Research On Peak-to-Average Power Ratio In OFDM Systems

The purpose of the next generation wireless communication system is to realize mobile-multimedia transmission with high quality and speed. Orthogonal Frequency Division Multiplexing (OFDM) is considered as a key physical layer technology of the next generation communication for its robustness against multi-path fading channel, and has been applied to many wireless communication systems. However, the main drawback of it is that the signal has a large PAPR (peak average power ratio) which will lead to the interference and the decrease of system performance. So, how to effectively reduce the PAPR in OFDM system is an urgent problem.At present, the most popular three types of technology which reducing the PAPR are pre-distorting technology, coding technology and non-distorting technology. The prominent merit of the pre-distorting technology is that system can be realized simply and can effectively reduce the PAPR. However, this technology may cause additional noise and seriously reduce the system performance. The basic principle of the coding technology is to create OFDM symbols with smaller PAPR using different coding. This process is linear, so the signal has no distorting. Consequently, the technology has not the shortcomings the pre-distorting technology owns. Yet, both coding and decoding technology is very complex and the data transmission rate is low. This technology is only appropriate for the system with few sub-carriers. The Coding efficiency will be very low when the number of sub-carriers is large, and the system performance will be reduced. The non-distorting technology decreases the probability of the occurrence of high PAPR by linear transformation of signal. Though a better performance can be obtained, the calculation is very complex and the realization of the hardware is very difficult. However, by far, many effective methods can be used to reduce the complex of the calculation. So, among the three types technologies, non-distorting technology is the most potential technology to solve the PAPR problem in OFDM.This thesis analyzes the representative methods of the three types, compares their performance through computer simulation, and focuses the studies on the PTS Sub-block Partition Scheme method of the non-distorting technology. At the meantime, we present the improved sub-block partition scheme which combines the adjacent, pseudo-random and interleaved partition scheme together. Though the performance of the new partition methods is slightly worse than the pseudo-random method, the calculation complexity of the system is reduced greatly. Besides, the thesis gives the improved Kwon sub-optimum method for increasing the number of the phase factor in each iteration by using Hamming-distance search principle. Moreover, the optimum threshold and parameter are set in order to obtain a lower operation complexity and a better PAPR performance. The coalescence of the two new methods has a better practicability because it can effectively enhance the system performance and maintain the low complexity at the same time.