Adaptive Space-Time Short-Frame Fountain Code With Plasma Sheath Channel

A hypersonic vehicle is covered by a plasma sheath during reentry, which seriously attenuates the power of electromagnetic (EM) waves and generates the so-called radio blackout phenomenon when the equivalent frequency of plasma is greater than the carrier frequency. However, the parameters of plasma sheath vary randomly with time and axial distance. The variation produces some random time slots where the equivalent frequency of plasma is lower than the carrier frequency, so the EM waves can penetrate the plasma sheath. Random time slots cause receiver unable to receive information with the form of complete frame, resulting in the traditional communication methods being no longer applicable. In order to receive the complete frame in random time slots and make full use of the spatial-temporal resources of the plasma sheath channel, we construct a spatial-temporal-varying plasma sheath channel mode, propose an adaptive space-time short-frame fountain code (ASTSFFC), and study the relationship between the ASTSFFC parameters and the characteristics of the channel. The ASTFFC has the characteristics of no-rate and short-frame, which can adapt to the short-time and random of the plasma sheath. In addition, ASTFFC contains an adaptive multilevel coding matrix to deal with the massive changes of plasma sheath parameters during reentry. Simulation shows that the proposed method achieves higher utilization of spatial-temporal resources of plasma sheath channel, and improves the reliability of communication by adaptively adjusting the coding strategy. When the plasma equivalent frequency is lower than the carrier frequency, information can be transmitted at high speed. Even when the plasma equivalent frequency is close to the carrier frequency, information can also be transmitted correctly.

Automated summary

During reentry, a hypersonic vehicle is covered by a plasma sheath, causing attenuation of electromagnetic waves and resulting in radio blackout when the equivalent frequency of plasma is higher than the carrier frequency. However, the parameters of the plasma sheath change randomly, allowing some random time slots where the plasma's equivalent frequency is lower than the carrier frequency, enabling electromagnetic waves to penetrate the sheath. In order to make use of the plasma sheath channel's spatial-temporal resources and receive complete frames in random time slots, an adaptive space-time short-frame fountain code (ASTSFFC) is proposed.