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

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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.