Research On The Joint Algorithm For PAPR Reduction In OFDM System

Orthogonal Frequency Division Multiplexing is a multi-carrier modulation technique, with its high spectrum efficiency and strong anti-interference ability and other advantages, it has been widely used in 4G LTE technology, and has become one of the three key technologies of LTE. However, the relatively high peak to average power is a defect in orthogonal frequency division multiplexing system which can not be ignored. High peak to average power requires the system power amplifier linear dynamic range is large enough, otherwise, it will cause the signal nonlinear distortion,resulting in the entire communication system performance degradation. Therefore it is necessary to take measures to reduce the peak to average ratio of OFDM systems. In view of this, this paper focuses on the algorithm to reduce the PAPR of OFDM system.This paper first introduced the basic principles and key technologies of OFDM system, analyzed the causes of high peak to average power. Then the definition and distribution of the statistical properties were given. Then researched and discussed algorithms to suppress PAPR in OFDM system at home and abroad, introduced the basic principles of the algorithms commonly used in various kinds of algorithms,analyzed and compared its inhibited performance, and analysis the advantages and disadvantages of various algorithms. It focused on the partial transmit sequences in probability technology, analysis the factors that affect its computational complexity and performance of the algorithm, and further studied improved PTS based on sub optimal iterative search algorithm, which can get a better PAPR suppression performance, while significantly reduced the amount of calculation of the system.Second, it focused on the constellation expansion algorithm. The basic principle is that extending the constellation points meet the requirements so that one data point has multiple mappings in the constellation, choose the appropriate transmitted constellation points. Through theoretical analysis and draw its lower PAPR problem is essentially a nonlinear programming problem, then explored the sub optimal solution. To solve this problem introduced convex set projection algorithm, and verified by simulation the POCS algorithm has a good inhibition in PAPR systems. But its disadvantage is that the convergence is slow, which does not meet the requirements of real-time communication system. And then on the basis of the algorithm, discussed the smart gradient projectionmethod which convergence is fast, and focused on the smart gradient projection algorithm to determine the optimal gradient step. Gradient projection algorithm and intelligent algorithm simulation results prove that with good suppression performance,and fast convergence. Simulation results showed that it has a very good suppression performance, and fast convergence.Finally, the algorithm focused on the joint algorithm based on partial transmission sequence and constellation expansion method. Let the optimized sequence by sub optimal iterative search partial transmission sequence algorithm via a FFT transform,and then entered into constellation expansion module based on the smart gradient projection algorithm with fast convergence. Simulation results show that the joint algorithm in this paper has good PAPR suppression performance, and lower complexity.