A Time Division Duplex CDMA System Using Asymmetric Modulation Scheme in Duplex Channel

Multi-carrier (MC) signal has a large peak to mean envelope power ratio, so that the MC signal suffers from a high level of inter-modulation distortion due to the nonlinearity of the power amplifier stage. For portable terminals, it is undesirable to use linear amplifiers because high power efficiency is needed. To solve this problem, we propose a time division duplex (TDD)–code division multiple access (CDMA) communication system which uses an asymmetric modulation scheme between the forward and reverse links. The system consists of multicarrier modulation for the forward link and single carrier modulation for the reverse link. A pre-equalization method for the forward link transmission is also presented in this paper. In frequency selective fading, the system achieves a path diversity effect without any channel estimation unit at the mobile station by using the pre-phase equalizer. From the simulation results, it it found that the proposed system achieves better BER performance than the conventional MC-CDMA system and the single carrier RAKE system equipped at the mobile unit since the proposed system has the ability to suppress other user interfering signals. key words: multi-carrier, CDMA, transmission diversity