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排序方式: 共有86条查询结果,搜索用时 9 毫秒
31.
针对地球同步轨道合成孔径雷达(GEO SAR)成像距离向处理复杂,方位向空变性强问题,该文提出一种基于Chirp_z变换与方位变标的成像算法。首先在回波模型中考虑停-走-停假设带来的相位误差,然后给出目标点的斜距表达式,并利用泰勒级数对斜距进行了高阶展开,通过级数反演法得到信号频谱表达式,利用高效的Chirp_z变换校正距离走动,简化距离向处理,利用改进的变标因子校正方位向信号一次,二次,三次展开项系数线性时变性,并在方位频域内补偿变标操作引入的相位误差。仿真结果表明该算法能够实现地球同步轨道SAR聚集成像。 相似文献
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Tae Chul Hong Kunseok Kang Bon‐Jun Ku Dae‐Ig Chang 《International Journal of Satellite Communications and Networking》2017,35(1):3-15
For the successful deployment of the long term evolution (LTE)‐based mobile satellite service, the price of a user terminal is one of the major factors. A user terminal for the LTE‐based satellite communication needs to be implemented with a similar hardware size that is used for a terrestrial LTE user terminal. However, for quality of service provision, the satellite user terminal needs a larger size of memories than the terrestrial terminal does. This is very evident by considering that the N‐channel stop and wait hybrid automatic repeat request requires proportionally increasing memory size by the propagation delay, resulting in unmanageable amount of memories in the satellite system. To resolve this problem, we propose an efficient memory management method at the user terminal when the size of memory is insufficient. The simulation results in this paper reveal that the proposed method can increase the throughput about 20.7% when a user terminal is operated under very low throughput condition with an insufficient memory size, compared with the case without memory management scheme. In addition, we show that the additional throughput gain can be obtained by the packet scheduling using the information of receiver memory status. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
34.
Zoltn Katona Michael Grßlin Anton Donner Norman Kranich Hartmut Brandt Hermann Bischl Martin Brück 《International Journal of Satellite Communications and Networking》2020,38(3):301-313
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. 相似文献
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在高轨(GEO)合成孔径雷达(SAR)成像中,超大的成像幅宽导致成像区域不满足平面近似,使得基于平面网格的快速BP算法失效。该文提出一种基于地表网格的快速BP算法来精确高效地处理高轨SAR信号。首先针对轨道弯曲和地表弯曲所带来的信号复杂空变问题,采用一种基于实际地表的曲面网格布置方法。针对子孔径BP图像的频谱混叠问题,提出基于曲面网格的两步频谱压缩函数,将子孔径图像在合成之前实现频谱解混叠。同时采用多级子孔径图像合成的方法提高成像效率。最后,通过对比仿真,证明了该文所提算法的精确性以及高效性。 相似文献
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信息高速公路中卫星无缝隙覆盖综合业务发展的技术问题与解决途径(下)陈如明(邮电部电信总局北京100804)4一些主要技术问题与可能的解决途径在明确了未来SDH/ATM卫星网络与地面网络无缝隙覆盖综合的基本网络结构考虑后,下面进一步讨论欲实施其相应互操... 相似文献
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本文讨论典型中、低轨道卫星通信系统网络结构和LEO/MEO/GEO系统性能对比方法,亦展望了其存在问题及发展前景。 相似文献
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Raúl Chvez Santiago Valeri Ya. Kontorovitch Mauricio Lara Barrn 《International Journal of Satellite Communications and Networking》2003,21(6):547-560
Computing interference is very important in satellite networks design in order to assure the electromagnetic compatibility (EMC) with other radiocommunication systems. There are different methods to compute interference in geostationary (GEO) satellite systems including conventional methods using link budget equations and alternate methods such as increase in noise temperature. However, computing interference in low earth orbit (LEO) systems represents a different problem. Due to the special characteristics of this kind of orbits, the elevation angle at any site changes continuously over time, meaning a time dependent change of the propagation path length between an interfering transmitter and an interfered‐with receiver, and of the discrimination provided by the transmitting and/or the receiving antenna. Thus, conventional interference prediction methods developed for fixed links must be adapted to the case of LEO systems. To overcome this problem a mathematical model that characterizes the path length variations by an average value obtained from the probability density function of the varying distance between an interfering transmitter and an interfered‐ with receiver is proposed in this paper. This average path length enables the use of conventional link budget methods to reduce the computation time for the evaluation of interference in LEO satellite environments. Two practical examples show the possible applications of the proposed model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
40.
Jonathan P. Castro 《International Journal of Satellite Communications and Networking》1994,12(1):71-75
This article presents an overview of the concept of a multiple purpose global satellite network. It identifies some of the main needs of telecommunication services today, and projects the potential of future demands. It also describes the great possibilities of economic expansion and mass participation in the growth and prosperity of a nation, if basic telecommunication services are accessible on a global scale. The study suggests that the rapid recovery of capital investments on universal satellite networks lies in developing regions through cost-effective service diversification. 相似文献