Ag(Nb0.8Ta0.2)O3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF2 addition on the structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics was investigated. The add...Ag(Nb0.8Ta0.2)O3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF2 addition on the structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics was investigated. The addition of CaF2 led the ceramics to a larger grain size and distortion of lattice. With the addition of 4.5 wt.% CaF2, the permittivity of the ceramics increased from 442 to 1028, the dielectric loss decreased sharply from 6.12 × 10^-3 to 8.6 × 10^-4, and the temperature coefficient of capacitance decreased from 1834 ppm/℃ to -50 ppm/℃ (at 1 MHz). These results indicated that the high permittivity was related with a large grain size, a low grain boundary density, and the weak Ta-O or Nb-O bond strength caused by the addition of CaF2.展开更多
We investigate a peculiar phenomenon by processing ZnO nanobelts with an atomic force microscope (AFM). In the contact mode of AFM, peculiar bending occurs in meso-scale when the nanobelt is applied with force in la...We investigate a peculiar phenomenon by processing ZnO nanobelts with an atomic force microscope (AFM). In the contact mode of AFM, peculiar bending occurs in meso-scale when the nanobelt is applied with force in lateral direction. We study the mechanical properties of ZnO nanobelts under the influence of small size effect, with finite element analysis and mathematical analysis by means of Matlab. Based on this abnormal effect, a novel measuring method is proposed, which allows the surface morphology and surface properties to be characterized at the same time.展开更多
Random access is the necessary process to establish the wireless link between the user equipment (UE) and network. The performance of the random access directly affects the performance of the network. In this work, ...Random access is the necessary process to establish the wireless link between the user equipment (UE) and network. The performance of the random access directly affects the performance of the network. In this work, we propose a method on the basis of the existing alternatives. In this method, we estimate the system load in advance to adjust the number of terminals. An access threshold is set to control the number of terminals which want to access the base station at an acceptable level. At the same time, we havean improvement on the existing power climbing strategy. We suppose that the power ramping is not always necessary for the re-access. And the selection ofpower ramping steps is studied in this paper. Simulations based on MATLAB are employed to evaluate the effectiveness of the proposed solution and to make comparisons with existing alternatives.展开更多
In this paper, the current known attack methods against WAI and the improvements of WAI called WAI' were analyzed. Through analyzing the unicast key agreement protocol in the WAI' by CPN model, the vulnerabili...In this paper, the current known attack methods against WAI and the improvements of WAI called WAI' were analyzed. Through analyzing the unicast key agreement protocol in the WAI' by CPN model, the vulnerabilities of WAI' were found out. The improvement of WAI' was made and a new protocol called WAI'-E was proposed. The WAI'-E was combined with the key exchange mechanism of Diffie-Hellman based on elliptic curve cryptography. Moreover, by using CK mode, it is the fact that WAI'-E was SK-secure with PFS and was provided with independent security of certificate authentication was proved.展开更多
The technique of surface acoustic waves (SAWs) is a very promising method for determining film properties such as Young's modulus, density and film thickness nondestructively and accurately. The dispersion property...The technique of surface acoustic waves (SAWs) is a very promising method for determining film properties such as Young's modulus, density and film thickness nondestructively and accurately. The dispersion property of SAWs is also affected largely from the adhesion property of films, which is revealed by the bonding spring assumption described. This SAW method could offer a quantitative evaluation of the film adhesion from the curvature of SAW dispersion lines affected by the normal and shear spring constants. The method is applied to numerically characterize the adhesion property of the typical ultra-large-scale integrated circuit interconnect layered structure of a thin Cu film deposited on the Si substrate as well as a SiO2 thin film on a Sisubstrate.展开更多
An innovative method of cooperative frequency domain differential modulation and demodulation is presented.This method applies the prior knowledge of channel propagation to selecting the variable differential length a...An innovative method of cooperative frequency domain differential modulation and demodulation is presented.This method applies the prior knowledge of channel propagation to selecting the variable differential length and carrying out frequency domain modulation.This strategy optimizes the design of system parameters to effectively improve the anti-interference ability of the differential system in time-varied multipath channel circumstance without making the execution more complicating.The simulations and comparisons demonstrate the proposed method is effective,and the results show that it is especially suitable for the fading channel with strong propagation and fast time-variation.展开更多
To achieve an optimal trade-off between video quality and energy efficiency in the uplink streaming of multi-user Scalable Video Coding (SVC) videos in relay-based Orthogonal Frequency Division Multiple Access (OFDMA)...To achieve an optimal trade-off between video quality and energy efficiency in the uplink streaming of multi-user Scalable Video Coding (SVC) videos in relay-based Orthogonal Frequency Division Multiple Access (OFDMA) cellular networks, a cross-layer design framework that jointly selects the Transmission Policy (TP) for SVC video frames, assigns OFDMA subcarriers, and allocates power for each subcarrier is proposed. We apply the dual decomposition method to the problem, and obtain a TP selection subproblem for each SVC video adaptation and a resource allocation subproblem of Joint Subcarrier, Relay and Power Allocation (JSRPA). A second level of dual decomposition is used to divide the JSRPA problem into independent subcarrier subproblems. The proposed Crosslayer Trade-off Optimization (CTO) algorithm is sub-distributed with significantly low complexity. A performance evaluation with typical SVC video traces demonstrates that the proposed algorithm is able to converge and efficiently achieve the optimal trade-off between the video quality and energy consumption at the MSs for uplink SVC streaming.展开更多
The surface acoustic wave (SAW) technique is a precise and nondestructive method to detect the mechanical charac- teristics of the thin low dielectric constant (low-k) film by matching the theoretical dispersion c...The surface acoustic wave (SAW) technique is a precise and nondestructive method to detect the mechanical charac- teristics of the thin low dielectric constant (low-k) film by matching the theoretical dispersion curve with the experimental dispersion curve. In this paper, the influence of sample roughness on the precision of SAW mechanical detection is inves- tigated in detail. Random roughness values at the surface of low-k film and at the interface between this low-k film and the substrate are obtained by the Monte Carlo method. The dispersive characteristic of SAW on the layered structure with rough surface and rough interface is modeled by numerical simulation of finite element method. The Young's moduli of the Black DiamondTM samples with different roughness values are determined by SAWs in the experiment. The results show that the influence of sample roughness is very small when the root-mean-square (RMS) of roughness is smaller than 50 nm and correlation length is smaller than 20 μm. This study indicates that the SAW technique is reliable and precise in the nondestructive mechanical detection for low-k films.展开更多
The dielectric properties of (AgxNa1-x)(NbyTa1-y)O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer (AgxNa1-x)(NbyTa1-y)O3 ceramic prepared by l...The dielectric properties of (AgxNa1-x)(NbyTa1-y)O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer (AgxNa1-x)(NbyTa1-y)O3 ceramic prepared by liquid method were better than that by conventional solid method. The average grain size of the nanometer powder(34 nm) obtained by citrate-gel method was small near 500 nm and homogeneous and the microstructure was dense and uniform. In addition, the sintering temperature had a great effect on properties. The dielectric properties of resultant samples were as follows: ε〉500, tgδ〈6 10^-4, αc〈 10 ppm/℃, ρv〉1 012Ω·cm.展开更多
A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary (GB...A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary (GB) and the average tensile stress within A1203 grains caused by SiC nanoparticles. The normal compressive stress strengthens the GB, and the average tensile stress weakens the grains. The model gives a reasonable interpretation of the strength changes of A1203-SiC nanocomposites with the number of SiC particles.展开更多
A wedge shape Si LED is designed and fabricated with 0.35 μm double-grating standard CMOS technology. The device structure is based on the N-well-P+ junction. The P+ has a wedge shape and is surrounded by the N-well....A wedge shape Si LED is designed and fabricated with 0.35 μm double-grating standard CMOS technology. The device structure is based on the N-well-P+ junction. The P+ has a wedge shape and is surrounded by the N-well. The micrographs of Si LEDs' emitting and layout are captured. The I-V characteristic and spectra of the Si LED are tested. Under room temperature and backward bias, its radiant luminosity is 12 nW at 100 mA, and the wavelength of the emitting peak is located at 764 nm.展开更多
In this paper, an improved k-means based clustering method (IKCM) is proposed. By refining the initial cluster centers and adjusting the number of clusters by splitting and merging procedures, it can avoid the algor...In this paper, an improved k-means based clustering method (IKCM) is proposed. By refining the initial cluster centers and adjusting the number of clusters by splitting and merging procedures, it can avoid the algorithm resulting in the situation of locally optimal solution and reduce the number of clusters dependency. The IKCM has been implemented and tested. We perform experiments on KDD-99 data set. The comparison experiments with H-means+also have been conducted. The results obtained in this study are very encouraging.展开更多
In this paper the photocurrent response of InP-based unitraveling-carrier photodetectors(UTC-PDs) is analyzed using the drift-diffusion approach.Based on the theoretical analysis,an InP/InGaAs UTC-PD is modeled utiliz...In this paper the photocurrent response of InP-based unitraveling-carrier photodetectors(UTC-PDs) is analyzed using the drift-diffusion approach.Based on the theoretical analysis,an InP/InGaAs UTC-PD is modeled utilizing a numerical device simulator(ATLAS),and the physics of the device's operation and its performance as a function of biasing and power level are simulated.The simulation results indicate that the linear dynamic range is up to 60 mW,the f-3 dB is about 40 GHz and the full-width at half-maximum(FWHM) of the current pulse is 28 ps with 10 mW optical power injection for an optimized structure UTC-PD.展开更多
The transient photoresponse of a backside-illuminated InP/InGaAs uni-traveling carrier photodetector(UTC-PD) is simulated by a 2D drift-diffusion approach utilizing a commercial numerical device simulator(ATLAS).The e...The transient photoresponse of a backside-illuminated InP/InGaAs uni-traveling carrier photodetector(UTC-PD) is simulated by a 2D drift-diffusion approach utilizing a commercial numerical device simulator(ATLAS).The effects of the epitaxial layer structure and device biasing are taken into account.The simulation results indicate that the absorption region has a critical effect on the photoresponse pulse,and an optimized epitaxial layer structure is given to achieve a fast response while maintaining a reasonable response.Here,the optimized material parameters of the absorption region are 180 nm and 5 × 1016 cm-3,respectively.展开更多
A large amount of one-dimensional ZnO nanorods with diameters in 15―50 nm aligned in radial cluster were successfully synthesized by polar polymer polyvinyl alcohol (PVA) as soft-template. The growth of ZnO nanorods ...A large amount of one-dimensional ZnO nanorods with diameters in 15―50 nm aligned in radial cluster were successfully synthesized by polar polymer polyvinyl alcohol (PVA) as soft-template. The growth of ZnO nanorods was controlled by changing annealing temperature. The evolution of the morphology and microstructure was investigated by scanning electron microscope, transmission electron micro- scope and X-ray diffraction. It is shown that ZnO nanorods tend to be uniform and the crystallization is gradually improved with the temperature increasing from 400℃ to 700℃. The photoluminescence spectra of products show a strong ultra violet emission and relatively weak defect emissions. The sharp strong emission peak at 354 nm owing to the inter-band transition indicates the extraordinary photoluminescence property of ZnO nanorods.展开更多
Spatial Modulation(SM) is a newlyintroduced wireless transmission scheme,andSpace Shift Keying(SSK) is its simplifiedversion.Their capacity performance has notbeen well examined to date.Starting frombasic definitions ...Spatial Modulation(SM) is a newlyintroduced wireless transmission scheme,andSpace Shift Keying(SSK) is its simplifiedversion.Their capacity performance has notbeen well examined to date.Starting frombasic definitions of information theory,through theoretical analyses and numericalcalculations,this paper evaluates the capacityof SM systems in various channels.Our conclusion is that under Rayleigh fading channels,the capacity of the SSK system is limited bythe Signal-to-Noise Ratio(SNR) or the number of transmit antennas,whichever one issmaller.From the capacity point of view,theSM system is better than the Single-Input andSingle-Output(SISO) system,but worse thanthe Multiple-Input and Single-Output(MISO)system.The correlation between transmit antennas will degrade the performance of theSSK system.Line-of-Sight(LOS) may causeperformance degradation for SSK,but capacity increases for SM.展开更多
In this paper,a portable 2.42 GHz transmitter for wireless communication systems,with 8dBm output power and small size is proposed.Several novel features exist in this transmitter.First,power consumption and output ar...In this paper,a portable 2.42 GHz transmitter for wireless communication systems,with 8dBm output power and small size is proposed.Several novel features exist in this transmitter.First,power consumption and output are balanced by introducing a differential oscillator with input signal controlled biasing,which acts as both a carrier generator and an OOK modulator.Then,power consumption of the transmitter is reduced by the OOK modulated signal via switching the oscillator and the power amplifier at the same time.Furthermore,the area size is also reduced by a class-AB power amplifier,which uses the PCB antenna as the resonance inductance.With these features,the total chip area is reduced to 670μm×740μm(In a 0.18μm CMOS process).展开更多
After analyzing the merits and shortcomings of Fixed-Alternated Routing algorithm (FAR) and Least Loaded Routing algorithm (LLR),we propose one novel dynamic optical routing algorithm. Having considered the influences...After analyzing the merits and shortcomings of Fixed-Alternated Routing algorithm (FAR) and Least Loaded Routing algorithm (LLR),we propose one novel dynamic optical routing algorithm. Having considered the influences of path’s length and path’s congestion just like in FAR and LLR,we take into account the network resource status-amount of free wavelengths in the network. Proposed algorithm sets up connections on three possible paths according to amount of available free wave-lengths in the network,which effectively decreases the blocking probability. The National Science Foundation (NSF) network and mesh-torus network simulation results show that the performance of this algorithm is better than that of FAR and LLR.展开更多
L-band digital aeronautical communication system 1(L-DACS1) is a promising candidate data-link for future air-ground communication, but it is severely interfered by the pulse pairs(PPs) generated by distance measure e...L-band digital aeronautical communication system 1(L-DACS1) is a promising candidate data-link for future air-ground communication, but it is severely interfered by the pulse pairs(PPs) generated by distance measure equipment. A novel PP mitigation approach is proposed in this paper. Firstly, a deformed PP detection(DPPD) method that combines a filter bank, correlation detection, and rescanning is proposed to detect the deformed PPs(DPPs) which are caused by multiple filters in the receiver. Secondly, a finite impulse response(FIR) model is used to approximate the overall characteristic of filters, and then the waveform of DPP can be acquired by the original waveform of PP and the FIR model. Finally, sparse representation is used to estimate the position and amplitude of each DPP, and then reconstruct each DPP. The reconstructed DPPs will be subtracted from the contaminated signal to mitigate interference. Numerical experiments show that the bit error rate performance of our approach is about 5 dB better than that of recent works and is closer to interference-free environment.展开更多
基金supported by the Program for New Century Excellent Talents in Universities (NCET)the National High-Tech Research and Development Program of China (No. 2007AA03Z423)China Postdoctoral Science Foundation
文摘Ag(Nb0.8Ta0.2)O3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF2 addition on the structure and dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics was investigated. The addition of CaF2 led the ceramics to a larger grain size and distortion of lattice. With the addition of 4.5 wt.% CaF2, the permittivity of the ceramics increased from 442 to 1028, the dielectric loss decreased sharply from 6.12 × 10^-3 to 8.6 × 10^-4, and the temperature coefficient of capacitance decreased from 1834 ppm/℃ to -50 ppm/℃ (at 1 MHz). These results indicated that the high permittivity was related with a large grain size, a low grain boundary density, and the weak Ta-O or Nb-O bond strength caused by the addition of CaF2.
文摘We investigate a peculiar phenomenon by processing ZnO nanobelts with an atomic force microscope (AFM). In the contact mode of AFM, peculiar bending occurs in meso-scale when the nanobelt is applied with force in lateral direction. We study the mechanical properties of ZnO nanobelts under the influence of small size effect, with finite element analysis and mathematical analysis by means of Matlab. Based on this abnormal effect, a novel measuring method is proposed, which allows the surface morphology and surface properties to be characterized at the same time.
基金partly supported by the Research of LTE Layer 2 and Smallcell Technology Tracking under Grant No.2013GFW-0005
文摘Random access is the necessary process to establish the wireless link between the user equipment (UE) and network. The performance of the random access directly affects the performance of the network. In this work, we propose a method on the basis of the existing alternatives. In this method, we estimate the system load in advance to adjust the number of terminals. An access threshold is set to control the number of terminals which want to access the base station at an acceptable level. At the same time, we havean improvement on the existing power climbing strategy. We suppose that the power ramping is not always necessary for the re-access. And the selection ofpower ramping steps is studied in this paper. Simulations based on MATLAB are employed to evaluate the effectiveness of the proposed solution and to make comparisons with existing alternatives.
文摘In this paper, the current known attack methods against WAI and the improvements of WAI called WAI' were analyzed. Through analyzing the unicast key agreement protocol in the WAI' by CPN model, the vulnerabilities of WAI' were found out. The improvement of WAI' was made and a new protocol called WAI'-E was proposed. The WAI'-E was combined with the key exchange mechanism of Diffie-Hellman based on elliptic curve cryptography. Moreover, by using CK mode, it is the fact that WAI'-E was SK-secure with PFS and was provided with independent security of certificate authentication was proved.
基金Supported by the National Natural Science Foundation of China under Grant No 60876072, and the New Century Excellent Talents in University under Grant No NCET-08-0389.
文摘The technique of surface acoustic waves (SAWs) is a very promising method for determining film properties such as Young's modulus, density and film thickness nondestructively and accurately. The dispersion property of SAWs is also affected largely from the adhesion property of films, which is revealed by the bonding spring assumption described. This SAW method could offer a quantitative evaluation of the film adhesion from the curvature of SAW dispersion lines affected by the normal and shear spring constants. The method is applied to numerically characterize the adhesion property of the typical ultra-large-scale integrated circuit interconnect layered structure of a thin Cu film deposited on the Si substrate as well as a SiO2 thin film on a Sisubstrate.
基金supported by the National Basic Research Program of China (973 Program) (2007CB310605)
文摘An innovative method of cooperative frequency domain differential modulation and demodulation is presented.This method applies the prior knowledge of channel propagation to selecting the variable differential length and carrying out frequency domain modulation.This strategy optimizes the design of system parameters to effectively improve the anti-interference ability of the differential system in time-varied multipath channel circumstance without making the execution more complicating.The simulations and comparisons demonstrate the proposed method is effective,and the results show that it is especially suitable for the fading channel with strong propagation and fast time-variation.
基金partially supported by the National Natural Science Foundation of China under Grants No. 610202380, No. 60932007Major Program of National Natural Science Foundation of China under Grant No. 60932007+2 种基金Tianjin Research Program of Application Foundation and Advanced Technology under Grant No. 12JCQNJC00300Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20110032120029the Innovation Foundation of Tianjin University
文摘To achieve an optimal trade-off between video quality and energy efficiency in the uplink streaming of multi-user Scalable Video Coding (SVC) videos in relay-based Orthogonal Frequency Division Multiple Access (OFDMA) cellular networks, a cross-layer design framework that jointly selects the Transmission Policy (TP) for SVC video frames, assigns OFDMA subcarriers, and allocates power for each subcarrier is proposed. We apply the dual decomposition method to the problem, and obtain a TP selection subproblem for each SVC video adaptation and a resource allocation subproblem of Joint Subcarrier, Relay and Power Allocation (JSRPA). A second level of dual decomposition is used to divide the JSRPA problem into independent subcarrier subproblems. The proposed Crosslayer Trade-off Optimization (CTO) algorithm is sub-distributed with significantly low complexity. A performance evaluation with typical SVC video traces demonstrates that the proposed algorithm is able to converge and efficiently achieve the optimal trade-off between the video quality and energy consumption at the MSs for uplink SVC streaming.
基金Project supported by the National Natural Science Foundation of China(Grant No.60876072)the Tianjin Research Program of Application Foundation and Advanced Technology,China(Grant No.10JCZDJC15500)
文摘The surface acoustic wave (SAW) technique is a precise and nondestructive method to detect the mechanical charac- teristics of the thin low dielectric constant (low-k) film by matching the theoretical dispersion curve with the experimental dispersion curve. In this paper, the influence of sample roughness on the precision of SAW mechanical detection is inves- tigated in detail. Random roughness values at the surface of low-k film and at the interface between this low-k film and the substrate are obtained by the Monte Carlo method. The dispersive characteristic of SAW on the layered structure with rough surface and rough interface is modeled by numerical simulation of finite element method. The Young's moduli of the Black DiamondTM samples with different roughness values are determined by SAWs in the experiment. The results show that the influence of sample roughness is very small when the root-mean-square (RMS) of roughness is smaller than 50 nm and correlation length is smaller than 20 μm. This study indicates that the SAW technique is reliable and precise in the nondestructive mechanical detection for low-k films.
基金863 Project(No.2007AA03z423)NCET and China Postdoctoral Science Foundation
文摘The dielectric properties of (AgxNa1-x)(NbyTa1-y)O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer (AgxNa1-x)(NbyTa1-y)O3 ceramic prepared by liquid method were better than that by conventional solid method. The average grain size of the nanometer powder(34 nm) obtained by citrate-gel method was small near 500 nm and homogeneous and the microstructure was dense and uniform. In addition, the sintering temperature had a great effect on properties. The dielectric properties of resultant samples were as follows: ε〉500, tgδ〈6 10^-4, αc〈 10 ppm/℃, ρv〉1 012Ω·cm.
基金Project supported by the Tianjin Natural Science Foundation, China (Grant No. 09JCZDJC22500).
文摘A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary (GB) and the average tensile stress within A1203 grains caused by SiC nanoparticles. The normal compressive stress strengthens the GB, and the average tensile stress weakens the grains. The model gives a reasonable interpretation of the strength changes of A1203-SiC nanocomposites with the number of SiC particles.
基金supported by the National Natural Science Foundation of China (Nos.60536030,60676038)the Key Project of Tianjin (No.06YFJZJC00200)
文摘A wedge shape Si LED is designed and fabricated with 0.35 μm double-grating standard CMOS technology. The device structure is based on the N-well-P+ junction. The P+ has a wedge shape and is surrounded by the N-well. The micrographs of Si LEDs' emitting and layout are captured. The I-V characteristic and spectra of the Si LED are tested. Under room temperature and backward bias, its radiant luminosity is 12 nW at 100 mA, and the wavelength of the emitting peak is located at 764 nm.
基金Supported by the Beijing Municipal Commission ofEducation Science and Technology Project (KM200511232004)
文摘In this paper, an improved k-means based clustering method (IKCM) is proposed. By refining the initial cluster centers and adjusting the number of clusters by splitting and merging procedures, it can avoid the algorithm resulting in the situation of locally optimal solution and reduce the number of clusters dependency. The IKCM has been implemented and tested. We perform experiments on KDD-99 data set. The comparison experiments with H-means+also have been conducted. The results obtained in this study are very encouraging.
基金Supported by the National Natural Science Foundation of China (Grant No.60736035)Youth Foundation of Tianjin University (Grant No.TJU-YFF-08B64)
文摘In this paper the photocurrent response of InP-based unitraveling-carrier photodetectors(UTC-PDs) is analyzed using the drift-diffusion approach.Based on the theoretical analysis,an InP/InGaAs UTC-PD is modeled utilizing a numerical device simulator(ATLAS),and the physics of the device's operation and its performance as a function of biasing and power level are simulated.The simulation results indicate that the linear dynamic range is up to 60 mW,the f-3 dB is about 40 GHz and the full-width at half-maximum(FWHM) of the current pulse is 28 ps with 10 mW optical power injection for an optimized structure UTC-PD.
基金supported by the National Natural Science Foundation of China (No.60736035)the Youth Foundation of Tianjin University(No.TJU-YFF-08B64)
文摘The transient photoresponse of a backside-illuminated InP/InGaAs uni-traveling carrier photodetector(UTC-PD) is simulated by a 2D drift-diffusion approach utilizing a commercial numerical device simulator(ATLAS).The effects of the epitaxial layer structure and device biasing are taken into account.The simulation results indicate that the absorption region has a critical effect on the photoresponse pulse,and an optimized epitaxial layer structure is given to achieve a fast response while maintaining a reasonable response.Here,the optimized material parameters of the absorption region are 180 nm and 5 × 1016 cm-3,respectively.
基金Supported by Tianjin Natural Science Foundation (Grant Nos. 06TXTJJC14600 and 07JCYBJC06400)Tianjin Education Committee Science and Technology De-velopment Foundation
文摘A large amount of one-dimensional ZnO nanorods with diameters in 15―50 nm aligned in radial cluster were successfully synthesized by polar polymer polyvinyl alcohol (PVA) as soft-template. The growth of ZnO nanorods was controlled by changing annealing temperature. The evolution of the morphology and microstructure was investigated by scanning electron microscope, transmission electron micro- scope and X-ray diffraction. It is shown that ZnO nanorods tend to be uniform and the crystallization is gradually improved with the temperature increasing from 400℃ to 700℃. The photoluminescence spectra of products show a strong ultra violet emission and relatively weak defect emissions. The sharp strong emission peak at 354 nm owing to the inter-band transition indicates the extraordinary photoluminescence property of ZnO nanorods.
基金supported by the National High Technical Research and Development Program of China(863Program)under Grant No.2011-AA010201the National Natural Science Foundation of China under Grant No.60972054
文摘Spatial Modulation(SM) is a newlyintroduced wireless transmission scheme,andSpace Shift Keying(SSK) is its simplifiedversion.Their capacity performance has notbeen well examined to date.Starting frombasic definitions of information theory,through theoretical analyses and numericalcalculations,this paper evaluates the capacityof SM systems in various channels.Our conclusion is that under Rayleigh fading channels,the capacity of the SSK system is limited bythe Signal-to-Noise Ratio(SNR) or the number of transmit antennas,whichever one issmaller.From the capacity point of view,theSM system is better than the Single-Input andSingle-Output(SISO) system,but worse thanthe Multiple-Input and Single-Output(MISO)system.The correlation between transmit antennas will degrade the performance of theSSK system.Line-of-Sight(LOS) may causeperformance degradation for SSK,but capacity increases for SM.
基金Supported by the National Natural Science Foundation of China(No.61072010)
文摘In this paper,a portable 2.42 GHz transmitter for wireless communication systems,with 8dBm output power and small size is proposed.Several novel features exist in this transmitter.First,power consumption and output are balanced by introducing a differential oscillator with input signal controlled biasing,which acts as both a carrier generator and an OOK modulator.Then,power consumption of the transmitter is reduced by the OOK modulated signal via switching the oscillator and the power amplifier at the same time.Furthermore,the area size is also reduced by a class-AB power amplifier,which uses the PCB antenna as the resonance inductance.With these features,the total chip area is reduced to 670μm×740μm(In a 0.18μm CMOS process).
文摘After analyzing the merits and shortcomings of Fixed-Alternated Routing algorithm (FAR) and Least Loaded Routing algorithm (LLR),we propose one novel dynamic optical routing algorithm. Having considered the influences of path’s length and path’s congestion just like in FAR and LLR,we take into account the network resource status-amount of free wavelengths in the network. Proposed algorithm sets up connections on three possible paths according to amount of available free wave-lengths in the network,which effectively decreases the blocking probability. The National Science Foundation (NSF) network and mesh-torus network simulation results show that the performance of this algorithm is better than that of FAR and LLR.
基金supported in part by the National Natural Science Foundation (Nos. U1533107 and U1433105)the Civil Aviation Science and Technology Innovation Foundation (No. MHRD20130217)the Fundamental Research Funds for the Central Universities of CAUC (No. 3122016D003)
文摘L-band digital aeronautical communication system 1(L-DACS1) is a promising candidate data-link for future air-ground communication, but it is severely interfered by the pulse pairs(PPs) generated by distance measure equipment. A novel PP mitigation approach is proposed in this paper. Firstly, a deformed PP detection(DPPD) method that combines a filter bank, correlation detection, and rescanning is proposed to detect the deformed PPs(DPPs) which are caused by multiple filters in the receiver. Secondly, a finite impulse response(FIR) model is used to approximate the overall characteristic of filters, and then the waveform of DPP can be acquired by the original waveform of PP and the FIR model. Finally, sparse representation is used to estimate the position and amplitude of each DPP, and then reconstruct each DPP. The reconstructed DPPs will be subtracted from the contaminated signal to mitigate interference. Numerical experiments show that the bit error rate performance of our approach is about 5 dB better than that of recent works and is closer to interference-free environment.