Shells On The Information Transmission Modulation And Demodulation Techniques

Missile data transmission system is used in the transmission between the ground and flying objects with a great speed, especially in the fields such as aviation, aerospace and missile, which have strict demands of the transmission system on confidentiality, anti-interference, real-time, quality and the removal of Doppler shift.To meet the demands of the missile data transmission system, direct-sequence spread spectrum system (DSSS) is chosen as a modulation/demodulation solution which is fully simulated, designed and verified. The software radio design method is used to reduce the system which conventionally comprised of several dedicated chips to a single FPGA chip and a complete missile data transmission system is built via this method based on DSSS.The system is comprised of a receiver and a transmitter, with a chip rates as high as lOMcps, whose functionalities such as code/decode, modulation/demodulation, filtering, etc. are implemented by software with the ability to reconfigure their parameters and behaviors via the software while the hardware remains the same. Therefore the flexibility and compatibility of the system are greatly improved. A Doppler shift of 26.7 kHz, which is produced by the fast flying objects, is removed in digital signal process, which also fulfills carrier recovery and signal demodulation. USB2.0 protocol is selected as a high-speed interface between the system and the host, and as a substitution for the conventional serial port and other chip-dedicated low-speed interfaces, USB2.0 has a good popularity.