Research On PAPR Optimization Method Of OFDM System Based On Unitary Transformation And PTS

Orthogonal frequency division multiplexing is a multi-carrier modulation technology, with small inter-carrier interference, high spectral efficiency and it can effectively suppress multipath fading. OFDM is the best and efficient modulation and multiplexing scheme adapted for 4G wireless communication applications. One of the major drawbacks of OFDM system is that the OFDM signal can have high peak to average power ratio(PAPR). The high peak to average power ratio brings on the OFDM signal distortion in the nonlinear region of high power amplifier and the signal distortion induces the degradation of bit error rate(BER). In this paper, we aim to study unitary transformation and partial transmit sequence(PTS) for PAPR reduction in OFDM system and its effect on system performance.First, this paper is focused on three kinds of unitary transformations scheme—Walsh Hadamard Transform(WHT) scheme? Discrete Fourier Transform(DFT) scheme and Discrete Hartley Transform(DHT) scheme. Comparison of the performance of three schemes for PAPR reduction through simulation, and analysis the principle of PAPR reduction, then simulate the unitary transformation OFDM under FWGN channel. The simulation results show that when the three options for reducing PAPR, DFT conversion scheme is the best, DHT conversion scheme is followed, WHT conversion scheme is the worst, and three schemes show the same performance at BER.Next, this paper presents a new method of PTS—Dual phase PTS(DP-PTS), DP-PTS uses two phase factor, corresponding to the real and imaginary parts of the sub-blocks after IFFT conversion, we use an iterative approach to process two phase factor. The simulation results show that DP-PTS scheme reduces the computational complexity while it shows almost the same performance of PAPR reduction as that of the IPTS. DP-PTS has two phase factor, in order to facilitate the transmission side information, this paper combine DP-PTS with method which transform side information through pilot, namely DP-PTS without sideinformation. The simulation results show that DP-PTS without side-information can almost obtain the same BER performance as PTS.Finally, the unitary transformation and PTS were applied to the multi-band orthogonal frequency division multiplexing ultra-wideband(MB-OFDM-UWB) system, then compared the impact of unitary transformation scheme to PAPR and BER performance with that of PTS scheme. Simulation results show that, DFT conversion scheme is more suitable for PAPR reduction at MB-OFDM-UWB system. Generally, unitary transformation scheme is suitable for low-level modulation system, and PTS has no such restriction.