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121.
在暗室中对窄带天线进行测量时,由于间接时域方法的测试带宽不足而无法有效地去除多径信号所产生的干扰,文中提出将现代频谱估计技术应用于此类天线的测试。以最大熵为约束条件,利用现代谱估计中的Burg算法求解接收到频域信号的AR模型参数,并对其进行频谱外推。从而在频域拓宽信号的测试带宽,在时域提高信号的分辨率,并运用间接时域测量技术精确加载时域门,达到去除多径干扰的目的。仿真和实测都验证了该方法的有效性及可靠性。  相似文献   
122.
This paper presents a study on multicast communications in cognitive radio networks (CRNs)using directional antennas. The objective is to maximize the throughput of the CRN. The spectrum is divided into multiple channels and licensed to the primary network. While the CRN is accessing the spectrum, the interference power is carefully controlled to avoid impacting the operation of the primary network. The mathematical model is presented and subsequently formulated as a mixed integer non‐linear programming (MINLP) problem, which is non‐deterministic polynomial‐time hard. Therefore, a greedy algorithm is designed to approximate the optimal performance. The MINLP problem is then relaxed and an upper bound is developed. Simulation results are presented to compare the performance of the greedy algorithm and the upper bound, which demonstrates the efficacy of the greedy algorithm as well as the tightness of the upper bound. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
123.
In this paper, we study the performance of time hopping pulse position modulation for impulse radio ultra‐wideband. We consider relay network applying decode‐and‐forward protocol. The channels between nodes adopt the IEEE 802.15.4a norms. The bit error rate performance is analyzed considering the effect of interference. Our results show significant improvement due to the diversity gain provided by the relay nodes. However, the performance is limited when multiple access interference (MAI) is present. To combat the MAI effect and further improve the detection reliability, we propose to use antenna selection at the relay. The relay receiver is assumed to be equipped with multiple antennas, and only the best antenna is selected. This is shown to improve the performance in the presence of MAI and improve the diversity gain.Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
124.
A new approach for multiantenna broadcast channels in cellular networks based on multiuser diversity concept is introduced. The technique called opportunistic interference management achieves dirty paper coding capacity asymptotically with minimum feedback required. When there are K antennas at the base station with M mobile users in the cell, the proposed technique only requires K integer numbers related to channel state information between mobile users and base station. The encoding and decoding complexity of this scheme is the same as that of point‐to‐point communications, which makes the implementation of this technique easy. An antenna selection scheme is proposed at the base station to reduce the minimum required mobile users significantly at the expense of reasonable increase in feedback. In order to guarantee fairness, a new algorithm is presented that incorporates opportunistic interference management into existing Global System for Mobile communications (GSM) standard. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
125.
Despite the great promise of printed flexible electronics from 2D crystals, and especially graphene, few scalable applications have been reported so far that can be termed roll‐to‐roll compatible. Here we combine screen printed graphene with photonic annealing to realize radio‐frequency identification devices with a reading range of up to 4 meters. Most notably our approach leads to fatigue resistant devices showing less than 1% deterioration of electrical properties after 1000 bending cycles. The bending fatigue resistance demonstrated on a variety of technologically relevant plastic and paper substrates renders the material highly suitable for various printable wearable devices, where repeatable dynamic bending stress is expected during usage. All applied printing and post‐processing methods are compatible with roll‐to‐roll manufacturing and temperature sensitive flexible substrates providing a platform for the scalable manufacturing of mechanically stable and environmentally friendly graphene printed electronics.

  相似文献   

126.
The efficient collection of solar energy relies on the design and construction of well‐organized light‐harvesting systems. Herein we report that supramolecular phenanthrene polymers doped with pyrene are effective collectors of light energy. The linear polymers are formed through the assembly of short amphiphilic oligomers in water. Absorption of light by phenanthrene residues is followed by electronic energy transfer along the polymer over long distances (>100 nm) to the accepting pyrene molecules. The high efficiency of the energy transfer, which is documented by large fluorescence quantum yields, suggests a quantum coherent process.  相似文献   
127.
以卟啉分子H2-pTCPP作为基础染料,通过配位自组装的方法将天线分子S3修饰到染料结构中。结果表明经天线分子修饰后染料敏化太阳能电池器件的整体性能得到了极大的改善。天线效应有效地提高了器件的光子捕获能力,光电流得到了显著的提高,并且电荷复合行为也得到了明显的抑制。基于H2-pTCPP的电池器件显示了1.18%的转换效率,而经过天线分子修饰后的Mn-pTCPP+S3显示了2.64%的转换效率,性能提高了1.2倍。  相似文献   
128.
研究了脉冲参数及其对测量的影响,根据时域场的平面波理论,给出了根据惠更斯源得到的时、频域远场方向图以及近远场变换公式。最后根据实测结果具体分析了脉冲天线测量中脉冲参数的选择要求。  相似文献   
129.
一种小型化多频段天线的研究   总被引:1,自引:0,他引:1  
针对移动终端小型化多功能的要求,研究了一种小型多频工作的天线。该天线由两部分构成,分别馈电,实现了无线通信中天线的小型化和多频段的要求。对其进行了仿真和测试,结果表明该天线可工作于850MHz、900MHz、1800MHz、1900MHz及2.4GHz 5个频段,覆盖频段较宽,性能较好。  相似文献   
130.
角锥喇叭天线制造工艺   总被引:1,自引:0,他引:1  
介绍了不同频段、不同尺寸的角锥喇叭天线成型方法,针对传统成型方法一些不足之处以及产品轻量化设计的要求,对喇叭的成型方法又提供了三种新的制造工艺,即电子束焊、真空钎焊及碳纤维复合材料成型法.  相似文献   
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