The novel compensating method directly demodulates the signals without the carrier recovery processes, in which the carrier with original modulation frequency is used as the local coherent carrier. In this way, the ph...The novel compensating method directly demodulates the signals without the carrier recovery processes, in which the carrier with original modulation frequency is used as the local coherent carrier. In this way, the phase offsets due to frequency shift are linear. Based on this premise, the compensation processes are： firstly, the phase offsets between the baseband neighbor-symbols after clock recovery is unbiasedly estimated among the reference symbols; then, the receiving signals symbols are adjusted by the phase estimation value; finally, the phase offsets after adjusting are compensated by the least mean squares （LMS） algorithm. In order to express the compensation processes and ability clearly, the quadrature phase shift keying （QPSK） modulation signals are regarded as examples for Matlab simulation. BER simulations are carried out using the Monte-Carlo method. The learning curves are obtained to study the algorithm＇s convergence ability. The constellation figures are also simulated to observe the compensation results directly.展开更多
A terahertz(THz)wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves.This paper presents the scattering attenuation characteristics of vegetation in a T...A terahertz(THz)wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves.This paper presents the scattering attenuation characteristics of vegetation in a THz range.The theoretical path loss model near the vegetation yields the average attenuation of THz waves in a mixed channel composed of air and vegetation leaves.Furthermore,a simplified model of the vegetation structure is obtained for generic vegetation types based on a variety of parameters,such as leaf size,distribution,and moisture content.Finally,based on specific vegetation species and different levels of air humidity,the attenuation characteristics under different conditions are calculated,and the influence of different model parameters on the attenuation characteristics is obtained.展开更多
空间飞行器指向误差严重影响太赫兹通信链路的可靠性,因此针对捕获、跟踪和瞄准系统不能对太赫兹天线指向误差实现完全补偿造成误差残留的问题,提出了对指向误差影响下的接收信号进行再次算法补偿的方案,评估了典型空间飞行器指向误差...空间飞行器指向误差严重影响太赫兹通信链路的可靠性,因此针对捕获、跟踪和瞄准系统不能对太赫兹天线指向误差实现完全补偿造成误差残留的问题,提出了对指向误差影响下的接收信号进行再次算法补偿的方案,评估了典型空间飞行器指向误差条件下算法的补偿效果。首先,建立指向误差影响下的信道模型,并分析指向误差带来的误比特率。然后,对比盲均衡(CMA)算法、自适应滤波算法(LMS、RLS)、卡尔曼滤波(KF)算法和粒子(PF)滤波算法的补偿效果。结果表明,粒子滤波算法的补偿效果是最优的,以OLYMPUS飞行器为例,PF算法比CMA算法、LMS和RLS算法、KF算法分别提高了3.07 d B、1.07 d B、1.01 d B、0.43 d B。展开更多
Sonication is a powerful technique to promote the dispersion of carbon nanotubes(CNTs) and enhance their solubility;this is necessary for CNT applications,especially in the biochemical and biomedical fields.In this st...Sonication is a powerful technique to promote the dispersion of carbon nanotubes(CNTs) and enhance their solubility;this is necessary for CNT applications,especially in the biochemical and biomedical fields.In this study,batch experiments were conducted to evaluate the role of sonication energy on the dispersion of CNTs in the presence of a widely used anionic surfactant,sodium dodecylbenzene sulfonate(SDBS).It was observed that the concentration of dispersed CNTs in the SDBS solution depended on the sonication energy,but not the sonication time or output power of the sonicator alone.The amount of dispersed CNTs was positively correlated with the concentrations of SDBS and CNTs,and the length of the CNTs.The promotion of oxygen-containing functional groups on the dispersed CNTs was observed at relatively low sonication energies.The optimal energy,i.e.the minimum energy supplied by sonication to achieve a saturated suspension of dispersed CNTs in the SDBS solution,was CNT diameter-dependent,because of the larger vdW forces between tubes of smaller diameter.An exponential decay curve was constructed for the optimal energy values as a function of the outer CNT diameter,to assist in determining the energy needed to disperse CNTs.展开更多
基金supported by the National Natural Science Foundation of China(60532030)
文摘The novel compensating method directly demodulates the signals without the carrier recovery processes, in which the carrier with original modulation frequency is used as the local coherent carrier. In this way, the phase offsets due to frequency shift are linear. Based on this premise, the compensation processes are： firstly, the phase offsets between the baseband neighbor-symbols after clock recovery is unbiasedly estimated among the reference symbols; then, the receiving signals symbols are adjusted by the phase estimation value; finally, the phase offsets after adjusting are compensated by the least mean squares （LMS） algorithm. In order to express the compensation processes and ability clearly, the quadrature phase shift keying （QPSK） modulation signals are regarded as examples for Matlab simulation. BER simulations are carried out using the Monte-Carlo method. The learning curves are obtained to study the algorithm＇s convergence ability. The constellation figures are also simulated to observe the compensation results directly.
基金the Fundamental Research Funds for the Central Universities(NT2021026).
文摘A terahertz(THz)wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves.This paper presents the scattering attenuation characteristics of vegetation in a THz range.The theoretical path loss model near the vegetation yields the average attenuation of THz waves in a mixed channel composed of air and vegetation leaves.Furthermore,a simplified model of the vegetation structure is obtained for generic vegetation types based on a variety of parameters,such as leaf size,distribution,and moisture content.Finally,based on specific vegetation species and different levels of air humidity,the attenuation characteristics under different conditions are calculated,and the influence of different model parameters on the attenuation characteristics is obtained.
文摘空间飞行器指向误差严重影响太赫兹通信链路的可靠性,因此针对捕获、跟踪和瞄准系统不能对太赫兹天线指向误差实现完全补偿造成误差残留的问题,提出了对指向误差影响下的接收信号进行再次算法补偿的方案,评估了典型空间飞行器指向误差条件下算法的补偿效果。首先,建立指向误差影响下的信道模型,并分析指向误差带来的误比特率。然后,对比盲均衡(CMA)算法、自适应滤波算法(LMS、RLS)、卡尔曼滤波(KF)算法和粒子(PF)滤波算法的补偿效果。结果表明,粒子滤波算法的补偿效果是最优的,以OLYMPUS飞行器为例,PF算法比CMA算法、LMS和RLS算法、KF算法分别提高了3.07 d B、1.07 d B、1.01 d B、0.43 d B。
基金supported by the Zhejiang Provincial Natural Science Foundation of China (R5110004)the National Natural Science Foundation of China (21137003 and 40973065)+3 种基金the National Science & Technology Pillar Program of China (2013BAC01B01)the Scholarship Award for Excellent Doctoral Student Granted by Ministry of Educationthe Fundamental Research Funds for the Central Universitiesthe Key Innovation Team for Science and Technology of Zhejiang Province (2009R50047)
文摘Sonication is a powerful technique to promote the dispersion of carbon nanotubes(CNTs) and enhance their solubility;this is necessary for CNT applications,especially in the biochemical and biomedical fields.In this study,batch experiments were conducted to evaluate the role of sonication energy on the dispersion of CNTs in the presence of a widely used anionic surfactant,sodium dodecylbenzene sulfonate(SDBS).It was observed that the concentration of dispersed CNTs in the SDBS solution depended on the sonication energy,but not the sonication time or output power of the sonicator alone.The amount of dispersed CNTs was positively correlated with the concentrations of SDBS and CNTs,and the length of the CNTs.The promotion of oxygen-containing functional groups on the dispersed CNTs was observed at relatively low sonication energies.The optimal energy,i.e.the minimum energy supplied by sonication to achieve a saturated suspension of dispersed CNTs in the SDBS solution,was CNT diameter-dependent,because of the larger vdW forces between tubes of smaller diameter.An exponential decay curve was constructed for the optimal energy values as a function of the outer CNT diameter,to assist in determining the energy needed to disperse CNTs.
