OFDM 시스템에서의 PAPR 감소를 위한 시간 영역의 큰 샘플을 이용한 저복잡도 PTS 기법

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.1 INTRODUCTION 1 1.1 Introduction 1 1.2 Overview of Dissertation 4 2 PRELIMINARIES 6 2.1 OFDM and PAPR 6 2.2 High Power Amplifier Models 8 2.3 Analysis of PAPR 11 2.3.1 PAPR of OFDM Signal 11 2.3.2 PAPR and BER 17 2.4 Iterative PAPR Reduction Schemes 18 2.4.1 Clipping and Filtering 19 2.4.2 Tone Reservation 20 2.4.3 Active Constellation Extension 24 2.5 Probabilistic PAPR Reduction Scheme: Selective Mapping 26 2.6 Conventional PTS Scheme 32 2.7 Low-Complexity PTS Schemes Using Dominant Time-Domain Samples 34 2.7.1 Dominant Time-Domain Samples 34 2.7.2 Low-Complexity PTS Schemes Using Dominant Time-Domain Samples 37 3 LOW-COMPLEXITY PTS SCHEMES WITHNEWSELECTION METHODS OF DOMINANT TIME-DOMAIN SAMPLES 40 3.1 Notations 40 3.2 Selection Methods of Candidate Samples for Dominant Time-Domain Samples 41 3.3 Proposed Low-Complexity PTS Schemes 50 4 IMPROVED PTS SCHEMES WITH ADAPTIVE SELECTION METHODS OF DOMINANT TIME-DOMAIN SAMPLES 52 4.1 Adaptive Selection Methods of Candidate Samples for Dominant Time-Domain Samples 52 4.1.1 A1-SM with W = 2 53 4.1.2 A1-SM with W = 4 54 4.1.3 A2-SM with W = 2 55 4.2 Mathematical Representations for Probability Distribution of Cn 66 4.2.1 A1-SM with W = 2 69 4.2.2 A1-SM with W = 4 69 4.2.3 A2-SM with W = 2 69 4.3 Multi-Stage Selection Method of Dominant Time-Domain Samples 70 4.4 Proposed PTS Schemes with Adaptive Selection Methods for Dominant Time-Domain Samples 71 5 PERFORMANCE ANALYSIS 74 5.1 Computational Complexity 74 5.2 Simulation Results 76 6 CONCLUSIONS 85 Abstract (In Korean) 92Docto

저복잡도 후보 OFDM 신호 생성을 이용한 새로운 PTS 방법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 노종선.This dissertation proposes several research results on the peak-to-average power ratio (PAPR) reduction schemes for the orthogonal frequency division multiplexing (OFDM) systems. The PAPR is the one of major drawback of OFDM system which causes signal distortion when OFDM signal passes through nonlinear high power amplifier (HPA). Various schemes have been proposed to reduce the PAPR of OFDM signals such as clipping, selected mapping (SLM), partial transmit sequence (PTS), active constellation extension (ACE), companding, and tone reservation (TR). Among them, PTS scheme can transmit an OFDM signal vector by generating many alternative OFDM signal vectors using the partitioned subblock signals and selecting the optimal OFDM signal vector with the minimum PAPR. However, the PTS scheme requires large computational complexity, because it needs many inverse fast Fourier transforms (IFFTs) of subblock signals and lots of alternative OFDM signal vectors are generated. In this dissertation, we concentrate on reducing the computational complexity of the PTS scheme. In the first part of this dissertation, we propose a new PTS scheme with low computational complexity using two search steps to find a subset of phase rotating vectors showing good PAPR reduction performance. In the first step, sequences with low correlation are used as phase rotating vectors for PTS scheme, which are called the initial phase vectors. Kasami sequence and quaternary sequence are used in this step as the initial phase vectors. In the second step, local search is performed based on the initial phase vectors to find additional phase rotating vectors which show good PAPR reduction performance. Numerical analysis shows that the proposed PTS scheme can achieve almost the same PAPR reduction performance as the conventional PTS scheme with much lower computational complexity than other low-complexity PTS schemes. In the second part of the dissertation, we propose another low-complexity PTS schemes using the dominant time-domain OFDM signal samples, which are only used to calculate PAPR of each alternative OFDM signal vector. In this PTS scheme, we propose efficient metrics to select the dominant time-domain samples. For further lowering the computational complexity, dominant time-domain samples are sorted in decreasing order by the proposed metric values and then the power of each sample is compared with the minimum PAPR of the previously examined alternative OFDM signal vectors. Numerical results confirm that the proposed PTS schemes using new metrics show large computational complexity reduction compared to other existing low-complexity PTS schemes without PAPR degradation. In the last part of the dissertation, for the reduced-complexity PTS scheme, a new selection method of the dominant time-domain samples is proposed by rotating the IFFTed signal samples to the area on which the IFFTed signal sample of the first subblock is located in the signal space. Moreover, the method of pre-exclusion of the phase rotating vectors using the time-domain sample rotation is proposed to reduce the number of alternative OFDM signal vectors. Further, three proposed PTS schemes are introduced to reduce the computational complexity by using simple OFDM signal rotation and pre-exclusion of the phase rotating vectors. Numerical analysis shows that the proposed PTS schemes achieve the same PAPR reduction performance as that of the conventional PTS scheme with the large computational complexity reduction.Docto

Chicken Swarm Optimization for PTS based PAPR Reduction in OFDM Systems

Partial transmit sequence (PTS) is a well-known PAPR reduction scheme for the OFDM system. One of the major challenge of this scheme is to find an optimal phase vector using exhaustive search over all the allowed phase factor combinations. This leads to increased search complexity which grows exponentially as the number of sub-blocks is increased. In this paper, chicken swarm optimization (CSO) based PTS system is designed that aims to find an optimal solution in less number of average iterations and therefore results in reduced computational complexity of the system. We have proposed two categories of the algorithm: (i) CSO-PTS system without threshold limit on PAPR (ii) CSO-PTS system with threshold limit on PAPR. Both the schemes offer effective trade-offs between the computational complexity and the PAPR reduction capability of the system. Simulation results confirm that our proposed schemes perform well in terms of low computational complexity, lesser number of average iterations and improved PAPR reduction capability of the OFDM signal without any loss in BER performance of the system

A Novel PTS Scheme for PAPR Reduction of Filtered-OFDM Signals without Side Information

In this paper, a novel partial transmit sequence (PTS) scheme is proposed for reducing the peak-to-average power ratio (PAPR) of filtered orthogonal frequency division multiplexing (f-OFDM) systems. The PTS method is modified such that no side information (SI) transmission is needed. The data and pilot recovery are accomplished by a simple detector, making use of the correlation property of the Hadamard sequence and the transparency property of the pilot signal and an iterative phase detection is further added in a fading channel. Simulation results show that the modified solution provides a higher correct detection probability without increasing the system complexity nor affecting the PAPR suppression performance

Computationally Efficient Modified PTS for PAPR Reduction in MIMO-OFDM

Nowadays wireless communication has taken its leap for a high data rate using the multi-carrier transmission technique.Orthogonal frequency division multiplexing(OFDM) is one of such popular method for achieving this high information rate.OFDM has several advantages,but one of the main drawbacks is its high peak-to-average power ratio(PAPR).This is due to a large number of the subcarrier,which leads to distortion problem at receiver. An OFDM signal with the high PAPR requires power amplifier’s(PAs)with large dynamic ranges.Such PAs are less efficient,costly to manufacture and very much difficult to design.There have been a large number of techniques are available in the literature to reduce the PAPR, such as Partial transmit sequence,Selective mapping,Block Coding, Tone rejection,etc.However,the challenging part is that most of the PAPR reduction schemes come with high computational complexity.Recent PAPR reduction techniques such as partial transmit sequence(PTS)has been considered as most popular for PAPR reduction.This research work explores to find a solution for the PAPR reduction by using PTS technique, which has been implemented by using sub-blocks partitioning.In sub-block partition consists of OFDM data frame which is partitioned into several sub-blocks.An adjacent partitioning(AP)method can be perceived as the best of the existing partitioning method when the cost and PAPR reduction performance are considered together.A new technique is based on modified PTS using phase rotation and circular shifting to attain the overall reduction of PAPR in MIMO-OFDM system, but computational complexity does not decrease for the same.A Co-operative PTS technique which is mainly based on alternative PTS technique is applied.In this technique although a slight loss of PAPR reduction performance is there but with much lower computational complexity

A Survey on Peak to Average Power Ratio Reduction Methods for LTE-OFDM

OFDM (Orthogonal Frequency Division Multiplexing) is generally preferred for high data rate transmission in digital communication. The Long-Term Evolution (LTE) standards for the fourth generation (4G) wireless communication systems. Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are the two multiple access techniques which are generally used in LTE.OFDM system has a major shortcoming of high peak to average power ratio (PAPR) value. This paper explains different PAPR reduction techniques and presents a comparison of the various techniques based on theoretical results. It also presents a survey of the various PAPR reduction techniques and the state of the art in this area

Intelligent genetic algorithms for next-generation broadband multi-carrier CDMA wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This dissertation proposes a novel intelligent system architecture for next-generation broadband multi-carrier CDMA wireless networks. In our system, two novel and similar intelligent genetic algorithms, namely Minimum Distance guided GAs (MDGAs) are invented for both peak-to-average power ratio (PAPR) reduction at the transmitter side and multi-user detection (MUD) at the receiver side. Meanwhile, we derive a theoretical BER performance analysis for the proposed MC-CDMA system in A WGN channel. Our analytical results show that the theoretical BER performance of synchronized MC-CDMA system is the same as that of the synchronized DS-CDMA system which is also used as a theoretical guidance of our novel MUD receiver design. In contrast to traditional GAs, our MDGAs start with a balanced ratio of exploration and exploitation which is maintained throughout the process. In our algorithms, a new replacement strategy is designed which increases significantly the convergence rate and reduces dramatically computational complexity as compared to the conventional GAs. The simulation results demonstrate that, if compared to those schemes using exhaustive search and traditional GAs, (1) our MDGA-based P APR reduction scheme achieves 99.52% and 50+% reductions in computational complexity, respectively; (2) our MDGA-based MUD scheme achieves 99.54% and 50+% reductions in computational complexity, respectively. The use of one core MDGA solution for both issues can ease the hardware design and dramatically reduce the implementation cost in practice