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

Analysis and Implementation of PAPR reduction algorithms for C-OFDM signals

Nowadays multicarrier modulation has become a key technology for communication systems; for example C-OFDM schemes are used in wireless LAN (802.11a/g/n), terrestrial digital television (DVB-T) and audio broadcaster (DAB) in Europe, and discrete multitone (DMT) in x.DSL systems. The principal difficulty with OFDM is the occurrence of the coherent alignment of the time domain parallel signals at the transmitted side which forces system designer to introduce either additional hard computationally device or a suitable power back-off at the high power amplifier in order to cope with the large magnitude signal fluctuation. This leads to a significant increment in computational cost in the former case whereas in a worse allowable power utilization in the latter case with respect to the original system. However since both allowable power and computational cost are subject to a design as well as regulatory limit others solution must be accomplished. Peak reduction techniques reduce maximum-to-mean amplitude fluctuations nominating as a feasible solution. Peak-to-average power ratio is the key metric to measure this amplitude fluctuations at transmitter and to give a clear figure of merit for comparison among different techniques

OFDM 시스템을 위한 새로운 저 복잡도 SLM 방식 및 클리핑 잡음 제거 기법 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 노종선.In this dissertation, several research results for the peak-to-average power ratio (PAPR) reduction schemes for orthogonal frequency division multiplexing (OFDM) systems are discussed. First, the basic principle and implementation of the OFDM systems are introduced, where high PAPR of OFDM signal is one of main drawbacks of OFDM systems. Thus, many PAPR reduction schemes to solve this problem have been studied such as clipping, selected mapping (SLM), partial transmit sequence (PTS), and tone reservation. In the first part of this dissertation, a low-complexity SLM scheme is proposed, where the proposed SLM scheme generates alternative OFDM signal sequences by cyclically shifting the connections in each subblock at an intermediate stage of inverse fast Fourier transform (IFFT). Compared with the conventional SLM scheme, the proposed SLM scheme achieves similar PAPR reduction performance with much lower computational complexity and no bit error rate (BER) degradation. The performance of the proposed SLM scheme is analyzed mathematically and verified through numerical analysis. Also, it is shown that the proposed SLM scheme has the lowest computational complexity among the existing low-complexity SLM schemes exploiting the signals at an intermediate stage of IFFT. In the second part of this dissertation, an efficient selection (ES) method of the OFDM signal sequence with the minimum PAPR among many alternative OFDM signal sequences is proposed, which can be used for various SLM schemes. The proposed ES method efficiently generates each component of alternative OFDM signal by utilizing the structure of IFFT and calculates its power, and such generation procedure is interrupted if the calculated power is larger than the given threshold. By using the proposed ES method, the average computational complexity of considered SLM schemes is substantially reduced without degradation of PAPR reduction performance, which is confirmed by analytical and numerical results. In the third part of this dissertation, a clipping noise cancellation scheme using compressed sensing (CS) technique is proposed for OFDM systems. The proposed scheme does not need reserved tones or pilot tones, which is different from the previous works using CS technique. Instead, observations of the clipping noise in data tones are exploited, which leads to no loss of data rate. Also, in contrast with the previous works, the proposed scheme selectively exploits the reliable observations of the clipping noise instead of using whole observations, which results in minimizing the bad influence of channel noise. From the selected reliable observations, the clipping noise in time domain is reconstructed and cancelled by using CS technique. Simulation results show that the proposed scheme performs well compared to other conventional clipping noise cancellation schemes and shows the best performance in the severely clipped cases.1. Introduction 1 1.1. Background 1 1.2. Overview of Dissertation 4 2. OFDM Systems 6 2.1. OFDM System Model 7 2.2. Peak-to-Average Power Ratio 8 2.2.1. Definition of PAPR 9 2.2.2. Distribution of PAPR 9 3. PAPR Reduction Schemes 11 3.1. Clipping 11 3.1.1. Clipping at Transmitter 11 3.1.2. A Statistical Model of Clipped Signals 13 3.1.3. Conventional Receiver without Clipping Noise Cancellation Scheme 15 3.2. Selected Mapping 16 3.3. Low-Complexity SLM Schemes 18 3.3.1. Lims SLM Scheme [25] 18 3.3.2. Wangs SLM Scheme [22] 19 3.3.3. Baxleys SLM Scheme [27] 19 3.4. Tone Reservation 20 4. A New Low-Complexity SLM Scheme for OFDM Systems 22 4.1. A New SLM Scheme with Low-Complexity 23 4.1.1. A New SLM Scheme 23 4.1.2. Relation Between the Proposed SLM Scheme and the Conventional SLM Scheme 26 4.1.3. Good Shift Values for the Proposed SLM Scheme 28 4.1.4. Methods to Generate Good Shift Values 31 4.1.5. Computational Complexity 33 4.2. Simulation Results 36 4.3. Conclusions 37 5. An Efficient Selection Method of a Transmitted OFDM Signal Sequence for Various SLM Schemes 42 5.1. ES Method and Its Application to the Conventional SLM Scheme 43 5.1.1. Sequential Generation of OFDM Signal Components in the Conventional SLM Scheme 43 5.1.2. Application of the ES Method to the Conventional SLM Scheme 45 5.1.3. Complexity Analysis for Nyquist Sampling Case 47 5.1.3.1. Characteristics of a Nyquist-Sampled OFDM Signal Sequence 48 5.1.3.2. Derivation of KN(b) 49 5.1.3.3. Distribution of pBu(bu) 51 5.1.4. Complexity Analysis for Oversampling Case 52 5.1.4.1. Characteristics of a Four-Times Oversampled OFDM Signal Sequence 52 5.1.4.2. Derivation of K4N(b) 53 5.1.4.3. Distribution of pBu(bu) 54 5.1.5. Comparison between Analytical and Simulation Results 55 5.2. Application of the ES Method to Various Low-Complexity SLM Schemes 57 5.2.1. Lims SLM Scheme Aided by the ES Method 57 5.2.2. Wangs SLM Scheme Aided by the ES Method 58 5.2.3. Baxelys SLM Scheme Aided by the ES Method 58 5.3. Simulation Results 59 5.3.1. Simulation Results for the Conventional SLM Scheme Aided by the ES Method 59 5.3.2. Simulation Results for Low-Complexity SLM Schemes Aided by the ES Method 60 5.4. Conclusions 62 6. Clipping Noise Cancellation for OFDM Systems Using Reliable Observations Based on Compressed Sensing 68 6.1. Preliminaries 71 6.1.1. Notation 71 6.1.2. Compressed Sensing 71 6.2. Clipping Noise Cancellation for OFDM Systems Based on CS 73 6.2.1. Sparsity of c 73 6.2.1.1. Sparsity of c for Clipping at the Nyquist Sampling Rate 73 6.2.1.2. Sparsity of c for Clipping and Filtering at an Oversampling Rate 74 6.2.2. Reconstruction of the Clipping Noise c by CS 75 6.2.3. Construction of the Compressed Observation Vector Y 77 6.2.3.1. Which Observations Should Be Selected 78 6.2.3.2. Estimation of θ(k) Based on H1(k)Y (k) 78 6.2.3.3. Selection Criterion of Observations 81 6.2.4. Computational Complexity 81 6.3. Simulation Results 82 6.3.1. AWGN Channel 82 6.3.2. Rayleigh Fading Channel 83 6.4. Conclusion 86 7. Conclusions 93 Bibliography 96 초록 104Docto

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