PAR Reduction Of An OFDM System

The mobile communication techniques developed much fast and is being carried out the transition from simple voice era to the multimedia era that the voice; data, network business is being merged, and has played more and more important roles in peoples' daily life. 1G, 2G are both narrowband mobile communication, and 3G will be only a narrowband multimedia era in theory, now the public have turned sight to the fourth generation of mobile communication, which just uses Orthogonal Frequency Division Multiplexing (OFDM ) as the key technology.OFDM is an effective data transmission technology which can be against multi-path propagation, inter-code interference and narrowband interference, and it also a high spectral efficiency. However, OFDM has its two main drawbacks: it is more sensitive to frequency offset and phase noise, and it has inherent very high peak-to-average power ratio (PAR).This thesis discussed three kinds of major technologies to reduce high PAR on the basis of the principle of OFDM system: pre-distortion technology techniques (clipping and filtering, peak windowing and companding technique), code techniques (Reed-Muller coding algorithm of Golay complementary sequence), and scrambling techniques (selected mapping, partial transmit sequence and selective scrambling), these techniques have some certain limitations. There is no domestic and oversea technique can get all good result in the following aspects: reducing PAR, calculating amount, complexity, system performance.So aiming at solving the problem of PAR reduction, the author proposed a hybrid algorithm to reduce the complexity of PAR reduction system by using the SLM method and the PTS method with the different phase searching algorithms. The results obtained indicate that the PAR and the calculating amount of system can be significantly reduced while the system performance degradation can be negligible. Then proposed a Threshold Control Algorithm (TCA) for the further reducing processing time in the scheme. We show that the hybrid system with the TCA has an additional capability for the use of a large number of side information bits resulting in better PAR reduction even compared to the PTS and the SLM.