Research The Algorithms Of Reducing The Peak-to-average Power Ratio Of OFDM System

Orthogonal Frequency Division Multiplexing(OFDM) is a special kind ofmultiple carrier transmission technique, which has the characteristics of highefficiency spectrum、 resistance to decline ability、 anti inter-symbol interferenceability and is suitable for high-speed data transmission. At present, orthogonalfrequency division multiplexing system have many key problems which is not wellsolved. For example, it is more sensitive to doppler frequency shift and phase noiseand has a high Peak-to-Average Power Ratio (PAPR), so the applications of OFDMtechnology are limited. In order to reduce the PAPR, there are three kinds of method,which are signal distortion method、signal scrambler method and signal encodingmethod. This thesis I mainly researched the method which is used to reduce the PAPR,and focused on the algorithm of Partial Transmit Sequence (PTS) and SelectiveMapping (SLM).This paper, firstly introduces and analyses of the OFDM basic principle、keytechnology and it’s advantages and disadvantages, then analyses and summarizes themethod to reduce the PAPR; finally, puts forward two improving algorithms toreduce the PAPR. The main achievements are as follows:First, the computational complexity of the traditional PTS algorithm is very high,and has to traverse all the optional phase factors so the search complexity isexponentially increasing with the number of sub sequence. This paper, proposes aninverted binary tree algorithm with a multi-phase sequence, which combines thesymmetrical tree searching and subprime PTS and searchs out the optimal phasesequence. Simulating results show that the algorithm reduces the system complexityand suppresses the PAPR.Second, the processing of Side Information (SI) in the SLM algorithm is a hottopic around the world. The quality of SI transmission and detection processing isdirectly related to whether the receiver can recover the original signal correctly or not.This paper, towards the QPSK modulation, proposes a phase rotation algorithm thatbased on periodic sequence, which divides the carrier into the corresponding numberof size according to the cycle and then does the corresponding phase rotation on theodd cycle and even cycle according to the value of phase factor. This algorithm notonly saves the spectrum resources but also detects the SI easily in receiver. At the same time, the accuracy of recovery the original information has been improvedgreatly.The last, the conclusion of the thesis is summarized, and the achievements andinsufficiencies are analysed.Besides, an expecting of the further work is made.