A Model for the Handover Traffic and Channel Occupancy Timein LEO Satellite Networks

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多业务LEO卫星网络中最优呼叫允许控制及切换管理策略

该文针对多业务条件下的LEO(Low-Earth-Orbit)卫星网络,提出了一种新的基于最优多门限信道预留(OMTCR)的呼叫允许控制(CAC)及切换管理策略,建立了评价LEO卫星网络连接级QoS性能的理论分析模型框架。借鉴经济学收益函数的概念分别建立了无QoS约束和有QoS约束的系统收益目标优化模型,求解在给定系统参数和输入业务条件下OMTCR的最优门限参数矢量。仿真结果表明OMTCR能够在不同用户QoS要求和系统收益目标的多业务环境下获得比传统CS(Completely Sharing)策略及GC(Guard Channel)策略更好的性能。     

LEO卫星通信系统的呼叫接入性能分析

在均匀业务模型的基础上,根据LEO卫星通信系统自身特点,提出了一种简单有效的呼叫接入控制策略,这种策略能在非均匀业务下较好地工作,此时系统新呼叫阻塞率和切换呼叫失败率能达到更好的平衡。在分析随机接入（RANDOM）算法和预留保护信道（GC）算法的基础上,进行了计算机仿真,并给出了相应的仿真结果。     

Satellite handover techniques for LEO networks

Low earth orbit satellite constellations could play an important role in future mobile communication networks due to their characteristics, such as global coverage and low propagation delays. However, because of the non‐stationarity of the satellites, a call may be subjected to handovers, which can be cell or satellite handovers. Quite many techniques have been proposed in the literature dealing with the cell handover issue. In this paper, a satellite handover procedure is proposed, that investigates and exploits the partial satellite diversity (namely, the existing common coverage area between contiguous satellites) in order to provide an efficient handover strategy, based always on a tradeoff of blocking and forced termination probabilities for a fair treatment of new and handover calls. Three different criteria were examined for the selection of a satellite. Each one of them could be applied either to new or handover calls, therefore we investigated nine different service schemes. A simulation tool was implemented in order to compare the different service schemes and simulation results are presented at the end of the paper. Copyright © 2004 John Wiley & Sons, Ltd.     

QoS Handover Management in LEO/MEO Satellite Systems

Low Earth Orbit (LEO) satellite networks are foreseen to complement terrestrial networks in future global mobile networks. Although space segment topology of a LEO network is characterized by periodic variations, connections of mobile stations (MSs) to the satellite backbone network alter stochastically. As a result the quality of service delivered to users may degrade. Different procedures have been proposed either as part of a resource allocation mechanism or as part of an end-to-end routing protocol to manage transitions of MSs from one satellite to another (handover). All of these techniques are based on the prioritization of requested handovers to ease network operation and therefore enhance provision of service. This paper proposes a new handover procedure that exploits all geometric characteristics of a satellite-to-MS connection to provide an equable handover in systems incorporating onboard processing satellites. Its performance is evaluated by simulations for a variety of satellite constellations to prove its general applicability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Q-Win – A New Admission and Handoff Management Scheme for Multimedia LEO Satellite Networks

Low Earth Orbit (LEO) satellite networks are deployed as an enhancement to terrestrial wireless networks in order to provide broadband services to users regardless of their location. In addition to global coverage, these satellite systems support communications with hand-held devices and offer low cost-per-minute access cost, making them promising platform for Personal Communication Services (PCS). LEO satellites are expected to support multimedia traffic and to provide their users with the negotiated Quality of Service (QoS). However, the limited bandwidth of the satellite channel, satellite rotation around the Earth and mobility of end-users makes QoS provisioning and mobility management a challenging task. One important mobility problem is the intra-satellite handoff management. The main contribution of this work is to propose Q-Win, a novel call admission and handoff management scheme for LEO satellite networks. A key ingredient in our scheme is a companion predictive bandwidth allocation strategy that exploits the topology of the network and contributes to maintaining high bandwidth utilization. Our bandwidth allocation scheme is specifically tailored to meet the QoS needs of multimedia connections. The performance of Q-Win is compared to that of two recent schemes proposed in the literature. Simulation results show that our scheme offers low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, while maintaining bandwidth utilization high.     

ATM网络中综合连接接纳控制与路由选择的模糊决策策略

本文提出了一种新的模糊决策策略,用于综合考虑连续接纳控制和路由选择,以求在ＡＴＭ网络中增加整个网络的吞吐量和降低信元丢失率与呼损率。文章中详细阐述了该模糊决策系统的原理,并给出了一种自适应调节系统参数的方法。仿真结果说明利用神经网络能够成功地实现此模糊系统。     

Connection Admission Control in ATM Networks Based on the Foreground and Background Neural Networks

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低轨卫星通信系统中的一种波束小区切换算法

针对低轨卫星移动通信系统中终端切换频繁,以及因邻区列表动态变化特性使得邻区测量存在较大不确定性的问题,提出了一种基于波束可视时间与接收信号强度的波束小区切换准则。推导了定向天线信号场值广播至地面的时变表达式,基于此预测切换触发时间,并进一步计算终端的邻区列表。根据波束可视时间与接收信号强度计算邻区的切换权重并进一步选择目标波束,针对重复切换的情形设置同一波束切换次数上限。仿真结果表明,该算法可以有效降低终端切换的频次并避免“乒乓切换”的发生,且终端纬度越高,算法效果越明显。     

移动卫星网络中基于最小费用的切换算法

对于移动卫星网络,合理的星地链路切换方案需要在保证最小切换时延的同时,能够最优地使用网络资源。该文通过引入业务的中断概率和费用模型,给出了切换过程中重路由的最优触发条件,提出一种基于最小费用的切换(SMCH)算法。该算法可在保证切换业务通信的连续性和时延等指标不被破坏的基础上,通过适当的触发重路由来降低切换费用。仿真表明该算法在保证切换业务的QoS,降低切换费用以及适应性、灵活性等方面都优于同类切换算法。     

QoS Performance Bounds and Efficient Connection Admission Control for Heterogeneous Services in Wireless Cellular Networks

Quality-of-Service (QoS) performance and connection admission control (CAC) for heterogeneous services in wireless multiple access networks are investigated. The heterogeneous services include constant bit rate (CBR), variable bit rate (VBR) and available bit rate (ABR) services. Multiple access control is handled by a polling-based scheme with non-preemptive priority. Tight delay variation (jitter) bounds for CBR connections and delay bounds for VBR connections are derived. A CAC scheme based on the derived bounds is developed. The CAC makes use of user mobility information to reserve an appropriate amount of system resources for potential handoff connections to achieve low handoff connection dropping rate (HCDR). Simulation results show that the proposed CAC scheme can achieve both low HCDR and high resource utilization.     

LEO卫星网络动态混合卫星切换策略

LEO卫星网络切换协议中的路由选择策略应当综合考虑路由本身优化性,路由计算复杂性,路由更新的信令代价。提出适合LEO网络卫星切换要求的动态混合路由选择策略(DHRS:DynamicHybridRouteSelection),即发生卫星切换时,由卫星节点根据移动终端用户切换前所处位置和切换前路由表等信息,为移动终端选择合适的路由。     

Network Control in ATM-Based LEO Satellite Networks

Low Earth Orbiting (LEO) satellite networks with on-board asynchronous transfer mode (ATM) switches hold the promise of offering an economically viable extension of terrestrial ATM systems by providing connectivity to areas where existing terrestrial networks are either infeasible or impractical. Network management in ATM LEO satellite networks is typically performed by the Network Control Center (NCC). The main contribution of this paper is to propose a network management system configuration with a stand-by solution and to describe an experimental Satellite Management Information Base (SMIB) that we have developed for implementation in ATM LEO satellite networks.     

低轨卫星系统中结合时间和移动的位置更新策略

低轨(LEO)卫星快速运动,移动终端(MT)相对于卫星的位置信息也在不断变化,如何有效地管理MT的位置信息,减小位置更新频率和寻呼开销是研究位置管理的主要目的。为此,提出一种低轨卫星系统中的动态位置管理策略,基于时间和移动相结合进行位置更新,在不增加寻呼开销的条件下,减小了位置更新频率,从而有效降低了位置管理的总开销。     

低轨卫星通信系统中快速终端的切换技术

提出了低轨卫星通信系统（LEO）中两种支持快速终端的切换算法,详细介绍了系统模型的结构,以全球星系统和铱系统为例,通过仿真,分别对“最短路径优先”和“最长覆盖时间”2种算法下快速终端的切换时延情况进行统计和比较,得到了有一定参考价值的结果.     

一种GEO/LEO卫星网络中的路由优化策略

空间信息网络具有全球覆盖的能力,是能够保证高速率传输和较宽的带宽,支持灵活的、大规模的网络结构。GEO/LEO双层卫星网络由于具有覆盖关系简单、实施复杂性低等优势成为构建多层卫星网络的新思路。基于卫星群和卫星簇的分层结构,提出了一种GEO/LEO卫星网络中的路由优化策略,该策略主要是通过引入优化卫星路由表和路由信息数据报来实现的。最后的复杂性分析表明该策略在降低网络的星上存储开销和星间通信开销方面具有较高的优越性。     

适于低轨卫星IP网络的特定源组播算法

为了解决低轨卫星IP网络中现有特定源组播算法的信道资源浪费问题,本文提出了一套新的特定源组播算法,即基于核心群的特定源组播算法(CSSM)和加权的CSSM算法(w-CSSM).CSSM算法以源节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,所得的树代价最小,从而大大提高了网络的带宽利用率和传输效率.在w-CSSM算法中,加权因子可以自适应调整以适度增大树代价、降低端到端传播时延,以支持某些有严格端到端时延要求的实时组播业务.通过与低轨卫星IP网络中典型特定源组播算法MRA的仿真比较,可以看出CSSM和w-CSSM算法的树代价性能比MRA有较大改善,不过端到端传播时延略高.     

LEO卫星网络基于动态位置区的寻呼策略

针对LEO卫星网络中具有自主定位能力的用户终端,采用基于地理位置的动态位置区划分方案,根据用户移动速度设置位置区的大小。在动态位置区的基础上,对高速移动用户提出了一种基于时延限制的分组寻呼策略。仿真结果表明,对于低速移动用户,二次寻呼策略的时延和开销性能最佳;对于高速移动用户,基于时延限制的分组寻呼策略最佳。     

A Handover Strategy in the LEO Satellite-Based Constellation Networks with ISLs

A new handover strategy named minimal-hops handover(MHH) strategy for the lowearth orbit(LEO) satellite constellations networks equipped with inter-satellite links(ISLs) is proposed.MHH strategy,which is based on the hops of the end-to-end connection paths and makes good use of theregularity of the constellation network topology,can appropriately combine the handover procedure withrouting and efficiently solve the inter-satellite handover issue.Moreover,MHH strategy can providequality of services(QoS) guarantees to some extent.The system performances of the MHH strategy,suchas time propagation delay and handover frequency,are evaluated and compared with that of otherprevious strategies.The simulation results show that MHH strategy performs better than other previoushandover strategies.     

中低轨卫星跨层激光链路二次同步切换方法

中低轨卫星之间跨层激光链路的无缝切换直接决定了双层卫星光网络的稳定性.异步切换方法会导致网络拓扑频繁重构,而集中同步切换将造成两层间连接中断,网络运行状态失控.为此,本文提出了中低轨卫星星座激光链路的二次同步切换方法,在保证中低轨道卫星连通的基础上,可降低网络拓扑重构频率.研究了整数周期比的中轨道和低轨道卫星空间位置特性,建立了中低轨卫星星座构形二阶非球摄动模型,确定了中低轨道之间轨道周期比为3的双层卫星星座构形.按连接和切换顺序将该星座构形中跨层激光链路分为两组,以相对周期的1/4为基准,每次令其中一组同步切换,通过交替完成切换.研究结果表明,二次同步切换方法使得网络拓扑重构频率降低到链路切换频率的1/7,比集中切换方法在网络平均时延方面降低了30ms.