Research On The Impact Of Time-varying Plasma On PCM/FM Telemetry Signal

Communication blackout problem will be encountered when aerocraft re-entersfrom out space. During that time, real-time status of aerocraft can’t be monitored whichpose a great threat to the aerocraft. Therefore blackout problem becomes one of themost urgent problem to be solved in telemetry system. In order to sovle the blackoutproblem of aerocraft, we need to understand the effect of plasma on the telemetry signalfirst. PCM/FM telemetry system is a common used telemetry system. So it is necessaryto study the effect of plasma on the PCM/FM telemetry signal first.This paper introduces the generation and characteristics of plasma, analyses effectof plasma on electromagnetic wave, uses Simulink software platform for designingPCM/FM telemetry system according to features of PCM/FM telemetry signal andcharacteristics of plasma. The design of the system includes modules of data acquisition,data recovery, modulation and demodulation, involves communication theories such assampling theorem,interpolation theorem,symbol synchronization,carrier synchronization,digital up convert and digital down convert theory. Paper structures experimentalplatform of PCM/FM telemetry system based on USRP2in which plasma channel issimulated by DPSE(dynamic plasma sheath emulator), telemetry communicationexperiment in dynamic plasma environment is based on the platform. The effect ofplasma on the PCM/FM telemetry signal is got by changing density of plasma,modulation factor of FM signal and transmission frequency of PCM/FM signal in theexperiment. BER curves of PCM/FM telemetry system in different experimentconditions are drawn from experiment data and several possible methods to improvePCM/FM telemetry system performance are also tested in the experiment.