It is a challenging problem to design a high performance modulation for mobile satellite communications due to the limited power and bandwidth resource.The paper improves Feher patented Quadrature Phase Shift Keying(F...It is a challenging problem to design a high performance modulation for mobile satellite communications due to the limited power and bandwidth resource.The paper improves Feher patented Quadrature Phase Shift Keying(FQPSK) by redefining the waveform.The novel FQPSK,with con-stant envelope,can be used to improve the power efficiency and frequency efficiency of mobile satellite communication.The study shows that the improved FQPSK outperforms conventional FQPSK over AWGN and is immune to the non-linearity of high power amplifier.At last,the impact of flat fading and multi-path fading of channel on the BER performance of improved modulation is analyzed.展开更多
Given that satellite mobile channel is a time-varying channel,Adaptive Modulation and Coding(AMC) was proposed to provide robust and spectrally efficient transmission over satellite mobile channel.Three different kind...Given that satellite mobile channel is a time-varying channel,Adaptive Modulation and Coding(AMC) was proposed to provide robust and spectrally efficient transmission over satellite mobile channel.Three different kinds of channel environment were considered in this paper:the urban area,the rural area,and the open space.Four combinations of modulation and coding were designed to meet reliable communication on time-varying channel,and spectral efficiency and system throughput of these three kinds of channel environment were simulated.Based on the simulation results,this paper analysed the results and compared the performances of AMC with non-AMC system in these three kinds of channel environment.At last,we come to the conclusions:a system with AMC can achieve higher spectral efficiency and better system throughput;and the spectral efficiency and system throughput of AMC system will be higher on better satellite mobile channel.展开更多
With the advent of the wide-spread use of smart phones, video streaming over mobile wireless networks has suddenly taken a huge surge in recent years. Considering its enormous potential, mobile WiMAX is emerging as a ...With the advent of the wide-spread use of smart phones, video streaming over mobile wireless networks has suddenly taken a huge surge in recent years. Considering its enormous potential, mobile WiMAX is emerging as a viable technology for mobile TV which is expected to become of key importance in the future of mobile industry. In this paper, a simulation performance study of Mobile TV over mobile WiMAX is conducted with different types of adaptive modulation and coding taking into account key system and environment parameters which include the variation in the speed of the mobile, path-loss, scheduling service classes with the fixed type of modulations. Our simulation has been conducted using OPNET simulation. Simulation results show that dynamic adaptation of modulation and coding schemes based on channel conditions can offer considerably more enhanced QoS and at the same time reduce the overall bandwidth of the system.展开更多
Fuel cell powered vehicles have been developed as another alternative to internal combustion engine powered vehicles for some applications including passenger cars, buses, trains, motorcycles, forklifts, electric whee...Fuel cell powered vehicles have been developed as another alternative to internal combustion engine powered vehicles for some applications including passenger cars, buses, trains, motorcycles, forklifts, electric wheelchairs, electric trolleybuses, medical carts, military engines, personal sports craft, mobility devices and other self propelled equipment. Up to now, many researches have focused on the development of the power module in the Fuel cell vehicles (FCVs) and the components of these systems such as membranes, bipolar plates, and electrodes. However, our work in this study focuses on operating the integrated fuel cell power module system efficiently for various operating conditions such as pressure, relative humidity and operating modes. In our validation we have utilized PEMFC single cell, with active area geometry 16 cm2 and of 120 cm2. Some results obtained in our study shown significant performance indicators for PEMFC stack (composed of 2 cells and 4 cells in a series) at different humidification levels.展开更多
The transport properties of core–shell nanowires(CSNWs)under interface modulation and confinement are investigated based on the atomic-bond-relaxation(ABR)correlation mechanism and Fermi’s golden rule.An analytical ...The transport properties of core–shell nanowires(CSNWs)under interface modulation and confinement are investigated based on the atomic-bond-relaxation(ABR)correlation mechanism and Fermi’s golden rule.An analytical expression for the relationship between carrier mobility and interface mismatch strain is derived and the influence of size,shell thickness and alloyed layer on effective mass,band structures,and deformation potential constant are studied.It is found that interface modulation can not only reduce the lattice mismatch to optimize the band alignment,but also participate in the carrier transport for enhancing mobility.Moreover,the underlying mechanism regarding the interface shape dependence of transport properties in CSNWs is clarified.The great enhancement of electron mobility suggests that the interface modulation may become a potential pathway to improving the performance of nanoelectronic devices.展开更多
Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy(SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP ba...Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy(SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP based materials, growth conditions were deteriorated, but by an appropriate method and using reasonable process high electron mobility(77 K) of more than 1.50×10~5 cm^2/(V·s) can still be obtained. The structures and growth conditions have been studied and optimized via Hall measurements. For a typical sample, 2.0 K electron mobility as high as 1.78×10~6 cm^2/(V·s) is achieved, and the quantum Hall oscillation phenomena can be observed.展开更多
In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field p...In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.展开更多
基金Supported by the National Natural Science Foundation of China (No. 60972061,60972062,and 61032004)the National High Technology Research and Development Program of China ("863" Program) (No. 2008AA12A204)+1 种基金the Natural Science Foundation of Jiangsu Province (No.BK2009060)the "Triple Three" High Level Talent Development Plan of Jiangsu Province
文摘It is a challenging problem to design a high performance modulation for mobile satellite communications due to the limited power and bandwidth resource.The paper improves Feher patented Quadrature Phase Shift Keying(FQPSK) by redefining the waveform.The novel FQPSK,with con-stant envelope,can be used to improve the power efficiency and frequency efficiency of mobile satellite communication.The study shows that the improved FQPSK outperforms conventional FQPSK over AWGN and is immune to the non-linearity of high power amplifier.At last,the impact of flat fading and multi-path fading of channel on the BER performance of improved modulation is analyzed.
文摘Given that satellite mobile channel is a time-varying channel,Adaptive Modulation and Coding(AMC) was proposed to provide robust and spectrally efficient transmission over satellite mobile channel.Three different kinds of channel environment were considered in this paper:the urban area,the rural area,and the open space.Four combinations of modulation and coding were designed to meet reliable communication on time-varying channel,and spectral efficiency and system throughput of these three kinds of channel environment were simulated.Based on the simulation results,this paper analysed the results and compared the performances of AMC with non-AMC system in these three kinds of channel environment.At last,we come to the conclusions:a system with AMC can achieve higher spectral efficiency and better system throughput;and the spectral efficiency and system throughput of AMC system will be higher on better satellite mobile channel.
文摘With the advent of the wide-spread use of smart phones, video streaming over mobile wireless networks has suddenly taken a huge surge in recent years. Considering its enormous potential, mobile WiMAX is emerging as a viable technology for mobile TV which is expected to become of key importance in the future of mobile industry. In this paper, a simulation performance study of Mobile TV over mobile WiMAX is conducted with different types of adaptive modulation and coding taking into account key system and environment parameters which include the variation in the speed of the mobile, path-loss, scheduling service classes with the fixed type of modulations. Our simulation has been conducted using OPNET simulation. Simulation results show that dynamic adaptation of modulation and coding schemes based on channel conditions can offer considerably more enhanced QoS and at the same time reduce the overall bandwidth of the system.
基金The Center for Renewable Energies Development (CDER)The General Directorate for Scientific Research and Tech- nological Development (DG-RSDT)+1 种基金The Na- tional Observatory of the Environment and the Durable Development (ONEDD)The Ministry of Town and Country Planning and the Environment
文摘Fuel cell powered vehicles have been developed as another alternative to internal combustion engine powered vehicles for some applications including passenger cars, buses, trains, motorcycles, forklifts, electric wheelchairs, electric trolleybuses, medical carts, military engines, personal sports craft, mobility devices and other self propelled equipment. Up to now, many researches have focused on the development of the power module in the Fuel cell vehicles (FCVs) and the components of these systems such as membranes, bipolar plates, and electrodes. However, our work in this study focuses on operating the integrated fuel cell power module system efficiently for various operating conditions such as pressure, relative humidity and operating modes. In our validation we have utilized PEMFC single cell, with active area geometry 16 cm2 and of 120 cm2. Some results obtained in our study shown significant performance indicators for PEMFC stack (composed of 2 cells and 4 cells in a series) at different humidification levels.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91833302 and U2001215)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2022A1515010989)the Special Project in Key Fields of Guandong Universities,China(Grant No.2022ZDZX3015)。
文摘The transport properties of core–shell nanowires(CSNWs)under interface modulation and confinement are investigated based on the atomic-bond-relaxation(ABR)correlation mechanism and Fermi’s golden rule.An analytical expression for the relationship between carrier mobility and interface mismatch strain is derived and the influence of size,shell thickness and alloyed layer on effective mass,band structures,and deformation potential constant are studied.It is found that interface modulation can not only reduce the lattice mismatch to optimize the band alignment,but also participate in the carrier transport for enhancing mobility.Moreover,the underlying mechanism regarding the interface shape dependence of transport properties in CSNWs is clarified.The great enhancement of electron mobility suggests that the interface modulation may become a potential pathway to improving the performance of nanoelectronic devices.
文摘Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy(SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP based materials, growth conditions were deteriorated, but by an appropriate method and using reasonable process high electron mobility(77 K) of more than 1.50×10~5 cm^2/(V·s) can still be obtained. The structures and growth conditions have been studied and optimized via Hall measurements. For a typical sample, 2.0 K electron mobility as high as 1.78×10~6 cm^2/(V·s) is achieved, and the quantum Hall oscillation phenomena can be observed.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61106076)
文摘In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.
