Dissemination of information to citizens is a relevant component of governance. Expectedly, viewers tuned to broadcast stations within and outside their localities, expecting their receivers to faithfully reproduce th...Dissemination of information to citizens is a relevant component of governance. Expectedly, viewers tuned to broadcast stations within and outside their localities, expecting their receivers to faithfully reproduce the exact features of the transmitted signal. Akpabuyo is a dense forest zone near the creeks leading to the Atlantic ocean in Cross River State, Nigeria. The location has distinct environmental characteristics that made Akpabuyo Area Council, a challenging location to propagate electromagnetic waves;and therefore recipe for further investigation. Radio frequency analyzer, with 24 channels spectrum, ranging between 46 - 870 MHz (model: RO.VE.R.-“DLM3-T”) was deployed to capture signals from terrestrial television stations (TV). CATV measured signal of TV stations in dB, dBμV and dBmV. Its frequency ranged from 40 - 860 MHz;while varying from channel 1 to channel 69. Measurements taken from Akpabuyo L.G.A. showed the following results: the signal strength received from VHF Channel 11 ranged from 20 dBμV to 49 dBμV. From recorded empirical statistics from the study, 50% of the area received signal from this station above 30 dBμV, while other regions had signals below this value;representing the fringe zone of the frequency. The results obtained from the study relatively showed acceptance with Egli’s model. The study recorded a steady fluctuation between 17 dBμV and 19 dBμV from both propagating stations. However, Channel 27 signal at 519 MHz, had very weak signal coverage in Akpabuyo Local Government Area;with signal strength dropped to as low as 13 dB in many parts of the rural area. The study discovered that the state’s broadcasting stations, both at UHF and VHF channels did not transmit successfully across this densely forest (rural) location. Remedial measures such as installing Repeater stations at different locations as signal booster were recommended.展开更多
Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short dis...Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short distances.Stacking waveforms from different airgun shots recorded by a single seismic station(shot stacking)is the most popular technique to detect weak signals from noisy backgrounds,and has been widely used to process the data of Fixed Airgun Signal Transmission Stations(FASTS)in China.However,shot stacking sacrifices the time resolution in monitoring to recover a qualified airgun signal by stacking many shots at distance stations,and also suffers from persistent local noises.In this paper,we carried out several small-aperture seismic array experiments around the Binchuan FAST Station(BCFASTS)in Yunnan Province,China,and applied the array technique to improve airgun signal detection.The results show that seismic array processing combining with shot stacking can suppress seismic noises more efficiently,and provide better signal-to-noise ratio(SNR)and coherent airgun signals with less airgun shots.This work suggests that the array technique is a feasible and promising tool in FAST to increase the time resolution and reduce noise interference on routine monitoring.展开更多
为解决城市非视距(non line of sight,NLOS)环境下三维单站定位方法精度低和需要先验信息的问题,提出基于多径信号到达角度(angle of arrival,AOA)和到达时间(time of arrival,TOA)的三维单站定位方法。利用移动基站在不同位置上的多径...为解决城市非视距(non line of sight,NLOS)环境下三维单站定位方法精度低和需要先验信息的问题,提出基于多径信号到达角度(angle of arrival,AOA)和到达时间(time of arrival,TOA)的三维单站定位方法。利用移动基站在不同位置上的多径AOA估计散射中心位置;利用散射中心的多径TOA构建定位目标函数,并通过散射中心位置对目标位置进行约束,将定位问题转换为带约束的优化问题;利用列文伯格-马夸尔特(Levenberg Marquardt,LM)算法求解目标位置。仿真结果表明,所提方法在无需额外环境先验信息情况下,较对比算法提高了定位精度。展开更多
随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,...随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,该文针对直流受端馈入站与近区风电场系统的振荡特性展开研究。首先,建立并验证系统的状态空间模型,基于该模型计算出系统特征值,确定LCC-HVDC与风电场共同参与的振荡主导模式并进行参与因子分析。进一步地,通过对比是否接入LCC-HVDC的主导模式,得到LCC-HVDC的接入会削弱系统阻尼的结论。最后,从系统额定容量、交流系统短路比、风电场并网线路长度等方面探究系统稳定性的影响因素,并分析系统的不同短路比、潮流比对风机网侧换流器(grid-side converter,GSC)外环控制和换流站定电流控制器性能的影响。展开更多
超宽带(Ultra-Wideband,UWB)技术在室内外定位中应用广泛,针对传统多基站定位方案的局限性,提出了一种基于超宽带信号到达相位差(Ultra-Wideband Phase Difference of Arrival,UWB-PDOA)的少基站自适应定位系统。该系统利用UWB-PDOA技...超宽带(Ultra-Wideband,UWB)技术在室内外定位中应用广泛,针对传统多基站定位方案的局限性,提出了一种基于超宽带信号到达相位差(Ultra-Wideband Phase Difference of Arrival,UWB-PDOA)的少基站自适应定位系统。该系统利用UWB-PDOA技术和基于ESP32信号强度的权重自适应定位技术,大幅降低了对环境部署的依赖性,提高了定位的精度和稳定性。结合环境先验信息和目标高度的先验知识,构建了先验知识库,采用自适应定位技术,利用多个传感器的信息来调整对不同定位基站的置信度权重,进一步提高了定位精度和鲁棒性。实验结果表明,所提出的系统在视距(Line of Sight,LOS)和非视距(Non Line of Sight,NLOS)环境下都具有较高的定位精度和稳定性,并且仅需要不超过3个基站便可以满足室内环境定位的需求。展开更多
文摘Dissemination of information to citizens is a relevant component of governance. Expectedly, viewers tuned to broadcast stations within and outside their localities, expecting their receivers to faithfully reproduce the exact features of the transmitted signal. Akpabuyo is a dense forest zone near the creeks leading to the Atlantic ocean in Cross River State, Nigeria. The location has distinct environmental characteristics that made Akpabuyo Area Council, a challenging location to propagate electromagnetic waves;and therefore recipe for further investigation. Radio frequency analyzer, with 24 channels spectrum, ranging between 46 - 870 MHz (model: RO.VE.R.-“DLM3-T”) was deployed to capture signals from terrestrial television stations (TV). CATV measured signal of TV stations in dB, dBμV and dBmV. Its frequency ranged from 40 - 860 MHz;while varying from channel 1 to channel 69. Measurements taken from Akpabuyo L.G.A. showed the following results: the signal strength received from VHF Channel 11 ranged from 20 dBμV to 49 dBμV. From recorded empirical statistics from the study, 50% of the area received signal from this station above 30 dBμV, while other regions had signals below this value;representing the fringe zone of the frequency. The results obtained from the study relatively showed acceptance with Egli’s model. The study recorded a steady fluctuation between 17 dBμV and 19 dBμV from both propagating stations. However, Channel 27 signal at 519 MHz, had very weak signal coverage in Akpabuyo Local Government Area;with signal strength dropped to as low as 13 dB in many parts of the rural area. The study discovered that the state’s broadcasting stations, both at UHF and VHF channels did not transmit successfully across this densely forest (rural) location. Remedial measures such as installing Repeater stations at different locations as signal booster were recommended.
基金jointly sponsored by National Natural Science Foundation of China(41574050,41674058)
文摘Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short distances.Stacking waveforms from different airgun shots recorded by a single seismic station(shot stacking)is the most popular technique to detect weak signals from noisy backgrounds,and has been widely used to process the data of Fixed Airgun Signal Transmission Stations(FASTS)in China.However,shot stacking sacrifices the time resolution in monitoring to recover a qualified airgun signal by stacking many shots at distance stations,and also suffers from persistent local noises.In this paper,we carried out several small-aperture seismic array experiments around the Binchuan FAST Station(BCFASTS)in Yunnan Province,China,and applied the array technique to improve airgun signal detection.The results show that seismic array processing combining with shot stacking can suppress seismic noises more efficiently,and provide better signal-to-noise ratio(SNR)and coherent airgun signals with less airgun shots.This work suggests that the array technique is a feasible and promising tool in FAST to increase the time resolution and reduce noise interference on routine monitoring.
文摘为解决城市非视距(non line of sight,NLOS)环境下三维单站定位方法精度低和需要先验信息的问题,提出基于多径信号到达角度(angle of arrival,AOA)和到达时间(time of arrival,TOA)的三维单站定位方法。利用移动基站在不同位置上的多径AOA估计散射中心位置;利用散射中心的多径TOA构建定位目标函数,并通过散射中心位置对目标位置进行约束,将定位问题转换为带约束的优化问题;利用列文伯格-马夸尔特(Levenberg Marquardt,LM)算法求解目标位置。仿真结果表明,所提方法在无需额外环境先验信息情况下,较对比算法提高了定位精度。
文摘随着高压直流输电工程的不断投产,以及风电项目的增多,越来越多的风电场出现在电网换相换流器高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)受端换流站近区,两者构成的系统存在振荡风险。为此,该文针对直流受端馈入站与近区风电场系统的振荡特性展开研究。首先,建立并验证系统的状态空间模型,基于该模型计算出系统特征值,确定LCC-HVDC与风电场共同参与的振荡主导模式并进行参与因子分析。进一步地,通过对比是否接入LCC-HVDC的主导模式,得到LCC-HVDC的接入会削弱系统阻尼的结论。最后,从系统额定容量、交流系统短路比、风电场并网线路长度等方面探究系统稳定性的影响因素,并分析系统的不同短路比、潮流比对风机网侧换流器(grid-side converter,GSC)外环控制和换流站定电流控制器性能的影响。
文摘超宽带(Ultra-Wideband,UWB)技术在室内外定位中应用广泛,针对传统多基站定位方案的局限性,提出了一种基于超宽带信号到达相位差(Ultra-Wideband Phase Difference of Arrival,UWB-PDOA)的少基站自适应定位系统。该系统利用UWB-PDOA技术和基于ESP32信号强度的权重自适应定位技术,大幅降低了对环境部署的依赖性,提高了定位的精度和稳定性。结合环境先验信息和目标高度的先验知识,构建了先验知识库,采用自适应定位技术,利用多个传感器的信息来调整对不同定位基站的置信度权重,进一步提高了定位精度和鲁棒性。实验结果表明,所提出的系统在视距(Line of Sight,LOS)和非视距(Non Line of Sight,NLOS)环境下都具有较高的定位精度和稳定性,并且仅需要不超过3个基站便可以满足室内环境定位的需求。
