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21.
APOLLONOV V V 《中国光学》2013,6(2):187-195
虽然人类的太空活动已经考虑了尽量减少空间碎片的措施,但近地轨道碎片的数量仍呈指数增长,特别是中小型碎片的现有数量已对在轨卫星构成了实质性的威胁。作为具有较高期待的消除碎片办法,用地基DF激光器和空基Nd∶YAG激光器消除碎片的方案令人关注,它们可以以低成本和非破坏性的方式清除空间轨道的危险碎片。本文介绍了使用平均功率为100 kW的高功率、高重复频率P-P Nd∶YAG激光器和平均功率约为1.5 MW的DF激光器来保护在轨飞行器和清除直径为1~10 cm空间轨道危险碎片涉及的相关工作。 相似文献
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文章阐述了微滤膜在电路板废水方面的应用,并将其与传统的斜板沉淀及现行的超滤系统进行了比较,突出了微滤系统在电路板废水回用方面的优势。 相似文献
24.
未来TD-SCDMA及WiMAX发展战略思考(下) 总被引:1,自引:0,他引:1
重点论述了TD-SCDMA及WiMAX的发展新动向、优势、作用与面临的挑战,及互补、融合发展战略思考。 相似文献
25.
With the low cost and low hardware complex considerations, cooperative systems are a tendency in the future communications. This work considers the secure cooperative communications systems. For a practical situation in the system, the scenario includes multiple source stations, multiple relay stations, multiple destination stations, and eavesdroppers. To analyze the optimal relay selection in the system, we begin with the performance analysis for a single source station and a single destination station. By applying two cooperative models, the amplify-and-forward (AF) mode and decode-and-forward (DF) mode, the secrecy capacity is derived. Then, we apply the derived results to the considered environment to find the optimal relay assignment. By the way, the relay selection can be obtained by the exhaustive search algorithm. However, there are a lot of steps needed if the number of source stations is large. Hence, applying the characters of the cooperative modes in the relay selection, the pre-selection step is proposed with a mathematical derivation. It could be used for the practical situation without a long-time calculation. 相似文献
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介绍了一种三通道权微扰谱估计测向方法。该方法首先利用权微扰方法来获得阵列的协方差矩阵,进而采用特征结构类算法估计波达方向,并采用空间平滑算法来处理相干信源。仿真结果表明,该方法的估计结果更加稳健、有效。且在接收机数目较少的情况下,该方法仍具有一定的实用性。 相似文献
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This paper proposes rate-maximized (MR) joint subcarrier pairing (SP) and power allocation (PA) (MR-SP&PA),a novel scheme for maximizing the weighted sum rate of the orthogonal-frequency-division multiplexing (OFDM) relaying system with a decode-and-forward (DF) relay.MR-SP&PA is based on the joint optimization of both SP and power allocation with total power constraint,and formulated as a mixed integer programming problem in the paper.The programming problem is then transformed to a convex optimization problem by using continuous relaxation,and solved in the Lagrangian dual domain.Simulation results show that MR-SP&PA can maximize the weighted sum rate under total power constraint and outperform equal power allocation (EPA) and proportion power allocation (PCG). 相似文献
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调谐系统是DF500A型短波发射机最重要的系统之一,对于整机的稳定和安全播音有重要意义。本文主要介绍DF500A型发射机调谐系统原理,并对两个常见故障进行分析,提出维护和改进建议以供同行参考。 相似文献
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Shao‐I Chu Wei‐Cheng Lin Hung‐Peng Lee Hsin‐Chiu Chang 《Wireless Communications and Mobile Computing》2013,13(16):1464-1481
This paper derives the asymptotic symbol error rate (SER) and outage probability of decode‐and‐forward (DF) cooperative communications over Rician fading channels. How to optimally allocate the total power is also addressed when the performance metric in terms of SER or outage probability is taken into consideration. Analysis reveals the insights that Rician factor has a great impact on the system performance as compared with the channel variance, and the relay–destination channel quality is of importance. In addition, the source–relay channel condition is irrelevant to the optimal power allocation design. Simulation and numerical evaluation substantiate the tightness of the asymptotic expressions in the high‐SNR regions and demonstrate the accuracy of our theoretical analysis. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献