A novel robust tuning approach based on model predictive control (MPC) for inductively coupled plasma (ICP) generation process is presented. Several key aspects related to this methodology are the modeling of the ICP generation process, robust joint tuning algorithm and semi-physical simulation of the MPC algorithm. The ICP generation process model is built by a system identification method based on steady and dynamic responses, followed by a general model predictive controller. Then, an automatic robust joint tuning (RJT) algorithm is developed for the MPC controller to quickly obtain the optimal weighting parameters. The proposed RJT algorithm can minimize the ICP generation control system's maximum total variations in the output with a specific dynamic performance requirement and model uncertainty, providing a trade-off between the dynamic performance and robustness. Finally, a semi-physical simulation system based on dSPACE and FPGA is designed to illustrate the effectiveness of the MPC controller for the ICP generation control process and the RJT algorithm. Experimental results indicate the validity and good performance of the proposed MPC controller and the RJT algorithm.

The surface of a hypersonic vehicle traveling at a speed exceeding Mach 10 is covered by a plasma sheath. The plasma sheath is a complex dynamic random medium that seriously attenuates electromagnetic (EM) waves and generates the so-called blackout phenomenon. However, owing to changes in vehicle flight parameters, such as the angle of attack, speed, and altitude, or the effects of plasma weakening control measures, the attenuation effect of the plasma sheath on EM waves weakens for a short time. At times, the amplitude of the EM waves is higher than the communication threshold, and the EM waves penetrate the plasma sheath in a so-called “communication window”. However, the random temporal variance of the plasma sheath parameters causes the required parameters of the “communication windows” to appear randomly, resulting in the traditional communication methods that needs to keep the communication link open for a long time being no longer applicable. To maximize the use of these “communication windows”, this paper proposes a short-frame fountain code (SFFC), constructs a time-varying plasma sheath channel model, and studies the relationship between the SFFC parameters and the transmission performance of this particular channel. Simulation and experimental results show that the use of SFFC improves the reliability of communication through the plasma sheath. The uninterrupted and correct transmission of information can be achieved even when the plasma equivalent frequency is close to the carrier frequency.

Radio blackout due to a plasma sheath during reentry has attracted much attention over several decades. However, radio blackout has long puzzled the aerospace industry and has not yet been completely resolved. A communication method based on adaptive classification fountain code is proposed to improve the transmission reliability of important information during a spacecraft's reentry. According to the deterioration of the plasma sheath channel, the classification parameters of the source information are adjusted to protect the most important information. This method allows the reliable transmission of the most important information. The deterioration of the communication quality of the plasma sheath channel is detected from the voltage standing wave ratio of the transmitting antenna in real time. The simulation results show that the transmission reliability of important information almost doubles when using the transmission method of adaptive classification fountain code. In contrast to the traditional communication method, the proposed method can be applied to TT&C (telemetry, tracking, and command) and communication of reentry vehicles and near-space hypersonic vehicles in the future, reducing the interruption time of communication blackout.

The phenomenon of radio blackout due to a plasma sheath during reentry has attracted much attention over the last several decades. However, radio blackout has long puzzled aerospace researchers and has not yet been completely resolved. Owing to the effects of the time-varying plasma sheath channel environment, the constellation of received signals exhibits multiple manifolds, making the traditional algorithms based on Euclidean distance unable to perform demodulation. In the current study, we proposed a novel demodulation method based on spectral clustering for phase-modulated signals interrupted by the plasma sheath channel. Experimental results revealed that as long as the receiving radio waves were above the floor of receiver's dynamic range, the proposed algorithm effectively classified received signals after time-varying plasma. The parasitic modulation interference caused by time-varying plasma was restrained effectively through the novel algorithm. In contrast to the traditional communication method, the proposed method can be applied to telemetry, track and command, as well as communication between reentry vehicles and near-space hypersonic vehicles in future.

Influenced by the special physical characteristics of the plasma sheath and the parameters of the aircraft’s attitude, the channel containing the plasma sheath can be regarded as a special kind of discontinuous channel. A code-division space-time fountain code form is proposed that is suitable for the spatial characteristics of the plasma sheath channel. Simulation results show that the use of code-division space-time fountain code maximizes the use of the airspace resources in the plasma sheath channel. The scheme proposed in this paper can be used to alleviate the “ionization blackout” problem faced by hypersonic vehicles in the reentry process.

A hypersonic vehicle is covered by a plasma sheath during flight, 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. 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 the receiver unable to receive information in the form of a complete frame, resulting in the traditional communication methods being no longer applicable. In order to receive the complete frame in random time slots and maximize the use of temporal resources of the plasma sheath channel, this article constructs a temporal-varying plasma sheath channel, proposes a soft-decision decoding algorithm for short-frame fountain codes (SFFCs), studies the relationship between the encode parameters and the characteristics of the channel, and designs communication experiments based on inductively coupling plasma (ICP). The short-frame fountain code (SFFC) has the characteristics of no-rate and short-frame, which can adapt to the short-time and random of the plasma sheath. In addition, soft-decision decoding algorithm can effectively reduce misjudgment of the receiver, reduce packet error rate, and improve the utilization of limited temporal resources of the plasma sheath channel. Simulation and experiments show that the proposed method achieves higher utilization of temporal resources of plasma sheath channel, and improves the reliability of communication. Even if the plasma equivalent frequency is higher than the carrier frequency, the uninterrupted and correct transmission of information can be realized.