Theoretical Research And Algorithm Realization Of Reducing PAPR In OFDM

This thesis studies one of the key technologies of the 4^th generation mobile system: PAPR (peak-to-average power ratio) reduction. Due to a high spectral efficiency, the robustness to the ISI (inter-symbol interference) and multi-path fading, OFDM (orthogonal frequency division multiplexing) has been applied in DAB (digital audio broadcasting), DVB (digital video broadcasting), and WLAN (wireless local area network) based on IEEE802.11. But the OFDM signal has a large PAPR, which results in the significant nonlinear distortion when it passes through a HPA (high power amplifier), thereby the performances of the system descend. So this thesis studies the algorithms which reduce the PAPR.This thesis is concerned with reducing PAPR in orthogonal frequency division multiplexing system that is belonged to the forth generation mobile communication systems. The main work of this dissertation is recapitulated as follows. Firstly, the orthogonality of OFDM signal is analyzed through the simulation of the time-domain and the frequency domain on the base of the system model that is analyzed. The definition of PAPR is got through the further simulation of the time-domain, the distribution of PAPR is theoretically deduced and simulated. Combined with the characteristic of nonlinear high power amplifier, the influence of PAPR is analyzed. Secondly, reducing PAPR using the signal predistortion is studied. The forced limit and the soft limit are simulated. Then, reducing PAPR using the signal non-predistortion is studied. The selective mapping and the partial transmit sequence are mostly simulated and analyzed. Lastly, making the monopoly phase sequence to improve the performances of the selective mapping, thus overcome the disadvantage of transmitting the side information and improve the use of frequency, through the analyses of the characteristic and the auto-correlation function and the simulation of the performance of PAPR. In order to obtain optimal PAPR reduction using the partial transmitted sequence, the total search for the number of sub-blocks and the rotation factors must be accomplished. As the number of sub-blocks and rotation factors increases, PAPR reduction improves. The number of calculation increases as the number of sub-blocks increases, such that complexity increases. In order to reduce the complexity in the system, the search of rotation factors is accomplished using the genetic algorithms. Compared with the search using iteration, the complexity can be reduced while thesame PAPR reduction from the simulation.