Research On Reducing Peak-to-average Power Ratio Of Orthogonal Frequency Division Multiplexing System

Orthogonal Frequency Division Multiplexing (OFDM) is a kind of multi-carriertransmission technology, as the core technology of4G, which has high spectrumefficiency and an excellent resistance against multipath fading and interference. However,if the peak to average power ratio (PAPR) is high, the system will produce signaldistortion and make the transmission efficiency extremely degrade. For transmittingterminal and the receiving terminal, the high power amplifier have to meet a certainrequirement, making the transport cost increase. Therefore reducing the PAPR is one ofimportant technologies of OFDM system. In this paper, we will research how to reducepeak to average power ratio of OFDM system.Firstly, we propose an improved partial transmit sequence method based on thepartial transmit sequence method to reduce PAPR of OFDM system. In this paper, theimproved Particle Swarm Optimization algorithm can find the optimal phase factor. TheParticle Swarm Optimization can find the minimum fitness function by iteration and thenfind the optimal phase factor, reducing the PAPR of OFDM system, avoiding into localoptima, and reducing the complexity of the calculation. Performance of this algorithm isverified by simulation.Secondly, cross entropy algorithm is applied to the partial transmit sequence method.Because in the partial transmit sequence method, it is so important to find the phasefactor and the search for the phase factor can be seen as NP-hard problem. For solvingsuch problems, the cross entropy is a very practical method, obtaining the optimalsolution by solving the probability estimates, reducing the PAPR of OFDM system,accelerating the search speed and improving the precision of search. Then the parametricminimum cross entropy method is applied to the partial transmit sequence method.Parametric minimum cross entropy method through sampling for the phase factor,compared with the traditional PTS method, avoid the exhaustive search and reduce thecomplexity of the search; Compared with the partial transmit sequence method based oncross entropy, reduce the PAPR of the system further. And two kinds of improved algorithm are verified by the simulation.Finally, the partial transmit sequence method based on parametric minimum crossentropy is combed with clipping algorithm. Parametric minimum cross entropy algorithmreduce the computational complexity and PAPR, coupled with clipping algorithm,achieving the optimal effect of reducing PAPR at last. And the improved algorithm isverified through the simulation.