Asymptotic analysis of multi-branch two-way amplify-and-forward relaying in Nakagami-m fading with arbitrary fading parameter

Two-way relay networks have received lots of attention, thanks to its ability to overcome the loss in the spectral efficiency due to half-duplex transmission. Asymptotic performance analysis can provide valuable insights in- to practical system designs. However, this is a gap in two-way relay network. In this paper, the asymptotic performance is studied for multi-branch dual-hop two-way amplify-and-forward （AF） relaying networks in independently but not necessarily identically distributed （i.n.i.d.） Nakagami-m fading channels, with arbitrary m 〉 5. The approximate prob- ability density function （PDF） of the instantaneous dual-hop link power at high SNR region is derived. Then we present the asymptotic outage probability expression, and analyze the diversity order and coding gain. Simulations are per- formed to verify the tightness of the presented analysis at medium and high SNR regions.

PERFORMANCE ANALYSIS OF TWO-WAY AMPLIFY-AND-FORWARD RELAYING SYSTEM WITH MULTIPLE INTERFERERS AT THE RELAY

In this paper,we investigate the performance of the two-way Amplify-and-Forward(AF) relaying systems in an interference-limited Rayleigh fading environment.More specifically,assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources,an approximate closed-form expression for the Overall Outage Probability(OOP) and an integral expression for the average Symbol Error Probability(SEP) are derived.The analysis results are verified through com-parison with the Monte Carlo simulation results.

Outage Performance of Opportunistic Amplify-and-Forward Relaying over Asymmetric Fading Environments

This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.

Parameter Optimization for Amplify-and-Forward Relaying Systems with Pilot Symbol Assisted Modulation Scheme

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.

Optimization of Cooperative RelayingMolecular Communications for Nanomedical Applications

Recently,nano-systems based on molecular communications via diffusion(MCvD)have been implemented in a variety of nanomedical applications,most notably in targeted drug delivery system(TDDS)scenarios.Furthermore,because the MCvD is unreliable and there exists molecular noise and inter symbol interference(ISI),cooperative nano-relays can acquire the reliability for drug delivery to targeted diseased cells,especially if the separation distance between the nano transmitter and nano receiver is increased.In this work,we propose an approach for optimizing the performance of the nano system using cooperative molecular communications with a nano relay scheme,while accounting for blood flow effects in terms of drift velocity.The fractions of the molecular drug that should be allocated to the nano transmitter and nano relay positioning are computed using a collaborative optimization problem solved by theModified Central Force Optimization(MCFO)algorithm.Unlike the previous work,the probability of bit error is expressed in a closed-form expression.It is used as an objective function to determine the optimal velocity of the drug molecules and the detection threshold at the nano receiver.The simulation results show that the probability of bit error can be dramatically reduced by optimizing the drift velocity,detection threshold,location of the nano-relay in the proposed nano system,and molecular drug budget.

Power control for two-way amplify-and-forward relaying over Rayleigh fading channels

We propose two novel power control policies for a two-way amplify-and-forward (AF) relaying system,in which each node (two sources and one relay) is assumed to operate under bothminimum and peak power constraints.Through the exploitation of instantaneous channel gains,the first policy can maximize the sum rate of the system.However,the instantaneous channel gains may be unavailable in a rapid time-varying system,where the first policy is inoperable.Consequently,a robust power control policy which requires only mean channel gains is proposed to maximize the upper bound of the average sum rate,and the properties of this policy are investigated.Simulation results show that,by comparison with the policy in which all the nodes use their peak transmit power,the proposed power control policies can provide considerable system performance improvement.Furthermore,the performance difference between the two proposed policies is negligible when the relay is close to one source.

Performance of two-way amplify-and-forward relaying with adaptive modulation over Nakagami-m fading channels

This paper investigates the performance of a two-way amplify-and-forward （AF） relay system with adaptive modulation over independent and non-identical Nakagami-m fading channels. The tight closed-form cumulative distribution function （CDF） expression of the instantaneous end-to-end signal-to-noise ratio （SNR） is provided. Further, approximate closed-form expression for the average spectral efficiency of the two-way AF system with adaptive modulation is obtained. Then, a tight lower bound of outage probability is derived. Finally, we use numerical simulations to verify the tightness of our analytical results.

Multi-user diversity analysis in MISO amplify-and-forward relaying network

This article analyzed multi-user diversity performance for multiple input single output （MISO） amplify-and-forward （AF） relaying network with selection combiner, and the closed-form outage probabilities for variable gain relaying and fixed gain relaying network are derived. Based on these results, diversity order is presented for variable gain relaying network. Simulation results validate the derived theoretical results, and the diversity order of variable gain relaying network with Nr available relays is K （Nt ＋ Nr） in K users＇ scenario, where Nt is the number of source transmitter antennas.

UAV-Assisted FSO Communication System with Amplify-and-Forward Protocol under AOA Fluctuations:A Performance Analysis

Free space optical(FSO)communication has recently aroused great interest in academia due to its unique features,such as large transmission band,high data rates,and strong anti-electromagnetic interference.With the aim of evaluating the performance of an FSO communication system and extending the line-of-sight transmission distance,we propose an unmanned aerial vehicle(UAV)-assisted dual-hop FSO communication system equipped with amplifyand-forward protocol at the relay node.Specifically,we consider impairments of atmospheric absorption,pointing errors,atmospheric turbulence,and link interruptions due to angle-of-arrival fluctuations in the relay system.The Gamma-Gamma and Malaga distributions are used to model the influence of atmospheric turbulence on the source-to-UAV and UAVto-destination links,respectively.We derive closedform expressions of the probability density function(PDF)and cumulative distribution function(CDF)for the proposed communication system,in terms of the Meijer-G function.Based on the precise PDF and CDF,analytical expressions for the outage probability,average bit error rate,and ergodic capacity are proposed with the aid of the extended generalized bivariate Fox’s H function.Finally,we show that there is a match between the analytical results and numerical results,and we analyze the influence of the system and channel parameters on the performance.

Arbitrary Decode-Forward Relaying with Re-Encoded Bits Selection Strategy for Polar Codes

In this paper,we propose an arbitrary decode-forward single-relay scheme for finite blocklength polar codes,which can be applied to the general symmetric discrete memoryless relay channel with orthogonal receiver components.The relay node decodes the received message.The relay node selectively re-encodes the message and transmits it to the destination node.Furthermore,in order to minimize the upper-bound of the block error probability,we propose a selection strategy to decide the proper re-encoded bit set by the relay.Simulation results are presented to illustrate the improvement in decoding performance of the proposed scheme compared to conventional relay schemes in both additive white Gaussian noise(AWGN)channel and Rayleigh fading channel(RFC).

Secure Wireless Multicasting through Nakagami-m Fading Channels with Multi-Hop Relaying

The additional diversity gain provided by the relays improves the secrecy capacity of communications system significantly. The multiple hops in the relaying system is an important technique to improve this diversity gain. The development of an analytical mathematical model of ensuring security in multicasting through fading channels incorporating this benefit of multi-hop relaying is still an open problem. Motivated by this issue, this paper considers a secure wireless multicasting scenario employing multi-hop relaying technique over frequency selective Nakagami-m fading channel and develops an analytical mathematical model to ensure the security against multiple eavesdroppers. This mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multicasting (SOPM) to ensure the security in the presence of multiple eavesdroppers. Moreover, the effects of the fading parameter of multicast channel, the number of hops and eavesdropper are investigated. The results show that the security in multicasting through Nakagami-m fading channel with multi-hop relaying system is more sensitive to the number of hops and eavesdroppers. The fading of multicast channel helps to improve the secrecy multicast capacity and is not the enemy of security in multicasting.

继电保护远程运维系统报文合规检测及入侵阻断技术应用

继电保护远程运维中数据传输各环节存在网络入侵风险,现有安全措施未有效处理业务层风险,且存在风险阻断不及时等问题。为此,提出一种报文合规检测方法及入侵阻断技术,分析报文的对象、格式、业务逻辑和行为模式,建立报文合规规则库及不合规报文阻断策略,设计开发不合规报文阻断模块及“一键阻断”紧急控制模块。通过模拟仿真环境测试,结果表明,上述技术对不同类型异常报文进行的阻断效果与预期一致,可有效阻断非法入侵攻击,从而提高继电保护远程运维的安全性和稳定性。

电工实验台热继电器故障频发的研究与分析

电工实验室核心过载保护装置热继电器的频繁损坏,严重影响实验的顺利进行。随着电工实验台模块的不断增加,电路结构复杂程度不断上升,实验中频繁使用热继电器会导致其损坏越来越多,进而使实验准备时间成倍增加,极大地影响了学生做实验的积极性。针对以上问题及实验教学的实际需要,采用COMSOL Multiphysics有限元仿真软件,结合Siemens NX软件完成热继电器线圈在持续工作电流及短路电流下,电流、电磁及温度三场的耦合仿真,并通过与实际数据对比分析查找热继电器频繁损坏的根本原因。这为之后的建模仿真打下良好的基础,同时也为实验室继电保护模块的选型提供了依据。

适用于双馈风电场送出线的纵联方向保护研究

考虑风电场接入电网时,传统方向元件在短路故障发生时易受到风电场内部电力电子器件动态特性的干扰影响,导致频率特性偏移,系统参数不稳定和弱馈性等问题,使继电保护装置不能及时或正确判断故障发生区域。针对上述问题,首先对含有风电场的故障附加网络进行分析,寻找故障发生后纵联保护安装处各测量点电气量之间的关联性,确定其故障逻辑关系。其次通过对常用的相模变换解耦方式进行分析,选择一个合理的方法代入相关性表达式,根据相关系数值完成故障区域判定。最后利用PSCAD/EMTDC搭建双馈风电场并网模型,设置各种不同的故障类型和场景,并利用Matlab进行保护算法验证,检验故障区域判断结果,验证所提保护方法的正确性与合理性,并且仿真结果表明该方法具有较高的可靠性。

基于自谐振线圈参数优化的多中继无线供电系统效率提升研究

印刷电路板(printed circuitboard,PCB)自谐振线圈可以避免绕线引起的偏差,且不受分立补偿电容的影响,应用在多中继无线供电系统中极具前景。针对PCB自谐振线圈结构参数优化不完全所导致的多中继无线供电系统传输效率低下的问题,该文给出了一种用以提升系统传输效率的PCB自谐振线圈结构参数优化设计方法。首先,建立了多中继无线供电系统的传输效率模型,并分析了线圈的电参数对传输效率的影响机理;其次,详细推导了线圈电参数与线圈的匝数、介质厚度、线宽、铜箔厚度、介质损耗角正切值以及介电常数之间的关系;然后,基于上述关系,以传输效率最高为目标,优化了线圈参数;最后,利用优化后的PCB自谐振线圈搭建了一套五线圈无线供电系统实验样机。实验结果表明,采用优化后的PCB自谐振线圈传输效率最高可达76.5%,相比优化前33.1%的传输效率,提高了43.4%。

禁飞区约束的CSTBC无人机中继通信系统航迹优化

中继无人机的飞行路径对无人机中继通信系统的链路传输可靠性具有重要影响。为提高无人机中继通信系统链路传输的可靠性,提出协作空时分组编码(CSTBC)无人机中继通信方案,并以链路中断概率最小化准则为基础,提出中继无人机的航迹优化方法;理论分析给出系统遍历容量和分集增益;为保障中继无人机飞行安全,并获取信道的分集增益,提出无人机禁飞区规避方法。结果表明:协作空时分组编码无人机中继通信系统可充分获取信道的分集增益,改善无人机中继通信系统链路传输的可靠性。

认知物联网中继传感节点最小功耗布置方法研究

物联网数据传输过程中,中继传感节点能量不足或者能量消耗过多将导致部分节点失效,降低物联网的使用寿命。为解决这一问题,提出认知物联网中继传感节点最小功耗布置方法。根据中继节点结构特征、有向加权图,建立数据传输功耗的数学模型;以最小功耗布置为目的,制定数据流向、通信容量、数据最大传输次数的约束条件,阻止中继节点逆向传输,使节点满足通信容量范围的同时,避免出现逐条传输数据的事件;引入贪婪算法布置中继传感节点,实现中继传感节点最小功耗布置。仿真结果表明,所提方法的中继传感节点布置最大功耗为17.58 J;在传感节点分布密度为370个/m^(3)时,中继节点布置数量为126个;在11.9 s内即可完成150个中继节点的布置。

5G超密集网络绿色中继算法研究

文章针对轻载蜂窝网络中待转移移动台在切换中继接入点过程中存在的能耗管控问题,提出一种服务质量级的5G超密集网络绿色中继算法。该算法通过识别中继站及中继网络类型来制定基于信道差异化的绿色中继方案。所制定的方案有效地约束了设备到设备数据通信全信道、中继站以及移动台的能耗。同时引入载荷评估机制并通过最优速率接入函数从最优中继信道中再次筛选出更优中继方案,有效地规避了待转移移动台接入点切换后全网载荷失衡的风险。实验结果表明,绿色中继算法可在确保设备到设备数据通信服务质量的同时实现能耗最优管理。在覆盖范围越大、移动台越多的5G超密集网络中,算法能耗管理优势越加明显。

多簧片结构的磁保持继电器多物理场刚柔耦合仿真模型建立和实验分析

多簧片结构的磁保持继电器衔铁转动引起的触点碰撞、弹跳现象使运动过程复杂,静、动态特性理论分析和仿真模型建立困难。以某型号多簧片结构的磁保持继电器为研究对象,理论分析结构拓扑及工作机理,考虑触点间切入深度,引入狄拉克函数和赫维赛德函数,解决簧片受力分散及触点由于碰撞、弹跳引起的作用力不连续问题;将簧片等效为悬臂梁,基于欧拉-伯努利梁理论建立触簧系统三簧片分段耦合动力学模型。利用Ansys Maxwell引入基于误差的自适应网格划分方法求解电磁机构静态特性;考虑触簧系统簧片运动变形效应,通过ADAMS基于模态理论,构建刚柔耦合动力学仿真模型。基于分段动力学思想,搭建电-磁-机械运动多物理场刚柔耦合仿真模型。利用高速摄像机、电流探头等设计磁保持继电器实验方案,搭建实验平台,测试并分析磁保持继电器触点吸合运动时间、触点压力、弹跳时间、线圈电流,并分析人工装配簧片引起触点压力不同使继电器动作过程存在的不一致性问题,验证该文所提多簧片结构的磁保持继电器特性分段耦合分析方法和多物理场刚柔耦合仿真模型的有效性。

中国式刑事证明结构:分段包干与选择性接力

1979年颁行的《刑事诉讼法》确立了我国分段包干与选择性接力的证明结构。它既体现在侦诉审关系中,也体现在上下审关系中。在这一结构中,公检法在各自主导的诉讼阶段只有调查程序和方式的差异,并无查证责任和目标的差异。后端办案机关有接力查证的责任。接力者具有依照法定证明标准选择是否接力的判断权,也有选择接力主体、范围和方法的裁量权。《刑事诉讼法》虽然历经多次修改,但均朝着优化结构的方向前行。我国刑事证明结构具有如下鲜明特色:一是事实认定权力的去中心主义,二是专门机关查证责任的同质化,三是查证范围认定权的单元化,四是“调查”真相演变为“接着查”真相,五是作为查明真相协助者的辩方。