Research On The Technologies To Redue The PAPR In MC-CDMA System

Multi-carrier code division multiple access (MC-CDMA), which is a new technology in the field of mobile communications, is the combination of orthogonal frequency division multiplexing and spread spectrum communication technology. As one of the key technologies of the next generation mobile communication, it also can against the multipath interference, has the effect of frequency diversity and high spectrum efficiency, etc. But as one kind of multi-carrier modulation communication system, some inherent weaknesses has been inherited in the MC-CDMA system, and the high Peak-to-Average Power Ratio (PAPR) is one of the major drawbacks of MC-CDMA system. The high PAPR requires an A/D or D/A converter and a power amplifier have a very wide linear working range, which can result in the waste of resources and increasing power consumption of mobile devices. In this paper, a variety of methods to reduce the PAPR of MC-CDMA system is studied and some improved schemes are proposed.In this paper, the basic principle of OFDM Technology is introduced, then the principle and performance of three kinds of technologies which combine OFDM technology and CDMA technology are analyzed, especially the MC-CDMA system. Then the paper gives the definition of the PAPR and analyzes the reason why the MC-CDMA system causes high PAPR. Then, the paper analyzes the principle of three Methods which can reduce the PAPR in MC-CDMA system. They are the pre-distortion techniques, coding techniques and the probability techniques.The paper also analyzes the principle of two typical probability technologies—selective mapping method (SLM) and partial transmit sequence method (PTS). And then, according the two algorithms, the paper proposes two kinds of improved methods. First, an improved SLM is proposed which the phase sequence is embedded on the check symbols of the MC-CDMA data block after channel coding, avoiding the loss of transmission speed which is caused by the usage of transmission side information. Then after the usage of clipping method, the improved method has a better PAPR reduction performance. The simulation result shows that the improved method has a better performance than the traditional SLM method in the situation that both the two methods have the similar bit error rate. Secondly the paper proposes an improved PTS-Clipping combined algorithm according to the traditional PTS. The signal is firstly dealt with by a improved PTS method in the time domain, and then processed by the repeated clipping-filtering method in the frequency domain. Using the complementary of the two methods in performance, the combined algorithm has a better performance in reducing the MC-CDMA system PAPR as well as making the computing complexity down.