Carrier frequency and symbol rate estimation are the main contents of parameter estimation,which is the basis of modulation recognition and further processing of signals especially in non-cooperative communication.Wit...Carrier frequency and symbol rate estimation are the main contents of parameter estimation,which is the basis of modulation recognition and further processing of signals especially in non-cooperative communication.With the development of wireless communication,the signal transmission environment has become increasingly bad,causing more difficulties in parameter estimation.It is well known that the signal cycle spectrum is robust to noises and signal parameters are closely related.In practice,it is impossible to calculate the cyclic spectrum of infinite length data signals.When using finite length data to obtain a cycle spectrum,the truncation noise is induced,resulting in interference.It is necessary to overcome the influence of noises in order to improve the detection ability of discrete spectral lines.An improved method of the discrete spectral line extraction algorithm is proposed by reflecting the amplitude advantage of discrete spectral lines through salient features of continuous noises in discrete spectral line neighborhood.展开更多
A serological survey conducted among 196 pregnant women resident in and around Maiduguri, an urban town in north eastern Nigeria showed that 33 (16.8%) were asymptomatic carriers of hepatitis B virus surface antigen (...A serological survey conducted among 196 pregnant women resident in and around Maiduguri, an urban town in north eastern Nigeria showed that 33 (16.8%) were asymptomatic carriers of hepatitis B virus surface antigen (HBsAg). They are within the age range of 14-40 years with mean (± SD) age of 24.7 (± 6.3). The women attend antenatal clinic at the State Specialist Hospital, a secondary health facility in Maiduguri, Borno state. The women are all heterosexuals. The distribution of HBsAg carrier rate according to age of women studied showed a significant (p = 0.0061) increase of the prevalence of HBsAg from 4 (8.7%) in the lower age group (39 years). According to the number of pregnancies, the prevalence of HBsAg infection increased significantly from 6 (9.2%) among primiparous to 13 (13.7%) and 14 (38.9%) among multiparous and grand multiparous respectively. The carrier rate of HBsAg infection among the pregnant women studied based on their duration of pregnancies and their social class showed no significant differences. However, according to the factors known to be commonly associated with the highest risk of transmission of HBV such as history of blood transfusion, Tribal marks/tattooing, use of sharps, sharing of articles, history of jaundice in the women and husbands, history of sexually transmitted infections (STIs) of the women and husbands and the type of marriage (monogamous or polygamous), number of sexual relationships per week, only the history of blood transfusion was significantly associated with HBsAg carrier rate (RR = 3.71., 95% Confidence Interval (C.I.), 1.89-7.30, p = 0.0078). The study confirms that pregnant women who attend antenatal clinic in this secondary health facility are at higher risk of being infected with the HBV, which could lead to both prenatal and post natal transmission to their newborns.展开更多
This paper presents a Kerr-lens mode-locked Ti：sapphire laser at the repetition rate of 525 MHz, stable laser pulse as short as 10 fs with average output power of 480 mW is obtained. By injecting the pulse into photo...This paper presents a Kerr-lens mode-locked Ti：sapphire laser at the repetition rate of 525 MHz, stable laser pulse as short as 10 fs with average output power of 480 mW is obtained. By injecting the pulse into photonics crystal fibre, octave-spanning spectrum covered from 500 to 1050 nm is generated, carrier-envelope phase frequency with signal-to- noise ratio of 31dB is measured, which paves the way for the generation of a compact frequency comb.展开更多
针对基于载噪比(carrier to noise ratio,CNR)的GNSS干扰源定位,在存在多个干扰源、多径传输且接收机间距较远时定位难度大、精度低的问题,提出了一种加权K均值(K-Means)聚类算法与基于差分接收信号强度(differential received signal s...针对基于载噪比(carrier to noise ratio,CNR)的GNSS干扰源定位,在存在多个干扰源、多径传输且接收机间距较远时定位难度大、精度低的问题,提出了一种加权K均值(K-Means)聚类算法与基于差分接收信号强度(differential received signal strength,DRSS)的方程解算定位相结合的多干扰源定位方法.在假设干扰源个数确定以及单个接收机只受到一个干扰源影响的前提下,设计了改进的加权K-Means聚类算法实现对多个干扰源位置的初步估计.为了进一步降低在观测接收机相距较远时加权K-Means方法的定位误差,在聚类后选取各簇内受干扰影响显著的接收CNR构建基于DRSS的定位方程组,通过方程解算得到更加精细的定位结果.仿真结果表明,所提出的定位方案可以实现对多干扰源的定位,结合DRSS参数定位后,单干扰源场景下定位误差可降低19%以上,存在两个单音干扰源的场景下定位误差可降低38%以上.展开更多
针对位置欺骗如何影响接收机的问题,使用TEXBAT(Texas Spoofing Test Battery)提供的2组无欺骗干扰场景数据集和2组不同场景的GPS位置欺骗数据集,建立了GPS位置欺骗模型,分析了欺骗场景下两种相位对齐模式对欺骗攻击的影响;利用GNSS-SD...针对位置欺骗如何影响接收机的问题,使用TEXBAT(Texas Spoofing Test Battery)提供的2组无欺骗干扰场景数据集和2组不同场景的GPS位置欺骗数据集,建立了GPS位置欺骗模型,分析了欺骗场景下两种相位对齐模式对欺骗攻击的影响;利用GNSS-SDR软件接收机对TEXBAT的原始高保真数字采样数据进行数据处理,分别得到软件接收机受欺骗与未受欺骗时的接收机载噪比、载波多普勒、码速率等随时间的变化情况;分析了两个位置欺骗场景对软件接收机跟踪阶段输出值的影响。实验结果表明,载噪比有大于3(dB·Hz)的波动,码速率方差会发生阶段性的增加和减少;多普勒频率的变化取决于欺骗场景的选取,不同场景的位置欺骗从不同角度有效影响了接收机定位结果。展开更多
基金supported by the National Key R&D Program of China(2016YFB0800203)
文摘Carrier frequency and symbol rate estimation are the main contents of parameter estimation,which is the basis of modulation recognition and further processing of signals especially in non-cooperative communication.With the development of wireless communication,the signal transmission environment has become increasingly bad,causing more difficulties in parameter estimation.It is well known that the signal cycle spectrum is robust to noises and signal parameters are closely related.In practice,it is impossible to calculate the cyclic spectrum of infinite length data signals.When using finite length data to obtain a cycle spectrum,the truncation noise is induced,resulting in interference.It is necessary to overcome the influence of noises in order to improve the detection ability of discrete spectral lines.An improved method of the discrete spectral line extraction algorithm is proposed by reflecting the amplitude advantage of discrete spectral lines through salient features of continuous noises in discrete spectral line neighborhood.
文摘A serological survey conducted among 196 pregnant women resident in and around Maiduguri, an urban town in north eastern Nigeria showed that 33 (16.8%) were asymptomatic carriers of hepatitis B virus surface antigen (HBsAg). They are within the age range of 14-40 years with mean (± SD) age of 24.7 (± 6.3). The women attend antenatal clinic at the State Specialist Hospital, a secondary health facility in Maiduguri, Borno state. The women are all heterosexuals. The distribution of HBsAg carrier rate according to age of women studied showed a significant (p = 0.0061) increase of the prevalence of HBsAg from 4 (8.7%) in the lower age group (39 years). According to the number of pregnancies, the prevalence of HBsAg infection increased significantly from 6 (9.2%) among primiparous to 13 (13.7%) and 14 (38.9%) among multiparous and grand multiparous respectively. The carrier rate of HBsAg infection among the pregnant women studied based on their duration of pregnancies and their social class showed no significant differences. However, according to the factors known to be commonly associated with the highest risk of transmission of HBV such as history of blood transfusion, Tribal marks/tattooing, use of sharps, sharing of articles, history of jaundice in the women and husbands, history of sexually transmitted infections (STIs) of the women and husbands and the type of marriage (monogamous or polygamous), number of sexual relationships per week, only the history of blood transfusion was significantly associated with HBsAg carrier rate (RR = 3.71., 95% Confidence Interval (C.I.), 1.89-7.30, p = 0.0078). The study confirms that pregnant women who attend antenatal clinic in this secondary health facility are at higher risk of being infected with the HBV, which could lead to both prenatal and post natal transmission to their newborns.
基金supported by National Natural Science Foundation of China (Grant Nos 60490281 and 60621063)National Basic Research Program of China (Grant No 2007CB815104)
文摘This paper presents a Kerr-lens mode-locked Ti：sapphire laser at the repetition rate of 525 MHz, stable laser pulse as short as 10 fs with average output power of 480 mW is obtained. By injecting the pulse into photonics crystal fibre, octave-spanning spectrum covered from 500 to 1050 nm is generated, carrier-envelope phase frequency with signal-to- noise ratio of 31dB is measured, which paves the way for the generation of a compact frequency comb.
文摘针对基于载噪比(carrier to noise ratio,CNR)的GNSS干扰源定位,在存在多个干扰源、多径传输且接收机间距较远时定位难度大、精度低的问题,提出了一种加权K均值(K-Means)聚类算法与基于差分接收信号强度(differential received signal strength,DRSS)的方程解算定位相结合的多干扰源定位方法.在假设干扰源个数确定以及单个接收机只受到一个干扰源影响的前提下,设计了改进的加权K-Means聚类算法实现对多个干扰源位置的初步估计.为了进一步降低在观测接收机相距较远时加权K-Means方法的定位误差,在聚类后选取各簇内受干扰影响显著的接收CNR构建基于DRSS的定位方程组,通过方程解算得到更加精细的定位结果.仿真结果表明,所提出的定位方案可以实现对多干扰源的定位,结合DRSS参数定位后,单干扰源场景下定位误差可降低19%以上,存在两个单音干扰源的场景下定位误差可降低38%以上.
文摘针对位置欺骗如何影响接收机的问题,使用TEXBAT(Texas Spoofing Test Battery)提供的2组无欺骗干扰场景数据集和2组不同场景的GPS位置欺骗数据集,建立了GPS位置欺骗模型,分析了欺骗场景下两种相位对齐模式对欺骗攻击的影响;利用GNSS-SDR软件接收机对TEXBAT的原始高保真数字采样数据进行数据处理,分别得到软件接收机受欺骗与未受欺骗时的接收机载噪比、载波多普勒、码速率等随时间的变化情况;分析了两个位置欺骗场景对软件接收机跟踪阶段输出值的影响。实验结果表明,载噪比有大于3(dB·Hz)的波动,码速率方差会发生阶段性的增加和减少;多普勒频率的变化取决于欺骗场景的选取,不同场景的位置欺骗从不同角度有效影响了接收机定位结果。
