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The time-varying plasma sheath can potentially degrade electromagnetic systems through increasing time-varying amplitude attenuation and phase fluctuation. The BPSK modulated GPS signals could be affected by phase fluctuation. Utilizing electron density and collision frequency provided by NASA, transmission coefficient is calculated by using the scattering matrix method and phase fluctuation characteristic is obtained. GPS signal affected by phase fluctuation are acquired by the Hilbert method. Then by means of Electromagnetic propagation theory and GPS software receiver, the effects of phase fluctuation caused by plasma sheath on GPS signal and its positioning before there occurs blackout are analyzed. Results show that the effect on positioning accuracy is closely related to the variance of phase fluctuation. When the calculated variance is 0.1142, the maximal percentage of variation larger than 5m is up to 14% and the percentage larger than 10m is up to 1.5%. [ABSTRACT FROM AUTHOR]

An experiment of electromagnetic wave propagation in plasma is proposed to obtain the attenuation characteristics of L and S band electromagnetic waves. The controllable large scale plasma is generated based on the glow discharge principle in low pressure gas to reproduce a 'blackout' phenomenon with long duration in an environment of the ordinary laboratory. The attenuation characteristics versus electron density of electromagnetic wave at 1. 57GHz and 2. 49GHz are obtained, and then the experimental results are compared with two theoretical expected values, the classical theory and thin-layer theory. The experimental results support the validity of the classical theory, the attenuation trend is consistent with that expected in classical theory, and the thin-layer effect is not observed under the condition that the plasma thickness is about 1 and 1.5 times of wavelength. [ABSTRACT FROM AUTHOR]

Because the boundary layer of the plasma sheath formed around the hypersonic vehicle flying in atmosphere is turbulent, the parameters of plasma sheath such as the electron density and so on become time-varying. The effects of electron density fluctuations on electromagnetic wave propagation are focused in this paper. Both amplitude and phase of EM signal are modulated by the time-varying plasma, and the modulation has much to do with the carrier wave frequency and the plasma parameter. The EM signal propagation through the time-varying plasma is simulated under different conditions in this paper, and the propagation of QPSK signals is simulated, when carrier wave frequency is 35GHz and 12GHz. The simulation results demonstrate that the modulation will make the constellation of the QPSK signals circumvolving, and the modulation is weakened when the carrier wave frequency is much higher than the plasma frequency. [ABSTRACT FROM AUTHOR]

The X-ray pulsar with weak signal buried in strong noise leads to the low signal-to-noise ratio of folded pulse profiles in short time, both estimation accuracy and efficiency are affected. A denoising method for X-ray pulsar is proposed in the paper. By preprocessing and folding the pulse profiles, and the measured data are employed for Daubechies wavelet, the SNR of pulse profile is improved. The RXTE data are used for verification and the simulation results show the method proposed can eliminate the noise from equipments and space environment, thus shorting the observing time and improving the efficiency of X-ray pulsar navigation without reducing the accuracy of TOA. [ABSTRACT FROM AUTHOR]