Theoretical Research And Algorithm Realization Of PAPR In MC-CDMA System

Multicarrier communication technology, particularly in the MC-CDMA system which owe to the inhibition spectrum frequency-selective fading and the high spectrum-using efficiency, is suitable for high-speed data transmission technology in wireless environment. However, the high peak-to-average power ratio has always been one of the main obstacle to it widespread application, the article dose a lower system algorithm PAPR improvements and research in MC-CDMA system.First of all, the fundamental principles of OFDM-CDMA system are introduced. The study is focused on MC-CDMA system. Paper according to analyze the process of signal delivering in MC-CDMA system, then make sure the reasons of high PAPR , and combined with the current researches on reducing PAPR schemes. In the article, we summarize the problems needed to be resolved and proposed lowering of the existing PAPR algorithm improvement.In view of the performance of wireless communications systems mainly by mobile communication channel restrictions, and mobile communication channel also showed strong randomness and unpredictability, in the third part of this paper is to establish MC-CDMA system channel model. Through Simulink got a multi-path fading channel amplitude frequency response simulation map. The simulate result shows that is an ideal slow fading channel model. Because of MC-CDMA system synchronization in high demand and the slow decline of time-varying channel can be effective in raising circuit response. This part gives technical support to the next two parts.Signal pre-distortion technology is the most extensive application method to control the PAPR. However, the signal cutting nonlinear distortion will lead to in-band distortion and out-of-band radiation. Particularly when threshold is low, clipping noise performance the major obstacle. In the fourth part, though analyze the pre-distortion of signal to know that the technology is only a compromise between the in-band distortion and out-of-band radiation in reducing PAPR. In this part, based on the relationship of the loss of power and limiting noise power we get an improved clipping noise suppression algorithm, and through analysis of the mathematical simulation model and experimental verification of the algorithm. Using this method, especially in multi-carrier, multi-user circumstances can reduce the PAPR.In the fifth part of this thesis, According to the signal lower-distortion algorithm's main ideas, and in view of the Logistic chaotic map with the strong self-related, inter-related features. One can do chaotic sequence as spread spectrum sequence in spread spectrum communication to change the phase sequence in order to reduce the high probability of PAPR. At the same time, due to the non-cyclical and chaotic sequence of the initial parameters of the highly sensitive nature, it can make a lot of different sequence spread spectrum collection; the final generation of launch sequence not appears to repeat the cycle, thereby maintaining low PAPR. Through mathematical analysis and simulation experiments proved that the Logistic map is prior to do spread spectrum sequences in MC-CDMA system, and through comparing the simulation with the traditional sequence prove that apply Logistic chaotic spread spectrum sequence can improve the PAPR and BER in MC-CDMA system.