Protection of Digital TV from Cognitive Radio Interference

Analytic modeling and computational simulation for the protection of DTV from cognitive radio interference are performed. Protection is achieved by using the protection ratio, which is derived through system modeling and its analysis. On the frequency coordination between digital TV and cognitive radio, an analysis in a co‐channel environment, in a rural area in Korea, is performed.     

Highly Crystalline Soluble Acene Crystal Arrays for Organic Transistors: Mechanism of Crystal Growth During Dip‐Coating

The preparation of uniform large‐area highly crystalline organic semiconductor thin films that show outstanding carrier mobilities remains a challenge in the field of organic electronics, including organic field‐effect transistors. Quantitative control over the drying speed during dip‐coating permits optimization of the organic semiconductor film formation, although the kinetics of crystallization at the air–solution–substrate contact line are still not well understood. Here, we report the facile one‐step growth of self‐aligning, highly crystalline soluble acene crystal arrays that exhibit excellent field‐effect mobilities (up to 1.5 cm V^?1 s^?1) via an optimized dip‐coating process. We discover that optimized acene crystals grew at a particular substrate lifting‐rate in the presence of low boiling point solvents, such as dichloromethane (b.p. of 40.0 °C) or chloroform (b.p. of 60.4 °C). Variable‐temperature dip‐coating experiments using various solvents and lift rates are performed to elucidate the crystallization behavior. This bottom‐up study of soluble acene crystal growth during dip‐coating provides conditions under which one may obtain uniform organic semiconductor crystal arrays with high crystallinity and mobilities over large substrate areas, regardless of the substrate geometry (wafer substrates or cylinder‐shaped substrates).     

Dihydroazulene Photoswitch Operating in Sequential Tunneling Regime: Synthesis and Single‐Molecule Junction Studies

Molecular switches play a central role for the development of molecular electronics. In this work it is demonstrated that the reproducibility and robustness of a single‐molecule dihydroazulene (DHA)/vinylheptafulvene (VHF) switch can be remarkably enhanced if the switching kernel is weakly coupled to electrodes so that the electron transport goes by sequential tunneling. To assure weak coupling, the DHA switching kernel is modified by incorporating p‐MeSC₆H₄ end‐groups. Molecules are prepared by Suzuki cross‐couplings on suitable halogenated derivatives of DHA. The synthesis presents an expansion of our previously reported bromination–elimination–cross‐coupling protocol for functionalization of the DHA core. For all new derivatives the kinetics of DHA/VHF transition has been thoroughly studied in solution. The kinetics reveals the effect of sulfur end‐groups on the thermal ring‐closure of VHF. One derivative, incorporating a p‐MeSC₆H₄ anchoring group in one end, has been placed in a silver nanogap. Conductance measurements justify that transport through both DHA (high resistivity) and VHF (low resistivity) forms goes by sequential tunneling. The switching is fairly reversible and reenterable; after more than 20 “ON‐OFF” switchings, both DHA and VHF forms are still recognizable, albeit noticeably different from the original states.     

Does Multitasking Increase or Decrease Persuasion? Effects of Multitasking on Comprehension and Counterarguing

This study examined the effects of multitasking on persuasion, including comprehension and counterarguing of persuasive messages, which were presented in three different contexts: (a) nonmultitasking with full attention paid to the message, (b) multitasking with primary attention paid to the message, and (c) multitasking with secondary attention paid to the message. Consistent with predictions, the results suggested that multitasking reduced the actual and perceived levels of comprehension and also reduced counterarguing. The implications for research on persuasion are further discussed.     

Joint optimization of power allocation and relay location for regenerative relaying with multi‐antenna reception at destination

We consider joint power allocation (PA) and relay positioning in a dual‐hop regenerative relay system with multiple antennas equipped at the destination. With a fixed relay location, an adaptive PA strategy at the source and relay under a sum power constraint that minimizes the system outage probability is presented. With a fixed PA strategy, the optimal relay location is derived. We then propose to jointly optimize PA and relay location. It is shown that employing more destination antennas and/or choosing an appropriate relay location can significantly save the power needed at the relay. Numerical results are presented to demonstrate the performance of the proposed PA and relay positioning algorithms. Copyright © 2011 John Wiley & Sons, Ltd.     

Distributed User Association with Resource Partitioning in Heterogeneous Cellular Networks

To fully utilize the resources of heterogeneous cellular networks (HCNs), an effective approach that offloads users to the underloaded small cells from overloaded macrocells is widely advocated. However, this operation often leads to a bad result that the offloaded users achieve lower signal-to-interference-plus-noise-ratio (SINR) than these users in macrocells. Thus, some appropriate interference avoidance techniques should be adopted to partially alleviate the SINR degradation. For this, we consider the resource (frequency) partitioning that turns off some fraction of such resources in a macrocell. Naturally, an optimal offloading strategy should be closely coupled with resource partitioning, and in turn the optimal partition decides the offloading performance. In this paper, we propose a distributed association strategy with joint offloading and resource partitioning for HCNs. We reveal that load balancing, by itself, is insufficient, and additional resource partitioning is required to improve system performance. Meanwhile, we also show that, compared with the best power association and range extension association, the proposed scheme provides better association performance.

     

各向异性海洋湍流对外差式DPSK无线光通信系统的性能研究

应用广义的惠更斯-菲涅耳原理及改进的Rytov方法,采用基于Gamma-Gamma光强概率分布的海洋湍流信道模型,得到了中断概率解析式.并在此基础上对各向异性海洋湍流高斯光束外差式差分相移键控(DPSK)调制的中断概率性能进行了研究.仿真分析了不同的各向异性海洋湍流下各种海洋湍流参数(温度与盐度波动对功率谱变化贡献之比...     

球面近场测试高阶探头补偿算法及其在超宽带探头上的应用

为了提高基于超宽带探头的球面近场天线测试系统精度,相应的探头补偿算法需要考虑超宽带探头的高阶方位模式.文中采用文献[3]中基于球面波的迭代法方案实现了高效高精度的高阶探头补偿算法,并将其应用到一种工作在2~18 GHz的超宽带双脊喇叭探头中.同时以偶极子阵列为例,研究了本文算法相较于传统低阶算法的精度优势,测试了该算法在多种条件下的收敛性.结果显示:在相同条件下,高频端比低频端的高阶补偿效应更加明显;当待测天线完全落在该探头的主瓣6 dB宽度区域内时,算法均可以在几次(小于10)迭代后达到理想的精度.因此,本文算法可以有效地提高基于超宽带探头的球面近场测试系统的精度,并且具有较高的单机计算效率.     

3G无线网络建设问题探讨

移动通信低速语音通信向高速数据通信转变,通信业务由室外向室内转移,无线网络从信号覆盖型向信息容量型演进,网络架构正在发生深刻变革。变革对网络建设、技术和管理提出了新的挑战和要求。针对存在的问题和挑战,提出了相关建议,并介绍了广东联通在技术和管理创新方面的有益尝试。     

MPPSK调制解调器研究

为深入研究多元位置相移键控(MPPSK)调制信号的功率谱特性且改善其接收端解调性能,给出了(M>2)时的MPPSK理论功率谱的一般表达式,并设计了一种新的基于BP神经网络的解调器。在MPPSK调制原理的基础上,利用交变波和稳态波分解法推导了(M=3)3PPSK的理论功率谱解析式,并推广得到了(M>3)时的MPPSK理论功率谱一般表达式,通过仿真验证了理论推导的正确性,分析了影响MPPSK功率谱的主要因素。同时,基于已有的锁相环解调和数字冲击滤波器多路判决解调的两种方案,充分利用数字冲击滤波器输出的显著波形差异,提出了一种基于BP神经网络的MPPSK解调器,并对三种解调方案进行了仿真。仿真结果表明:新的MPPSK解调器解调性能要明显好于已有的两种解调方案。