Research On Reducing The PAPR In OFDM System

With the rapid development of wireless communications technology, the combination of high-speed multimedia data services including voice, picture and data are more and more popular, the research in data transmission technology of real-time and high-speed turns into a hot spot. OFDM (Orthogonal Frequency Division Multiplexing) technology with good performance on anti multipath interference and inter symbol interference attracts more and more attention.The main idea of OFDM is firstly to transfer the high-speed serial data stream into multiple parallel low rate data stream, and then map them to a group of orthogonal sub-carriers, so that the original channel is devived into many subchannels, OFDM symbol's time of duration is more than single-carrier symbol's, so it is much better than single-carrier on anti-multipath interference and inter symbol interference.However, its output signal is formed by multiple sub-channel signal, which can easily cause high PAPR.The transmitter power amplifier needs to have good linearity in order to avoid occuring signal distortion during its transmission. Conversely, if the amplifier's linearity can not achieve the requirements of the range of signal change, then the signal distortion occurs, which will destroy the orthogonality of subchannels, so the OFDM system needs to reduce its PAPR.This paper mainly makes a researchment on how to reduce the peak to average power ratio of OFDM system.Paper firstly reviews the historical development of OFDM technology, and then explains the principle and key points of OFDM, also introduces the definition of peak to average power ratio and distribution of OFDM system. Then mainly discusses several methods to reduce the PAPR of OFDM system including clipping,SLM and PTS, then simulate them through MATLAB to demonstrate their effections on reducing PAPR in OFDM system.Finally, puts forward two improved algorithm, the first one is a combined algorithm of Clipping and PTS,which firstly makes use of the linear of PTS to reduce the PAPR, and then operates Clipping to Suppress the PAPR, in this case, noise which is generated by interfence is significantly reduced.The second one is an improved SLM method which selects the send sequence according to the randomness of the candidate sequence,it only needs one IFFT module and it reduces the complexity of the system. Finally, the MATLAB simulation proves that the combined algorithm has obvious effects result to reduce the peak to average power ratio, it also proves the improved SLM algorithm has about the same effection on reducing PAPR of OFDM system compared to the conventional SLM algorithm, but on the complexity of the system implementation, the improved SLM method is better than the original SLM algorithm.