Research On The Performance Effect Of High-dynamic Doppler Offset On PCM/FM Telemetry Signal

Currently, PCM/FM mechanism is mainly utilized in the telemetry system of our country, because of its high accuracy and the flexible frame format of telemetry signal, which makes fast data process at both transmitter and receiver possible in telemetry systems. Thus, the telemetry system with PCM/FM mechanism can make use of large-scale and very large-scale integrated circuit and has the advantages of directly connecting with terminals for data processing. Considering these merits, telemetry technology based on PCM/FM is widely applied in spacecraft field, such as missile, satellite and rocket.Telemetry systems usually works in highly dynamic environment and aerospace crafts fly at high speed under complex and changeable orbit, leading to a displacement shift between craft and receiver and the existence of a Doppler offset at receiver. As we all know, Doppler offset depends on the speed of the craft and the frequency of the carrier. The higher its speed and frequency, the more violent change its orbit, and the higher the Doppler offset in receiver, the severer effect on the demodulation performance of receiver, and thus affecting the reliability of telemetry systems. Consequently, it is a focus in this field to research on the effect of Doppler offset on telemetry signal and further to propose novel methods to refrain signals from Doppler offset.This paper is to verify how Doppler offset affects the performance of telemetry systems. Firstly, we study on modulating and demodulating technologies for PCM/FM telemetry signals by theoretical analysis as well as simulation experiment, discuss time-frequency features of PCM/FM signals, and emphatically deal with the effect of highly dynamic Doppler offset on received signals. Secondly, On the basis of synthetically channel model, through theoretical analysis and simulation,the performance of PCM/FM telemetry communication system under highly dynamic flying scenes is evaluated. It is shown that when operating non-coherent demodulating methods, its performance still acceptable under lower Doppler offset. However, the performance gets worse and worse, if Doppler offset is higher. For highly dynamic Doppler offset, the performance is decreasing very fast. Doppler offset eliminating module is embedded into receivers. At last, we build a simple telemetry communication system with the software of Lab VIEW and USRP, and evaluate the performance of the telemetry communication system, which deepens the understanding of telemetry communication systems.