The Modeling Simulation And The Verification Platform Design Of The PCSS-OFDM Communication System

Since proposed,the orthogonal frequency division multiplexing(OFDM)technique,which has high bandwidth efficiency and can combat multipath fading,has been applied to many communication fields.With the abilities of anti-interference and anti-multipath,the multicarrier code division multiple access(MC-CDMA)technique,where spread spectrum technique and OFDM technique are combined,has drawn people's attention gradually.However,because spread spectrum technique will occupied much spectrum resources in wireless communication,MC-CDMA has lower bandwidth efficiency when compared with the traditional OFDM.Parallel combinatory spread spectrum(PCSS)is an improved tamed spread spectrum,which not only inherits the advantage of spread spectrum technique,like anti-interference,but also improves the communication efficiency.In order to solve the problem of low bandwidth efficiency in MC-CDMA communication system using direct sequence spread spectrum,the PCSS-OFDM communication system which combines PCSS with OFDM and takes MC-CDMA as reference,is designed in this paper.The performances of the new communication scheme are studied.The main research contents are as follows.(1)After the theory of OFDM and PCSS is studied and the realizing way of MC-CDMA is for reference,the PCSS and OFDM are combined and two communication schemes are designed in this paper.In the first scheme,.the PCSS modulation is realized in each sub-channel of the OFDM modulation.So we can name the first scheme as orthogonal multicarrier PCSS communication scheme.In the second scheme,the PCSS modulation is realized before the serial data converts to parallel data in the OFDM modulation.So we can call the second scheme the frequency domain spread spectrum PCSS-OFDM communication scheme.Then the block diagrams of two schemes are given and the mathematical expressions of transmitter signal are analyzed.(2)The performances of the frequency domain spread spectrum PCSS-OFDM communication scheme are analyzed.The bandwidth efficiency of PCSS-OFDM scheme is discussed and compared with the one of MC-CDMA scheme.The frequency spectrum and the peak to average power ratio of the modulated signal are analyzed.The bit error rate(BER)expression equation under additive white Gaussian noise(AWGN)channel is derived.Also the BER is simulated under both the AWGN and the multipath fading channel by MATLAB.(3)The digitized demonstrate platform of frequency domain spread spectrum PCSS-OFDM communication scheme demonstrate platform has been build.The main processing unit is XC5VSX95 T,which is a FPGA of Xilinx company.The programming language is Verilog HDL and the programming environment is ISE 14.3.The software consists of serial port,the mapping of data and spreading sequence,FFT and IFFT,digital up and down converter,AWGN channel and so on.