The Research Of Modulation Technology On Near Space TT & C Communication System And Its Simulation

To realize high quality of near space TT&C communication system, it is much more depend on the modulation technology, the research of near space TT&C communication system is mainly through the research of the characteristic of near space channel, and combined with modern efficient digital modulation and demodulation technology as well as other signal process method to process the transmitting and receiving signal of near space TT&C communication system, in order to achieve better effect at the receiving part. The paper mainly research on the highly efficient digital modulation method of near space channel transmitting system with the characteristic of constant envelop as well as DSSS combination modulation and demodulation method.This paper firstly analyzed the characteristics of near space TT&C communication system and constructed model for communication channel, then acquired the result that near space TT&C communication system have multipath interference and severe attenuation, so proposed to combine spread spectrum with strong resistance of interference , inhibition of multipath fading, and good hidden characters into the near space TT&C communication system.Secondly, compared and analyzed the modern typical constant envelope modulation technology, and got the result that QPSK have higher power efficiency and bandwidth efficiency. Meanwhile, acquired the result that in the condition of low BER, the system performance could be greatly improved with the combination of QPSK and DSSS.On the bases of above research, the article has mainly research on the combination of FQPSK and DSSS modulation technology, gave the combination modulation system of near space TT&C communication channel system, and resolved the synchronization problem which is relatively critical and difficult to fulfill. The simulation result proved that at the low rate of signal and noise, this system could also realize carrier synchronization and spread spectrum code synchronization at a better level, and finally achieve low BER of the whole system.