Studies On Peak-to-Average Power Ratio (PAPR) In OFDM Systems

Orthogonal Frequency Division Multiplexing ( OFDM ) becomes one common technology in the high-speed communication owing to their high spectrum efficiency, robustness to mutlipath fading, great simplification of channel equalization and fast digital implementation with Fast Fourier Transform ( FFT ) . However, the high PAPR (Peak-to-Average Power Ratio) is the main drawback of the OFDM system. OFDM transmitters therefore require linear amplifiers with wide dynamic range. Linear amplifiers are expensive and inefficient. Any amplifier non-linearity will cause intermodulation products resulting in unwanted out-of-band power and increased interference.The definition and distribution of PAPR are introduced. Besides, three techniques on reducing the PAPR are summarized. In the last part, PTS(Partial Transmit Sequences)method and virtual carrier method in probability technology are researched and improved.(1) The SPS (Subblock Partition Scheme) based on modulate constellation in PTS method is adopted. The PAPR performance based on immobility sub-modulated constellation SPS is better than traditional interleave and adjacent SPS, and it is nearly the same to the pseudo-random SPS. Another scheme based on permutation sub-modulated constellation can reduce the complexity of the system by five iteratives in PTS method, which can get better PAPR performance when componded with the traditional SPS.(2) Know's Sub-Optimal scheme is improved by introducing the Hamming distance theoretic to increase the number of weighting factor explored. So it can get further improvement in performance while keeping low complexity.(3) Traditional method to insert the side information into PTS-OFDM signals are improved. the side imformation (SI) is added into the OFDM symbol after the PAPR optimization in thraditional method. It can cause peak regrowth. The improved method solve the problem by SI participate the peak optimization and delay transmition.(4) The method to reduce PAPR by virtual carrier is further discussed. A low complexity flow and iterative method of virtual carrier data are designed in the paper. Emullation shows that it can effectively reduce the PAPR of the system.