Crest Factor Reduction Techniques For4G Mobile Communication System And Corresponding Hardware Implementation

With the increasing demands for information transmission rate in recent years，communication systemswith higher performance are immensely needed. The orthogonal frequency division multiplexing(OFDM)as a mobile communication of multi-carrier modulation scheme is being paid more and moreattention．OFDM has a good ability to combat multi-path fading in frequency-selective communicationchannel; meanwhile, the sub-carriers are mutually orthogonal in OFDM. Therefore, OFDM has a betterspectrum utilization and inter-carrier interference compared with conventional frequency divisionmultiplexing systems. Moreover, by adding a cyclic prefix in OFDM symbols, we can effectively eliminatethe inter-symbol interference，and improve the equalizer of receiver．Furthermore，combining withmultiple-input multiple-output (MIMO) scheme，MIMO-OFDM can provide more higher data rate thansingle-input single-output(SISO)OFDM．With the benefits of these outstanding properties，OFDM hasbeen widely used in data transmission systems and adopted as the physical-layer transmission scheme．However，with the increasing of sub-carriers，the time-domain OFDM signals exhibit high crestfactor(or PAPR)．When the OFDM signals go through a power amplifier，the high peaks will be cut-off，this will increase the bit error rate. Besides, the interference of adjacent channel will be enlarged due to thespectrum spreading．To reduce the nonlinear distortion，we need a power amplifier with a high linearity andDA/AD converters with a large dynamic range. Unfortunately, it will increase the hardware cost and reducethe validity of power amplifier. Hence, crest factor reduction is an efficient solution for OFDM signals withhigh peaks．This thesis mainly studies the crest factor reduction techniques and is corresponding implemented byusing FPGA．Firstly, we provide a overview of OFDM starting with a brief history and its basic principles，and then analyze the parameters of crest factor reduction for OFDM，afterwards analyze a variety of crestfactor reduction techniques．Secondly，we propose a new method for reducing crest factor based on convexoptimization theory. The decomposition theory is adopted to decompose clipped OFDM signals, meanwhile,the smallest error vector magnitude(EVM) optimization model is used to obtain the goal of reducing highpeak signals．Computer simulation results show that the proposed method is superior in performance to thetraditional non-optimized modeling method. Also, the computational complexity of the new method islower at the expense of only a slight performance degradation．Finally，based on the new method，we propose a low complexity FPGA scheme. The performance ofnew algorithm is tested with the baseband LTE signals，and experimental results show that FPGA systemscan effectively reduce the crest factor of original signals．...