中继卫星资源调度问题研究现状与展望

随着跟踪与数据中继卫星系统(TDRSS)的发展以及中继应用需求的增加,其资源调度成为决定系统性能的关键因素之一.分析了包括描述方法、活动与资源、约束条件等在内的中继卫星资源调度问题基本内涵,研究了目前中继卫星资源调度的数学模型和实现算法,比较了不同数学模型和实现算法的优缺点.针对未来卫星激光和微波链路联合组网的发展趋势,提出了基于多终端-多节点及基于资源故障的激光/微波混合链路中继卫星资源调度的基本方法.     

广电数字微波的线路指标设定、分配与性能计算

2010年和2012年,广电总局分别发布了《广播电视数字微波传输电路运行维护规程》(GY/T 244)和《广播电视SDH数字微波安装及验收规范》(GY/T5032),但目前没有数字微波的线路设计规范。本文详细分析了多径衰落、上衰落、雨衰等影响微波传输的因素和计算公式,深入比较了对国际电联(ITU-T和ITU-R)、国标及行标的微波通道指标,通过六个中继段的实例计算和图表分析,对广电数字微波设计中全线路指标设定、中继段指标分配、差错性能和可用性计算等提出了一些建议。     

L波段小信号放大器ADS设计与仿真

对小信号晶体管放大器的设计步骤、设计理论进行了阐述,利用ADS软件通过实例详细地设计了L波段小信号放大器,并给出了仿真结果.仿真结果表明,放大器匹配电路设计完全满足性能指标要求.本文提出的利用ADS软件对L波段的LNA和小信号功率放大器的设计方法可以加速放大器产品化进程,具有重要的实用价值.这种放大器主要应用于微波中继、数字音频卫星直播、全球定位系统等无线系统中.     

基于负荷平衡的混合式中继选择新算法

现有的中继选择算法通常带来中继负荷失衡问题,可能导致中继节点资源的非公平利用。为解决这个问题,首先对中继负荷失衡问题进行了分析,接着使用链路信噪比和中继节点负荷作为模糊控制的输入参量,提出了负荷平衡中继选择(LBRS)算法;其次,针对LBRS算法中存在的低信噪比区域误比特率偏高的问题,进一步提出了LBRS的改进算法,即基于负荷平衡的混合式中继选择(HRS)算法。仿真结果表明,与典型的最优中继选择(BRS)算法比较,HRS算法在平衡中继节点负荷上具有非常显著的优势,在误比特率性能上稍逊,总的来说是一种性能优异的中继选择算法。     

链路可靠性关系认知DTN无线中继组播路由

认知无线电Ad hoc网络(CAN)可看作一类特殊的延迟容忍网络(DTN),并由移动二次用户(SUs)与社会特征组成。网络的间歇连通性和频谱利用率是一个具有挑战性的问题,如何在CANs的SUs之间进行可靠而有效的消息发送。为此,提出一种链路可靠性关系认知DTN无线中继组播路由算法,首先,该预测基于新的社会关系感知移动模型链路可靠性和SUs的关系进行路由融合和中继选择,并根据节点不同关系设计不同的预测方案。消息被转发到与目的地具有最大相遇概率的中继节点。评价结果表明,这种社会关系路由方案可大幅提高路由算法性能,并可降低网络计算复杂度。     

基于人工蜂群算法的中继卫星任务调度研究

研究中继卫星任务调度问题可以为跟踪与数据中继卫星系统(TDRSS)的任务计划编排提供科学合理的决策方法,任务调度模型的建立与调度算法的设计是中继卫星任务调度的两个关键问题。该文针对中继卫星任务调度问题特点,综合考虑中继卫星与用户航天器之间具有可见时间窗、用户提交的任务属性、中继卫星前向资源受限等约束条件,建立了中继卫星任务调度约束规划模型并提出基于人工蜂群(ABC)算法的中继卫星任务调度算法。最后,通过仿真数据分析,表明基于人工蜂群算法的中继卫星任务调度算法是一种有效的、合理的调度方法。     

微波电路仿真软件在无源电路设计中的应用

简述微波无源电路的设计方法，比较了几种常用的微波CAD软件在通用无源电路设计中的优点，阐明了无源电路设计在微波集成设计中的重要性。     

集成化故障检测电路设计

讨论了高频 (微波 )通讯系统中故障检测电路设计的一般方法及设计中应注意的问题 ,并给出了一个设计实例     

基于集成学习的全双工中继系统安全中继选择方案研究

当处于无线信道状态信息(Channel State Information,CSI)快速变化或者多跳中继等应用场景时,利用集成学习算法解决安全中继选择问题能减少实时处理时延及计算复杂度.将合法信道和窃听信道的CSI作为训练模型输入,使系统安全容量到达最大的中继节点索引作为输出,把全双工中继系统安全中继选择问题转化为一个多类分类问题,并利用随机森林(Random Forest,RF)算法求解.安全中继选择方案的实现分为数据准备、模型建立和结果预测三个阶段.在数据准备阶段,由于RF算法要求训练模型输入为离散值,给出了均匀量化和非均匀量化两种特征提取法将CSI转化为离散值.最后,通过仿真实验验证方案性能.     

广义预测控制系统的仿真软件设计与开发

介绍了基于广义预测控制的模型预测控制（MPC）系统仿真软件的开发与实现过程。该软件包含了MAC，IMAC，DMC，DDMC和GPC五种预测控制算法，可以用不同的方法实现对预测控制系统的综合性仿真以及控制器参数的调整。利用该软件可对模型预测控制系统的作用机理做进一步仿真分析，并有助于定性分析各种算法中设计参数对系统性能的影响以及不同算法之间的区别。     

一种移动无线网络分组公平调度算法

提出了一种支持时延限制的无线多媒体流公平调度算法。算法根据无线信道的服务质量,动态调整该信道连接的业务速率,并根据各个业务请求当时的时延因子的大小来公平地补偿和再分配带宽。仿真验证了算法的可行性和科学性。支持对时延敏感的流和对差错敏感的流,能做到区别补偿调度,满足各自的QoS需求。     

Routing for cognitive radio networks consisting of opportunistic links

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter–receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co‐existing multi‐radio systems. Unfortunately, appropriate routing in CRN of coexisting multi‐radio systems remains an open problem. We explore the fundamental behaviors of CR links to conclude three major challenges, and thus decompose general CRN into cognitive radio relay network (CRRN), CR uplink relay network, CR downlink relay network, and tunneling (or core) network. Due to extremely dynamic nature of CR links, traditional routing to maintain end‐to‐end routing table for ad hoc networks is not feasible. We locally build up one‐step forward table at each CR to proceed based on spectrum sensing to determine trend of paths from source to destination, while primary systems (PSs) follow original ways to forward packets like tunneling. From simulations over ad hoc with infrastructure network topology and random network topology, we demonstrate such simple routing concept known as CRN local on‐demand (CLOD) routing to be realistic at reasonable routing delay to route packets through. Copyright © 2009 John Wiley & Sons, Ltd.     

基于Google Earth的无人机中继布局优化软件

建立了一个无人机作为中继的通信网络系统,并通过对中继链路和高空中继覆盖区域进行几何建模,推导获得了无人机在一定飞行高度的信号覆盖区域。在此基础上,基于Google Earth和Visual C++6.0软件平台,开发了一套无人机中继系统可视化网络优化软件。测试结果表明,该软件操作简便且运行稳定,能够实现无人机的静态最优布置与动态飞行路径规划,对于解决网络节点高速和大范围移动导致的网络中断问题,具有重要的工程应用价值。     

Relay selection in mixed RF/FSO system using DF relaying

In this paper, we carry out the performance analysis of relay selection in decode-and-forward (DF)-based mixed radio frequency/free-space optical (RF/FSO) system. We consider two relay selection schemes, namely max-select and distributed switch and stay, and compare their performance with the system having all relays active. The selected DF relay decodes the received RF signal from source and converts it into an optical signal using the subcarrier intensity modulation scheme for transmission over FSO links. The RF links follow generalized \(\eta -\mu \) distribution, while the FSO links are subjected to pointing errors and are assumed to follow gamma–gamma distribution. Novel analytical expressions for cumulative density function and the moment generating function of the equivalent end-to-end signal-to-noise ratio are derived. Capitalizing on the derived statistics, we provide the new closed-form expressions of the outage probability for different relay selection schemes.     

Channelization for dynamic multi-frequency, multi-hop wireless cellular networks

Multi-hop relaying in cellular networks can greatly increase capacity and performance by exploiting the best available links to a base station. We envision an environment in which relay networks are dynamically formed when performance on the radio access network is degraded and then dissolved when the performance improves or the radio spectrum on which the relay network is operating is reclaimed. Each relay network operates on a different frequency band. Likewise, a relay network may channelize its frequency band to offer non-interfering links among the mobile nodes within a single relay network. We propose a set of algorithms used to form such relay networks on-demand. Each algorithm provides a simple and distributed frequency assignment scheme. We also propose two enhancements to improve network throughput of resulting relay networks. We evaluate these algorithms in terms of the overhead of the relay network formation. The evaluation results show that having nodes outmost from the BS initiate route discovery first is the best approach for reducing the formation overhead. The results also show that there is a large increase in throughput when using multiple frequencies in a relay network. Further, the performance of the network using multiple frequencies based on our simple frequency assignment is very close to that of a network using optimal frequency assignment.     

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.     

NASA未来的空间C&N体系及关键技术

介绍了NASA空间通信体系工作组(SCAWG)所提出的2005～2030年NASA空间通信与导航体系。该体系包括地基地球、近地中继、月球中继和火星中继4个物理单元,以及叠加在这4个物理单元之上的网络、安全、频谱及导航4个贯穿的公共体系。为实现这一体系,SCAWG提出了未来6大关键的技术领域,包括上行链路组阵、光通信、航天器RF技术、X射线导航、网络技术和可编程通信系统(软件定义无线电)。通过对NASA未来空间通信与导航体系及关键技术领域进行研究,可为未来的空间探测活动及相关技术发展提供参考。     

放大转发认知中继协作系统中继增益分配方案和性能分析

由于在传统的放大转发认知中继协作方案中,中继增益因子的分配只考虑了部分主、从系统参数,使得系统的能量效率较低、系统资源未被充分利用。为此,基于主系统传输速率约束和从系统终端接收信号平均误符号率最小准则,文章提出了一个新颖的中继增益最优化分配方案,获得了中继增益最优化精确解以及相应的上、下限封闭解析解;并基于获得的最优化中继增益,分析了系统的平均误符号率。结果表明,文章所获得的中继增益因子分配方案由于不仅考虑了从信源功率和从信源-中继链路增益,而且还综合考虑了中继-从信宿链路和主系统参数,可以实现系统资源的最优化配置,系统性能得到改善。      

Performance evaluation of direct and cooperative transmissions in body area networks

Body area networks (BAN) offer amazing perspectives to instrument and support humans in many aspects of their life. Among all possible applications, this paper focuses on body monitoring applications having a body equipped with a set of sensors transmitting in real time their measures to a common sink. In this context, at the application level, the network fits with a star topology, which is quite usual in the broad scope of wireless networks. Unfortunately, the structure of the network at the physical layer is totally different. Indeed, due to the specificity of BAN radio channel features, all radio links are not stationary and all sensors suffer from link losses during independent time frames. In wireless networks, link losses are often coped with multi-hop transmission schemes to ensure a good connectivity. However, since the radio links are not stationary, the multi-hop routes should adapt quickly to BAN changes. We instead propose in this work a different approach based on opportunistic relaying. The concept relies on electing some sensors to support the transmission of other ones having a worst connection. Instead of changing the relay time to time, we rather select a relay node from a statistical perspective. We evaluate this approach from a theoretical point of view and on realistic simulations using the packet error rate outage probability as a performance criterion.     

Joint Clustering Relay Selection and Beamforming in Cooperative Cognitive Radio Networks

This paper proposes a joint clustering relay selection and beamforming method for a more realistic cooperative cognitive radio network, in which a secondary network of multiple secondary links and a relay network coexist with a primary network of one primary link. We aim to improve performance of the system in terms of maximizing the received signal power of the secondary destinations, subject to the constraint of received interference plus noise power of the primary destination using the proposed method. Since different relays cooperate differently towards the signals at the secondary and primary destinations, the proposed method can improve the performance of the system and enables the relay network to simultaneously transmit signals of all secondary links toward the destinations by clustering the relays. Results of simulations confirm validity of the method and improve the system performance compared to the existing cooperative beamforming and Zero-Forcing beamforming, in which no relay selection strategy is used.