Abstract
During the reentry process, the plasma sheath covering the surface of the hypersonic aircraft will cause the amplitude attenuation and phase jitter of the communication electromagnetic waves. Channel parameters such as the electron density and collision frequency of the plasma sheath reflect the changing trend of the plasma sheath, and these parameters can be measured by physical means. However, these parameters cannot directly reflect the change of the channel communication ability and cannot directly serve the design of communication methods in the plasma sheath. Due to the particularity of the plasma sheath, the traditional channel estimation method for Additive White Gaussian Noise channels will no longer be applicable. This paper presents a channel capacity estimation method for dynamic plasma sheath. First, the plasma sheath is equivalent to a discrete input continuous output memoryless channel, and then the channel capacity expression is derived according to Shannon formula. Finally, the channel capacity of the dynamic plasma sheath is estimated by calculating the transition probability density function. The simulation results show that the channel capacity of the dynamic plasma sheath is affected by both the signal-to-noise ratio (SNR) and the dynamic parameters of the plasma sheath. When the electron density is small, the channel capacity is mainly affected by the SNR. As the electron density increases, the dynamic parameters of the plasma sheath gradually become the main factor affecting the channel capacity. This method is a theoretical analysis of the channel capacity when the channel parameters of the plasma channel are known, and it is meaningful for conducting the work of communication methods design.
Highlights
When a hypersonic vehicle is flying in the atmosphere at hypersonic speed, owing to the tremendous heat generated by air compression and ablation surrounding the vehicle, a plasma sheath covering the vehicle is generated [1]. e plasma sheath attenuates the energy of communication signal and influences the quality of the signal which will lead to lost or at least severely degraded communication, telemetry, navigation signals, etc. [2,3,4]
As shown by the blue curve (Ne 4 × 1017m−3), when the signal-to-noise ratio (SNR) is increased from −5 dB to 5 dB, the channel capacity is increased by about 60%. is is mainly because the proportion of useful information in the channel increases with the increase of SNR, which leads to an increase in the system transition probability, so the overall channel capacity shows an upward trend
The channel capacity calculation method for dynamic plasma sheaths under different modulation systems can be derived from the Shannon formula. e variation of the PSK channel capacity under the dynamic plasma sheath channel can be summarized as follows: (1) Parasitic modulation effects can cause severe rotation and distortion of the constellation of the phasemodulated signal
Summary
Received November 2019; Revised 4 March 2020; Accepted March 2020; Published 9 April 2020. The plasma sheath covering the surface of the hypersonic aircraft will cause the amplitude attenuation and phase jitter of the communication electromagnetic waves. Channel parameters such as the electron density and collision frequency of the plasma sheath reflect the changing trend of the plasma sheath, and these parameters can be measured by physical means. As the electron density increases, the dynamic parameters of the plasma sheath gradually become the main factor affecting the channel capacity. As the electron density increases, the dynamic parameters of the plasma sheath gradually become the main factor affecting the channel capacity. is method is a theoretical analysis of the channel capacity when the channel parameters of the plasma channel are known, and it is meaningful for conducting the work of communication methods design
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