60 research outputs found

    Peak-to-Average Power Ratio Reduction of DOCSIS 3.1 Downstream Signals

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    Tone reservation (TR) is an attractive and widely used method for peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals, where both transmitter and receiver agree upon a number of subcarriers or tones to be reserved to generate a peak canceling signal that can reduce the peak power of the transmitted signals. The tones are selected to be mutually exclusive with the tones used for data transmission, which allows the receiver to extract the data symbols without distortions. This thesis presents two novel PAPR reduction algorithms for OFDM signals based on the TR principle, which do not distort the transmitted signals. The first proposed algorithm is performed in the time domain, whereas the second algorithm is a new clipping-and-filtering method. Both algorithms consist of two stages. The first stage, which is done off-line, creates a set of canceling signals based on the settings of the OFDM system. In particular, these signals are constructed to cancel signals at different levels of maximum instantaneous power that are above a predefined threshold. The second stage, which is online and iterative, reduces the signal peaks by using the canceling signals constructed in the first stage. The precalculated canceling signals can be updated when different tone sets are selected for data transmission, accommodating many practical applications. Simulation results show that the proposed algorithms achieve slightly better PAPR reduction performance than the conventional algorithms. Moreover, such performance is achieved with much lower computational complexity in terms of numbers of multiplications and additions per iteration. Among the two proposed algorithms, the time-domain algorithm gives the best peak reduction performance but the clipping-and-filtering algorithm requires considerably less number of multiplications per iteration and can be efficiently implemented using the fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT) structure

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

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    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

    Enhanced Multicarrier Techniques for Professional Ad-Hoc and Cell-Based Communications (EMPhAtiC) Document Number D3.3 Reduction of PAPR and non linearities effects

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    Livrable d'un projet Européen EMPHATICLike other multicarrier modulation techniques, FBMC suffers from high peak-to-average power ratio (PAPR), impacting its performance in the presence of a nonlinear high power amplifier (HPA) in two ways. The first impact is an in-band distortion affecting the error rate performance of the link. The second impact is an out-of-band effect appearing as power spectral density (PSD) regrowth, making the coexistence between FBMC based broad-band Professional Mobile Radio (PMR) systems with existing narrowband systems difficult to achieve. This report addresses first the theoretical analysis of in-band HPA distortions in terms of Bit Error Rate. Also, the out-of band impact of HPA nonlinearities is studied in terms of PSD regrowth prediction. Furthermore, the problem of PAPR reduction is addressed along with some HPA linearization techniques and nonlinearity compensation approaches

    Adjustable dynamic range for paper reduction schemes in large-scale MIMO-OFDM systems

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    In a multi-input-multi-output (MIMO) communication system there is a necessity to limit the power that the output antenna amplifiers can deliver. Their signal is a combination of many independent channels, so the demanded amplitude can peak to many times the average value. The orthogonal frequency division multiplexing (OFDM) system causes high peak signals to occur because many subcarrier components are added by an inverse discrete Fourier transformation process at the base station. This causes out-of-band spectral regrowth. If simple clipping of the input signal is used, there will be in-band distortions in the transmitted signals and the bit error rate will increase substantially. This work presents a novel technique that reduces the peak-to-average power ratio (PAPR). It is a combination of two main stages, a variable clipping level and an Adaptive Optimizer that takes advantage of the channel state information sent from all users in the cell. Simulation results show that the proposed method achieves a better overall system performance than that of conventional peak reduction systems in terms of the symbol error rate. As a result, the linear output of the power amplifiers can be minimized with a great saving in cost

    Boosted PTS Method with Mu-Law Companding Techniques for PAPR Reduction in OFDM Systems

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    This paper proposes an enhanced PAPR reduction technique which combines an enhanced PTS method with Mu-Law companding. The enhanced PTS method improves performances in both the partitioning and phase rotation steps. Enhancement in partitioning is achieved through a judicious incorporation of AP-PTS scheme into the IP-PTS. As for phase rotation, an optimal set of rotation vectors is derived based on the correlation properties of candidate signals. The PAPR reduction of this enhanced PTS method is further improved by annexing Mu-Law companding at the end of the enhanced PTS. This application of Mu-Law characteristic in the time domain of OFDM signal significantly improves the PAPR reduction capability of the approach. Simulation results show that the PAPR performance of the enhanced PTS method with Mu-Law companding technique on various scenarios with different modulation schemes is better than that of the PRP-PTS. This approach can be considered as a very attractive candidate for achieving a significant reduction of PAPR, while maintaining a low computational complexity

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

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    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

    Low Complex PAPR Reduction Schemes for OFDM Systems

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    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

    PAPR Reduction of OFDM Signals Using Clipping and Coding

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    The problem of the high peak to average ratio (PAPR) in OFDM signals is investigated with a brief presentation of the various methods used to reduce the PAPR with special attention to the clipping method. An alternative approach of clipping is presented, where the clipping is performed right after the IFFT stage unlike the conventional clipping that is performed in the power amplifier stage, which causes undesirable out of signal band spectral growth. In the proposed method, there is clipping of samples not clipping of wave, therefore, the spectral distortion is avoided. Coding is required to correct the errors introduced by the clipping and the overall system is tested for two types of modulations, the QPSK as a constant amplitude modulation and 16QAM as a varying amplitude modulation
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