Research On Reducing Peak-To-Average Power Ratio Of OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) has been regarded as the core technology of 4G wireless communication system, and it provides higher spectrum efficiency and greater immunity to multi-path fading. However, the higher peak-to-average power ratio (PAPR) is the drawbacks of OFDM signals. The higher peak-to-average power ratio requires that the power amplifier of system must have great linear dynamic range, otherwise it will cause signal distortion, then destroy the orthogonality relation among sub-carriers and reduce the performance of the system. So the problem of higher PAPR in OFDM system must be solved. This paper mainly focuses on the methods of PAPR reduction.In this paper, the basic characteristics of OFDM are studied and analyzed deeply, and several typical algorithms to reduce PAPR are compared. It emphasises on introducing the applications of carrier interference in the OFDM systems. And then, the simulation results prove the uniqueness and superiority. Two improved methods are proposed based on the characteristics of using carrier interference to reduce PAPR. The first method named group which is the input grouping signals adopted after adding CI. It could reduce the probability of high peak power appeared, and reduction of PAPR is also achieved further. Another method is computing the average of K signals which are from N signals of the system after IFFT transformation. The K signals are the signals which begin with and contain the original signal, and then replace the original signal with the average. In order to ensure the performance of BER, the theoretical analysis and simulation results demonstrate that the two improved schemes in the paper can reduce peak power significantly, and reduction of PAPR is also achieved further. The improved methods with their unique algorithms can accomplish better performance. They are not required for sub-carrier number with good flexibility, which are not only applicable to BPSK modulation and QPSK modulation, but also are used in many other M-ary modulations. The improved methods are convenient to be combined with other techniques and valuable to be applied with good feasibility.