While operators have started deploying fourth generation(4G) wireless communication systems,which could provide up to1 Gbps downlink peak data rate,the improved system capacity is still insufficient to meet the drasti...While operators have started deploying fourth generation(4G) wireless communication systems,which could provide up to1 Gbps downlink peak data rate,the improved system capacity is still insufficient to meet the drastically increasing demand of mobile users over the next decade.The main causes of the above-mentioned phenomenon include the following two aspects:1) the growth rate of the network capacity is far below that of user's demand,and 2) the relatively deterministic wireless access network(WAN) architecture in the existing systems cannot accommodate the prominent increase of mobile traffic with space-time domain dynamics.In order to address the above-mentioned challenges,we investigate the time-spatial consistency architecture for the future WAN,whilst emphasizing the critical roles of some spectral-efficient techniques such as Massive multiple-input multiple-output(MIMO),full-duplex(FD)operation and heterogeneous networks(HetNets).Furthermore,the energy efficiency(EE)of the HetNets under the proposed architecture is also evaluated,showing that the proposed user-selected uplink power control algorithm outperforms the traditional stochastic-scheduling strategy in terms of both capacity and EE in a two-tier HetNet.The other critical issues,including the tidal effect,the temporal failure owing to the instantaneously increased traffic,and the network wide load-balancing problem,etc.,are also anticipated to be addressed in the proposed architecture.(Abstract)展开更多
The change of light output power of LEDs based on A1GalnP heterostructures with multiple quantum wells （590 nm and 630 nm） under irradiation by fast neutrons depends on the operating current density. It can be disti...The change of light output power of LEDs based on A1GalnP heterostructures with multiple quantum wells （590 nm and 630 nm） under irradiation by fast neutrons depends on the operating current density. It can be distinguished the regions of high, average and low electron injection. Operating current, this corresponds to the position of the boundary between the selected levels of the electron injection, increases with increasing neutron fluence. The final stage of the reducing process of the light output power under irradiation is the regime of low electron injection. The relative change in light output power depends on the operating current （operating current density） and can be described by a fairly simple equation. Established relations predict radiation resistance of LEDs, and it makes the most rational justification of operating modes of light-emitting diodes in terms of radiation resistance.展开更多
The operating circuits for LED （light emitting diode） lamp composed of diodes and DC capacitors only are proposed. The proposed circuit is based on a double-voltage rectifier circuit and a Cockcroft-Walton circuit. ...The operating circuits for LED （light emitting diode） lamp composed of diodes and DC capacitors only are proposed. The proposed circuit is based on a double-voltage rectifier circuit and a Cockcroft-Walton circuit. The circuit can operate LED without flicker, and is free from switching noise since high frequency switching circuit is not used. To replace an AC capacitor by a DC capacitor for the ballast, a diode is connected across the capacitor in parallel, and the operating voltage of LED unit is kept at the value greater than the peak voltage of the input power source. The circuit realizes high efficiency and high input power factor compared with the operating circuits on the market. Cockcroft-Walton-type circuit can operate many LED devices in series connection. Series connection is preferable for fabricating LED unit of a constant voltage characteristic. Moreover, fairly flat waveform of LED operating current is realized by Cockcrofl-Walton-type circuit, even though capacitor ballast is used.展开更多
Many conventional switching power supplies in input AC line voltage and filtering it with large electrolytic computers and low power motor drive systems operate by rectifying the capacitors. This results in undesirabl...Many conventional switching power supplies in input AC line voltage and filtering it with large electrolytic computers and low power motor drive systems operate by rectifying the capacitors. This results in undesirable side effects such as the generation of distorted input current waveform. The input power factor is also poor. Further, the input current has the shape of narrow pulses, which in turn increases its value. The reduction in input current harmonics and improved power factor operation of motor drive systems and switching power supplies are important from the energy saving point of view and also to satisfy the harmonic standards. This paper proposes a full bridge PWM rectifier with load current feedforward. The proposed approach has some advantages, including a quick response for the load fluctuation, the reduction of the number of sensors and simplified control, as compared with the conventional methods. From simulated results, it is clarified that the proposed control method is effective and useful.展开更多
基金supported by the key project of the National Natural Science Foundation of China(No.61431001)the 863 project No.2014AA01A701+4 种基金Program for New Century Excellent Talents in University(NECT12-0774)the open research fund of National Mobile Communications Research Laboratory Southeast University(No.2013D12)Fundamental Research Funds for the Central Universities(FRF-BD-15-012A)the Research Foundation of China Mobilethe Foundation of Beijing Engineering and Technology Center for Convergence Networks and Ubiquitous Services
文摘While operators have started deploying fourth generation(4G) wireless communication systems,which could provide up to1 Gbps downlink peak data rate,the improved system capacity is still insufficient to meet the drastically increasing demand of mobile users over the next decade.The main causes of the above-mentioned phenomenon include the following two aspects:1) the growth rate of the network capacity is far below that of user's demand,and 2) the relatively deterministic wireless access network(WAN) architecture in the existing systems cannot accommodate the prominent increase of mobile traffic with space-time domain dynamics.In order to address the above-mentioned challenges,we investigate the time-spatial consistency architecture for the future WAN,whilst emphasizing the critical roles of some spectral-efficient techniques such as Massive multiple-input multiple-output(MIMO),full-duplex(FD)operation and heterogeneous networks(HetNets).Furthermore,the energy efficiency(EE)of the HetNets under the proposed architecture is also evaluated,showing that the proposed user-selected uplink power control algorithm outperforms the traditional stochastic-scheduling strategy in terms of both capacity and EE in a two-tier HetNet.The other critical issues,including the tidal effect,the temporal failure owing to the instantaneously increased traffic,and the network wide load-balancing problem,etc.,are also anticipated to be addressed in the proposed architecture.(Abstract)
文摘The change of light output power of LEDs based on A1GalnP heterostructures with multiple quantum wells （590 nm and 630 nm） under irradiation by fast neutrons depends on the operating current density. It can be distinguished the regions of high, average and low electron injection. Operating current, this corresponds to the position of the boundary between the selected levels of the electron injection, increases with increasing neutron fluence. The final stage of the reducing process of the light output power under irradiation is the regime of low electron injection. The relative change in light output power depends on the operating current （operating current density） and can be described by a fairly simple equation. Established relations predict radiation resistance of LEDs, and it makes the most rational justification of operating modes of light-emitting diodes in terms of radiation resistance.
文摘The operating circuits for LED （light emitting diode） lamp composed of diodes and DC capacitors only are proposed. The proposed circuit is based on a double-voltage rectifier circuit and a Cockcroft-Walton circuit. The circuit can operate LED without flicker, and is free from switching noise since high frequency switching circuit is not used. To replace an AC capacitor by a DC capacitor for the ballast, a diode is connected across the capacitor in parallel, and the operating voltage of LED unit is kept at the value greater than the peak voltage of the input power source. The circuit realizes high efficiency and high input power factor compared with the operating circuits on the market. Cockcroft-Walton-type circuit can operate many LED devices in series connection. Series connection is preferable for fabricating LED unit of a constant voltage characteristic. Moreover, fairly flat waveform of LED operating current is realized by Cockcrofl-Walton-type circuit, even though capacitor ballast is used.
文摘Many conventional switching power supplies in input AC line voltage and filtering it with large electrolytic computers and low power motor drive systems operate by rectifying the capacitors. This results in undesirable side effects such as the generation of distorted input current waveform. The input power factor is also poor. Further, the input current has the shape of narrow pulses, which in turn increases its value. The reduction in input current harmonics and improved power factor operation of motor drive systems and switching power supplies are important from the energy saving point of view and also to satisfy the harmonic standards. This paper proposes a full bridge PWM rectifier with load current feedforward. The proposed approach has some advantages, including a quick response for the load fluctuation, the reduction of the number of sensors and simplified control, as compared with the conventional methods. From simulated results, it is clarified that the proposed control method is effective and useful.
