Research of soft decision modulations based on parallel combinatory spread spectrum system

The modulation methods are discussed in parallel combinatory spread spectrum (PCSS) system. Several modulation methods which can be demodulated without threshold judging (that is soft decision) is mainly studied. The system model is built and simulated in this paper. According to the correlation of superposition PN sequences, a new soft decision QPSK modulation in PCSS system is proposed. This simulation results show that the reliability of proposed soft decision QPSK modulation is better than that of hard decision QPSK modulation and this method is useful in engineering application.