Research On Technology Of Peak-to-average Power Ratio Reduction In OFDM Systems

Orthogonal Frequency Division Multiplexing(OFDM)is a kind of multi-carrier transmission technology,it has high spectrum efficiency and good anti-multipath performance,but the Peak-to-Average Power Ratio(PAPR)of the OFDM system is very high,and it will reduce the performance of the system.So we need to solve the high PAPR of the OFDM system urgently.This paper will give the research on the techniques for OFDM Peak-to-Average Power Ratio reduction,and it mainly includes the following respects:Firstly,this paper starts from the background and development of the OFDM technology,makes a simple introduction of the principle of OFDM and its advantages and disadvantages,then studies the definition and distribution of the PAPR of OFDM system,and makes a summary of three kinds of methods of reducing PAPR,finally Selective Mapping(SLM)is discussed in detail.SLM requires many times IFFT operation in the process of reducing PAPR of OFDM system,this will make system complexity increasing.In order to solve this problem,this paper will introduce the idea of selecting the fixed phase sequence according to the order.Firstly setting the PAPR that the system can accept,then choosing the phase sequence one by one according to the order of the phase sequence until the PAPR of the OFDM signal meets system requirements.Under the condition of keeping the effects of reducing PAPR of OFDM system,this algorithm reduces the number of IFFT operation effectively,so it can reduce the complexity of the system.SLM algorithm uses Cross Entropy(CE)algorithm to get the most optimal phase sequence so that SLM can make the effect of PAPR Reduction achieve optimum.However,it needs too many times iterative computations,so it will increase the complexity of the algorithm.In order to solve this problem,a fast convergence factor was introduced in the CE-SLM algorithm to reduce times of iterative computations to get the most optimal phase sequence.This algorithm reduces the iterative times of getting the optimal phase sequence under the condition of having the same effect of reducing PAPR with the CE-SLM algorithm,eventually reducing the complexity of the algorithm effectively.Clipping algorithm is easy to realize and has a good effect on reducing PAPR of the OFDM system,but it will rise the error rate of the system because of it makes the signal directly intercept.To solve this drawback of clipping technique,this paper introduces CE to clipping algorithm,when the peak of signal is greater than the system allows,applying the CE algorithm to optimize the phase sequence used in SLM algorithm until the PAPR of the signal meets system requirements.The improved algorithm keep the same effect of reducing PAPR of OFDM system with the clipping algorithm,it doesn't introduce nonlinear distortion and effectively solves the drawbacks that the clipping algorithm make the error rate of the system rise.Finally,making a summary of the work has been done,and looking forward to the direction for future research.