A flexible LEO satellite modem with Ka‐band RF frontend for a data relay satellite system

From a geostationary Earth orbit (GEO) satellite's perspective, a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free‐space loss of an inter‐satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper, we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.     

CCSDS分包遥测在航天器通信中的设计及应用

天地通信链路是航天器与地面测控站之间的数据通道,数据的安全性对航天器非常重要。针对航天器天地通信链路长、易受干扰、数据量大的特点,提出了一种适于航天器天地通信用的CCSDS分包遥测策略。结合空间通信协议规范,设计了可用于航天器空间网络和地面环境通信的方法,并在天地通信链路中进行试验验证。结果表明,采用CCSDS分包遥测策略,通过空间通信网络下传的遥测数据可被地面正确的获取和解析。同时,通过模块化的软件设计,可方便地将CCSDS分包遥测策略移植于多种航天器型号中。     

一种基于系统采样时钟量化的无人机测距方法

为了解决基于单载波频域均衡(SC-FDE)高速数据链无人机测控系统的地空双向距离测量问题,提出了一种基于系统采样时钟量化的无人机测距方法,将机载/地面测距信息分别量化至机/地系统采样时钟的计时器,完成地空双向距离的测量。理论分析和地空链路测试平台实验结果表明,新方法在复杂多径环境下实现了地空双向距离测量,降低了测距分系统的设计复杂度,地空双向实际测距均值与等效自由空间传输延迟一致,且测距精度满足理论测距误差设计值。该测距方法在无人机测控系统中具有良好的应用前景。     

An atmospheric optical ring network

An experimental 10-Mb/s token-ring local area network (LAN) that uses atmospheric optical communication links is described. Objective and subjective performance results are reported for operation over a 170-m-long outdoor path. The data support the following hypotheses. Atmospheric optical communications may find LAN applications as bridges between buildings containing cable subnetworks or as temporary quick connects for new outlying hosts for which cable runs are initially unavailable. LAN protocols for networks incorporating atmospheric optical communications should be modified to best insulate users from the occasional error bursts and bad-weather outages suffered by such links     

Overview of the space station communications networks

Within the Space Station Freedom Program (SSSP), the communications and dataprocessing capabilities that will be used to handle the operational and scientific information needs will be provided by a space station information and communications system. This system will be composed of a variety of elements, networks, and subnetworks. The networks and how they are interconnected are described. The discussion covers communications system elements and services, elements of the onboard systems, wide-area transport network elements, and command and control elements     

ATM local area networks

LAN emulation offers a best-effort, connectionless, packet transfer service at the MAC sublayer, implemented on top of a connection-oriented ATM network LAN emulation using switched virtual connections requires address resolution to locate the destination end station followed by connection establishment to the resulting ATM address. Address resolution may be implemented by a broadcast technique or by an address server. The broadcast method is the simplest for small networks but a combination of both is probably better. The use of the MAC address to identify an end station, with dynamic binding to its current physical location in the ATM network, allows the ATM LAN segment to be viewed as a virtual LAN. The virtual LAN model permits end stations to move and change physical location while maintaining connection to the same ATM LAN segment. This greatly simplifies the management of large data networks     

基于STK二次开发的链路测控仿真

在航空航天任务过程中,测控覆盖率高就能提供实时、连续、可靠的信息支持。利用VC结合STK二次开发,建立了测控链路仿真模型。软件利用STK/X模块较好的显示效果与Access模块计算、显示测控链路的余量和测控链路覆盖范围。针对不同的地面站部署,可计算空间飞行器的测控覆盖率。实现VC与STK集成的二次开发可大幅节省了开发时间,该仿真方法对测控系统的设计具有参考价值。     

The IEEE 802.16 Working Group on broadband wireless

This article describes the new initiative on broadband wireless access (BWA) that has formed Working Group 802.16 in the IEEE 802 LAN/MAN Standards Committee. The aim is to provide the reader with highlights of the IEEE 802 activities in order to enable better dissemination of these standards into marketable products as well as seek new ideas to be brought into the IEEE 802 arena. BWA systems, utilizing base stations to provide broadband data to business or homes, offer an alternative to wired “last-mile” access links using fiber, cable, or telephone lines. As illustrated, the base stations may be either terrestrial, in orbit, or mounted on airplanes or dirigibles in the stratosphere. The customer terminals can carry two-way communications for Internet access, digital video, telephony, and other services     

Design of a Switched Broad-Band Communications Network for Interactive Services

The congestion in broad-band communications networks resulting from the increased demand for interactive services is considered. It is shown that services such as a video library could not be provided to the majority of subscribers in a conventional CATV network. A design is developed for a space division multiplex broad-band network which can be expanded at minimum cost to meet an increasing demand for interactive services. The network contains two signal distribution networks: a cablecast system similar to the Rediffusion system, and a switched communication network providing point-to-point circuits for both one-way and two-way services. All broad-band signals are transmitted to the subscribers in the 1- to 10-MHz spectrum, permitting the use of twisted pair video cables and a minimum number of cable amplifiers. The broad-band cable network (BCN) is organized around 15 local switching exchanges and one central exchange. Multipoint switches in local exchanges under wired-logic circuit control connect individual subscriber communication lines to any channel. Crosspoint matrix switching groups in the local and central exchanges connect communication circuits in the broad-band communication network under programmed computer control. This network is accessed via links terminating on one channel of the multiposition switches. Per-subscriber costs are estimated to be 190 dollars for a cablecast system serving 3800 subscribers. Additional expenditures per subscriber of 40 dollars for fixed costs and 40 dollars for variable costs would provide interactive services. The range of interactive services provided would be extremely flexible, including both one-way video library service and point-to-point two-way communications.     

Asymmetric physical layer design for high-speed wireless digitalcommunications

High data rates and portability are conflicting requirements in the design of reliable indoor wireless data communication systems. Asymmetric system design addresses this problem by exploiting the major differences in the availability of resources (i.e., energy, space) that exist between base stations and portable units. Such an approach seeks to concentrate most of the signal processing tasks involved in the operation of the two-way wireless link at the base station. This paper presents and discusses the implications of a set of techniques for asymmetric physical layer system design based on the use of channel precoding for forward transmission. System performance is assessed via simulations using a realistic time-varying channel model. Simplified two-way antenna diversity implemented exclusively at the base station and the key issue of automatic gain control at the receive side of the precoded link are also addressed and evaluated. Simulation results confirm that the adoption of these techniques enables reliable digital communication at a data rate of 20 Mbit/s on both links while significantly reducing the power consumption of the portable unit     

TDM Virtual-Circuit Configuration for Network-on-Chip

In network-on-chip (NoC), time-division-multiplexing (TDM) virtual circuits (VCs) have been proposed to satisfy the quality-of-service requirements of applications. TDM VC is a connection-oriented communication service by which two or more connections take turns to share buffers and link bandwidth using dedicated time slots. In the paper, we first give a formulation of the multinode VC configuration problem for arbitrary NoC topologies. A multinode VC allows multiple source and destination nodes on it. Then we address the two problems of path selection and slot allocation for TDM VC configuration. For the path selection, we use a backtracking algorithm to explore the path diversity, constructively searching the solution space. In the slot allocation phase, overlapped VCs must be configured such that no conflict occurs and their bandwidth requirements are satisfied. We define the concept of a logical network (LN) as an infinite set of associated (time slot, buffer) pairs with respect to a buffer on a given VC. Based on this concept, we develop and prove theorems that constitute sufficient and necessary conditions to establish conflict-free VCs. They are applicable for networks where all nodes operate with the same clock frequency but allowing different phases. Using these theorems, slot allocation for VCs is a procedure of assigning VCs to different LNs. TDM VC configuration can thus be predictable and correct-by-construction. Our experiments on synthetic and real applications validate the effectiveness and efficiency of our approach.     

MAC for dedicated short range communications in intelligent transport system

The need for critical improvements to the North American surface transportation infrastructure vis-a-vis alleviation of congestion while enhancing public safety has led to new intelligent transportation system (ITS) infrastructure based on vehicle-to-vehicle (v2v) wireless communications. The allocation of 75 MHz in the 5.9 GHz band for dedicated short-range communications (DSRC) may also enable future delivery of rich media content to vehicles at short to medium ranges via vehicle-to-roadside (v2e) links. Recently, AASTM committee E17.51 endorsed a variant of the IEEE wireless LAN standard, denoted 802.11a roadside applications (R/A), as the platform for the DSRC link and data link layer. In this article, we provide a tutorial overview of DSRC applications and assess IEEE802.11 PHY and MAC layer characteristics in this context. It is anticipated that current 802.11 specifications need to be suitably altered to meet requirements for DSRC environments of multihop connectivity, high vehicle mobility, and heterogeneous services with a variety of QoS requirements for which the original design was not intended. This article captures the current state of the art of 802.11-based multiple access protocols and highlights open research issues.     

航天地面测控系统的健康管理应用

健康管理技术为管理对象提供健康状态管理和维护功能,已成为航空航天装备系统的重要组成部分.针对航天地面测控系统的健康管理需求,提出了基于多层级健康状态采集信息的健康管理体系架构,为地面测控设备提供状态监视、故障诊断和健康状态评估服务,并对相关健康管理功能的业务模型进行了分析,对全系统的健康管理体系工作流程进行了设计.该健...     

新型协议及设备架起连通以太网与SONET世界的桥梁

通信领域受控于两种截然不同的技术，即用于局域网（LAN）中内部业务通信的以太网及广域网（WAN）中的SONET/SDH。在网络可靠性至关重要的企业环境中，以太网已经成为普遍使用物数据网络协议，以太网具有简单，高效和可靠性极高等优点，适用于LAN环境，本介绍了虚级联和通用成帧规程。     

分布式虚拟小区网络及其反向链路容量分析

本文提出了一种新的无线系统结构:基于分布式天线的分布式虚拟小区网络.在新型无线系统结构里,虚拟小区可自主移动与改变面积,这有益于容量提高,给无线资源管理带来诸多方便;其次,在不考虑阴影效应和多径衰落的情况下,对虚拟小区的反向容量进行了理论计算分析,并与分布式天线系统进行了对比.理论分析证明,虚拟小区可以降低用户发射功率,从而减少多用户干扰,提高系统容量.     

Transmission Characteristics Evaluation Under Bad Weather Conditions in Optical Wireless Links with Different Optical Transmission Windows

Optical wireless links offer gigabit per second data rates and low system complexity. For ground space and or terrestrial communication systems, these links suffer from atmospheric loss mainly due to fog, scintillation and precipitation. Optical Wireless link provides high bandwidth solution to the last mile access bottleneck. However, an appreciable availability of the link is always a concern. Wireless Optics links are highly weather dependent and fog is the major attenuating factor reducing the link availability. Optical wireless links offer gigabit per second data rates and low system complexity. For ground space and or terrestrial communication scenarios, these links suffer from atmospheric loss mainly due to fog, scintillation and precipitation signals and then to upgrade the transmission bit rate distance product for ultra long transmission links. This paper has presented the bad weather effects such as rain, fog, snow, and scattering losses on the transmission performance of wireless optical communication systems. It is taken into account the study of bit error rate, maximum signal to noise ratio, maximum transmission optical path lengths and maximum transmission bit rates under these bad operating conditions.     

Designing a practical ATM LAN

The adaptor cards and driver software for workstations and local asynchronous transfer mode (ATM) switches and switch control software used in an ATM local area network (LAN) system are discussed. It is shown that the ATM hardware and software components together provide services that are essential for ATM to be considered a realistic alternative to current shared-media LANs. These services include: completely transparent support for the TCP/IP protocol suite, an application programming interface for full access to the underlying ATM capabilities, support for AAL5, AAL3/4, and the null AAL, both connection-oriented and connectionless service, dynamic connection establishment or switched virtual circuits, resource reservation of guaranteed bandwidth and quality of service, full-bandwidth multicast and broadcast, virtual path and channel routing among multiple switches, automatic configuration and failure recovery, dynamic address assignment and internetwork address resolution, and network management via the simple network management protocol (SNMP)     

空间干扰对卫通站接收的影响及解决措施

卫星通信系统是一个开放的无线远程点对点或点对多点的传输系统,其电波传播不受地球表面环境条件的影响,不仅通信信号质量好而且易于网络扩容。但是由于卫星通信的特殊性,其电波容易受到来自空间的同频或异频干扰。针对卫星地面站链路瞬断现象的实例,通过对链路瞬断时卫星地面站接收系统频谱的分析,确定了空间干扰对卫星地面站接收系统的影响,并对此提出了解决办法,以供工程技术人员参考使用。     

A simple data link (SDL) protocol for next generation packet network

The simple data link (SDL) is a new framing protocol for variable/fixed length packets over a general-purpose point-to-point communications channel. SDL extends the HEC-like framing mechanism used in ATM to variable-length data. Its low implementation complexity makes it particularly suitable for high-speed transport links in wavelength channels and dark fiber applications. SDL is a very attractive alternative to conventional solutions such as ATM and PPP-over-SONET (POS) for high data rate environments. SDL has also been designed to facilitate many OAM&P functions needed in next generation multiservice optical packet networks including multiprotocol encapsulation, virtual links, quality-of-service (QoS) differentiation, link management, and control. We describe framing and data link synchronization procedures in SDL, and evaluate its performance over octet and bit synchronous transport facilities.