Telemetry、Track And Communication Signals Propagation Within Dynamics Plasma Sheath

In recent years, the development and utilization of nearspace has become a focal point. With the rapid evolution of space technology, the ultra high-speed aircrafts are more widely used. But when the vehicle speed is greater than Mach 10, the air molecules near the vehicle’s surface would be dissociated and ionized to form plasma sheath, which could cause the disruption of communication, telemetry and GPS navigation This phenomenon is called "blackout", which greatly endanger the aircraft flight safety.The current mainstream solutions are simply to improve the communication frequency or to reduce the concentration of plasma sheath through some sort of intervention methods. Research shows that, even if most of the waves’ s energy can penetrate the plasma sheath, when the communication frequency is higher than the cut-off frequency of plasma sheath, the error rate of the communication system is very high. The communication is still not reliable. Therefore, the interaction between the plasma sheath and the communication signals has to be taken into account. The plasma sheath is found not steady, but dynamic, through theoretical and experimental analysis. Its effect is very different with the steady-state plasma’s. This article focuses on the deterioration of communication quality caused by the dynamic plasma sheath, expoundes the mechanism of the electromagnetic transmission in the dynamic plasmas, discovers and explains the parasitical modulation of signals due to the dynamic plasma sheath, establishes a suitable dynamic plasma sheath channel model for the communication system simulation, simulates the transmission of several kinds of TT&C signals in the dynamic plasma sheath channel, and build a dynamic plasma generator for the signals transmission in the dynamic plasma experiments. The paper’s main innovations and The author’s major contributions are outlined as follows:1. The parasitic modulation of the signals caused by the dynamic plasma sheath. In this paper is discovered and explained, We derivated the mechanism of the electromagnetic transmission in the dynamic plasmas and explained the occurence mechanism of the unnecessary parasitical modulation. The variational form of the amplitude and phase of signals is similar with the dynamic plasma’s variational form. And the relationship among the degree of modulation, the carrier frequency and the plasma parameters was analyzed.2. A suitable dynamic plasma sheath channel model for the communication system simulation is established. Based on the classic dynamic plasma wave propagation theory, we discussed some of the channel characteristics and the corresponding measure dynamic plasma sheath channel. Base on the propagator matrix method, we proposed a dynamic plasma sheath channel, and analyzed its coherence time and coherence bandwidth.3. The effects of dynamic plasma sheath on the transmission characteristics of TT&C signals such as MPSK and 2FSK signals are simulatied and analyzed. Meanwhile, we studied the spectrum characteristic and the Reduced-complexity detectors of Multi-h CPM signal, and analyed the impact of dynamic plasma sheath on Multi-h CPM.Emulational results show that: Firstly, the parasitic modulation will make the constellation of the MPSK signals to circumvolve and its judgment tolerance margin smaller. The communication quality is deteriorated. The parasitic modulation is weakened when the carrier wave frequency is much higher the plasma frequency, but the parasitic modulation still exists. And spread-spectrum technologies can enhance effectively communication quality. Secondly, parasitic modulation will lead to 2FSK signal spectrum broadening. But if the spectral interval is large enough(larger than the maximum frequency of the dynamic varying of plasma), 2FSK would have good quality, almost not affected by dynamic plasmas. At last, the continuous phase modulation is very easy affected by parasitic modulation caused by dynamic parasitic plasma sheath and difficult to work properly in the presence of dynamic plasmas.4. Built a dynamic plasma generator for the signals transmission in the dynamic plasma experiments, based on radio-frequency discharge, which output power is adjustable. We accomplished the experiment of the transmission of typical MPSK, 2FSK and Multi-h CPM signals under L/S band in the dynamic plasma. Experimental results are consistent with emulational results.