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101.
论述了空间积分声光相关器对脉冲调制连续波信号的瞬时响应,分析了从实时光电检测器中检测出的波形,该波形是脉冲宽度,加权函数参量和与脉冲位置相关的空间衍射光分布的函数。进一步提出了脉冲序列相关时的光分布关系并通过实验加以论证。 相似文献
102.
回顾了中国发展卫星通信的简要历史,介绍了中国卫星通信的现状和作用。在调查国内用户需求的基础上,预测了1988-2002年国内用户对卫星通信转发器需要的数量。 相似文献
103.
Noise in wireless systems from solar radio bursts 总被引:1,自引:0,他引:1
L.J. Lanzerotti D.E. Gary G.M. Nita D.J. Thomson C.G. Maclennan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2253-2257
Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960–1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f 1 GHz (near current wireless bands), there can be a burst with amplitudes >103 solar flux units (SFU; 1 SFU = 10−22 W/m2) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems. 相似文献
104.
R. Giacconi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The status of institutional arrangements and of the hardware development for Space Telescope are highlighted. After a brief summary of instrument characteristics, some examples are given on the possible use of the ST to study objects of interest to cosmology. 相似文献
105.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2475-2496
This paper focused on online scheduling of distributed Earth observation satellite system in a dynamic environment. The objective was to maximize the total profit of the overall system by efficiently coordinating the different satellites with stochastic arrival of urgent tasks, subject to rigid communication and observation time window constraints. We formulated this problem as a single-task, single-robot, time-extended assignment problem with intra-schedule dependency using the multi-robot task assignment taxonomy and formulated the sub-problem after releasing urgent tasks in a mixed-integer linear programming model. We first described the online scheduling algorithm for a single satellite, then we proposed the modified consensus-based bundle algorithm (m-CBBA) and modified asynchronous consensus-based bundle algorithm (m-ACBBA) with synchronous and asynchronous communication, respectively. Compared with initial versions of CBBA and ACBBA, the modified versions added the communication loop prediction phases to efficiently utilize scarce communication opportunities and reduce the communication requirements. Additionally, we introduce two contract net protocol (CNP)-based algorithms for comparison, respectively SingleItem-CNP-based (SI-CNP) algorithm and Batch-CNP-based (BA-CNP) algorithm. Computational experiments indicated that both the total profit and percentage of scheduled urgent tasks achieved by the m-ACBBA and m-CBBA algorithms were much higher than those achieved by both SI-CNP and BA-CNP. Additionally, the number of communications needed by either m-ACBBA or m-CBBA algorithm was lower than that by SI-CNP. When the communication cost in the system is high, the m-CBBA algorithm is preferred because it balances the profit and the required number of communications. When the communication cost is low, the m-ACBBA algorithm is preferred because it achieves high total profit and high percentage of scheduled urgent tasks. 相似文献
106.
P.T. Gallagher C.A. Young J.P. Byrne R.T.J. McAteer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field that can produce adverse space weather at Earth and other locations in the Heliosphere. Due to the intrinsic multiscale nature of features in coronagraph images, wavelet and multiscale image processing techniques are well suited to enhancing the visibility of CMEs and suppressing noise. However, wavelets are better suited to identifying point-like features, such as noise or background stars, than to enhancing the visibility of the curved form of a typical CME front. Higher order multiscale techniques, such as ridgelets and curvelets, were therefore explored to characterise the morphology (width, curvature) and kinematics (position, velocity, acceleration) of CMEs. Curvelets in particular were found to be well suited to characterising CME properties in a self-consistent manner. Curvelets are thus likely to be of benefit to autonomous monitoring of CME properties for space weather applications. 相似文献
107.
108.
由于空间激光通信系统的信道状态和链路捕获跟踪的不确定性,多种形式的信道纠错编码技术正被广泛发展研究。结合空间激光通信链路中误码性能的主要影响因素,分别选择合适的编码方案进行分析。通过仿真实验可知,对于在大气结构参数为1.5×10~(-14) m~(-2/3)、风速为20 m/s的空地激光链路的环境下,在系统数据速率为2 Gbit/s、要求误码率为10~(-6)时,LDPC码结合交织码相对未编码系统有3 dB的等效编码增益,LT码相对未编码系统有3.8 dB的等效编码增益。提供了一种能快速生成、扩展和校验的编码和交织实现方法,以抵抗大气湍流的快速变化对系统性能产生的影响。 相似文献
109.
星地链路计算作为卫星通信的重要技术,是卫星通信系统设计的基础和理论依据,直接决定了卫星通信系统的链路通信质量。由于影响卫星链路的因素很多,设计中存在一处不合理即使得整条星地链路不可用,造成巨大的损失。而且在实际设计中无法做到最理想的链路状态,往往需要在某方面有所取舍,这也是链路计算中的一大难点。基于目前国际通用的链路计算方法,将星地链路上下行拆分,独立计算,综合分析,再结合实际工程经验,分析和计算实际工程案例,针对不同的链路配置给出相应合理的设计方法,可作为静止轨道通信卫星星地链路计算分析的参考。 相似文献
110.
For the performance issues of satellite transceivers suffering passive intermodulation interference,a novel and effective digital suppression algorithm is presented in this paper.In con trast to analog approaches,digital passive intermodulation (PIM) suppression approaches can be easily reconfigured and therefore are highly attractive for future satellite communication systems.A simplified model of nonlinear distortion from passive microwave devices is established in consid eration of the memory effect.The multiple high-order PIM products falling into the receiving band can be described as a bilinear predictor function.A suppression algorithm based on a bilinear poly nomial decorrelated adaptive filter is proposed for baseband digital signal processing.In consideration of the time-varying characteristics of passive intermodulation,this algorithm can achieve the rapidness of online interference estimation and low complexity with less consumption of resources.Numerical simulation results show that the algorithm can effectively compensate the passive intermodulation interference,and achieve a high signal-to-interference ratio gain. 相似文献