Research On Transmission Modes And Soft Demodulation Technologies Of PCSS System

To satisfy the demand for high-speed and efficient transmission of wireless communication system and take advantage of Parallel Combinatory Spread Spectrum(PCSS)communication system,PCSS system transmission mode and its modulation methods are studied.In order to improve the performance of PCSS system,some existing sequence combined-transmission modes are discussed in details.According to existing "baseband constant superposition" sequence transmission scheme,two new schemes of "band-pass constant amplitude superposition" and "base-band and band-pass superposition" of PCSS system are proposed.Mathematical models and their characteristics of this three transmission schemes are established,analyzed and compared.BER performance in the Gaussian white noise conditions of the three schemes of PCSS system are compared.Multipath propagation is added on Gaussian white noise,and anti-interference and anti-multipath fading capacity of three PCSS schemes is compared through software simulation,and the feasibility of the scheme in certain application scenarios is verified.In order to reduce the complexity of PCSS system and improve the BER performance of the system,basing on the studied of spread spectrum sequence modulation soft decision algorithm,weighted soft decision method in QPSK modulation system and direct soft decision method in BPSK modulation are proposed.The weighted soft decision algorithm recovers the relevant characteristics of spread spectrum sequence by introducing weighting coefficient to weighted sum the received two way correlation values.The direct soft decision algorithm demodulates and despreads at the same time by taking correlation calculation directly to the received signal.Through software imitation,the soft decision algorithm was verified to be easier and more reliable than the hard decision algorithm.