Study on the characteristics of IFFT output and phase rotation for PTS-based OFDM systems

• Main Authors: Chao-teng Lee, 李肇燈
• Other Authors: Jyh-horng Wen
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/37739198604446397309

碩士 === 國立中正大學 === 通訊工程學系 === 98 === Orthogonal frequency division multiplexing (OFDM) is one of the applications of a parallel-data-transmission scheme, which reduces the influence of multipath fading and makes complex equalizers unnecessary. It is well-known that the OFDM system suffers from the high peak-to-average power ratio (PAPR) problem. The OFDM signal with high PAPR requires high linear amplifiers. Otherwise, its performance will be decreased. To solve high PAPR problem, many various PAPR reduction schemes have been published. In the PTS-based OFDM system, exhaustive search is needed to obtain the optimal phase rotation. However, the computational complexity of the algorithm exponentially increases with the number of sub-sequences and the number of phase factors. In this thesis, we thoroughly investigate the characteristics of each IFFT output and its related phase rotation for the PTS-based OFDM system. Based on the characteristics, we find that several different combinations of phase rotation can result in identical PAPR output. Two relation equations among different combinations of phase rotation with identical PAPR output have been derived. With these two equations, we can collect all the sets of combinations of phase rotation with identical PAPR output in advance, and then propose a new exhaustive search algorithm based on one time search for each set. The search complexity of the proposed new search algorithm is drastically reduced as compared to the conventional exhaustive search algorithm while the PAPR performance is kept identical for both algorithms.