Some practical strategies for reducing intermodulation in satellitecommunications

Various heuristic procedures for obtaining practical solutions to the general one-level carrier frequency assignment problem are described. The problem treated is general in the sense that it accommodates the case where L of the N slots may be explicitly designated as prohibited and unavailable for assignment. This problem occurs in satellite transmission with many small carriers accessing the same transponder where, due to multipath and TV interference from crosspolarized transponders of the same satellite and from copolarized transponders of the adjacent satellites, some portions of the bandwidth of the considered transponder cannot be used. To permit comparison with respect to the intermodulation advantage and central-processing-unit time required, the case without prohibited slots is considered. The sequential insertion procedure in which, starting with two carriers at the two end slots, one additional carrier at a time is optimally inserted into one of the unassigned slots is found best when the ratio between the available bandwidth and the total carrier bandwidth is greater than about 125%. All the heuristic procedures produced assignments whose intermodulation advantages are all greater than the bandwidth ratio     

A Domestic Satellite Design

This paper deals with the design parameters of a communications satellite which would be capable of providing domestic telephony, data, and television distribution services. Certain important aspects of the design are discussed, including satellite antenna beam coverage, transponder bandwidth, and transponder radiated power for a given weight range. A baseline satellite design is then presented which has 24 transponders (with 4000 watts radiated power on-axis and 34-MHz radio-frequency bandwidth) fully accessible from the 48 contiguous United States. The design uses crossed linear polarization to reuse the satellite transmit and receive frequency spectrum.     

Optimum Transponder Design for Pseudonoise-Coded Ranging Systems, Weak Signals

Optimization of the bandwidth of a turnaround transponder is carried out for weak signals at the transponder receiver. Optimum transponder bandwidth is found to be around 0.77-1, where T is the period of one element of the ranging code. Linear transponders are compared with transponders having baseband limiting. Phase modulation is assumed. It is shown that, for weak signals, linear transponders are preferable for a partitioning of the transponder transmitted power giving (carrier power)/(total power) > 0.43, while baseband limiters are preferred for (carrier power)/(total power) < 0.43.     

Optimum Design of Single Channel per Carrier Satellite Systems

Optimization of available satellite power and transponder bandwidth is utilized to minimize the Earth station G/T in satellite channel per carrier (SCPC) systems. The corresponding optimum transponder output backoff is obtained. Applications in system design are given. In a previous paper [1] the channel capacity of a satellite transponder handling single channel per carrier (SCPC) transmission was derived. The link carrier-to-noise (C/N) ratio was maximized over the output backoff and the maximum bandwidth available was determined. Given the bandwidth per channel for each carrier, the channel capacity was obtained. The objective of the present investigation is to derive the minimum G/T of the Earth station in SCPC systems by optimum utilization of available satellite power and transponder bandwidth. Applications in system design are discussed.     

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.     

Low-cost TDRSS communications for NASA's long duration balloonproject

A transponder and RF ground support equipment that are making tracking and data relay satellite system (TDRSS) communications available to lower budget NASA projects are discussed. The Goddard Space Flight Center (GSFC)/Wallops Flight Facility's long duration balloon project (LDBP) will be the first to take advantage of this TDRSS user hardware for communications through the TDRSS S-band multiple access system during their around-the-world scientific balloon flight campaigns. The transponder is one tenth the cost of the current generation space-qualified transponder, and the TDRSS user RF test set (TURFTS) is less than one half the cost of the currently available transponder test equipment     

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.     

民用飞机航电数据网络带宽资源分配优化设计

民用飞机航电数据网络在设计过程中,通过对带宽资源的合理分配,来满足网络成员系统的数据传输需求。而在设计过程中,存在因网络带宽需求分布的非均匀性等因素造成的局部带宽资源不足的问题,因此需要在初步带宽资源分配结果上进行局部优化设计。提出一种通过网络带宽资源使用率最高的链路和端系统进行识别,以及进行针对性物理链路连接关系调整,从而实现降低交换机之间链路带宽资源使用率的方法。通过网络仿真对该方法的优化效果进行了分析,发现这种方法能够降低网络局部链路的较高带宽资源使用率,单轮优化的有效降幅超过15%。该网络带宽资源分配优化设计方法,一方面能够有效解决因飞机网络局部带宽不足问题,降低由此导致的网络拥堵、排队、丢包等风险,确保网络确定性;另一方面还能尽量保持当前分配结果,减少设计优化变更对网络时延性能和网络布线方面的影响。     

测控应答机下行调制度问题的技术分析

针对应答机采用不同的接收信号功率控制方式，对下行测距调制度、残留遥控调制度以及转发噪声调制度的情况进行了理论分析，得到了各种情况下的调制度数学模型，可供读者在航天工程的测控链路设计及应答机设计时参考。     

网络处理器编程模型研究

随着网络带宽的提高以及大量新协议及服务的出现,传统基于专用硬件芯片或者软件的网络处理技术很难同时兼顾高性能和灵活性两方面的要求.网络处理器的高速处理和灵活的可编程性使得它成为解决当今网络数据处理的有效解决方案.本文分析了目前在网络处理器应用开发中存在的问题和面临的挑战,介绍了网络处理器编程模型以及目前相关研究工作,并展望了其未来的发展方向.     

Mobile Satellite Plans and Status

A variety of new communication functions will become available near the end of the decade when mobile satellite services (MSS) are introduced commercially in the United States and Canada. Mobile radios, hand carried radios and small fixed transponders will communicate directly through satellites into the telephone network or to private base stations. Voice, data, and position fixing services will be distance insensitive with good performance in difficult terrain and remote locations. Experiments with NASA satellites and studies in the U.S. and Canada demonstrated the technical feasibility and practical applications of mobile satellites. In 1983 Mobile Satellite Corporation, followed by Skylink Corporation, applied to the FCC for authorization to build and operate a land and aeronautical mobile satellite system for the United States. Canada had advanced its plans for an MSAT system. In response to these initiatives, the FCC issued a ``Notice of Proposed Rulemaking' that proposed the allocation of radio spectrum for the new service and asked for applications from prospective providers. Twelve applications were received. The shortage of radio spectrum in the U.S. has resulted in much contention over the proposed allocations, and the numerous applications have introduced competing systems concepts. The paper describes a likely system implementation, its services and markets, and the current regulatory status.     

COTS星载双模测控应答机基带设计与实现

提出了一种星载双模测控应答机基带设计方案,采用COTS（商用现货）器件实现,能较好解决星载功率受限和空间辐射效应引起的相关问题。测控应答机主处理器由反熔丝FPGA（现场可编程门阵列）实现,可在低功耗条件下保证最基本测控需求,解调上行DPSK（差分相移键控）信号,调制下行扩频信号;协处理器受主处理器控制,由SRAM（静态存储器）FPGA来实现,对上行扩频信号进行解扩解调。测控应答机可根据星载电源功率情况和不同测控任务切换模式,具有成本低、可靠性高、使用灵活等优势。     

Satellite mobile communication and radio positioning systemplanning aspects

System aspects of mobile communication and position determination by satellite are described. Topics of discussion are the choice of frequency, type of modulation/multiple access and system design, and considering the effects of active and passive intermodulation and multipath interference. Communication performance and position determination analyses are conducted with respect to small-scale domestic mobile communication systems, where the satellite mobile transponder constitutes only a fraction of the otherwise fixed services C-band or Ku-band payload, and where the orbit position of the spare satellite(s) is dictated by considerations other than purely radio positioning. The system tradeoffs and arguments presented lead to a particular modulation/multiple access system, which provides high channel capacity, good ranging accuracy, and high resistance to multipath fading     

6G service-oriented space-air-ground integrated network: A survey

As an indispensable component of the emerging 6G networks, Space-Air-Ground Integrated Networks (SAGINs) are envisioned to provide ubiquitous network connectivity and services by integrating satellite networks, aerial networks, and terrestrial networks. In 6G SAGINs, a wide variety of network services with the features of diverse requirements, complex mobility, and multi-dimensional resources will pose great challenges to service provisioning, which urges the development of service-oriented SAGINs. In this paper, we conduct a comprehensive review of 6G SAGINs from a new perspective of service-oriented network. First, we present the requirements of service-oriented networks, and then propose a service-oriented SAGINs management architecture. Two categories of critical technologies are presented and discussed, i.e., heterogeneous resource orchestration technologies and the cloud-edge synergy technologies, which facilitate the interoperability of different network segments and cooperatively orchestrate heterogeneous resources across different domains, according to the service features and requirements. In addition, the potential future research directions are also presented and discussed.     

基于QoS的卫星网络端-端通信可靠性分析

针对卫星网络动态环境下的高速信息传输、业务类型差异大等特点，提出一种综合考虑各业务QoS（Quality of Service）指标的可靠性分析方法。在卫星通信网络实际运行周期内，通信系统往往处于逐渐劣化过程中，导致卫星的节点和链路除正常工作和完全失效外，还存在部分失效的工作状态。本文在链路多状态基础上基于最小路集算法（Minimum Path Set Algorithms，MPSA）在不同业务的QoS指标（时延、带宽和丢包率）约束下，得出满足该业务QoS约束的所有可靠路径集，对路径集中路径进行不交化处理得到网络端-端可靠性。研究结果表明，不同业务由于QoS需求的差异导致网络端-端可靠性不同，所提算法与传统算法相比更加符合实际。由于实际卫星网络环境中会采用端-端并行多路径传输（Multi-Path Transmission，MTP），本文在上述研究的基础上，进一步对多路径的端-端可靠性进行了研究，结果表明多路径数据传输可靠性高。     

Communication system architecture for planetary exploration

Future human missions to Mars will require effective communications supporting exploration activities and scientific field data collection. Constraints on cost, size, weight, and power consumption for all communications equipment make optimization of these systems very important. These information and communication systems connect people and systems together into coherent teams performing the difficult and hazardous tasks inherent in planetary exploration. The communication network supporting vehicle telemetry data, mission operations, and scientific collaboration must have excellent reliability and flexibility. We propose hybrid communication architectures consisting of space-based links, a surface-based deployable mid-range communications network and a cluster of short-range links to solve the problems of connectivity and bandwidth, while meeting the other constraints of weight and power. A network of orbiting satellites could cover much of the planet surface, but this space-based capability may not be optimal for cost or performance. Specifically, a minimal space-based capability can be augmented using mobile cellular repeaters deployable by robots and human EVA. This method results in an increase in the number of radio nodes, but the distances separating them is decreased. This results in a significant increase in bandwidth and decrease in radio power, and therefore, node size, complexity, and power consumption. This paper will discuss the results of field testing such hybrid radio systems for the support of scientific surveys. System analysis of design tradeoffs will yield insight into optimal solutions that will be compared to other approaches providing a method of effectively evaluating new candidate architectures     

图论最大流理论在机场登机口分配中的应用

为提高登机口的利用率、提升航空旅客出行的便捷性与舒适性、提高机场的运行效率及航空公司的运营效益,在图论中网络最大流理论的基础上,将旅客步行距离、机场资源运行效率、飞机最短过站时间、＂航班对＂、机型等作为约束条件,考虑航站楼布局、始发/终到及中转旅客数量等因素对登机口分配结果的影响,建立旅客登机口分配的优化网络模型,并对该算法的复杂度和最优性进行分析和证明。最后,运用实例来验证该方法在缩短旅客步行距离和提高机场运行资源利用率方面的可行性,该算法也可用于飞机停靠机位的优化安排。     

Bandwidth maximization for satellite laser communication

Free space optical communication between satellites networked together can make possible high speed communication between different places on Earth. The basic free space optical communication network includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. The pointing systems for laser satellite communication suffer during tracking from vibration due to electronic noise, background radiation from interstellar objects such as Sun, Moon, Earth, and Stars in the tracking field of view, and mechanical impact from satellite internal and external sources. Due to vibrations the receiver receives less power. This effect limits the system bandwidth for given bit error rate (BER). In this research we derive an algorithm to maximize the communication system bandwidth using the transmitter telescope gain as a free variable based on the vibration statistics model and the system parameters. Our model makes it possible to adapt the bandwidth and transmitter gain to change of vibration amplitude. We also present an example of a practical satellite network which includes a direct detection receiver with an optical amplifier. A bandwidth improvement of three orders of magnitude is achieved in this example for certain conditions, as compared with an unoptimized system     

一种基于P2P MMOG的乐观同步算法

根据P2P MMOG的特点引入周期时间桶算法对游戏状态进行同步,将基于因果关系的事件分布到不同时间桶内执行以维护游戏的一致视图,并针对该算法的缺陷定义最小时间桶来衡量事件执行的乐观度,使每一轮尽可能处理足够多的事件。在此基础上给出全局虚拟时间GVT的计算,以保证及时进行内存的回收。实验结果表明改进的算法可以有效减少回滚次数,降低网络带宽的占用,并能在一定程度上提高系统资源的利用率。     

应答机测距转发性能分析

分析了采用视频AGC（自动增益控制）、射频AGC和限幅器等3种测距转发模式的应答机性能,分析结果表明：视频AGC模式下,应答机测距通道的输出功率恒定,测距转发性能不随上行信号强度变化而变化;射频AGC模式下,应答机测距通道的输出功率不恒定,测距转发性能随着上行信号强度变化而变化;而限幅器模式可看作射频AGC的一种特殊情况。仿真分析了我国研制的限幅器和射频AGC两种模式应答机的性能,结果表明理论计算的性能与实测结果一致,理论分析正确且理论分析结果可作为链路计算的依据。