In this paper, multipath temporal spreading distributions of laser pulses are calculated when they travel through the seawater. Individual photon is followed in Monte Carlo calculation A modified Henyey-Greenstein （H...In this paper, multipath temporal spreading distributions of laser pulses are calculated when they travel through the seawater. Individual photon is followed in Monte Carlo calculation A modified Henyey-Greenstein （HG） function is applied to represent the scattering phase function of seawater. This paper proposes a new scaling method, which uses the effective scattering thickness τd to replace the optical thickness used in the traditional scaling technique. This paper compares the temporal spreading distributions of photons on conditions of different attenuation coefficients and target depths. The experiments reveal that these mutual deviations are changing in the range from 0.5% to 5%, so long as the corresponding effective scattering thicknesses τd remains the same. Therefore, a conclusion can be obtained, that the temporal spreading distribution is only dependent on the effective diffusion thickness τd .展开更多
Orthogonal frequency division multiplexing(OFDM) is an attractive technique to realize high data rate in light emitting diodes(LEDs)-based visible light communication(VLC). However, high peak-to-average power ratio(PA...Orthogonal frequency division multiplexing(OFDM) is an attractive technique to realize high data rate in light emitting diodes(LEDs)-based visible light communication(VLC). However, high peak-to-average power ratio(PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread(DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios(CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak(PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate(BER) of the system can be reduced from 0.003 7 to 0.000 287.展开更多
该文分析了天波超视距雷达(Over The Horizon Radar,OTHR)多径扩展多普勒杂波(Spread Doppler Clutter,SDC)的产生机理。由于阵列存在幅相误差且期望信号的功率大于SDC功率,自适应数字波束形成(Adaptive Digital Beam Forming,ADBF)将降...该文分析了天波超视距雷达(Over The Horizon Radar,OTHR)多径扩展多普勒杂波(Spread Doppler Clutter,SDC)的产生机理。由于阵列存在幅相误差且期望信号的功率大于SDC功率,自适应数字波束形成(Adaptive Digital Beam Forming,ADBF)将降低SDC抑制能力,同时还会导致信号对消,严重降低信噪比。针对以上问题,该文提出一种自适应抑制SDC的方法。该方法首先采用改进噪声子空间拟合自校正法消除阵列幅相误差,得到期望信号和SDC准确的到达仰角,然后采用正交投影权矢量进行ADBF处理,避免了强期望信号条件下ADBF权矢量估计不准的问题。理论分析和仿真实验表明该方法能够较彻底地抑制多径SDC。展开更多
基金Supported by the National Natural Science Foundation of China (60572015)
文摘In this paper, multipath temporal spreading distributions of laser pulses are calculated when they travel through the seawater. Individual photon is followed in Monte Carlo calculation A modified Henyey-Greenstein （HG） function is applied to represent the scattering phase function of seawater. This paper proposes a new scaling method, which uses the effective scattering thickness τd to replace the optical thickness used in the traditional scaling technique. This paper compares the temporal spreading distributions of photons on conditions of different attenuation coefficients and target depths. The experiments reveal that these mutual deviations are changing in the range from 0.5% to 5%, so long as the corresponding effective scattering thicknesses τd remains the same. Therefore, a conclusion can be obtained, that the temporal spreading distribution is only dependent on the effective diffusion thickness τd .
文摘Orthogonal frequency division multiplexing(OFDM) is an attractive technique to realize high data rate in light emitting diodes(LEDs)-based visible light communication(VLC). However, high peak-to-average power ratio(PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread(DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios(CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak(PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate(BER) of the system can be reduced from 0.003 7 to 0.000 287.
文摘该文分析了天波超视距雷达(Over The Horizon Radar,OTHR)多径扩展多普勒杂波(Spread Doppler Clutter,SDC)的产生机理。由于阵列存在幅相误差且期望信号的功率大于SDC功率,自适应数字波束形成(Adaptive Digital Beam Forming,ADBF)将降低SDC抑制能力,同时还会导致信号对消,严重降低信噪比。针对以上问题,该文提出一种自适应抑制SDC的方法。该方法首先采用改进噪声子空间拟合自校正法消除阵列幅相误差,得到期望信号和SDC准确的到达仰角,然后采用正交投影权矢量进行ADBF处理,避免了强期望信号条件下ADBF权矢量估计不准的问题。理论分析和仿真实验表明该方法能够较彻底地抑制多径SDC。
