S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Electrical and Computer Engineering (전기·정보공학부) Theses (Ph.D. / Sc.D._전기·정보공학부)
Low-Complexity PTS Schemes Using Dominant Time-Domain Samples in OFDM Systems : OFDM 시스템에서의 PAPR 감소를 위한 시간 영역의 큰 샘플을 이용한 저복잡도 PTS 기법
- 공과대학 전기·컴퓨터공학부
- Issue Date
- 서울대학교 대학원
- Dominant time-domain samples ; Orthogonal frequency division multiplexing (OFDM) ; Partial transmit sequence (PTS) ; Peak-to-average power ratio (PAPR)
- 학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 노종선.
- In orthogonal frequency division multiplexing (OFDM) systems, high peak-to-average power ratio (PAPR) of OFDM signals is one of the most important problems.
The high PAPR of OFDM signals causes serious nonlinear distortions in process of passing through high power amplifier (HPA). These distortions have a effect on in-band distortion and out-of-band radiation, which result in bit error rate degradation of received OFDM signals and interference in adjacent channel, respectively. In order to solve the PAPR problem of OFDM signals, various PAPR reduction schemes have been proposed.
This dissertation includes research results on a kind of the PAPR reduction schemes, called the partial transmit sequence (PTS) for the OFDM systems. As a solution to the PAPR problem in OFDM systems, the PTS scheme is a fairly suitable scheme due to its PAPR reduction performance and distortionless characteristics. The PTS scheme generates several candidate OFDM signals to represent an original OFDM signal and selects one with the lowest PAPR among them for transmission. However, a serious problem in the PTS scheme is high computational complexity, which is mainly required to generate and process the candidate OFDM signals. In this dissertation, in an effort to reduce its computational complexity, new PTS schemes are proposed using dominant time-domain samples of OFDM signals. Dominant time-domain samples is a small number of samples of OFDM signals used to estimate PAPRs of candidate OFDM signals efficiently.
In the first part of this dissertation, low-complexity PTS schemes are proposed using new selection methods of dominant time-domain samples. The proposed selection methods of dominant time-domain samples are based on selection methods of candidate samples in candidate OFDM signals. These methods select dominant time-domain samples with reduced computational complexity. The dominant time-domain samples selected by the proposed methods are used to estimate PAPRs of candidate OFDM signals with high accuracy. Therefore, the proposed low-complexity PTS schemes can achieve the optimal PAPR reduction performance with considerably reduced computational complexity.
In the second part of this dissertation, improved PTS schemes are proposed to lower the computational complexity of previous PTS schemes further while maintaining high performance of PAPR reduction. Similar with the PTS schemes proposed in the previous part of this dissertation, the improved PTS schemes utilize dominant time-domain samples and candidate samples. However, they use more efficient methods, which select the candidate samples by adaptive method or multi-stage method to select dominant time-domain samples. Therefore, the improved PTS schemes reduce computational complexity further while maintaining the optimal PAPR reduction performance.
The proposed PTS schemes in this dissertation use efficient methods to select dominant time-domain samples and thus they reduce the computational complexity considerably compared to previous PTS schemes. In addition, they achieve the optimal PAPR reduction performance, which is equivalent to that of the conventional PTS scheme with the low complexity. Due to the high performance and low complexity, they are fully expected to be used in the practical implementation of OFDM systems.