Improved Gain Characteristics in Er3+-Doped Alumina (Al2O3) Channel Optical Waveguide Amplifiers for WDM Systems

Er3+-doped Al2O3 optical waveguides are analyzed both as single amplifiers and as elements of a 16-channel wavelength division multiplexing transmission system; their performance is compared with that from Er3+-doped SiO2 optical waveguide amplifiers. The amplifier model, based on propagation and population-rate equa tions, includes both uniform and pair-induced up-conversion mechanisms and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis showed that Er3+-doped Al2O3 waveguides exhibit much higher signal gains than Er3+-doped SiO2 waveguides and also that the use of Er3+-doped Al2O3 waveguides reduces the deleterious gain peaking effect, increasing the maximum transmission distance.     

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li⁺ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li⁺. The channels attract and enrich Li⁺ ions by up to orders of magnitude. As a result, our material sieves Li⁺ out of various common ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺ and Al³⁺. Moreover, by spontaneously enriching Li⁺ ions, it realizes an effective Li⁺/Na⁺ selectivity of 1422 in artificial seawater where the Li⁺ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.     

A Robust (10,3)-a Network Containing Chiral Micropores in the AgI Coordination Polymer of a Bridging Ligand that Provides Three Bidentate Metal-Binding Sites

Framework integrity is retained when water molecules replace the nitromethane molecules in the coordination polymer [Ag(hat)ClO₄]⋅2 CH₃NO₂ (see picture for structure), which are arranged in a helical fashion within the chiral micropores of the three-dimensional [Ag(hat)⁺]_n network with a (10,3)-a topology. Remarkably, this is also the case after subsequent displacement of the water by nitromethane molecules. hat=1,4,5,8,9,12-hexaazatriphenylene.     

Channel estimation with ISFLA based pilot pattern optimization for MIMO OFDM system

In multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the channel state information should be known by the receiver for obtaining transmitted data. Channel estimation algorithms are used to examine the multipath effects of frequency selective Rayleigh fading channels. In this paper, Compressed Sensing (CS) based channel estimation technique is considered for reconstructing the signal with improved spectral efficiency. It requires transmitting the known pilot data to the receiver for estimating channel information. The optimum pilot patterns are selected through reducing the mutual coherence of measurement matrix. In order to maximize the accuracy of sparse channel estimation and to reduce the computational complexity, an optimization algorithm Improved Shuffled Frog Leaping (ISFL) is proposed. When compared with the traditional estimation methods like least squares (LS), and minimal mean square error (MMSE), 4.7% of spectral efficiency is increased with ISFLA based channel estimation. Implementation results show that, by using the proposed algorithm, the bit error rate (BER) and Mean Square Error (MER) performance of the system is increased with 1.5 dB and 2 dB respectively.     

可重构智能表面中的低复杂度毫米波信道追踪算法

针对可重构智能表面(RIS)中的毫米波通信系统,用户至RIS端信道角度参数的缓慢变化,该文提出一种基于牛顿算法的低复杂度信道追踪方案。该方案将RIS部分元件连接射频(RF)链,首先使用2维快速傅里叶变换 (2D-FFT)算法初始化估计角度,并且使用最大似然算法估计路径增益。在后续时隙中,使用牛顿算法追踪每个时隙的角度参数。由于环境突然变化和终端缓慢变化会导致信道矩阵发生突变,若检测到信道突变,则再次初始化参数,否则使用牛顿算法继续追踪角度参数。仿真结果表明,该方案在具有优良性能的前提下复杂度可以达到最低,极大节约算力资源,在计算复杂度和性能之间可以取得很好的平衡。     

Characterization survey of Ga<Subscript>x</Subscript>In<Subscript>1−x</Subscript>As/InAs<Subscript>y</Subscript>P<Subscript>1−y</Subscript> double heterostructures and InAs<Subscript>y</Subscript>P<Subscript>1−y</Subscript> multilayers grown on InP

Low-bandgap, lattice-mismatched Ga_xIn_1−xAs (GaInAs) grown using InAs_yP_1−y (InAsP) compositional-step grades on InP is a primary choice for lightabsorbing, active layers in high-efficiency thermophotovoltaic (TPV) devices. The GaInAs/InAsP double heterostructures (DHs) show exceptional minority carrier lifetimes of up to several microseconds. We have performed a characterization survey of 0.4–0.6-eV GaInAs/InAsP DHs using a variety of techniques, including transmission electron microscopy (TEM). Dislocations are rarely observed to thread into the GaInAs active layers from the InAsP buffer layers that terminate the graded regions. Nearly complete strain relaxation occurs in buried regions of the InAsP grades. The buffer-layer strain prior to deposition of the active layer is virtually independent of the net misfit. Foreknowledge of this buffer-layer strain is essential to correctly lattice match the buffer to the GaInAs active layer.     

Mitigating adjacent channel interference in vehicular communication systems

In the last few decades, dedicated wireless channels were specifically allocated to enable the development and implementation of vehicular communication systems. The two main protocol stacks, the WAVE standards proposed by the IEEE in the United States and the ETSI ITS-G5 in Europe, reserved 10 MHz wide channels in the 5.9 GHz spectrum band. Despite the exclusive use of these frequencies for vehicular communication purposes, there are still cross channel interference problems that have been widely reported in the literature. In order to mitigate these issues, this paper presents the design of a two-stage FIR low-pass filter, targeting the integration with a digital baseband receiver chain of a custom vehicular communications platform. The filter was tested, evaluated and optimized, with the simulation results proving the effectiveness of the proposed method and the low delay introduced in the overall operation of the receiver chain.     

20单元双压电片变形镜对Zernike像差空间拟合能力的实验研究

利用20单元双压电片变形镜和13×13阵列哈特曼波前传感器所构成的闭环自适应光学系统,实验测试了双压电片变形镜对3～20项静态Zernike像差的空间校正能力,并将实验结果与仿真计算结果进行了对比.最后分析了哈特曼传感器与双压电片变形镜之间的对准误差对实验结果的影响.研究表明,除了少数几项外,双压电片变形镜对3～20项Zernike像差的拟合误差都小于0.5,各项Zernike仿真和实验结果之差平均小于0.1.计算表明,与严格对准的理想情况相比,双压电片变形镜对3～20项Zernike像差中大多数项的拟合误差都随着失配程度的增加而增大,对准精度对于高阶像差拟合效果的影响尤其严重.     

基于堤防工程技术的油墩港航道两侧护岸结构型式设计方案研究

文章从堤防工程设计角度出发, 兼顾河道的航道要求, 对油墩港航道两侧护岸结构进行稳定及结构计算, 提出了安全且经济可行的设计方案。     

Graph coloring based channel assignment framework for rural wireless mesh networks

IEEE 802.11 based wireless mesh networks with directional antennas are expected to be a new promising technology and an economic approach for providing wireless broadband services in rural areas. In this paper, we discuss interference models and address how they can affect the design of channel assignment in rural mesh networks. We present a new channel assignment framework based on graph coloring for rural wireless mesh networks. The goal of the framework is to allow synchronously transmitting or receiving data from multiple neighbor links at the same time, and continuously doing full-duplex data transfer on every link, creating an efficient rural mesh network without interference. Channel assignment is shown to be NP-hard. We frame this channel allocation problem in terms of Adjacent Vertex Distinguishing Edge Coloring （AVDEC）. Detailed assignment results on grid topology are presented and discussed. Furthermore, we design an algorithm. Finally, we evaluate the perform- ance of the proposed algorithm through extensive simulations and show the algorithm is effective to the regular grid topologies, and the number of colors used by the algorithm is upper bounded by A ~ 1. Hence the algorithm guarantees that the number of channels available in standards such as IEEE 802.11a is sufficient to have a valid AVDEC for many grid topologies. We also evaluate the proposed algorithm for arbitrary graphs. The algorithm provides a lower upper bound on the minimum number of channels to the AVDEC index channel assignment problem.