Missile Command Transmission System Design

The command transmission system in antiaircraft missile is an important constituent part of the command guidance weapon system, which must be ensured not only receiving guidance commands fast, accurately, real-timely, but also resisting against the electronic jamming, pressing or deception from the enemy. In view of the demands that the good system performance in real-time, confidentiality, anti-interference and automatic error correction function need be insured, and it must be abated that the information transmission is harmed by the Doppler frequency shift coming from high speed flight in practical application, the missile command transmission system was carried out in this paper.Considering the complexity of the electromagnetic environment in battlefield, a method based on Direct Sequence Spread Spectrum(DSSS) is adopted in the information transmission system. After analysis and comparison, the nonlinear Gold sequence is chosen as the spreading code, which improves the anti-interference and confidentiality in the process of communication. A channel coding scheme based on convolution and intertwined cascade is utilized so that the system can automatically correct the bit error coming from the channel transmission, which improves communication reliability. The Costas digital loop is applied to tail after the carrier frequency offset, which eliminates the information transmission harmed by the Doppler shift coming from high speed flight. To avoid the faults that the parameters of a system composed by a plurality of dedicated chip are changed difficultly and the system bulk is large, in this paper, a FPGA core hardware design based on the software radio idea is adopted to realize the digital modulation and demodulation functions in intermediate frequency(IF), which allowed that the system can be configured by software and be flexibly upgraded and extended in function easily, and lessened the system volume. The broadband IF band-pass sampling digital structure is used to reduce the requirements on the performance of ADC system, the difficulty of hardware realization and the cost of hardware.In this paper, the design and the parameter analysis of a system based on a DSSS communication system are completed. The feasibility of the scheme is verified using simulation tools such as Matlab. The module functions of the system are achieved in a FPGA board by the Verilog programming language.