High Capacity: Low Delay Packet Broadcast Multiaccess

Demand assigned packet radio schemes using satellites can achieve high bandwidth utilizations but they generally exhibit relatively poor delay performance at low traffic when compared with random access schemes. A modified demand assigned scheme is proposed which improves delay performance at low traffic by allowing random access transmissions by users who are waiting for channel assignments. The proposed scheme provides low average delays at low traffic (comparable to slotted ALOHA) and bandwidth utilizations comparable to that of demand assigned schemes. The scheme has potential application in situations where the traffic loading tends to vary widely.     

A New Exposed-terminal-free MAC Protocol for Multi-hop Wireless Networks

This article presents a new multichannel medium access control (MAC) protocol to solve the exposed-terminal (ET) problem for efficient channel sharing in multi-hop wireless networks. It uses request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and flexibly opts for conflict-free traffic channels to carry out the data packet transmission on the basis of a new channel selection scheme. The acknowledgment (ACK) packet for the data packet transmission is sent back to the sender over another common channel thus completely eliminating the exposed-terminal effects. Any adjacent communication pair can take full advantage of multiple traffic channels without collision and the spatial reuse of the same channel is extended to other communication pairs which are even within 2 hops from them. In addition, the hidden-terminal effect is also considerably reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multichannels. Finally, a performance comparison is made between the proposed protocol and other typical MAC protocols. Simulation results evidence its obvious superiority to the MAC protocols associated with other channel selection schemes and traditional ACK transmission scheme as well as cooperative asynchronous multichannel MAC (CAM-MAC) protocol in terms of four performance indices: total channel utilization, average channel utilization, average packet delay, and packet dropping rate.     

Single Channel Per Carrier Satellite Repeater Channel Capacity

This paper analyzes the performance of a number of modulation and speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assignment systems, which make possible the most efficient loading of the satellite transponder in applications where the traffic at individual Earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required Earth terminal G/T. The fraction of the total link noise allocated to uplink noise is treated as a parameter, so that the cost of improving G/T may be traded against the cost of providing increased Earth terminal transmitter power. Both analog and digital modulation techniques are considered, together with various practical combinations of syllabic companding, voice-actuated carriers, and error-correcting codes. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Curves showing required G/T as a function of the total number of voice channels per transponder are also presented for the above-mentioned signal processing techniques, assuming "CCIR/CITT type" speech quality and transponder EIRP and bandwidth typical of current domestic satellite configurations.     

UMR: A utility-maximizing routing algorithm for delay-sensitive service in LEO satellite networks

This paper develops a routing algorithm for delay-sensitive packet transmission in a low earth orbit multi-hop satellite network consists of micro-satellites. The micro-satellite low earth orbit(MS-LEO) network endures unstable link connection and frequent link congestion due to the uneven user distribution and the link capacity variations. The proposed routing algorithm,referred to as the utility maximizing routing(UMR) algorithm, improve the network utility of the MS-LEO network for carrying flows with strict end-to-end delay bound requirement. In UMR, first, a link state parameter is defined to capture the link reliability on continuing to keep the end-to-end delay into constraint; then, on the basis of this parameter, a routing metric is formulated and a routing scheme is designed for balancing the reliability in delay bound guarantee among paths and building a path maximizing the network utility expectation. While the UMR algorithm has many advantages, it may result in a higher blocking rate of new calls. This phenomenon is discussed and a weight factor is introduced into UMR to provide a flexible performance option for network operator. A set of simulations are conducted to verify the good performance of UMR, in terms of balancing the traffic distribution on inter-satellite links, reducing the flow interruption rate,and improving the network utility.     

Traffic class dependent routing in ISL networks

This work addresses traffic class dependent (TCD) routing, using different link-cost functions, in the intersatellite link (ISL) network of a nongeostationary packet-switched satellite communication system. Three different traffic classes are introduced, each with its particular optimisation criteria. Performance analysis of TCD routing, in terms of average packet delay and average data throughput of a particular traffic class, is evaluated for homogeneous and nonhomogeneous traffic scenarios using a specifically developed simulation model of the ISL network.     

Overview of multiple satellite communication networks

Recently interest in packet communications has stimulated an interest in constellations of low altitude satellites. Such a configuration would have less propagation delay and be cheaper to launch than satellites at higher or geosynchronous altitude. However, many more satellites are necessary at low altitude to achieve reasonable coverage of the earth and insure availability of the resource. Further, the geometry of such a constellation would be dynamic with communication links of short duration as the satellites speed past each other or a ground site. The most difficult design issue in these systems is a stable method of routing messages that will sustain a reasonable level of traffic. This paper explores the problems of routing and switching messages through a constellation of low altitude satellites and examines some of the related demands on technology. The dynamic nature of crosslinks, uplinks, and downlinks requires a very agile antenna system, and the volume of information for routing of traffic is overwhelming. Use of some type of facetted phased array antenna is advocated to solve the former problem, but the latter problem is more subtle. Since the volume of ephemeris and constellation data as well as the rate of update is unmanageable, schemes relying on some form of broadcast or random access may be considered. It is concluded that none of the known or examined approaches to routing and switching is completely satisfactory     

Single Channel Per Carrier Satellite Repeater Capacity, Part 2

This paper analyzes the performance of a number of speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assigiment systems, which make possible the most efficient loading of the satellite transponder applications where the traffic at individual earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required earth terminal G/T. Both analog and digital modulation techniques are considered, and the effects of syllabic companding and voice actuation of carriers are demonstrated. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Full carrier modulation is assumed. Curves are also furnished showing the required G/T and uplink per carrier EIRP as a function of the number of voice channels per transponder and the transponder gain. "CCIR/CCITT type" speech quality is assumed, together with a transponder El RP and bandwidth typical of current domestic satellite configurations.     

DBV-RCS中一种提高时延性能的时隙分配方法(英文)

在DVB-RCS卫星通信中,为某个业务分配的时隙在MF-TDMA帧中的位置分布将影响该业务的时延特性。本文分别针对固定速率和实时可变速率业务,对MF-TDMA的帧长度、终端分配的时隙数量及位置分布与业务时延性能之间的关系进行了建模分析。理论分析表明时隙位置是影响业务时延的一个重要因素,位置分布越均匀,越能提高业务的时延性能;时隙均匀分配相比传统的时隙连续分配可以有效降低业务平均时延,且时延不随帧长的变化而变化;在时隙均匀分配方式下,提高实时可变速率业务的带宽分配可以更有效的提高时延性能。在DVB-RCS标准基础上,提出了一种与标准完全兼容的时隙均匀分配方法(TUAM),通过计算机仿真验证了算法的有效性以及建模分析的正确性,该算法可有效地保证业务具有极低的平均时延和时延抖动,使得VoIP等实时业务不会由于端到端时延过大而丢包,提高了DVB-RCS系统对于实时业务QoS的保障能力。     

低轨卫星可控式冗余分包遥测技术

随着卫星功能日趋复杂,遥测参数越来越多,处理要求越来越快,遥测设计面临越来越大的压力,必须拓展新的设计思路.本文讨论了一种低轨卫星可控式冗余分包遥测技术,更好地缓解遥测信道“瓶颈”,满足用户多样化的遥测需求,提高卫星遥测能力.该设计采用PCM（Pulse Code Modulation,脉冲编码调制）遥测和分包遥测相结合的方案,在信道资源有限,遥测参数庞大、用户需求多样的约束条件下,通过星载软件模式控制的方法实现了动态可编程遥测处理和遥测数传通道的冗余处理,提高了遥测信道的资源利用率、遥测设计的灵活性和系统的可靠性,该技术已成功应用于某在轨卫星,并被多颗在研卫星所采用.     

TP-Satellite: A New Transport Protocol for Satellite IP Networks

As a result of the exponential growth of the worldwide Internet, satellite systems are used to support broadband Internet access. Existing TCP protocols perform very well for Internet access on wired networks. However, in the case of satellite channels, due to the effects of high bandwidth asymmetry, long propagation delay, high sporadic bit error rate (BER) and burst errors, TCP performance degrades significantly. In this paper, a new end-to-end transport protocol, TP-Satellite, is proposed for satellite IP networks. TP-Satellite replaces the traditional slow start algorithm with a novel super start algorithm. In order to distinguish congestion events from link errors, a new scheme is introduced, which is based on alternate transmission of different class priority packets. Bandwidth asymmetry problems are addressed by the adoption of a modified negative acknowledgement (M-NACK) strategy, which periodically sends M-NACK packets. Simulation results show that TP-Satellite enhances the throughput performance on the forward path, reduces the bandwidth used in the reverse path, and offers a fair share of network resources.     

Oscillation suppression for traffic class dependent routing in ISL network

Adaptive per-hop routing in the intersatellite link (ISL) network of a packet-switched, nongeostationary satellite system is addressed. In particular, a traffic class dependent (TCD) routing is proposed with different optimization criteria for different traffic classes. Furthermore, for delay sensitive traffic, performance is enhanced by an exponential smoothing link-cost function, which reduces traffic load oscillations in the network. The performance of the proposed procedures is evaluated in two different traffic scenarios using an appropriate simulation model     

全球卫星导航星座网络协议体系与运行模式

针对全球卫星导航星座网络建设初期或论证阶段所涉及的网络体系结构、协议体系及相关组网等技术问题,开展了基于导航星座星间链路构建空间信息网络的技术研究,分别提出了由子网、接入网、骨干网等节点及其相互之间星间、星地无线链路构成的分层网络系统结构,设计了兼容遥控、遥测、测量与网络交互支持等业务的基于IP over CCSDS(基于空间数据系统咨询委员会标准的空间链路承载互联网协议业务)的协议体系,给出了全系统基本通信业务运行模式等。与传统高轨卫星通信系统相比,该星座网络具有高覆盖、低时延、随遇接入等优点,可实现星座导航性能与中低轨及地面用户通信性能的全方位提升,相关结果对我国全球卫星导航星座网络技术研究具有一定的参考意义。     

分布式控制系统稳定性分析及控制器设计

针对存在总线通信时延和掉包的航空发动机分布式控制系统,分别进行了时延和掉包情况下的系统建模和稳定性分析;利用增广离散化方法将时延系统转化为增广无时延模型,利用迭代方法将数据掉包建模为一定掉包界内的切换系统;分别提出时延和掉包条件下系统的稳定性条件,并通过求解线性矩阵不等式确定系统输出反馈控制增益;最后比较了基于保持输入和重构增益的2种掉包补偿措施。研究结果表明:采用基于时延的反馈控制增益设计和重构增益掉包补偿措施,可以保证分布式发动机控制系统的稳定性并获得最佳性能。     

Cross-layer design of LT codes and LDPC codes for satellite multimedia broadcast/multicast services

According to large coverage of satellites, there are various channel states in a satellite broadcasting network. In order to introduce an efficient rateless transmission method to satellite multimedia broadcasting/multicast services with finite-length packets, a cross-layer packet transmission method is proposed with Luby transform （LT） codes for efficiency in the network layer and low density parity check （LDPC） codes for reliability in the physical layer jointly. The codewords generated from an LT encoder are divided into finite-length packets, which are encoded by an LDPC encoder subsequently. Based on noise and fading effects of satellite channels, the LT packets received from an LDPC decoder either have no error or are marked as erased, which can be mod- eled as a binary erasure channels （BECs）. By theoretical analysis on LT parameters and LDPC parameters, the relationships between LDPC code rates in the physical layer and LT codes word lengths in the network layer are investigated. With tradeoffs between the LT codes word lengths and the LDPC code rates, optimized cross-layer solutions are achieved with a binary search algorithm. Verified by simulations, the proposed solution for cross-layer parameters design can provide the best transmission mode according to satellite states, so as to improve throughput performance for satellite multimedia transmission.     

NEW DYNAMIC SLOT ASSIGNMENT SCHEME OF SELF-ORGANIZED TDMA VHF DATA LINK

Self- organized TDMA ( S- TDMA ) protocolproposed by Johnsson[1] in aeronautical VHF-band is the representation of the new generationVHF aeronautic data communication system.　　 A mobile station or a ground station can oc-cupy one time slot. A group of slots that span aperiod of one minute constitute one superframe.Each station broadcasts current and future slotreservation information periodically.A stationwill build up and maintain a reservation tablethrough receiving the periodic bro…     

混合SDN的多目标路由优化算法

为充分利用SDN(Software Defined Network,软件定义网络)节点的优势来优化网络性能,混合SDN的流量工程成为当前的研究热点,而路由优化是实现流量工程目标的重要策略之一.但是,当前混合SDN的流量工程中未考虑网络整体的负载均衡以及SDN节点的处理能力.针对上述问题,提出了一种多目标路由优化算法——MCS(Minimum Cost Sum,最小化代价和),综合考虑整个网络的传输延迟与链路利用率,同时保证SDN节点的处理能力满足实际约束,最终实现全网综合性能的最优化.实验结果表明,当网络整体负载较轻,MCS与现有的SOTE(SDN/OSPF Traffic Engineering,软件定义网络/开放最短路径优先流量工程)算法性能相近;而当网络负载加重时,MCS相比于SOTE,可将网络负载降低约9％,因此,MCS算法具有更高的优化能力.     

TCP-ATCA： Improved Transmission Control Algorithm in Satellite Network

An adaptive transmission control algorithm based on TCP （TCP-ATCA） is proposed to reduce the effects of long propagation delay and high link error rate of the satellite network on the performances. The flow control and the error recovery are differentiated by combined dynamic random early detection-explicit congestion notification （DRED-ECN） algorithm, and, moreover, the pertaining congestion control methods are used in TCP-ATCA to improve the throughput. By introducing the entire recovery algorithm, the unnecessary congestion window decrease is reduced, and the throughput and fairness are improved. Simulation results show that, compared with TCP-Reno, TCP-ATCA provides a better throughput performance when the link capacity is higher （ ≥600 packet/s）, and roughly the same when it is lower. At the same time, TCP-ATCA also increases fairness and reduces transmission delay.     

Satellite Communication System Using TDM and SSMA

An outline and the multiple access techniques used in a domestic satellite communications system accommodating numerous small Earth stations are presented. Two kinds of Earth stations are employed in this system, a small Earth terminal (SET) and a master Earth station (MES). Forty-eight two-way satellite channels were achieved in the 6/4 GHz bands with a transponder eirp of about 62 dBm. Time division multiplex is employed in the MES to SET link and spread spectrum multiple access in the SET to MES link.     

Adaptive Forward Error Control for Digital Satellite Systems

Two hybrid schemes of time-frequency resource sharing to increase the rain margin of Ku-and Ka-band satellite systems are proposed. Scheme 1 requires sharing a small pool of bandwidth for adaptive forward error control coding, sharing a small pool of time frame for rate reduction, and sharing a portion of low frequency time-division multiple access (TDMA) back-up frame for downlink transmission to the rain affected stations. Scheme 2 utilizes variable rate modulation and forward error correction, shares a small pool of time frame for rate reduction, and shares a portion of low frequency TDMA back-up frame. Effective usable capacities of the system using these schemes are calculated. Distribution of resources in order to maximize the effective usable capacity is also analyzed. The results obtained are compared with other adaptive schemes. Preliminary analysis shows that the utilized capacity of scheme 1 exceeds 99 percent of the effective usable capacity possible if it never rains for an outage of 0.05 percent and fade margin of 2.5 dB. For scheme 2 similar performance is achievable at a fade margin of 1.5 dB. For higher outage objectives the loss of effective utilized capacity is higher for scheme 2.     

基于数字包络检波的RNSS通道时延标定方法

提出一种采用数字处理的时延测试方法,用于对导航卫星导航信号发射通道分数码片时延的精确测量。该方法是通过高速A/D（模/数）转换器,对导航卫星下行的BPSK（二进制相移键控）信号和卫星导航秒脉冲进行双通道采样,读取采样数据并进行数据处理。根据秒脉冲信号触发门限上升沿确定时延测量起点,对BPSK采样数据进行平方律检波,获取码片换相点,计算换相点和秒脉冲之间的分数码片时延,并进行滤波器时延校准,从而得到导航卫星发射链路的分数码片时延,该方法不需要进行伪随机信号的捕获和跟踪,测量精度主要取决于采样器采样率。通过在测试中使用一根校准电缆对该方法进行验证,验证结果表明,采用本文提出测试方法的测量误差优于0.3ns。