Research On PAPR Reduction Methods Based On Low Complexity Precoding For OFDM Systems

Orthogonal frequency division multiplexing(OFDM)is an efficient multi-carrier transmission scheme.Nowadays,OFDM is extensively adopted in high data rate communications systems for its advantages of robustness against narrow band interference and frequency selective fading,high spectral efficiency,high quality service and good design flexibility.However,there are some shortcomings of OFDM technology,especially its high peak average power ratio(PAPR)problem,which greatly limits its practical application and development.In OFDM systems,there are a large number of non-linear devices.When OFDM signal passes through these devices,its peak tends to fall into the non-linear region,resulting in serious in-band distortion and out-of-band interference,thereby degrading system performance.This paper aims to study the high PAPR problem of OFDM systems and propose innovative solutions.This paper first introduces the development of OFDM and the evolution of its standard.Then the basic principles of OFDM and the key technologies involved are introduced.After that,this paper analyzes the theoretical reasons for the high PAPR problem of OFDM and introduces three kinds of PAPR reduction techniques.Furthermore,the typical PAPR reduction algorithms are simulated and analyzed.In addition,this paper also introduces the over-sampling technique and the high-power amplifier technique which are often involved in PAPR reduction studies.Most RAPR reduction methods for OFDM systems achieve PAPR performance improvement at the cost of system complexity,bit error rate performance or spectral performance.To solve the problem,a low complexity Walsh-Hadamard precoding algorithm is proposed to achieve PAPR reduction.The algorithm combines the Walsh-Hadamard precoding matrix and IFFT matrix into a single fast orthogonal matrix,and greatly reduce its implementation complexity by a new kind of butterfly algorithm.The proposed algorithm can achieve significant PAPR reduction without increasing the complexity of the system and affecting spectral performance,but also improve BER performance when used in frequency selective fading channels.Although Walsh-Hadamard precoding can reduce PAPR to a certain extent,PAPR may be still high because it does not take the signal property into consideration.To further reduce the PAPR of OFDM signals,this paper presents a joint algorithm combining the low complexity Walsh-Hadamard precoding algorithm with parameter-adjustable piecewise exponential companding.Parameter-adjustable piecewise exponential companding combines the advantage of piecewise companding and exponential companding,it can effectively reduce the PAPR of OFDM signals while reducing signal distortion.The joint algorithm reduces the PAPR of OFDM signals from reducing the correlation between OFDM frequency domain signals and changing the probability distribution of the OFDM time domain signals.Also,the joint algorithm can reduce the BER performance degeneration caused by companding algorithm.In addition,the joint algorithm has the advantages of simple implementation,adjustable parameters and high design freedom.In this paper,the simulations take into account the combined effects of high power amplifier and PAPR reduction algorithm on OFDM signals.The performance of the algorithm is verified from PAPR performance,BER performance and spectral performance in various channels.