第三代卫星移动通信发展前景分析

主要论述第3代卫星移动通信的现状、发展前景、市场定位策略、尚待研究开发的技术。经济和信息全球化给第3代卫星移动通信的发展提供了良好的机遇,同时,陆地移动通信网的迅猛发展向第3代卫星移动通信提出了严重的挑战。因而,第3代卫星移动通信既有美好的发展前景,也会遇到种种困难。     

关于第四代移动通信的思考与探索

第三代移动通信即将面市，人们已开始谈论２１世纪未来一代无线移动通信的发展前景，其中第四代移动通信已提上议事日程。文章扼要探讨了其发展的必要性、基本特征、系统结构以及演进到第四代的基本步骤，最后提出了我国发展第四代移动通信的建议。     

卫星移动通信系统发展现状

卫星移动通信系统已被作为第三代卫星移动通信的一个重要组成部分。文章介绍了近年来卫星移动通信系统的最新发展概况及其特点。     

刍议第三代移动通信系统

对现代移动通信系统的体制和发展前景以及第三代移动通信系统中关键性的CDMA多址技术作了简要的介绍,就第三代移动通信系统在我国的发展作了展望。     

第三代移动通信系统

本文对现代移动通信系统的体制和发展前景,并就第三代移动通信系统中的关键性多址技术CDMA作了简要介绍,最后就第三代移动通信系统在我国的发展作了展望。     

4G移动通信网络技术的发展现状及前景分析

移动通信技术分为四个发展阶段:在模拟技术的基础上形成的第一代移动通信,融合了数字技术的第二代移动通信,基于第二代技术发展起来的第三代移动通信,提供语音及各种多媒体服务的第四代移动通信。文章从4G移动通信技术的产生、概念及发展现状入手,分析4G的网络体系结构及技术要求,深入探讨4G的关键技术,对4G通信技术的发展前景进行预测与展望。     

TD-SCDMA与其它3G提案

叙述了第三代移动通信(3G)的当前进展,对中国提案TD-SCDMA与其它3G提案进行了比较,并预测TC-SCDMA提案的发展前景。     

世纪之交的移动通信（上）

本从第一代移动通信－ＧＳＭ的演进方向和第三代移动通信系统提案的技术分析入手,阐述了世纪之交的移动通信的发展走向,中涉及了陆地移动通信外,还涉及了卫星移动通信以及移动数据通信。     

第三代移动通信技术中的Turbo码

本文简要介绍了移动通信网络的发展,特别是对第三代移动通信网作了阐述。对解决移动通信中极低信噪比情况下的无误传输所用的差错控制编码问题,作了深入论述,并详细论述了Turbo码在第三代移动通信中的应用及发展前景。     

国际海事卫星移动通信系统与下一代IMT系统在扩展C频段的共存

根据《中华人民共和国无线电频率划分规定》和国际电信联盟《无线电规则》的相关规定可知,在我国第四代国际海事卫星移动通信系统的空对地(下行)链路与下一代IMT系统存在频率重叠.为了保证第四代国际海事卫星移动通信系统与下一代IMT系统在扩展C频段的共存,给出了使上述两系统正常工作的前提条件或保护措施.通过理论分析、仿真计算以及调研厂商的制造水平,给出了关于第四代国际海事卫星移动通信系统与下一代IMT系统在扩展C频段共存的建议.     

国外卫星移动通信新进展与发展趋势

在地面移动通信迅猛发展的新形势下,提供相似业务的卫星移动通信的发展动态和趋势值得关注.首先介绍了国外卫星移动通信市场发展动态,然后分别介绍了静止轨道、中轨道和低轨道三类卫星移动通信系统的最新进展,其中静止轨道卫星移动通信发展最好,中低轨道卫星移动通信系统发展相对不景气;最后探讨了卫星移动通信的发展趋势,指出通过星地集成...     

Use of Remotely Sensed Data for Assessing Forest Stand Conditions in the Eastern United States

The results of three interrelated research activities conducted by Goddard scientists in support of the AgRISTARS Renewable Resources Inventory (RRI) project are summarized. The central theme of the research conducted at Goddard was the development of techniques for the detection, classification, and measurement of forest disturbances using digital, remotely sensed data. Three study areas located in Pennsylvania, North Carolina, and Maine were investigated with respect to: a) the delineation and assessment of forest damage associated with two different forest insect defoliators, and b) an assessment of the improved capabilities to be expected from Landsat Thematic Mapper (TM) data relative to Multispectral Scanner (MSS) data for delineating forest stand characteristics. Key results include the development of a statewide MSS digital data base and associated image processing techniques for accurately delineating (approximately 90 precent correct classification accuracy) insect damaged and healthy forest. Comparison of analyses using MSS and TM Simulator (TMS) data indicated that for broad land cover classes which are spectrally homogeneous, the accuracy of the classification results are similar. However, TMS data provided superior results (20 percent overall accuracy increase relative to MSS results) when detailed (Level III) forest classes were mapped. These studies also illustrated the utility of having at least one band in the visible, near infrared, and middle infrared portion of the electromagnetic spectrum for assessing specific (Level III) forest cover types.     

MSS4TQM-a management support system for total quality management

The paper describes the research and development of a management support system (MSS) for total quality management (TQM). A prototype system called management support system for total quality management (MSS4TQM) is designed and developed to facilitate management or a quality team in conducting quality barrier assessment and critical factor analysis of TQM for an organization. MSS4TQM is implemented on personal computers under a Microsoft Windows^TM environment. To evaluate the performance of MSS4TQM, selected quality practitioners in manufacturing and service industries in Hong Kong, as well as quality experts from thirteen nations, are invited to participate in testing the system. The evaluation study of the prototype system in the context of a proposed MSS evaluation framework is described. The results of prototype evaluation are satisfactory and support the contention that MSS4TQM performs its functions as expected     

Location-Aware Mobile Intrusion Detection with Enhanced Privacy in a 5G Context

The paper proposes a location-aware mobile Intrusion Prevention System (mIPS) architecture with enhanced privacy that is integrated in Managed Security Service (MSS). The solution is envisaged in a future fifth generation telecommunications (5G) context with increased but varying bandwidth, a virtualised execution environment and infrastructure that allows threads, processes, virtual machines and storage to be migrated to cloud computing services on demand, to dynamically scale performance and save power. 5G mobile devices will be attractive targets for malicious software, and this threat will in some cases change with location. Mobile devices will store more sensitive information and will also be used to a larger extent for sensitive transactions than they typically do today. In addition, a distributed execution environment in itself gives raise to some new security challenges. In order to handle these security challenges, we have proposed the location-aware mIPS architecture, which benefits from a distributed execution environment where processor intensive services can be outsourced to Cloud hosting providers. The mIPS supports querying location threat profiles in a privacy-preserving way, and ensures that mIPS alerts sent to the the first-line MSS are anonymised. We finally perform an analysis of potential strengths and weaknesses of the proposed approach.     

移动卫星系统与LTE网络间干扰共存性能的研究

The interference coexistence performance between the systems of a Long Term Evolution (LTE) network and Mobile Satellite Service (MSS) system, both of which work around the frequency of approximately 2 GHz according to the bandwidth allocation in China, is proposed in this article. The related background of an MSS system and the common terminologies are introduced. Further, the coexistence scenarios of different coverage situations shared by the two systems are discussed. The interference impact of an MSS transmission on an LTE system is evaluated using a specific Monte Carlo method. Finally, simulation results show that although no crucial issues for the coexistence of an LTE downlink and the MSS are observed, the LTE uplink suffers a considerable amount of interference from the MSS transmission. Given the insufficient isolation between LTE and MSS existing networks, and the rapid advance in the field of LTE, problems may emerge in the near future. Further, this article can be of sig-nificance in providing reference for frequency spectrum planning in the existing LTE net-works.     

Predictive Dynamic Channel Allocation Scheme for Improving Power Saving and Mobility in BWA Networks

The radio spectrum of IEEE 802.16 medium access control (MAC) protocol ranges from 2–66 GHz, which is one of potential solutions for broadband wireless access (BWA) or beyond third generation (B3G)/4G networks. The maximum transmission range can reach about 48 km. However, with the property of radio propagation, the maximum transmission distance is proportioned inversely to the frequency the mobile subscriber station (MSS) carries. According to this property, the channel allocation can be based on how far the distance between the MSS and the base station (BS) in a macrocell. Therefore, this paper first proposes a new concept of channel allocation model for BWA system and investigates the relations between the signal propagation and the distance as well as propose a signal-aware dynamic channel allocation (SDCA) scheme for dynamic channel allocation (DCA) in BWA networks (BWANs). The SDCA enables the BS to allocate appropriate channels to MSSs according to the received signal-to-noise ratio (SNR) value from the MSSs. Besides, according to the frequency, the SDCA can estimate a minimum power for MSS to communicate. The SDCA not only increases the capacity of the system but saves the overall power consumption of the system well. We also present a new out-of-service prevention scheme for supporting mobility in the system. Simulation results show that the proposed SDCA can achieve the channel utilization (throughput) by up to 94.4% when the spectrum ranges from 2–11 GHz.

Comparison of the Information Content of Data from the LANDSAT-4 Thematic Mapper And the Multispectral Scanner

Simultaneous data acquisition by the Landsat-4 Thematic Mapper (TM) and the Multispectral Scanner (MSS) permits the comparison of the two types of image data with respect to engineering performance and data applications. In this paper the ?information? contained in data from the visible and near-IR channels is evaluated for five agricultural scenes, leading to the conclusion that the TM provides a significant advance in information gathering capability as expressed in terms of bits per pixel or bits per unit area. The six reflective channels of the TM acquire 18 bits of information per pixel out of a possible 6 × (8 bits) = 48 bits, while the four MSS channels acquire 10 bits of information per pixel out of a possible 4 × (7 bits) = 28 bits. Thus the TM and MSS are equally efficient in gathering information (18/48 ? 10/28), contrary to the expected tendency toward lower efficiency as spatial resolution is improved and spectral channels are added to an observing system. The result is attributed to: 1) Superior selection of spectral channels in the TM; 2) Higher precision of the TM data, i.e., lower system noise, and 3) the advantage of higher spatial resolution, even in agricultural areas where fields are larger than the MSS pixel size. Because the MSS lacks a thermal IR channel, the 10-12-micrometer data of the TM at 120-m resolution are analyzed theoretically using an energy balance approach.     

A model for interference studies relating to multisatellite non-geostationary systems in the mobile satellite service

An option being considered by current and prospective mobile satellite service (MSS) operators is the use of constellations of non-geostationary orbit (NGSO) satellites to provide global personal communications. The scarcity of free spectrum, together with the bandwidth typically required, means that any new MSS system must consider sharing spectrum with other systems and services. Spectrum sharing must be based on defined interference criteria being satisfied. When multiple NGSO satellites are considered there is no accepted method for assessing interference. This paper describes a model used as the basis for a computer simulation of interference scenarios involving MSS, fixed service (FS) and fixed satellite service (FSS) systems. The simulation includes NGSO dynamics, constellations of MSS satellites with multi-spot antennas, multiple geostationary FSS satellites and multiple hop FS links. Interference events are based on C/I calculations, and statistics, such as the percentage of time that the C/I falls below a required protection ratio, are calculated. More generally C/I cumulative distribution functions are produced.     

How WARC '92 will affect mobile services

The US proposals to, and the decisions of, the 1992 World Administrative Radio Conference (WARC '92) that relate to mobile and mobile-satellite services are described. Mobile-satellite service (MSS) issues addressed at WARC '92 include new allocations for low Earth-orbit (LEO) satellite operations, new MSS spectrum allocations, and modifications to current allocations used to support mobile-satellite operations. Allocation issues on the agenda of WARC '92 that related to the terrestrial mobile services include allocations for mobile services between 1 and 3 GHz, allocations for aeronautical public correspondence, and designation of frequency bands for future public land mobile telecommunications services. A number of proposals which were put forward by the US to support MSS allocations and operations that did not explicitly require allocations to the MSS are discussed     

Feasibility of Coexistence of Mobile‐Satellite Service and Mobile Service in Cofrequency Bands

Interference scenarios and methodologies between a terrestrial mobile service (MS) system and mobile‐satellite service (MSS) system in a co‐channel environment are established. Taking into account a practical deployment situation for both systems, we perform computational simulation of interference in terms of carrier‐to‐interference ratio (C/I) and interference‐to‐noise ratio (I/N) to evaluate the cofrequency interference from an MS system into an MSS system, and from an MSS system into an MS system, respectively. The methodology and results can be used as a guide when planning the deployment of MSS and MS systems with no unacceptable interference impact between them.