Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion

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 of an offset modulation transmission

In this article, a method called offset modulation (OM-OFDM) is proposed to control the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. The theoretical bandwidth occupancy of the proposed offset modulated signal is derived. Using these bandwidth occupancy results, a closed-form theoretical bit error rate (BER) expression for an offset modulated transmission is derived and validated. Thereafter, a BER comparison between OM-OFDM and OFDM at a PAPR value of 13 dB shows that both methods offer similar BER characteristics for frequency selective fading channel conditions. The OM-OFDM method in addition is able to accurately control the PAPR of a transmission for a targeted BER. The authors have further proposed a newly applied power performance decision metric, which can be used throughout the PAPR field, in order to compare various methods. By using this power performance decision metric, the authors show that OM-OFDM offers between 4 dB–1.2 dB (60.34%–24.6%) and 4.1 dB–1.2 dB (60.8%–23.6%), net power performance gain (at a BER of 10−4) when compared to a clipped OFDM, OFDM, tone reserved (TR) OFDM and an active constellation extended (ACE) OFDM transmission in a frequency selective fading channel. Finally, by using a complementary cumulative distribution function (CCDF), the OM-OFDM method is shown to offer between 3.2 dB and 2 dB PAPR reduction (at a CCDF of 10−1) when compared to an OFDM, TR, clipped, and ACE OFDM transmission.This work is currently being patented by the University of Pretoria. Both authors are inventors on the patent, with the University of Pretoria holding the patent rights. This paper is based on work, for which the author has been awarded a PhD at the University of Pretoria. The necessary permissions have been obtained to publish such material.http://jwcn.eurasipjournals.com/content/2013/1/19am2013ai201

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

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

Nonlinear effects in OFDM signal transmission over radio over fibre links

The dynamic range limitations that arise from nonlinearity in low-cost and low complexity directly modulated radio over fibre (RoF) links are examined. Statistical non linear models are presented and applied to the case of a RoF link with a low biased laser diode. The effects of distortion on the Error Vector Magnitude (EVM) performance of Orthogonal Frequency-Division Multiplexing (OFDM) signals with different numbers of subcarriers and the connection to the Peak-ta-Average Power Ratio (PAPR) of the signals are investigated. Statistical distributions of the EVM over a large number of transmitted OFDM frames are gained from experimental measurements and analyses of idealized processes. The measurement results show that as the number of subcarriers is reduced the distribution means are not dependent in the expected way on the statistical PAPR of the transmitted OFDM signals. Instead, it is shown that in regions of moderate distortion the median of the EVM is more closely related to the statistical PAPR and to the required back-off for signals with different numbers of subcarriers. Through the employed statistical analysis, the asymptotic convergence of the EVM result to that expected in the idealized case is observed. The results of this analysis also show, how, including the EVM variance in estimations for back-off might be useful, how, in a measurement, the number of transmitted OFDM frames affects the estimated mean EVM. Differing EVM results for subcarriers at the edge and middle of the signal band show that distortion affects the subcarriers at the middle of the band to a stronger degree and that their behaviour is correlated "to the statistical PAPR of the individual signals. Then, a laser model validated against measured performance is designed arid used for simulating the performance of a subcarrier multiplexed 4th generation mobile/wireless RoF transmission system. Predictions indicate that the architecture provides adequate performance in terms of EVM, for different IFFT sizes and modulation levels of up to 256 QAM (at leastL and a combined raw data rate of up to 3.2 Gbps. Based on a 1.5% EVM transmitter requirement with 256 QAM, a system dynamic range of approximately 5.1 dB is predicted. Finally, the use of companding in a directly modulated RaF link, with the aim of reducing the amplification (and isolation) requirements in the remote antenna unit, is demonstrated, quantified through EVM measurements. The resulting improvements in output power are approximately 4.7 dB at an EVM transmitter requirement of 5.6 %, while in terms of the point of onset of distortion-induced EVM increase, the improvement is approximately 7.6 dB

Algoritmos para la reducción de los picos de potencia en los sistemas OFDM

La modulación OFDM (Orthogonal Frequency Division Multiplexing) es una técnica de transmisión multiportadora, que debido a sus grandes ventajas se utiliza en numerosos estándares de comunicaciones de banda ancha. Sin embargo, uno de los principales inconvenientes que presenta la modulación OFDM, en el lado transmisor, es la presencia ocasional de grandes picos en su potencia instantánea con respecto a su potencia media, conocido en la literatura como el problema de la PAPR (Peak-to-Average Power Ratio) de los sistemas OFDM. Al pasar la señal con PAPR elevada por el amplificador de alta potencia (HPA - High Power Amplifier ) se produce saturación del dispositivo, provocando radiación fuera de banda, que afecta a las bandas adyacentes, y radiación dentro de banda, que produce rotación, atenuación y desplazamiento de la señal, provocando un incremento en la tasa de error de bit (BER - Bit Error Rate). Para contrarrestar estos efectos, se debe reducir la PAPR de la senñal OFDM transmitida con algún tipo de manipulación en la señal. Una de las técnicas de reducción de la PAPR más prometedoras es la técnica CE (Constellation Extension), que mueve inteligentemente ciertos puntos externos de la constelación del símbolo OFDM en el dominio de la frecuencia, de tal forma que la señal en el dominio del tiempo tenga una PAPR menor. La extensión de la constelación de esta forma no afecta a la distancia mínima de la constelación y, consecuentemente, no se experimenta degradación en la BER del sistema. Además, no hay pérdida en la tasa de transmisión de datos porque no se requiere la transmisión de información de control. Sin embargo, se introduce un incremento de la energía por símbolo. El objetivo principal de esta Tesis es proponer varios algoritmos de reducción de la PAPR, basados en técnicas CE. Por un lado, como primer objetivo (capítulo 4) se presentan algoritmos eficientes en energía, que se consiguen al combinar adecuadamente un esquema CE, basado en métrica, con secuencias piloto. Dicha combinación deja tres posibles arquitecturas de implementación dependiendo del orden en que se usa cada algoritmo. Se determina la arquitectura que proporciona un compromiso adecuado entre reducción de la PAPR y complejidad, esta última medida en términos del número de ciclos adicionales del procesador (que se traducen en energía consumida) que se requieren para procesar la reducción de la PAPR. Además, se demuestra que las tres arquitecturas propuestas demandan una energía por símbolo menor que otras técnicas CE, si se insertan adecuadamente las secuencias piloto en el símbolo OFDM Por otro lado, como segundo objetivo se presentan los esquemas de reducción de la PAPR, basados en técnicas CE, que se formulan como problemas de optimización (capítulo 5). Se propone una solución óptima, en térrminos de reducción de la PAPR, llamada algoritmo GBDCE (Generalized Benders Decomposition for Constellation Extension), el cual se plantea como un problema no lineal mixto-entero (MINLP - Mixed Integer Non-Linear Programming) y que sirve como cota inferior de referencia para comparar con otras técnicas CE. Además, se proponen los algoritmos subóptimos: BBCE (Branch-and-Bound for Constellation Extension) que se formula como un problema de programación entera, y DCE (Dynamic Constellation Extension) que combina un esquema BBCE con un algoritmo basado en métrica. El objetivo de ambos algoritmos subóptimos es reducir la complejidad del algoritmo óptimo.OFDM (Orthogonal Frequency Division Multiplexing) modulation is a multicarrier transmission technique that, due to its important advantages, has been widely used in many wideband communication standards. However, one of the major drawbacks of the transmitted OFDM signal is the infrequent high peak power with respect to average power, which is known in the literature as the PAPR (Peak-to-Average Power Ratio) problem in OFDM systems. When the signal with high PAPR passes through an HPA (High Power Amplifier), it suffers from saturation, which causes both out-of-band radiation, that affects the adjacent channels, and in-band radiation, which produces rotation, attenuation and shift of the signal, that increases the BER (Bit Error Rate). In order to address the PAPR problem, the OFDM signal must be manipulated. One of the most promising PAPR techniques is CE (Constellation Extension), that intelligently moves certain outer constellation points of the OFDM signal in the frequency domain, in such way that the OFDM signal in the time domain has a lower PAPR. The constellation extension in this way does not affect the minimum distance of the constellation, and BER degradation is not consequently experienced by the system. Moreover, there is no user's data rate loss because these methods do not require side information. Nevertheless, they introduce an increase in the energy per symbol. The main aim of this Thesis is to propose several PAPR reduction algorithms, based on CE techniques. On one side, the first objective (chapter 4) is to present an energy efficient algorithm, which consists in the adequate combination of a metric-based CE technique with pilot sequences. The combination allows three possible implementation architectures, depending on the order of use of the algorithms. It has been determined the architecture that provides an adequate trade-o_ between PAPR reduction and complexity, the latter measured in number of additional CPU cycles (which translates into energy consumption) needed to perform the PAPR reduction. Moreover, the three proposed architectures require less energy per symbol than other CE techniques, if the pilot sequences are appropriately inserted in the OFDM symbol. On the other side, the second objective is to present CE based algorithms, which are formulated as an optimization problem (chapter 5). The optimal solution, in terms of PAPR reduction is called GBDCE (Generalized Benders Decomposition for Constellation Extension) algorithm. GBDCE is formulated as a MINLP (Mixed Integer Non-Linear Programming) problem, and it turns out to be a lower bound for CE schemes and provides a benchmark to compare with other CE technique. Moreover, two suboptimal algorithms are proposed: BBCE (Branch-and-Bound for Constellation Extension), which is formulated as Integer Programming, and DCE (Dynamic Constellation Extension), that combines a BBCE scheme with a metric-based algorithm. The objective of both suboptimal algorithms is to reduce the GBDCE complexity.Financiación de la Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) de Ecuador, Fundación Carolina (España) y del Proyecto Nacional de España GRE3N-SYST (TEC2011-29006-C03-03).Doctor en Programa Oficial de Posgrado en Multimedia y ComunicacionesPresidente: Ana García Armada.- Secretario: Sancho Salcedo Sanz.- Vocal: Santiago Zazo Bell

PAPR reduction in FBMC using an ACE-based linear programming optimization

This paper presents four novel techniques for peak-to-average power ratio (PAPR) reduction in filter bank multicarrier (FBMC) modulation systems. The approach extends on current PAPR reduction active constellation extension (ACE) methods, as used in orthogonal frequency division multiplexing (OFDM), to an FBMC implementation as the main contribution. The four techniques introduced can be split up into two: linear programming optimization ACE-based techniques and smart gradient-project (SGP) ACE techniques. The linear programming (LP)-based techniques compensate for the symbol overlaps by utilizing a frame-based approach and provide a theoretical upper bound on achievable performance for the overlapping ACE techniques. The overlapping ACE techniques on the other hand can handle symbol by symbol processing. Furthermore, as a result of FBMC properties, the proposed techniques do not require side information transmission. The PAPR performance of the techniques is shown to match, or in some cases improve, on current PAPR techniques for FBMC. Initial analysis of the computational complexity of the SGP techniques indicates that the complexity issues with PAPR reduction in FBMC implementations can be addressed. The out-of-band interference introduced by the techniques is investigated. As a result, it is shown that the interference can be compensated for, whilst still maintaining decent PAPR performance. Additional results are also provided by means of a study of the PAPR reduction of the proposed techniques at a fixed clipping probability. The bit error rate (BER) degradation is investigated to ensure that the trade-off in terms of BER degradation is not too severe. As illustrated by exhaustive simulations, the SGP ACE-based technique proposed are ideal candidates for practical implementation in systems employing the low-complexity polyphase implementation of FBMC modulators. The methods are shown to offer significant PAPR reduction and increase the feasibility of FBMC as a replacement modulation system for OFDM.http://asp.eurasipjournals.com/hb201

PAPR Reduction Solutions for 5G and Beyond

The latest fifth generation (5G) wireless technology provides improved communication quality compared to earlier generations. The 5G New Radio (NR), specified by the 3rd Generation Partnership Project (3GPP), addresses the modern requirements of the wireless networks and targets improved communication quality in terms of for example peak data rates, latency and reliability. On the other hand, there are still various crucial issues that impact the implementation and energy-efficiency of 5G NR networks and their different deployments. The power-efficiency of transmitter power amplifiers (PAs) is one of these issues. The PA is an important unit of a communication system, which is responsible from amplifying the transmit signal towards the antenna. Reaching high PA power-efficiency is known to be difficult when the transmit waveform has a high peak-to-average power ratio (PAPR). The cyclic prefix (CP)-orthogonal frequencydivision multiplexing (OFDM) that is the main physical-layer waveform of 5G NR, suffers from such high PAPR challenge. There are generally many PAPR reduction methods proposed in the literature, however, many of these have either very notable computational complexity or impose substantial inband distortion. Moreover, 5G NR has new features that require redesigning the PAPR reduction methods. In line with these, the first contribution of this thesis is the novel frequencyselective PAPR reduction concept, where clipping noise is shaped in a frequencyselective manner over the active passband. This concept is in line with the 5G NR, where aggressive frequency-domain multiplexing is considered as an important feature. Utilizing the frequency-selective PAPR reduction enables the realization of the heterogeneous resource utilization within one passband. The second contribution of this thesis is the frequency-selective single-numerology (SN) and mixed-numerology (MN) PAPR reduction methods. The 5G NR targets utilizing different physical resource blocks (PRBs) and bandwidth parts (BWPs) within one passband flexibly. Yet, existing PAPR reduction methods do not exploit these features. Based on this, novel algorithms utilizing PRB and BWP level control of clipping noise are designed to meet error vector magnitude (EVM) limits of the modulations while reducing the PAPR. TheMNallocation has one critical challenge as inter numerology interference (INI) emerges after aggregation of subband signals. Proposed MN PAPR reduction algorithm overcomes this issue by cancelling INI within the PAPR reduction loop, which has not been considered earlier. The third contribution of this thesis is the proposal of two novel non-iterative PAPR reduction methods. First method utilizes the fast-convolution filteredOFDM (FC-F-OFDM) that has excellent spectral containment, and combines it with clipping. Moreover, clipping noise is also allocated to guard bands by filter passband extension (FPE) and clipping noise in out-of-band (OOB) regions is essentially filtered through FC filtering. The second method is the guard-tone reservation (GTR) which is applied to discrete Fourier transform-spread-OFDM (DFT-s-OFDM). Uniquely, GTR estimates the time domain peaks in data symbol domain before inverse fast Fourier transform (IFFT), and uses guard band tones for PAPR reduction. The fourth contribution of the thesis is the design of two novel machine learning (ML) algorithms that improve the drawbacks of frequency-selective PAPRreduction. The first ML algorithm, PAPRer, models the nonlinear relation between the PAPR target and the realized PAPR value. Then, it auto-tunes the optimal PAPR target and this way minimizes the realized PAPR. The second ML algorithm, one-shot clipping-and-filtering (OSCF), solves the complexity problem of iterative clipping and filtering (ICF)-like methods by generating proper approximated clipping noise signal after running only one iteration, leading to very efficient PAPR reduction. Finally, an over-arching contribution of this thesis is the experimental validation of the performance benefits of the proposed methods by considering realistic 5GNR uplink (UL) and downlink (DL) testbeds that include realistic PAs and associated hardware. It is very important to confirm the practical benefits of the proposed methods and, this is realized with the conducted experimental work