Multi-scale mapping algorithm for INI cancellation and a novel mixed-numerologies OFDM transceiver

OFDM with mixed-numerologies enhances the system flexibility effectively to meet the demands of diversified application scenarios. However, the coexistence of waveforms with different numerologies leads to serious inter-numerology interference (INI), and the corresponding relationship between the number of guard subcarriers and the power of INI needs to be considered for scheduling subcarriers. In this paper, we propose a multi-scale mapping (MSM) and INI cancellation (MSM-INIC) algorithm as well as the corresponding de-MSM algorithm for mixed-numerologies OFDM system. Based on the proposed algorithms, we provide a novel transceiver in the scenario of multi-path fading channel, in which subcarrier scheduling does not need to consider whether the guard band is allocated. In the proposed transmitter, an additional MSM-INIC module is employed to pre-compensate signal distortion for downlink, and in the receiver, a de-MSM module is applied to de-map the received signals for recovering the original numerologies. Furthermore, we reveal the inherent property of the mapped signals, and propose a low computational complexity de-MSM algorithm accordingly. Simulation results verify the superiority of the proposed transceiver in BER performance as well as spectrum efficiency even without any guard band.     

Characterization of dark noise in CdZnTe spectrometers

Systematic measurements of dark noise spectra of CdZnTe x- and γ-ray spectrometers, correlated with the dc I-V characteristics and detector technology, are reported. The dark noise of two innovative CdZnTe spectrometer configurations are studied: metal-semiconductor-metal (MSM) resistive detectors with three terminals as well as heterostructure PIN detectors with thermally evaporated n⁺ CdS and p⁺ ZnTe contacts, which are fabricated on high pressure Bridgman CdZnTe (Zn=10%) crystals. The two innovative CdZnTe spectrometer configurations presented here exhibit very low dark (leakage) current. By reducing the dc value of the dark (leakage) current below 1 nA, shot noise becomes the dominant noise mechanism and the contribution of 1/f noise becomes negligible. The use of non-injecting contacts (evaporated gold) for the MSM detectors and the operation of the PIN detector in the reverse bias mode prevent generation-recombination noise which becomes dominant with injecting contacts (for example MSM detectors with evaporated indium and titanium contacts) or when operating the PIN detector in the forward bias mode. Surface leakage is reduced by applying surface passivation but is eliminated only by using the three terminal MSM configuration which exhibits simple shot noise instead of the suppressed shot noise observed in the two terminal MSM spectrometers. The noise measurements are useful for optimizing detector technology.     

Atomistic evaluation of the stress concentration factor of graphene sheets having circular holes

Stress concentration factor concept has been developed for single-layered graphene sheets (SLGSs) with circular holes through an atomistic point of view by the application of molecular structural mechanics (MSM) approach. In this approach the response of SLGSs against unidirectional tensile loading is matched to the response of a frame-like macro structure containing beam elements by making an equivalence between strain energies of beam elements in MSM and potential energies of chemical bonds of SLGSs. Both chirality and size effects are considered and the atomistic evaluation of stress concentration factor is performed for different sizes of circular holes. Also, molecular dynamics simulations are implemented to verify the existence and location of the predicted stress concentration. The results reveal that size effects and the diameters of circular holes have a significant influence on the stress concentration factor of SLGSs and armchair SLGSs show a larger value of stress concentration than zigzag ones.     

Hybrid Integration of 1 × 12 Metal-Semiconductor-Metal Photodetector and Polyimide Waveguide Array

We report here a demonstration of hybrid integration of a 1 × 12 metal-semiconductor-metal (MSM) photodetector array and polyimide channel waveguides via 45° total-internal-reflection (TIR) micro-couplers. The two-layer polyimide waveguide array was constructed using Ultradel 9120D for the core and Ultradel 9020 for the lower cladding layer. The coupling loss and propagation loss of the waveguide are 0.2dB and 0.21 dB/cm, respectively. The cross talk of the adjacent channels is -32 dB. The MSM photodetector array was fabricated on a semi-insulated GaAs wafer. The photodetectors are integrated to operate in the conventional vertical illumination mode. We measured the external quantum-efficiency and 3 dB bandwidth of the integrated MSM photodetectors at 0.4 A/W and 2.648 GHz, respectively. The aggregate 3 dB bandwidth of the 12-channel integrated system is 32 GHz.     

Structural and dc conduction studies on PbTe thin films

Lead Telluride (PbTe) films of different thickness were prepared onto precleaned glass substrates under the pressure of 2?×?10^?5 Torr by thermal evaporation. X-ray diffraction technique, scanning electron microscopy, and current–voltage characteristics were used to characterize the films. The structural analysis of the films was carried using X-ray diffractometer. The surface morphology was analyzed by using scanning electron microscope. The dc electrical conduction mechanism in vacuum-evaporated Al/PbTe/Al thin film sandwich system in the thickness range 500–5,000 Å at different temperature (303–483 K) was found to be a modified Poole–Frenkel type. The results of variation of activation energy with applied voltage and thickness are discussed.     

金属-半导体-金属光电探测器的瞬态特性分析

给出了金属—半导体—金属光电探测器(MSM—PD)高频特性的等效电路模型，在此模型基础上编写模拟分析程序，分析了探测器相关器件参数对器件截止频率的影响，为探测器与前置放大器的优化匹配提供了理论依据。     

多载波调制在通信系统的应用

首先简单解释多载波调制MCM/多路副载波调制MSM的由来和在高速率通信系统的可能利用。其后着重 地提出多路副载波调制适合于光无线通信的应用。最后说明大气光通信对多路副载波调制的影响。     

Al0.3Ga0.7N MSM紫外探测器研究

用MOCVD生长的未掺杂的n-Al0.3Ga0.7N制备了MSM结构紫外探测器.器件在5.3 V偏压时暗电流为1 nA,在315nm波长处有陡峭的截止边,在1 V偏压下305 nm峰值波长处探测器的电流响应率为0.023 A/W,要进一步提高器件的响应率,方法之一是优化器件的结构参数,尽量减小叉指电极的宽度.为了检验Au/n-Al0.3Ga0.7N肖特基接触特性,电击穿MSM右边结,由正向I-V特性曲线计算出理想因子n～1.05,零偏势垒高度φB0～1.16eV,表明形成的Au/n-Al0.3Ga0.7N肖特基结较为理想.     

GaN-based MSM photovoltaic ultraviolet detector structure modeling and its simulation

Based on the principles of metal-semiconductor-metal Schottky barrier photodetectors(MSM-PD), using the carrier rate equations,the circuit simulation model of a GaN-based MSM photovoltaic ultraviolet detector is constructed through an appropriately equivalent process.By using the Pspice analytical function of Cadence soft on the model,the relationship between the photocurrent and the terminal voltage under different UV light powers is analyzed.The result shows that under the given UV power,the photocurrent increases and tends to become saturated gradually as the terminal voltage of the device increases,and that under different UV powers,the photocurrent increases with increasing incident power.Then the analysis of the relationship between the photocurrent and the terminal voltage under the different ratios of interdigital electrode space and width is carried out when the UV power is given.The results show that when the ratio of interdigital electrode space and width(L/W) equals 1,the photocurrent tends to be at a maximum.     

异质结光电探测器的性能研究

光电探测器用于将光纤传输的光信号转变为电信号,是半导体光电子学的重要器件。本文主要介绍几种异质结光电探测器的器件结构和工作原理,旨在探讨异质结光电探测器的研究现状和发展趋势。