Mc-cdma System In Papr Suppression Technique

Multicarrier Code Division Multiple Access (MC-CDMA), which is a combination of two radio access techniques called Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA), has attracted more and more attentions as a very promising modulation technique. MC-CDMA can realize high spectrum efficiency and large capacity transmission. The intersymbol interference (ISI) and the influence of delayed waves are almost completely eliminated by introducing a guard time in MC-CDMA symbols.However, one of the major disadvantages of MC-CDMA is its high peak-to-average power ratio (PAPR), which require a long linear range of the high power amplifier (HPA), otherwise a significant power efficiency penalty and the degradation of the bit error rate (BER) will occur. To overcome this drawback, in this paper we investigate the PAPR problem and propose many solutions.We first discuss the construction of MC-CDMA system and the deveolpment of PAPR reduction methods. Then we research the PAPR property of MC-CDMA signal, which provides the foundation of following discussion.The paper mainly give two kinds of method on PAPR reduction:The first is on the research of spreading sequences. The paper analyze some commonly used spreading sequences, draw conclusion on their PAPR properties. Them emphasis on the allocation strategy of spreading sequences, such as using more than one kind of spreading sequences in one system, or different combination schemes of spreading sequences. In this way more candidate signals will be generated, the one with least PAPR will be transmitted. The second way is to apply the PAPR reduction methods of OFDM system into MC-CDMA system. The paper give an example of Partial Transmit Sequences(PTS) appended at the end of conventional MC-CDMA transmitter, the simulation results show that this method achieve good PAPR reduction performance.