Study On Papr Reduction In OFDM Systems

OFDM(Orthogonal frequency division multiplexing) a multi-carrier modulation technique。The basic idea is to transform the data stream to a lower rate of N parallel sub-way data flow, modulation to the interval of a group of orthogonal subcarriers. Because the data flow rate into the 1 / N of original , which expanded the original symbol period N times, each OFDM symbol duration much longer than the single-carrier,and it is far greater than the channel maximum delay spread. Besides,OFDM as full use of orthogonal frequency signals, allowing N-sub-channel spectrum overlap, therefore, compared with the conventional FDM systems, OFDM systems can maximize the use of spectrum resources.However, in OFDM system, there are also some shortcomings, which restricts the improvement of system performance, one of the most important one is the high peak to average power ratio. In OFDM systems, if we use the multiple carriers with frequency synchronization relationship to modulate the signal since the value of the carrier envelope statistically independent, with the increasing number of carriers, after superposition of the signal, peak power and average power ratio (PAPR) values larger. Therefore, the required system power amplifier with high linear amplification range, it also requires follow-up of the D / A converter with large conversion width, it will not only increase the difficulty of achieving, but also increases the cost of the system.We first discuss the principles of the OFDM, OFDM system model,the key technology and shortcomings is introduced, this leads to the importance and significance of OFDM system peak average power ratio . The paper then introduces the meaning and causes of the OFDM PAPR problem, for the three method:limiting-iltering, coding, and signal crambling code techniques which can reduction PAPR, in his paper, we give the eaborate and theoretical simulation. We focus on the type of the SLM and PTS techniques algorithms in signal scrambling code ,based on the existing method ,we propose improved SLM and PTS algorithms based on TR transform and reduce the number of IFFT transform core operations. At the same time, we also propose a hrarchical Search-suboptimal iterative algorithm used in PTS algorithm and improve the transmission of SLM side information. Finally, we use the FPGA to implement the the improved algorithm of SLM ,they greatly reducing system complexity.