With the rapid development of new energy power generation and high-power traction technology,the voltage and power levels of converter devices have been continuously improved,and the application of high-power converte...With the rapid development of new energy power generation and high-power traction technology,the voltage and power levels of converter devices have been continuously improved,and the application of high-power converters is becoming increasingly widespread.However,high-power converters are affected by switching losses and heat dissipation,meaning they are not suitable for high carrier conditions.Therefore,research of low carrier ratio converter systems has received increased attention.Based on existing research,the problems of large current harmonics,low observation accuracy,and poor stability that may occur at low carrier ratios are explained.In addition,the topologies,modulation strategies,and control methods of the low carrier ratio converter system are analyzed and classified.Finally,future research directions of low carrier ratio converter systems are proposed.展开更多
The frequency band between 5 010 MHz and 5 030 MHz allocated as C band has been used as a candidate in the global navigation satellite systems （GNSS） along with more and more naviga- tion services in L band. The pot...The frequency band between 5 010 MHz and 5 030 MHz allocated as C band has been used as a candidate in the global navigation satellite systems （GNSS） along with more and more naviga- tion services in L band. The potential benefits and technical requirements of C band for satellite navi- gation have been analyzed before. However the degradation of effective carrier-power-to-noise densi- ty ratio（ A （C/No ）eu） based on code tracking spectral sensitivity coefficient（ CT_SSC ） as a compati- bility assessment methodology for potential GNSS radio frequency compatibility in C-Band has not been discussed clearly. So the compatibility of the signals in the C band between BeiDou （BD） B1 C and GPS L1C, L1C/A, Galileo E1Os as the interoperability or classical signals in L band is analyzed. Simulation results reveal the interference degree between BD III B1C and GPS L1C/A, L1C, Galileo E1OS. The results can also reveal that the multiplexed binary offset carrier （MBOC） and binary phase shift keying （BPSK） modulation is not appropriate for C band.展开更多
As wireless data applications over cellular networks become more widespread, the pressure to increase capacity will become even more intense. Capacity in the 800 and 900 MHz bands, where bandwidth is restricted, is al...As wireless data applications over cellular networks become more widespread, the pressure to increase capacity will become even more intense. Capacity in the 800 and 900 MHz bands, where bandwidth is restricted, is already becoming a limiting factor. This paper attempts to address how the application of smart antenna systems has brought about improvements in call quality and increased capacity through reduced Interference in Mobile Communication. The smart antenna may be in a variety of ways to improve the performance of a communications system. Perhaps most importantly is its capability to cancel co-channel interference. It helps in improving the system performance by increasing the channel capacity, spectrum efficiency, extending range coverage, speech quality, enabling tighter reuse of frequencies within a cellular network and economically, feasible increased signal gain, greater, reduced multipath reflection. It has been argued that Smart antennas and the Algorithms to control them are vital to a high-capacity communication system development.展开更多
Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to ...Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to acquire main carrier exactly becomes a hot focus for deep space communications.Already there emerged some main carrier acquisition algorithms,but they all require high SNR and small modulation index.In this paper,we develop a new acquire algorithm.First we use the spectral energy center algorithm to shorten the original sequence,filter out some noise and make the spectral more symmetric.Then we adopt the spectral symmetry algorithm to make full use of the whole spectrum information,and utilize FFT to reduce computation complexity.Simulation results show that our algorithm can acquire main carrier successfully under large modulation index and get good performance with low Carrier to Noise Ratio(CNR).展开更多
A contrast study on the effects of manual acupuncture and electroacupuncture wasconducted in 60 cases of chronic hepatitis B carriers.The results demonstrated that theimmunological functions,both cellular and humoral,...A contrast study on the effects of manual acupuncture and electroacupuncture wasconducted in 60 cases of chronic hepatitis B carriers.The results demonstrated that theimmunological functions,both cellular and humoral,were markedly regulated asevidenced by the negative turnover rates of HBsAg,HBeAg,anti-HBc and HBcAg,as wellas the positive turnover rate of anti-HBe.展开更多
基金Supported by the National Natural Science Foundation of China(51907061)Natural Science Foundation of Hunan Province of China(2019JJ50119).
文摘With the rapid development of new energy power generation and high-power traction technology,the voltage and power levels of converter devices have been continuously improved,and the application of high-power converters is becoming increasingly widespread.However,high-power converters are affected by switching losses and heat dissipation,meaning they are not suitable for high carrier conditions.Therefore,research of low carrier ratio converter systems has received increased attention.Based on existing research,the problems of large current harmonics,low observation accuracy,and poor stability that may occur at low carrier ratios are explained.In addition,the topologies,modulation strategies,and control methods of the low carrier ratio converter system are analyzed and classified.Finally,future research directions of low carrier ratio converter systems are proposed.
基金Supported by the National High Technology Research and Development Program of China(863Program)(2011AA120502)
文摘The frequency band between 5 010 MHz and 5 030 MHz allocated as C band has been used as a candidate in the global navigation satellite systems （GNSS） along with more and more naviga- tion services in L band. The potential benefits and technical requirements of C band for satellite navi- gation have been analyzed before. However the degradation of effective carrier-power-to-noise densi- ty ratio（ A （C/No ）eu） based on code tracking spectral sensitivity coefficient（ CT_SSC ） as a compati- bility assessment methodology for potential GNSS radio frequency compatibility in C-Band has not been discussed clearly. So the compatibility of the signals in the C band between BeiDou （BD） B1 C and GPS L1C, L1C/A, Galileo E1Os as the interoperability or classical signals in L band is analyzed. Simulation results reveal the interference degree between BD III B1C and GPS L1C/A, L1C, Galileo E1OS. The results can also reveal that the multiplexed binary offset carrier （MBOC） and binary phase shift keying （BPSK） modulation is not appropriate for C band.
文摘As wireless data applications over cellular networks become more widespread, the pressure to increase capacity will become even more intense. Capacity in the 800 and 900 MHz bands, where bandwidth is restricted, is already becoming a limiting factor. This paper attempts to address how the application of smart antenna systems has brought about improvements in call quality and increased capacity through reduced Interference in Mobile Communication. The smart antenna may be in a variety of ways to improve the performance of a communications system. Perhaps most importantly is its capability to cancel co-channel interference. It helps in improving the system performance by increasing the channel capacity, spectrum efficiency, extending range coverage, speech quality, enabling tighter reuse of frequencies within a cellular network and economically, feasible increased signal gain, greater, reduced multipath reflection. It has been argued that Smart antennas and the Algorithms to control them are vital to a high-capacity communication system development.
基金Supported by the National Natural Science Foundation of China (No. 61032003 and No. 61021001)
文摘Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to acquire main carrier exactly becomes a hot focus for deep space communications.Already there emerged some main carrier acquisition algorithms,but they all require high SNR and small modulation index.In this paper,we develop a new acquire algorithm.First we use the spectral energy center algorithm to shorten the original sequence,filter out some noise and make the spectral more symmetric.Then we adopt the spectral symmetry algorithm to make full use of the whole spectrum information,and utilize FFT to reduce computation complexity.Simulation results show that our algorithm can acquire main carrier successfully under large modulation index and get good performance with low Carrier to Noise Ratio(CNR).
文摘A contrast study on the effects of manual acupuncture and electroacupuncture wasconducted in 60 cases of chronic hepatitis B carriers.The results demonstrated that theimmunological functions,both cellular and humoral,were markedly regulated asevidenced by the negative turnover rates of HBsAg,HBeAg,anti-HBc and HBcAg,as wellas the positive turnover rate of anti-HBe.
