A novel combined PAPR reduction and channel estimation approach for OFDM systems

International audienceIn this paper, a novel combination of peak-to-average power ratio (PAPR) reduction and channel estimation techniques for orthogonal frequency division multiplexing (OFDM) systems is addressed. In order to reduce the spectrum efficiency loss due the insertion of dedicated pilots for PAPR reduction issues, we propose to use some pilots dedicated for channel estimation to reduce the PAPR value. These pilots follow particular laws which allow their blind detection at the receiving side and avoid sending side information. At the receiver, based on these properties, the pilots are detected and channel estimation is then performed. The proposed laws operate in discrete domain to mitigate the performance degradation due to residual estimation error in continuous domain. Simulation results performed using the new DVB-T2 standard parameters show that the proposed approach gives better performance and higher spectral efficiency when compared to conventional Tone Reservation (TR) method

Prise en compte du facteur de crête dans le dimensionnement des systèmes de télécommunications

OFDM is a well known modulation scheme used in many digital communication systems due to its strong immunity to multi-path fading and impulse noise while providing high bit rates at the same time. Complex time-domain samples of OFDM signals are approximately Gaussian distributed due to the statistical independence of carriers and centrallimit theorem. This means that there could be some very high peaks present in the signal characterized by the Peak to Average Power Ratio (PAPR). This document covers my researchers regarding PAPR issue whose aim is to mitigate it so as to increase power amplifier efficiencies. It covers too applications to software and cognitive ratio.Toute forme de signal mettant en oeuvre une sommation de porteuses (orthogonales ou non) génère de fait des fluctuations temporelles, qui selon l'occurrence et l'amplitude, peuvent occasionner des distortions sévères au passage d'éléments non linéaires. Ces fluctuations sont le plus souvent désignées sous l'acronyme Peak to Average Power Ratio (PAPR). Ce PAPR peut être très élevé et il est alors nécessaire de le diminuer en proposant des méthodes appropriées. Ce document d'HDR synthétise l'ensemble de mes activités de recherche entre 1997 et 2010. Il aborde de façon très large la problématique de réduction du PAPR dans des problématiques variées (OFDM, radio logicielle, radio intelligente) et des contextes différents (projets collaboratifs et bilatéraux). J'ai été amené dans ce cadre à encadrer des étudiants en thèse ainsi que des post-doctorants

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

Interleaving Technique Implementation to Reduce PAPR of OFDM Signal in Presence of Nonlinear Amplification with Memory Effects, Journal of Telecommunications and Information Technology, 2018, nr 3

In OFDM systems, peak-to-average power ratio (PAPR) reduction of the signal is one of the main challenges that need to be overcome in order to use the transmitter in an efficient manner. As one of attractive techniques, interleaving can be used in PAPR reduction for multicarrier signals without spectrum distortion. In this paper, the authors propose to extend the possibilities of interleaving to improve PAPR reduction, to use a new coding of interleaver keys at the transmitter and a robust decoding procedure at the receiver. In order not to degrade the data rate, the use of null subcarriers to transmit side information to the receiver is proposed and evaluated. Simulation results in the context of the WLAN 802.11a standard in the presence of a nonlinear power amplifier model with memory, show a reduction of PAPR of approximately 5.2 dB, and an improvement of bit error rate and error vector magnitude of about 2 decades and 4% respectively, while respecting the spectral mask specification

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

Joint design of PAPR, PICR and OBP in OFDM systems

Orthogonal frequency division multiplexing (OFDM) technique has been adopted by many existing and future wireless communication systems for high-speed data transmission. However, a major problem of OFDM systems is the high peak-to-average power ratio (PAPR) of OFDM signals, which results in inefficient operations of nonlinear devices in the system such as power amplifiers (PAs). On the other hand, at the receiver end, frequency offset, caused by Doppler frequency shifts, mismatched oscillators, or a fast fading channel, destroys the orthogonality among subcarriers and results in inter-carrier interference (ICI), thus degrades the detection performance of OFDM systems. Analogous to the definition of PAPR, the peak interference-to-carrier ratio (PICR) is defined to represent the effect of ICI. In addition, due to the sidelobes of modulated subcarriers, OFDM systems also suffer from high out-of-band power (OBP) radiations. High OBP results in the need for wide guard band and thus inefficient usage of frequency band

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

Advanced Linear Identification Techniques For Signal Processing And Digital Video Broadcasting

Linear identification technique is to linearly embed a piece of unique information into digital media data for the purpose of satisfying specific demands such as identification, annotation, and copyright, etc. We need to consider the quantity and the quality of identification data to be embedded as well as the corresponding interference to the original subject signal. However, there exist no generalized computationally-efficient optimization techniques for linear identification up to now. Therefore, in this dissertation work, we try to theoretically investigate the advanced linear identification techniques and combat the tradeoff problems between the quality of the embedded identification data and the quality of the subject signal. Two particular signal processing and telecommunication applications, namely transmitter identification and digital watermarking, will be exploited in this work. We propose a novel optimization paradigm for both digital terrestrial television (DTV) systems and multiple digital watermarking systems to maximize the overall signal-to-interference-plus-noise ratio (SINR) over both identification and subject signals. The new theories and practice related to pseudo random sequences, extended arithmetic-geometric mean inequality, and constrained overall system performance are also presented in this dissertation

Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications

Preliminary definition and evaluation of advanced space concepts. Volume 2: Analyses and results

For abstract, see N78-28106