Design Of M-ary Spread Spectrum Communication System Combined With LDPC And Modules Realization

Spread Spectrum Communication has characteristics of strong anti-interference, resistance to multipath fading and good security. M-ary spread spectrum makes signal much more randomness compared with that of direct sequence spread spectrum. M-ary spread spectrum has stronger anti-interception and confidentiality of information.Channel coding can achieve reliable signal transmission. LDPC is one of the channel codes which is the most close to the Shannon limit,LDPC also is the one of main alternatives as the error correction code in the next generation of broadband mobile communication system.The thesis studys the non-coherent and coherent reception of M-ary spread spectrum system, advantages and disadvantages of both systems are analyzed; For the M-ary despreading and demodulation, the current symbol is the symbol corresponding to the biggest correlation value. For LDPC decoding in this kind of system, BF algorithm is usually used, but for M-ary despreading correlation value, the size of the correlation value of each branch reflects the reliability of the corresponding symbol. Based on this, combined the demodulation and decoding, two improved BF decoding algorithms are proposed. Meanwhile, considering system requirements of the anti-jamming, anti-interception, anti-reconnaissance and reliability, the M-ary spread spectrum system combined the fountain code,CRC check code and LDPC code is given. The system scheme is designed.The parameters of the system are analysed and given. Finally the corresponding modules are realized.