically determine rendezvous intervals based on incoming applications’ QoS needs, while conserving battery power. In this paper, we present the basic RRP mechanism and an enhanced mechanism called Rendezvous Reservation Protocol with Battery Management (RRP-BM) that incorporates node battery level information. The performance of the system is studied using discrete-event simulation based experiments for different network topologies. The chief metrics considered are average power consumption and system lifetime (that is to be maximized). The QoS metrics specified are packet latency and end-to-end setup latency. It is shown that the use of the RRP-BM can increase the lifetime up to 48% as compared to basic RRP by efficiently reducing the energy consumption. This work was supported by a grant from the Natural Sciences and Engineering Research Council of Canada and Communications and Information Technology Ontario (CITO). Part of the research was supported by Air Force Office of Scientific Research grants F-49620-97-1-0471 and F-49620-99-1-0125; Laboratory for Telecommunications Sciences, Adelphi, Maryland; and Intel Corporation. The authors may be reached via e-mail at todd@mcmaster. ca, krishna@umbc. edu. The basic RRP mechanism was presented at the IASTED International Conference on Wireless and Optical Communications, Banff, Canada, July 2002. Subalakshmi Venugopal received her Bachelors in Computer Science from R.V. College of Engineering, Bangalore, India and her M.S. degree in Computer Science from Washington State University. She interned as a student researcher at the Indian Institute of Science, Bangalore, India. Ms. Venugopal is currently employed with Microsoft Corporation in Redmond, WA and is part of the “Kids and Education Group”. Her research interests include low power wireless ad hoc networks. Zhengwei (Wesley) Chen received the M.E. in Electrical & Computer Engineering Dept from McMaster University in Canada in 2002. He joined Motorola Inc. as a CDMA2000 system engineer in 2000. In 2002, he joined UTStarcom as a manager of the Global Service Solution Department. He is currently in charge of R&D for Advanced Services related to the TVoIP and Softswitch products. Terry Todd received the B.A.Sc, M.A.Sc and Ph.D degrees in Electrical Engineering from the University of Waterloo in Waterloo, Ontario, Canada. While at Waterloo he also spent 3 years as a Research Associate with the Computer Communications Networks Group (CCNG). During that time he worked on the Waterloo Experimental Local Area Network, which was an early local area network testbed. In 1991 Dr. Todd was on research leave in the Distributed Systems Research Department at AT&T Bell Laboratories in Murray Hill, NJ. He also spent 1998 as a visiting researcher at The Olivetti and Oracle Research Laboratory (ORL) in Cambridge, England. While at ORL he worked on the piconet project, which was an embedded low power wireless network testbed. Dr. Todd is currently a Professor of Electrical and Computer Engineering at McMaster University in Hamilton, Ontario, Canada. At McMaster he has been the Principal Investigator on a number of major research projects in the optical and wireless networking areas. He currently directs a large group working on wireless mesh networks and wireless VoIP. Professor Todd holds the NSERC/RIM/CITO Chair on Pico-Cellular Wireless Internet Access Networks. Dr. Todd’s research interests include metropolitan/local area networks, wireless communications and the performance analysis of computer communication networks and systems. Professor Todd is a Professional Engineer in the province of Ontario. Krishna M. Sivalingam is an Associate Professor in the Dept. of CSEE at University of Maryland, Baltimore County. Previously, he was with the School of EECS at Washington State University, Pullman from 1997 until 2002; and with the University of North Carolina Greensboro from 1994 until 1997. He has also conducted research at Lucent Technologies’ Bell Labs in Murray Hill, NJ, and at AT&T Labs in Whippany, NJ. He received his Ph.D. and M.S. degrees in Computer Science from State University of New York at Buffalo in 1994 and 1990 respectively; and his B.E. degree in Computer Science and Engineering in 1988 from Anna University, Chennai (Madras), India. While at SUNY Buffalo, he was a Presidential Fellow from 1988 to 1991. His research interests include wireless networks, optical wavelength division multiplexed networks, and performance evaluation. He holds three patents in wireless networks and has published several research articles including more than thirty journal publications. He has published an edited book on Wireless Sensor Networks in 2004 and edited books on optical WDM networks in 2000 and 2004. He served as a Guest Co-Editor for special issues of the ACM MONET journal on “Wireless Sensor Networks” in 2003 and 2004; and an issue of the IEEE Journal on Selected Areas in Communications on optical WDM networks (2000). He is co-recipient of the Best Paper Award at the IEEE International Conference on Networks 2000 held in Singapore. His work has been supported by several sources including AFOSR, NSF, Cisco, Intel and Laboratory for Telecommunication Sciences. He is a member of the Editorial Board for ACM Wireless Networks Journal, IEEE Transactions on Mobile Computing, Ad Hoc and Sensor Wireless Networks Journal, and KICS Journal of Computer Networks. He serves as Steering Committee Co-Chair for IEEE/CreateNet International Conference on Broadband Networks (BroadNets) that was created in 2004. He is currently serving as General Co-Vice-Chair for the Second Annual International Mobiquitous conference to be held in San Diego in 2005 and as General Co-Chair for the First IEEE/CreateNet International Conference on Security and Privacy for Emerging Areas in Communication Networks (SecureComm) to be held in Athens, Greece in Sep. 2005. He served as Technical Program Co-Chair for the First IEEE Conference on Sensor and Ad Hoc Communications and Networks (SECON) held at Santa Clara, CA in 2004; as General Co-Chair for SPIE Opticomm 2003 (Dallas, TX) and for ACM Intl. Workshop on Wireless Sensor Networks and Applications (WSNA) 2003 held in conjunction with ACM MobiCom 2003 at San Diego, CA; as Technical Program Co-Chair of SPIE/IEEE/ACM OptiComm conference at Boston, MA in July 2002; and as Workshop Co-Chair for WSNA 2002 held in conjunction with ACM MobiCom 2002 at Atlanta, GA in Sep 2002. He is a Senior Member of IEEE and a member of ACM.     

Improving energy efficiency of incremental relay based cooperative communications in wireless body area networks

In this paper, we investigate the energy efficiency of an incremental relay based cooperative communication scheme in wireless body area networks (WBANs). We derive analytical expressions for the energy efficiency of direct and cooperative communication schemes taking into account the effect of packet error rate. The following communication scenarios specific to a WBAN are considered: (i) in‐body communication between an implant sensor node and the gateway, and (ii) on‐body communication between a body surface node and the gateway with line‐of‐sight (LOS) and non‐LOS channels. The results reveal a threshold behavior that separates regions where direct transmission is better from regions where incremental relay cooperation is more useful in terms of energy efficiency. It is observed that, compared with direct communication, incremental relay based cooperative communication schemes improves the energy efficiency significantly. Further, cooperation extends the source‐to‐destination hop length over, which energy efficient communication can be achieved as compared with direct communication. We also observe that, for both direct as well as cooperative transmission schemes in error prone channels, an optimal packet size exists that result in maximum energy efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

新型随机多址接入无线传感器网络MAC控制协议与能量有效性分析

提出了一种新的随机多址接入无线传感器网络的MAC控制协议,在发送分组的时间1+a中,采用P概率检测与1-坚持的联合控制策略,并对多通道的随机多址接入无线传感器网络进行了分析,理论分析了系统的吞吐量和多通道中不同业务的吞吐量,以及信息分组的发送时延等参数,理论分析与仿真实验结果相一致.还结合无线传感器网络的能量有效性,通过对概率P值的选取,控制忙周期侦听信道的节点数和空闲期的休眠站点数,采用休眠技术实现了系统的节能效果.通过对2种无线传感器网络控制协议的能量有效性分析,证明了改进的控制协议其节点具有更长的生命周期,更适合作为无线传感器网络的MAC控制协议.     

Performance of cognitive relay network with energy harvesting relay under imperfect CSI

This paper evaluates the performance of an underlay cognitive relay network under imperfect channel state information (CSI) where a secondary user (SU) transmits using a secondary relay (SR) based on decode and forward scheme. The outage probability (OP) of SU is investigated in a scenario where the decode and forward relay harvests energy from radio frequency signal of SU. The relay uses a fraction of time for harvesting in time switching–based relaying (TSR) while a fraction of received power is used for harvesting in power splitting–based relaying (PSR) scheme. The SU and relay control their transmit power using a scaling factor, based on CSI of the interfering links (ie, links from SU transmitter and SR to the primary user [PU] receiver) to protect the quality of service of PU. The available CSI at the SU and SR are imperfect due to practical limitation. Analytical expressions of the OP are derived for TSR‐ and PSR‐based schemes. The impact of harvesting time, power splitting ratio, imperfect CSI, PU outage constraint and interference threshold on the OP of the SU network, and average transmit power of SR is indicated. Further, the impact of multiple SRs is also shown.     

Power allocation algorithm for cognitive radio energy harvesting networks based on energy cooperation

An algorithm to optimize the power allocation by maximizing the system throughput in cognitive radio energy harvesting networks was proposed.The algorithm formulated the throughput optimization model subject to the causality constraints of the harvested energy within the two secondary users and the interference constraint of the primary user.In addition,by applying the variable-substitution method and problem equivalence transformation,the joint optimization problem of power and cooperative energy was decoupled into two problems:a power allocation problem and a cooperative energy one.The former problem could be solved by iterating the two decoupled problems.As shown in the simulation results,the energy cooperation can significantly improve the system throughput when the harvested energy difference between two nodes is rather large.