Research on Digitalized Spread Spectrum Communication System Using Real-Valued Sequences

该项目于1998年至1999年完成，目的是为无信道间干扰和码间干扰的准同步码分多址系统开发实值序列，并为该码分多址系统实现实验性的去噪调制解调器，为目前的码分多址系统带来一种新的技术。本研究的目的基本达到。由于构造了适用于快速信号处理算法的实值序列，因此在现场可编程门阵列上实现了码生成和相关的数字快速处理器。在多址实验中，相关处理的性能基本达到了设计值。本研究开发的实值有限长序列对于设计不受保护间隔的高效数据传输的码以避免干扰是有效的，本课题的主要成果如下：(1)研究了码分多址系统中的码分多址序列和快速相关算法。(2)码产生器和相关器的试制。对长度为33的实值移位正交有限长序列，采用只读存储器和相关器，分别对应10,000个逻辑门，实现了码产生器和相关器的组合运算(3)码分多址传输实验基于两个实数有限长序列的光和空间复用传输实验表明，相关器输入端的0dBD/U比提高到了40dBD/U输出端的D/U比，在误差允许的范围内满足正交性。

This project has been performed from 1998 to 1999, for the purpose of developing real-valued sequences for a quasi-synchronous CDMA system with no interchannel interference and with little intersymbol interference and implementing trial degitalized modems for this CDMA system, to bring a novel technique to the current CDMA systems. The aim of this research is nearly attained. Digital fast processors of code generation and correlation are implemented on FPGA, because of construction of the real-valued sequences applicable to fast signal processing algorithm. Performances of correlation processing in the multiple access experiment almost follow those of designed values. The real-valued finite-length sequences developed in this research are effective to design the codes of high efficiency data transmission free from the guard interval to avoid interferences, and so expected to be developed to the future concrete application system.The achievements of this project are the followings.(1) Developments of the sequences for CDMA and the algorithm of fast correlationOrthogonal sets of real-valued finite-length sequences with sharp autocorrelation function are derived from the convolution of element sequences that leads to fast correlation algorithm.(2) Trial production of code generator and correlatorThe code generator using ROM and correlator using FPGA corresponding to 10,000 logic gates are implemented for the aproximated integer sequence from the real-valued shift-orthogonal finite-length sequence of length 33.The combining operation of 8-bit generator output and 8-bit correlator input presents 16Mchips/s rate and correlation pulse of 1% error.(3) Experiment of CDMA transmissionThe experiment of optical and spatial multiplexing transmission based on two real-valued finite-length sequences shows that 0dB D/U ratio at the correlator input is improved to 40dB D/U ratio at its output, satisfying the orthogonality within allowable error.