New SLM scheme to reduce the PAPR of OFDM signals using a genetic algorithm

AbstractSelected mapping (SLM) is a popular peak-to-average power ratio (PAPR) reduction technique suitable for use in orthogonal frequency division multiplexing (OFDM) systems as it achieves good PAPR reduction performance without signal distortion. However, SLM requires a bank of inverse fast Fourier transforms (IFFTs) to produce candidate signals, resulting in high computational complexity. In this paper, we introduce a novel SLM technique based on conversion matrices (CM) and a genetic algorithm (GA) that requires only one IFFT module. Simulation results indicate that the proposed method obtains desirable PAPR reduction performance with low computational complexity

Low-Complexity Schemes for Class-III and CORR SLM in OFDM Systems

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 노종선.In this dissertation, orthogonal frequency division multiplexing (OFDM) system is studied. Since OFDM signal sequence undergoes high peak-to-average power ratio (PAPR), several schemes are proposed to mitigate the PAPR problem. PAPR reduction schemes such as selected mapping (SLM) and partial transmit sequence (PTS) are introduced. Due to the high computational complexity of the SLM scheme, low-complexity SLM schemes have been proposed by many researchers. Class-III SLM scheme [55] requires only one inverse fast Fourier transform (IFFT) operation, whereas the conventional scheme needs U IFFT operations. By randomly selecting the cyclic shift and rotation values, this scheme can generate up to N3 alternative OFDM signal sequences. The PAPR reduction performance of Class-III SLM scheme is little degraded compared to the conventional SLM scheme. Recently, instead of PAPR reduction, the different performance criteria for SLM scheme are proposed such as inter modulation distortion [38] and correlation (CORR) [56]. The objective of these schemes are enhancing the bit error rate (BER) performance instead of PAPR reduction performance. In the first part of this dissertation, a deterministic selection method of phase sequences is proposed for Class-III SLM scheme [55]. First, the optimal condition of cyclic shift values in the Class-III SLM scheme is proposed. Then, the cyclic shift values satisfying the optimal condition is also derived. Compared to the random selection method, the proposed selection method guarantees the optimal PAPR reduction performance. Second, two generation methods for good alternative OFDM signal sequences are proposed, one by using rotation values which do not have linear relation and the other with no rotation values. The advantages of the proposed selection schemes are: (a) The second proposed selection scheme does not need the rotation values. (b) Both of the proposed selection schemes require less side information than random selection scheme. (c) The first proposed selection scheme guarantees the optimal PAPR reduction performance in terms of variance of correlation. In the second part of this dissertation, the proper oversampling rate for the CORR SLMscheme is proposed. It is known that four times oversampling is enough to estimate the PAPR of the continuous OFDM signal. By calculating the correlation coefficient between the continuous and two times oversampled OFDMsignal sequences, it is found that two times oversampling is enough to achieve the same BER performance as four times oversampling case in the CORR SLM scheme. In the simulation results, the same BER performance can be achieved by the proposed two times oversampling rate as four times oversampling case.Abstract i Contents iii List of Tables vii List of Figures ix 1. Introduction 1 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2. Overview of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. OFDM System Model 7 2.1. OFDM System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2. Modulation and Demodulation of OFDM Signal . . . . . . . . . . . . 9 2.2.1. Orthogonality Principle . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2. OFDM Signal Modulation and Demodulation . . . . . . . . . . 10 2.3. Fast Fourier Transform . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4. Guard Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.5. Peak-to-Average Power Ratio . . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.5.2. The distribution of PAPR . . . . . . . . . . . . . . . . . . . . . 13 2.5.3. PAPR of Oversampled Signal . . . . . . . . . . . . . . . . . . 15 3. PAPR Reduction Schemes 17 3.1. Clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2. Tone Reservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.3. Partial Transmit Sequence . . . . . . . . . . . . . . . . . . . . . . . . 19 3.4. Selected Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.5. Low-Complexity SLM Schemes . . . . . . . . . . . . . . . . . . . . . 24 3.5.1. SLM Scheme with Divided IFFT Stages . . . . . . . . . . . . . 24 3.5.2. Modified SLM Scheme . . . . . . . . . . . . . . . . . . . . . . 25 3.5.3. SLM Scheme with Conversion Matrices . . . . . . . . . . . . . 26 3.6. Considerations for PAPR Reduction Schemes . . . . . . . . . . . . . . 28 4. BER Reduction Schemes 30 4.1. PTS Scheme with PICR Metric . . . . . . . . . . . . . . . . . . . . . . 30 4.2. IMD Reduction Scheme . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.3. PTS Scheme with MSE Metric . . . . . . . . . . . . . . . . . . . . . . 33 4.4. DSR Reduction Scheme with Distortion Prediction . . . . . . . . . . . 34 5. Low-Complexity Class-III SLM Scheme 37 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.2. Overview of Class-III SLM Scheme . . . . . . . . . . . . . . . . . . . 39 5.3. Selection of Optimal Alternative OFDM Signal Sequences for Class-III SLM Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.3.1. Correlation Analysis . . . . . . . . . . . . . . . . . . . . . . . 41 5.3.2. Selection of Optimal Cyclic Shift Values . . . . . . . . . . . . 44 5.3.3. Maximum Number of Optimal Alternative OFDM Signal Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.3.4. Selection of Additional Alternative OFDM Signal Sequences . . 49 5.4. Side Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 5.5. Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 5.6. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 5.7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 6. Low-Complexity CORR SLM Scheme 61 6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.2. Overview of SLM Scheme Using CORR Metric . . . . . . . . . . . . . 62 6.2.1. Overview of CORR Metric . . . . . . . . . . . . . . . . . . . . 62 6.2.2. BER Performance of SLM Scheme under HPA . . . . . . . . . 65 6.3. Oversampling Effect on SLM Scheme Using CORR Metric . . . . . . . 67 6.3.1. Expression of Oversampled Signal and CORR Metric . . . . . . 67 6.3.2. Correlation Coefficients between Coefficient Sequences Derived from CORR Metric Computation . . . . . . . . . . . . . . . . 70 6.4. Computational Complexity . . . . . . . . . . . . . . . . . . . . . . . . 72 6.5. Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 6.6. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.6.1. Effect of 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.6.2. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.6.2.1. Comparative CORR . . . . . . . . . . . . . . . . . . 82 6.6.2.2. Low Sampled CORR . . . . . . . . . . . . . . . . . 83 6.7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 7. Conclusions 86 Bibliography 88 초록 96Docto

Low Complex PAPR Reduction Schemes for OFDM Systems

In this thesis, three low-complex PAPR reduction schemes for OFDM systems are proposed. All the proposed schemes can be considered as modi ed versions of the conventional SLM scheme, which can signi cantly reduce high PAPR of OFDM signals with no distortion. In the rst proposed scheme, a new set of the candidate sequences is generated by partial phase weighting in the time domain and the combination of sub-blocks by applying IFFT properties. In the second scheme which is based on a combination of SLM and PTS, a simple phase optimization technique is introduced. The third scheme forms di erent 16-QAM signals from 2 QPSK signals. Also, the circular convolution part in TPPW-SLM, which is also a part of Class-III SLM, is applied

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before. PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast. Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts

An efficient reconfigurable peak cancellation model for peak to average power ratio reduction in orthogonal frequency division multiplexing communication system

The peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) communication system will be reduced using reconfigurable peak cancellation (RPC). RPC will also aid in improves the error vector magnitude (EVM) and reduces adjacent channel leakage ratio (ACLR) in OFDM communication system. The proposed RPC design methodology and practical implementation using field programmable gate array (FPGA) are discussed. The proposed RPC has been demonstrated using VIRTEX-7 XC7Z100 dual-core FPGA device with less hardware difficulty and minimum utilization of FPGA resources. The proposed RPC improves the efficiency of OFDM communication process by reducing complementary cumulative distribution function (CCDF) with respect to instantaneous power in dB. A comparison analysis was done between the existing selective mapping (SLM) method with proposed RPS method with respect FPGA resource utilization. The proposed RPC is implemented using VIRTEX-7 XC7Z100 dual-core FPGA device. Its effectively utilizing sub-carriers, fast Fourier transform (FFT) filter, bandwidth, and sampling frequency. Due to parallel switching operation, it reduces the PAPR, ACLR and improves EVM in OFDM signal with less hardware complexity

OFDM System with g-CPFSK Mapper: Properties and Performance

Orthogonal Frequency Division Multiplexing (OFDM) system with a generalized Continuous Phase Frequency Shift Keying (g-CPFSK) mapper is considered which is used to introduce systematic correlation among the transmitted OFDM symbols. The correlation thus introduced is exploited at the receiver to enhance the physical layer performance of the system by using multiple-symbol observation detector. Three subclasses of g- CPFSK mapper, single-h CPFSK, multi-h CPFSK, and asymmetric multi-h CPFSK mappers, are considered; although the class of g-CPFSK mapper comprises of a large class of mappers. The resulting OFDM signals and their properties are examined. The Peak-to-Average Power Ratio (PAPR) characteristics of these signals in conjunction with three PAPR reduction techniques, namely, Selective Mapping (SLM), Partial Transmit Sequence (PTS), and Clipping and Filtering (CF) are also investigated. Maximum Likelihood (ML) multiple-symbol detection of OFDM signals in AWGN is addressed and the structure of the optimum detector/demapper is derived using the criterion of minimum probability of Bit Error Rate (BER). Closed-form expression for BER of this detector is derived in terms of high-SNR upper and lower bounds. It is noted that BER is a function of: i) Eb=No, Signal-to-Noise Ratio (SNR); ii) parameters of the g-CPFSK mapper; iii) n, observation length of the receiver; and iv) M, number of levels used in the mapper. Finally, the performance of OFDM system with g-CPFSK mapper is evaluated over nonfrequency selective Rayleigh and Nakagami-m fading channels. It is shown that OFDM system with single-h and multi-h CPFSK mappers in conjunction with PTS technique can be designed to achieve PAPR reductions of 6.1 dB and 3.5 dB, respectively, relative to corresponding OFDM system with conventional BPSK mapper. However, when SLM technique is used, PAPR reductions of 1.6 dB and 1 dB, respectively, can be achieved. Asymmetric multi-h and multi-h CPFSK mappers in conjunction with CF technique can be designed to realize PAPR reductions of 4.1 dB and 2.5 dB, respectively, with 25% clipping. Optimum sets of mapper parameters for single-h, multi-h and asymmetric multi-h CPFSK mappers are determined that minimize BER of the system. It is observed that the optimum asymmetric multi-h and multi-h CPFSK mappers outperform BPSK mapper by nearly 2.2 dB and 1.4 dB, respectively, when 4- symbol observation length detector is used. However, it is noted that the complexity of the detector increases as a function of observation length and the type of mapper used. Closed-form expressions for BER performance of OFDM system with g-CPFSK mapper are derived over Rayleigh and Nakagami-m frequency-non selective slowly fading channels and the penalty in SNR that must be paid as a consequence of the fading is assessed and illustrated

Peak to average power ratio reduction and error control in MIMO-OFDM HARQ System

Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMOOFDM) systems underlie crucial wireless communication systems such as commercial 4G and 5G networks, tactical communication, and interoperable Public Safety communications. However, one drawback arising from OFDM modulation is its resulting high peak-to-average power ratio (PAPR). This problem increases with an increase in the number of transmit antennas. In this work, a new hybrid PAPR reduction technique is proposed for space-time block coding (STBC) MIMO-OFDM systems that combine the coding capabilities to PAPR reduction methods, while leveraging the new degree of freedom provided by the presence of multiple transmit chairs (MIMO). In the first part, we presented an extensive literature review of PAPR reduction techniques for OFDM and MIMO-OFDM systems. The work developed a PAPR reduction technique taxonomy, and analyzed the motivations for reducing the PAPR in current communication systems, emphasizing two important motivations such as power savings and coverage gain. In the tax onomy presented here, we include a new category, namely, hybrid techniques. Additionally, we drew a conclusion regarding the importance of hybrid PAPR reduction techniques. In the second part, we studied the effect of forward error correction (FEC) codes on the PAPR for the coded OFDM (COFDM) system. We simulated and compared the CCDF of the PAPR and its relationship with the autocorrelation of the COFDM signal before the inverse fast Fourier transform (IFFT) block. This allows to conclude on the main characteristics of the codes that generate high peaks in the COFDM signal, and therefore, the optimal parameters in order to reduce PAPR. We emphasize our study in FEC codes as linear block codes, and convolutional codes. Finally, we proposed a new hybrid PAPR reduction technique for an STBC MIMO-OFDM system, in which the convolutional code is optimized to avoid PAPR degradation, which also combines successive suboptimal cross-antenna rotation and inversion (SS-CARI) and iterative modified companding and filtering schemes. The new method permits to obtain a significant net gain for the system, i.e., considerable PAPR reduction, bit error rate (BER) gain as compared to the basic MIMO-OFDM system, low complexity, and reduced spectral splatter. The new hybrid technique was extensively evaluated by simulation, and the complementary cumulative distribution function (CCDF), the BER, and the power spectral density (PSD) were compared to the original STBC MIMO-OFDM signal

Polar-Coded OFDM with Index Modulation

Polar codes, as the first error-correcting codes with an explicit construction to provably achieve thesymmetric capacity of memoryless channels, which are constructed based on channel polarization, have recently become a primary contender in communication networks for achieving tighter requirements with relatively low complexity. As one of the contributions in this thesis, three modified polar decoding schemes are proposed. These schemes include enhanced versions of successive cancellation-flip (SC-F), belief propagation (BP), and sphere decoding (SD). The proposed SC-F utilizes novel potential incorrect bits selection criteria and stack to improve its error correction performance. Next, to make the decoding performance of BP better, permutation and feedback structure are utilized. Then, in order to reduce the complexity without compromising performance, a SD by using novel decoding strategies according to modified path metric (PM) and radius extension is proposed. Additionally, to solve the problem that BP has redundant iterations, a new stopping criterion based on bit different ratio (BDR) is proposed. According to the simulation results and mathematical proof, all proposed schemes can achieve corresponding performance improvement or complexity reduction compared with existing works. Beside applying polar coding, to achieve a reliable and flexible transmission in a wireless communication system, a modified version of orthogonal frequency division multiplexing (OFDM) modulation based on index modulation, called OFDM-in-phase/quadrature-IM (OFDM-I/Q-IM), is applied. This modulation scheme can simultaneously improve spectral efficiency and bit-error rate (BER) performance with great flexibility in design and implementation. Hence, OFDM-I/Q-IM is considered as a potential candidate in the new generation of cellular networks. As the main contribution in this work, a polar-coded OFDM-I/Q-IM system is proposed. The general design guidelines for overcoming the difficulties associated with the application of polar codes in OFDM-I/Q-IM are presented. In the proposed system, at the transmitter, we employ a random frozen bits appending scheme which not only makes the polar code compatible with OFDM-I/Q-IM but also improves the BER performance of the system. Furthermore, at the receiver, it is shown that the \textit{a posteriori} information for each index provided by the index detector is essential for the iterative decoding of polar codes by the BP algorithm. Simulation results show that the proposed polar-coded OFDM-I/Q-IM system outperforms its OFDM counterpart in terms of BER performance