卫星网络传输控制协议研究

标准传输控制协议（TCP）直接用于卫星网络,由于其不能够区分丢包和慢启动的长时间需求等导致协议的非适应性。在分析卫星网络影响协议性能因素的基础上,总结了当前针对这些因素造成的不利影响所增加的额外技术,并对现有提高卫星网络TCP性能的方法进行了分类总结,比较了这些TCP的特点,最后指出了卫星网络TCP的未来研究策略和发展趋势。     

LEO卫星网络路由协议研究

低轨道（Loweadhorbit,LEO）卫星网络具有拓扑时变性、承载业务分布不均衡以及星上资源有限等特点。针对这些特点,如何设计简单、高效的LEO卫星网络路由搏议成为当前卫星网络研究的热点问题。通过深入分析已提出的LEO卫星网络路由协议,文章对LEO卫星网络路由协议进行了合理分类,详细阐述了各类典型的LEO卫星网络路由协议,讨论了每种协议的优点和适用环境,指出其中存在的不足,并对它们进行了综合对比。最后总结全文,指出LEO卫星网络路由协议进一步的研究方向。     

卫星网络中的TCP跨层技术研究

CCSDS链路层协议TC的重传功能可以减少误码丢包而导致TCP窗口缩减、吞吐量降低的情况,但是链路层对丢失的数据反复重传易引起数据包端到端传输时延的剧烈变化,可能导致TCP数据包失序和重传定时器发生超时,引起传输层和链路层重复重传的情况.该文通过链路层与传输层的差错控制信息交互,传输层将TCP数据的序列号通告链路层,链...     

卫星网络基于时空的动态IP路由

研究宽带卫星网络的拓扑结构和路由策略，设计了一个基于时空的分布式路由算法，其计算复杂性为O(1)。针对卫星移动性进行的仿真结果表明新算法能够有效确定最小时延传播路径。     

一种新的卫星网络传输控制协议

为了解决TCP协议在卫星通信网络中性能差的问题,该文提出了一种适合卫星网络的新型传输控制协议TP-Satellite。为了加速在连接开始阶段拥塞窗口(cwnd)增涨速度,该协议不再采用传统的Slow Start策略,而是采用一种新的窗口增涨策略超起始策略。为了将误码与网络拥塞造成的数据丢失区分开,协议还采用基于不同优先级IP数据交错发送的丢失判断策略。另外,协议采用了主动周期应答策略。通过理论分析和仿真比较,TP-Satellite协议能够迅速提升数据发送速率和有效地区分数据丢失原因,明显提高前向链路的吞吐量,同时降低反向链路的带宽占用。     

卫星网络中基于网络编码的ARQ机制

随着航空航天技术的发展,越来越多的应用任务需要利用卫星通信进行信息传输。在卫星网络中,已有的研究成果大都采用了ARQ机制来降低卫星信道的数据丢失率。然而由于卫星信道具有长时延的特点,因此ARQ所采用的反馈重传机制会大幅增加卫星信道的传输时延。因此,针对卫星网络,提出了一种基于网络编码的ARQ(SatNC-ARQ)机制来减少卫星信道的丢包数,并通过减少重传次数来降低卫星信道的传输时延。在Sat-NC-ARQ中,卫星终端除了发送几个真实业务终端的数据包外,还会创建一个虚拟业务终端发送网络编码数据包,从而在接收方,只要接收到足够多的数据包,就能对所有的数据包进行解码,于是可以大幅降低卫星信道的传输时延以及丢包数。还对Sat-NC-ARQ所具有的一些性质进行了理论分析。仿真结果显示,相对于选择性重传ARQ机制,Sat-NC-ARQ机制能够降低大约11%的传输时延和86%的丢包数。     

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。     

卫星网络基于广度优先树的报文扩散算法

卫星网络ISL子网的拓扑结构具有动态性、周期性和可预知性,时间离散化类的路 由算法是卫星网络的主流路由算法之一。由于ISL子网是网格状、存在物理环路的网络,运行 过程中有大量的信令报文需要从某一颗卫星扩散到整个ISL子网,为避免环路路径和重复报 文问题,提出基于广度优先搜索生成树的报文扩散算法。仿真结果证明算法正确有效。     

快速响应激光卫星通信网络的鲁棒动态拓扑控制

星间激光通信具有传输速率高、传输距离远、抗干扰能力强的优点,已成为卫星组网的重要趋势.星间激光网络存在高移动、点对点、波束窄等特点,已有的自由空间网络（FSO）拓扑控制策略应用于星间激光通信,存在计算复杂度高、网络延迟大的不足,无法满足星间激光组网需求.文中提出了一种基于代数连通度的星间激光组网动态拓扑控制方案,通过分布式构建卫星网络连通图与网络增强方法,实现网络动态重构,并通过基于矩阵摄动理论的相关方法,降低了网络动态重构计算复杂度.该方案具有分布式、自组织、近实时的优点,可满足空间激光通信网络的动态拓扑控制需求,提高卫星快速响应能力.     

A novel QoS routing protocol for LEO and MEO satellite networks

The rapid advance of communication and satellite technology pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter‐satellite links, and quality of service (QoS) of satellite networks cannot be reliably guaranteed because of great difficulties in processing of long distance‐dependent traffic. In this paper, a two‐layered low‐Earth orbit and medium‐Earth orbit satellite network (LMSN) is presented. A novel hierarchical and distributed QoS routing protocol (HDRP) is investigated, and an adaptive bandwidth‐constrained minimum‐delay path algorithm is developed to calculate routing tables efficiently using the QoS metric information composed of delays and bandwidth. The performance of LMSN and HDRP is also evaluated through simulations and theoretical analysis. Copyright © 2007 John Wiley & Sons, Ltd.     

多层卫星通信网络自适应路由策略

单层卫星网络由于轨道高度和覆盖能力的不同,以至构成通信的单层系统往往不能满足不同业务服务质量的需求。分析了Walkerdelta型星座构建多层卫星通信网络的拓扑结构和ISL性能,提出了在统计分布模型下的多层卫星自适应路由策略,综合考虑了路径时延和ISL链路负载。仿真结果表明了多层网络自适应路由策略能够更加有效地分配网络通信量,网络具有较小的丢包率、网络平均归一化链路负载和特定路径综合路径权重,有利于降低网络平均阻塞概率和特定路径阻塞概率,获得更高的可靠性,较传统的单层非自适应路由更加有效、可靠。     

Routing protocol based on social characteristics for opportunistic networks简

Opportunistic networks are derived from delay tolerant networks, where mobile nodes have no end-to-end connections. Nodes are represented by people, which means that opportunistic networks can be regarded as social networks. Human mobility plays an important role in affecting the performance of forwarding protocols in social networks, furthermore, the trajectory of people＇s movements are driven by social characteristics. However, current routing protocols rely on simple mobility models, and rarely consider social characteristics. Considering two heterogeneous network models, an social opportunistic networks routing（SONR） was proposed which brings an adapted discrete Markov chain into nodes＇ mobility model and calculates the transition probability between successive status. Comparison was made between Spray, Wait and Epidemic protocol. Simulation show that SONR can improve performance on delivery ratio, delivery latency and network overhead, meanwhile. SONR approaches the performance of Epidemic routing.     

Congestion management techniques for disruption‐tolerant satellite networks

Delay and disruption‐tolerant networks are becoming an appealing solution for extending Internet boundaries toward challenged environments where end‐to‐end connectivity cannot be guaranteed. In particular, satellite networks can take advantage of a priori trajectory estimations of nodes to make efficient routing decisions. Despite this knowledge is already used in routing schemes such as contact graph routing, it might derive in congestion problems because of capacity overbooking of forthcoming connections (contacts). In this work, we initially extend contact graph routing to provide enhanced congestion mitigation capabilities by taking advantage of the local traffic information available at each node. However, since satellite networks data generation is generally managed by a mission operation center, a global view of the traffic can also be exploited to further improve the latter scheme. As a result, we present a novel strategy to avoid congestion in predictable delay‐ and disruption‐tolerant network systems by means of individual contact plans. Finally, we evaluate and compare the performance improvement of these mechanisms in a typical low Earth orbit satellite constellation.     

Caching in heterogeneous satellite networks with fountain codes

In this paper, we investigate the performance of caching schemes based on fountain codes in a heterogeneous satellite network. We consider multiple cache-aided hubs, which are connected to a geostationary satellite through backhaul links. With the aim of reducing the average number of transmissions over the satellite backhaul link, we propose the use of a caching scheme based on fountain codes. We derive a simple analytical expression of the average backhaul transmission rate and provide a tight upper bound on it. Furthermore, we show how the performance of the fountain code-based caching scheme is similar to that of a caching scheme based on maximum distance separable codes.     

Network Mobility in satellite networks: architecture and the protocol

Mobility management is required to ensure the session continuity for multiple Internet Protocol‐enabled devices onboard a satellite that hands off between ground stations. Network Mobility (NEMO) can efficiently manage the mobility of multiple Internet Protocol‐enabled devices that are connected as a mobile network. However, existing mobility management solutions for satellite networks are unable to route through intermediate satellites links when a direct connection with a ground station is lost. We proposed an architecture of NEMO in satellite networks with routing through multiple satellite links using nesting, where a mobile network connects to another mobile network. However, NEMO Basic Support Protocol can be inefficient in satellite networks because of poor nesting formation leading to the routing loop, inefficient routes, and overloaded links. We extended NEMO Basic Support Protocol for the efficient use in satellite networks by augmenting it with a decision criteria for the nesting. Results verify that the extended protocol ensures loop‐free and continuous connection despite the loss of direct connection to the ground and provides an insight on how to form the nested NEMO to avoid overloading. The architecture and the extended NEMO protocol can be used for the efficient and continuous transfer of data from satellite networks to the ground. Copyright © 2011 John Wiley & Sons, Ltd.     

Routing optimization based on topology control in satellite network

A new double-layer satellite network model for space networking was established and a routing algorithm based on topology control (TCRA) was proposed considering the advantages of low earth orbit and stationary earth orbit satellite networks.This model used virtual node strategy and satellite grouping idea,which regarded the coverage area of each low earth orbit satellite as a virtual node.The network took into account the influence of the polar area on the division of the satellite footprints,such that the upper management satellites can accurately acquire the topology of the lower satellites.Using the improved virtual node strategy,the time slices were superior to other network models in quantity,length and other aspects.Based on the network topology,stationary earth orbit satellites calculate routing for low earth orbit satellites,while low earth orbit satellites were responsible for forwarding data.The simulation results show that the routing algorithm is superior to other algorithms in average end-to-end delay and packet loss rate.     

QoS routing based on mobile agent for LEO satellite IP networks

Current quality of service (QoS) routing schemes for low earth orbit (LEO) satellites IP networks either neglect the varying population density or fail to guarantee end-to-end delay. As a remedy, QoS routing protocol based on mobile agent (QoSRP-MA) is proposed. QoSRP-MA is a source-based routing protocol. Once connection requests arrive, QoS mobile agents are dispatched from ingress satellite to explore routes, which migrate using satellite routing tables. Upon arriving in egress satellite, QoS mobile agents migrate back towards ingress satellite to reserve bandwidth. To construct satellite routing tables, load balancing routing algorithm based on mobile agent (LBRA-MA) is presented. In LBRP-MA, at regular intervals mobile agents launched on all satellites migrate autonomously to evaluate path cost and update routing tables. Moreover, path cost between source and destination is evaluated considering satellite geographical position as well as inter-satellite link (ISL) cost. Furthermore, ISL congestion index is considered to update routing table. Through simulations on a Courier-like constellation, it shows that QoSRP-MA can achieve guaranteed end-to-end delay bound with higher throughput, lower connection failing ratio and signaling overhead compared to high performance satellite routing (HPSR) scheme.     

一种基于分时的LEO卫星网络无环路由算法

在分析传统卫星网络路由算法的基础上，提出一种基于分时的LEO卫星网络无环路由算法(DTRA)。针对卫星在各时间片之间进行路由表切换时可能出现的路由环问题，算法采用平滑路由表切换策略消除由于切换前后网络状态信息不一致而产生环路的可能性，保证分组在任何时刻都能够沿无环最短时延路径被转发。同时，DTRA也能够通过使用无环备份路径处理可能出现的链路拥塞、节点失败等突发情况。通过复杂性分析可知，算法只需较小的星上存储开销和星上处理开销，而无需星问通信开销。仿真实验结果也表明算法能够提供数据最优传送，具有较好的端到端时延性能。