通过对伪正交载波干涉(PO-CI)序列在不同调制方式下扩频解扩原理的分析,论证了其在复信号高阶调制(如四相移相键控(QPSK)、正交幅度调制(QAM)等)下无法正确解码,在此基础上提出了一种可行的扩频调制结构.该结构结合PO-CI扩频码,使用脉冲幅度调制(PAM)方式取代通常使用的复信号调制方式,能在仅有很小性能损失且不增加系统带宽的条件下,将传统多载波码分多址接入(MC-CDMA)系统容量提高2倍.
Through theoretical spreading principle analysis, it is proved that the benefit of pseudoorthogonal carrier interferometry (PO-CI) spreading code is not able to be supported when complex signal modulation(for example, quadrature phase-shift keying (QPSK) and quadrature amplitude modulation (QAM)) types are employed. On this basis, a feasible structure for its solution is brought forward. Within the structure mentioned, instead of complex modulation patterns, pulse amplitude modulation (PAM) combined with PO-CI spreading code is utilized, it manages to maintain the doubled throughput increase of multi-carrier code division multiple access (MC-CDMA) system with minimal loss in performance and no bandwidth expansion.