Abstract
To improve the anti-interference for ELF/VLF communication based on modulated heating lower-ionosphere, chirp spread spectrum technology with strong anti-interference is combined with square wave amplitude modulation, a novel method of chirp-BOK modulated heating lower-ionosphere is proposed in this paper. On this basis, to improve the radiation efficiency of ELF/VLF, the effects of heating parameters (effective radiation power, pump frequency, polarization mode, modulation frequency, duty cycle, and bandwidth) on the radiation efficiency of ELF/VLF were analyzed. The results show that the radiation amplitude of ELF/VLF increases with the increase of effective radiation power, while the radiation efficiency increases first and then decreases; the X-mode is better than the O-mode; the radiation intensity of ELF/VLF decreases with the increase of pump wave frequency from 4MHz to 10MHz; the ELF/VLF equivalent dipole moments increase with the rise of modulation frequency from 500Hz to 5kHz; with the change of duty cycle from 10% to 90%, the dipole moments first increase and then decrease, and the optimal range of duty cycle is 40% to 70%; with the increase of bandwidth, the dipole moments are unchanged. Furthermore, the ELF/VLF dipole moments of square wave amplitude modulated heating ionosphere is unchanged before and after the chirp spread spectrum.
Highlights
Low frequency (ELF:0.3-3kHz) and very low frequency(VLF:3-30kHz) radio wave has very efficient long-range propagation in the earth-ionosphere waveguide and relatively deep penetration into conducting media, such as earth and seawater
In [15], Cohen et al presented a summary of nearly 100 days of Extremely low frequency (ELF)/VLF wave generation experiment at a variety of ELF/VLF frequencies, seasons, and times of day based on AM heating the ionosphere
To improve the ELF/VLF radiation efficiency, we investigate heating parameters on the radiation efficiency of ELF/VLF by chirp-BOK modulated heating lower-ionosphere at mid-low latitudes, and obtain many valuable conclusions, which may provide some constructive suggestions for choosing the best experimental parameters in ionospheric modulated heating experiments at mid-low latitudes in the future
Summary
Low frequency (ELF:0.3-3kHz) and very low frequency(VLF:3-30kHz) radio wave has very efficient long-range propagation in the earth-ionosphere waveguide and relatively deep penetration into conducting media, such as earth and seawater. In [15], Cohen et al presented a summary of nearly 100 days of ELF/VLF wave generation experiment at a variety of ELF/VLF frequencies, seasons, and times of day based on AM heating the ionosphere. To enhance the anti-interference performance and robustness of the ELF/VLF communication system, CSS is combined with the technology of modulation heating ionosphere in this paper. The most commonly used modulation method in ionospheric heating experiments is amplitude modulation(AM), and the square wave AM has the highest radiation efficiency of ELF/VLF among the typical AM waves [13], [23]. A novel method of chirp-BOK modulated heating lower-ionosphere is proposed based on square wave AM from the perspective of communication in this paper.
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