The Passive Demodulation Technology Of Tracking, Telemetry, And Command Signals

With the development of the times, satellite TT&C(tracking, telemetry, and command) systems play an important role in civilian areas and military field. Multi-modulation technology is widely used in satellite TT&C system. This paper focuses on time-frequency characteristics, parameter estimation method and passive demodulation of unified carrier modulation signals in TT&C system. It presents five common TT&C signals, including PCM/PM, PCM/FM, PCM/BPSK/PM, PCM/QPSK/PM, DSSS/BPSK, and studies recognition, estimation, demodulation problem. The main work is as follows.In the first place, according to their different characteristics, for example, frequency spectral characteristics, squared spectral features, higher-order cumulants, carrier component and information component that obtained by orthogonal transform, and so on, we can make recognition process. Firstly, recognition the DSSS/BPSK signals by squared spectrum signal characteristic, then distinguishing the PCM/FM signals by spectral lines unity, moreover recognizing PCM/PM signals by information component. Finally, PCM/BPSK/PM and PCM/QPSK/PM signals are classified by squared and quartic spectrum features. The simulation results show that correct rate of modulation recognition is higher than 90% in SNR ?5 environment.On the basis of the reorganization, according to the signal characteristics, we can estimate the parameters, for example the symbol rate, carrier frequency subcarrier frequency, modulation index and so on. For the demodulations of unified Carrier modulation signals, this paper realized the main carrier tracking by phase-locked loop. By subcarrier signal branch processing in digital phase detector and digital frequency detector, the paper achieve the demodulation of PCM/PM signals PCM/FM signals. By tracking subcarrier signal in phase-locked loop, the PCM/BPSK/PM and PCM/QPSK/PM signals can be demodulated. By estimating pseudo-random code sequence, DSSS/BPSK can be despreaded and demodulated. The simulation results show that the demodulation performance is lower than 110? in SNR ?5 environment.