A novel PAPR reduction scheme based on selective mapping and a random-like coding with no explicit side information in OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for high data rate and reliable communication over fading channels. The main implementation drawback of this system is the possibility of high Peak to Average Power Ratio (PAPR). In this paper, we develop a novel Selective Mapping (SLM) PAPR reduction technique. In the novel proposed scheme, the alternative symbol sequences are generated by module 2 additions of data with the rows of cyclic Hadamard matrix with the same size, inserting the selected row's number to avoid transmitting any side information and specially using a random-like Irregular Repeat Accumulate (IRA) encoder for both PAPR and Bit Error Rate (BER) better performance. Keywords: IRA Codes, OFDM, PAPR, SLM method

On PAPR Reduction of OFDM using Partial Transmit Sequence with Intelligent Optimization Algorithms

In recent time, the demand for multimedia data services over wireless links has grown up rapidly. Orthogonal Frequency Division Multiplexing (OFDM) forms the basis for all 3G and beyond wireless communication standards due to its efficient frequency utilization permitting near ideal data rate and ubiquitous coverage with high mobility. OFDM signals are prone to high peak-to-average-power ratio (PAPR). Unfortunately, the high PAPR inherent to OFDM signal envelopes occasionally drives high power amplifiers (HPAs) to operate in the nonlinear region of their characteristic leading out-of-band radiation, reduction in efficiency of communication system etc. A plethora of research has been devoted to reducing the performance degradation due to the PAPR problem inherent to OFDM systems. Advanced techniques such as partial transmit sequences (PTS) and selected mapping (SLM) have been considered most promising for PAPR reduction. Such techniques are seen to be efficient for distortion-less signal processing but suffer from computational complexity and often requires transmission of extra information in terms of several side information (SI) bits leading to loss in effective data rate. This thesis investigates the PAPR problem using Partial Transmit Sequence (PTS) scheme, where optimization is achieved with evolutionary bio-inspired metaheuristic stochastic algorithms. The phase factor optimization in PTS is used for PAPR reduction. At first, swarm intelligence based Firefly PTS (FF-PTS) algorithm is proposed which delivers improved PAPR performance with reduced searching complexity. Following this, Cuckoo Search based PTS (CS-PTS) technique is presented, which offers good PAPR performance in terms of solution quality and convergence speed. Lastly, Improved Harmony search based PTS (IHS-PTS) is introduced, which provides improved PAPR. The algorithm has simple structure with a very few parameters for larger PTS sub-blocks. The PAPR performance of the proposed technique with different parameters is also verified through extensive computer simulations. Furthermore, complexity analysis of algorithms demonstrates that the proposed schemes offer significant complexity reduction when compared to standard PAPR reduction techniques. Findings have been validated through extensive simulation tests

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

Journal of Telecommunications and Information Technology, 2018, nr 3

kwartalni

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 base T-transform for wireless communication networks

The prominent features associated with orthogonal frequency division multiplexing (OFDM) have been exploited in the area of high-speed communication networks. However, OFDM is prone to impairments such as frequency selective fading channel, high peak-to-average power ratio (PAPR) and heavy-tailed distributed impulsive noise, all of which can have negative impacts on its performance. These issues have received a great deal of attention in recent research. To compensate for these transmission impairments, a T-OFDM based system is introduced using a low computational complexity T-transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. The key contribution in this thesis is on the use of the T-transform along with three novel receiver designs. Additionally, new theoretical bit error rate (BER) formulae for the T-OFDM system are derived over communications channels using zero forcing (ZF) and minimum mean square error (MMSE) detectors, that are validated via simulation and shown to have close performance with the obtained performance results. It has been found that the T-OFDM outperformed the conventional OFDM based systems in the investigated channel models by achieving a signal-to-noise ratio (SNR) gain range of between 9dB and 16dB measured at 10−4 BER. In addition, the sparsity and block diagonal structure of the T-transform, along with its lower summation processes are exploited in this study to reduce the superposition of the subcarriers, leading to reduce the peak of the transmitted signals by a range of 0.75 to 1.2 dB with preserved average power. Furthermore, these attractive features of T-transform are employed with the conventional selective mapping (SLM) and partial transmitted sequences (PTS) schemes to propose three low cost novel techniques; T-SLM, T-PTS-I, and T-PTS-II. Compared to the conventional schemes, the T-SLM and T-PTS-I schemes have achieved a considerable reduction in both computational complexity and in PAPR, further increasing multipath resilience, even in the presence of high power amplifier (HPA). Whereas using the T-PTS-II scheme, the complexity ratio has been significantly reduced by approximately 80%, as well as reducing the SI bits further by two, with negligible PAPR degradation. Moreover, the effect of the independent sections of T-transform on the performance of T-OFDM system over the impulsive channel is addressed in this work, by deriving a new theoretical BER formula over such a transmission media. Furthermore, two novel II schemes WHT-MI-OFDM and WHT-MI-OFDM incorporating nonlinear blanking, both of which utilise the WHT and a matrix interleaver (MI) with the OFDM system, are proposed to suppress the deleterious effects of a severe impulsive noise burst on the T-OFDM system performance. Comparing with the traditional MI-OFDM system, the proposed schemes are much more robust to disturbances arising from the impulsive channel.EThOS - Electronic Theses Online ServiceMinistry of Higher Education and Scientific ResearchIraqGBUnited Kingdo

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

Performance evaluation of T-transform based OFDM in underwater acoustic channels

PhD ThesisRecently there has been an increasing trend towards the implementation of orthogonal frequency division multiplexing (OFDM) based multicarrier communication systems in underwater acoustic communications. By dividing the available bandwidth into multiple sub-bands, OFDM systems enable reliable transmission over long range dispersive channels. However OFDM is prone to impairments such as severe frequency selective fading channels, motioned induced Doppler shift and high peak-to-average-power ratio (PAPR). In order to fully exploit the potential of OFDM in UWA channels, those issues have received a great deal of attention in recent research. With the aim of improving OFDM's performance in UWA channels, a T-transformed based OFDM system is introduced using a low computational complexity T-transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. Through real-world experiment, performance comparison between the proposed T-OFDM system and conventional OFDM system revealed that T-OFDM performs better than OFDM with high code rate in frequency selective fading channels. Furthermore, investigation of different equalizer techniques have shown that the limitation of ZF equalizers affect the T-OFDM more (one bad equalizer coefficient affects all symbols) and so developed a modified ZF equalizer with outlier detection which provides major performance gain without excessive computation load. Lastly, investigation of PAPR reduction methods delineated that T-OFDM has inherently lower PAPR and it is also far more tolerant of distortions introduced by the simple clipping method. As a result, lower PAPR can be achieved with minimal overhead and so outperforming OFDM for a given power limit at the transmitter

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

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