Wireless Spread Spectrum Data Transmission Technology Research

The transmission channel between flight equipment and ground-based observatories is complex. In order to achieve wireless transmission in the open space, system need to use spread spectrum communication technology. This technology could improve system's anti-noise, anti-interference ability. This paper has studied the base-band spread spectrum communication technology, and detailed analysis of the characteristics of spread spectrum communication and their reasons.This paper focuses on the work of digital down conversion and suppression of carrier tracking. It has introduced the principle and algorithm of digital down conversion and suppression of carrier tracking. Because classical carrier tracking loop does not apply in the high-speed conditions, this paper makes a modified digital COSTAS loop, combined with digital down conversion and suppression of carrier tracking. The modified digital COSTAS loop has simulated and analysis in the MATLAB.Reference of the internal structure of Spread Spectrum chip Z87200, we realize a spread spectrum baseband processor at FPGA platform. The processor contains digital oscillator, spread spectrum modulation, digital BPSK modulation and digital COSTAS loop. In order to be a reasonable application of the baseband processor, this paper designs a U disk directory inquiry system. Files in U disk are sent by the baseband processor after spread spectrum processing. Then the receiver despread and transfer to a computer terminal.