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

Multicarrier communication systems with low sensibility to nonlinear amplification

Actualment estem entrant a una nova era de la informació amb gran demanda de sistemes de comunicació sense fils. Nous serveis com dades i video requereixen transmissions fiables d'alta velocitat, fins i tot en escenaris d'alta mobilitat. A més a més, la dificultat d'assignar el limitat espectre radioelèctric juntament amb la necessitat d'incrementar el temps de vida de les bateries dels terminals mòbils, requereix el diseny de transceptors que usin la potència i l'ampla de banda disponibles de manera eficient. Les comunicacions multiportadora basades en OFDM són capaces de satisfer la majoria d'aquests requeriments. Però, entre altres reptes, reduir la sensibilitat a la amplificació no-lineal és un factor clau durant el diseny. En aquesta tesi doctoral s'analitza la sensibilitat dels sistemes multiportadora basats en OFDM a l'amplificació no-lineal i es consideren formes eficients per superar aquest problema. La tesi s'enfoca principalment al problema de reduir les fluctuacions de l'envolupant del senyal transmès. En aquest sentit es presenta també un estudi de les mètriques de l'envolupant del senyal, PAPR i CM. A més a més, basant-nos en l'anàlisis presentat es proposen noves tècniques per sistemes OFDM i MC-SS. Per MC-SS, també es tracta el diseny d'una tècnica de postprocessament en forma de detector multiusuari per canals no-lineals.Actualmente estamos entrando en una nueva era de la información donde se da una gran demanda de sistemas de comunicación inalámbricos. Nuevos servicios como datos y vídeo requieren transmisiones fiables de alta velocidad, incluso en escenarios de alta movilidad. Además, la dificultad de asignar el limitado espectro radioeléctrico junto con la necesidad de incrementar el tiempo de vida de las baterías de los terminales móviles, requiere el diseño de transceptores que usen eficientemente la potencia y el ancho de banda disponibles. Las comunicaciones multiportadora basadas en OFDM son capaces de satisfacer la mayoría de dichos requerimientos. Sin embargo, entre otros retos, reducir su sensibilidad a la amplificación no-lineal es un factor clave durante el diseño. En esta tesis se analiza la sensibilidad de los sistemas multiportadora basados en OFDM a la amplificación no-lineal y se consideran formas eficientes para superar dicho problema. La tesis se enfoca principalmente al problema de reducir las fluctuaciones de la envolvente. En este sentido también se presenta un estudio de las métricas de la señal, PAPR y CM. Además, basándonos en el análisis presentado se proponen nuevas técnicas para OFDM y MC-SS. Para MC-SS, también se trata el diseño de un detector multiusuario para canales no-lineales.We are now facing a new information age with high demand of wireless communication systems. New services such as data and video require achieving reliable high-speed transmissions even in high mobility scenarios. Moreover, the difficulty to allocate so many wireless communication systems in the limited frequency band in addition to the demand for long battery life requires designing spectrum and power efficient transceivers. Multicarrier communications based on OFDM are known to fulfill most of the requirements of such systems. However, among other challenges, reducing the sensitivity to nonlinear amplification has become a design key. In this thesis the sensitivity of OFDM-based multicarrier systems to nonlinear amplification is analyzed and efficient ways to overcome this problem are considered. The focus is mainly on the problem of reducing the envelope fluctuations. Therefore, a study of the signal metrics, namely PAPR and CM, is also presented. From the presented analysis, several new techniques for OFDM and MC-SS are proposed. For MC-SS, the design of a post-processing technique in the form of a multiuser detector for nonlinearly distorted MC-SS symbols is also addressed

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before. PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast. Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts

On Efficient Signal Processing Algorithms for Signal Detection and PAPR Reduction in OFDM Systems

The driving force of the study is susceptibility of LS algorithm to noise. As LS algorithm is simple to implement, hence it’s performance improvement can contribute a lot to the wireless technology that are especially deals with high computation. Cascading of AdaBoost algorithm with LS greatly influences the OFDM system performance. Performance of Adaptive Boosting based symbol recovery was investigated on the performance of LS, MMSE, BLUE were also compared with the performance of AdaBoost algorithm and MMSE has been found the higher computational complexity. Furthermore, MMSE also requires apriori channel statistics and computational complexity O(5N3) of the MMSE increases exponentially as the number of carrier increases. For the Adaboost case the computational complexity calculation is little different.Therefore, in the training stage of the AdaBoost algorithm, the computational complexity is only O(nT M) Furthermore, as it is a classification algorithm so in the receiver side we will require a separate de-mapper (or decoder) to get the desired data bits, i.e., a. SAS aided DCT based PAPR reduction 1326 and b. SAS aided DCT based PAPR reduction. A successive addition subtraction preprocessed DCT based PAPR reduction technique was proposed. Here, the performance of proposed method was compared with other preexisting techniques like SLM and PTS and the performance of the proposed method was seen to outperform specially in low PAPR region. In the proposed PAPR reduction method, the receiver is aware of the transmitted signal processing, this enables a reverse operation at the receiver to extract the transmit data. Hence the requirement of sending extra information through extra subcarrier is eliminated. The proposed method is also seen to be spectrally efficient. In the case of PTS and SLM it is inevitable to send the side information to retrieve the transmit signal. Hence, these two methods are spectrally inefficient. Successive addition subtraction based PAPR reduction method was also applied to MIMO systems. The performance of the SAS based PAPR reduction method also showed better performance as compared to other technique. An extensive simulation of MIMO OFDM PAPR reduction was carried out by varying the number of subcarriers and number of transmitter antennas. A detailed computational complexity analysis was also carried out. BATE aided SDMA multi user detection. A detailed study of SDMA system was carried out with it’s mathematical analysis.Many linear and non linear detectors like ML, MMSE, PIC, SIC have been proposed in literature for multiuser detection of SDMA system. However, except MMSE every receivers other are computational extensive. So as to enhance the performance of the MMSE MUD a meta heuristic Bat algorithm was incorporated in cascade with MMSE

Development of digital predistorters for broadband power amplifiers in OFDM systems using the simplicial canonical piecewise linear function

Power amplifiers (PAs) are inherently nonlinear devices. Linearity of a PA can be achieved by backing off the PA to its linear region at the expense of power efficiency loss. For signals with high envelope fluctuation such OFDM system, large backoff is required, causing significant loss in power efficiency. Thus, backoff is not a favourable solution. Digital predistorters (PDs) are widely employed for linearizing PAs that are driven to the nonlinear regions. In broadband systems where PAs exhibit memory effects, the PDs are also required to compensate the memory effects. This thesis deals with the development of digital PDs for broadband PAs in OFDM systems using the Simplicial Canonical Piecewise Linear (SCPWL) function. The SCPWL function offers a few advantages over polynomial models. It imposes a saturation after the last breakpoint, making it suitable for modelling nonlinearities of PA and PD. The breakpoints of the function can be freely placed to allow optimum fitting of a given nonlinearity. It is suitable for modeling strong nonlinearities. Analysis of the SCPWL spectra property shows that the function models infinite order of intermodulation distortion, even with small number of breakpoints. The accuracy of the model can be improved by increasing the number of breakpoints. The original real-valued SCPWL function is extended to include memory structure and complex-valued coefficients, resulting in the proposed baseband SCPWL model with memory. The model is adopted in the development of the Hammerstein-SCPWL PD and memory-SCPWL PD. Vector projection methods are developed for static SCPWL PDs identification. Adaptive algorithms employing the indirect and direct learning architectures are developed for identifying the Hammerstein-SCPWL PD and memory-SCPWL PD. By exploiting the properties of the SCPWL function, the algorithms are simplified. A modified Wiener model estimator is employed to circumvent the non-convex cost function problem of block models. This further reduces the complexity of the Hammerstein PD algorithms. The thesis also analyses the effects of measurement noise on indirect learning SCPWL filter. Due to its linear basis function, the SCPWL filter coefficients do not suffer the coefficient bias effects which are observed in polynomial models. The performance of the proposed SCPWL PDs are compared with state-of-the-art polynomial-based PDs by simulations and measurements

Outils d'analyse, de modélisation et de commande pour les radiocommunications Application aux amplificateurs de puissance

L'évolution croissante des télécommunications résulte de la combinaison de plusieurs facteurs comme les progrès de l'électronique, de la micro-électronique, de la radiofréquence mais aussi des avancées des techniques de communications numériques. Dans ce contexte, les études s'orientent de plus en plus vers l'amélioration de la couverture et de la qualité de service offertes aux usagers. C'est dans ce contexte que s'inscrivent les travaux exposés dans le cadre de cette Habilitation à Diriger des Recherches. Les problématiques soulevées concernent : - la connaissance et la maîtrise du comportement des composants en présence de signaux large bande, multiporteuses, - l'amélioration de la qualité des transmissions en tenant compte des aspects énergétiques, - la reconfigurabilité et l'adaptation des nouveaux systèmes à la multiplication des normes et des standards de communications. Pour chaque problématique, nous avons proposé des solutions théoriques et pratiques avec comme fil conducteur l'utilisation et la mise en \oe uvre d'outils issus de l'Automatique comme l'estimation paramétrique, la commande et la linéarisation, l'optimisation, etc. Concernant la modélisation des fonctions électroniques RF, je présente mes travaux concernant la prise en compte des effets statiques et dynamiques en temps continu et discret. Pour les circuits hautes fréquences qui se caractérisent par des constantes de temps avec des ordres de grandeurs divers, nous avons montré qu'il est important d'envisager la modélisation selon l'application visée et en déployant des outils d'estimation paramétrique adaptés. Des problématiques telles que la normalisation de l'espace paramétrique, l'initialisation, la convergence sont étudiées pour répondre aux caractéristiques des systèmes de radiocommunications.Dans le chapitre consacré à l'amélioration de la linéarité et du rendement, nous avons présenté des techniques de correction des imperfections des amplificateurs de puissances ainsi que des méthodes de traitement du signal qui permettent de réduire leurs impacts sur la transmission. Concernant la linéarisation, nous avons commencé par une comparaison d'une technique Feedback et d'un linéariseur à base d'une prédistorsion polynomiale sans mémoire. Cette étude a mis en évidence l'intérêt d'adjoindre de la mémoire sous forme de retards dans le linéariseur. Les fortes fluctuations des signaux multiporteuses, mesurées par le PAPR pour Peak-to-Average Power Ratio, contribuent aussi à dégrader le bilan énergétique de l'émetteur. La majorité des travaux sur la réduction du PAPR se limite à l'étude des performances en termes de gain de réduction, sans aborder la qualité de transmission en présence d'imperfections réalistes des éléments non-linéaires. C'est dans ce contexte que nous avons analysé cette problématique pour un système MIMO-OFDM en boucle fermée avec prise en compte du canal, des non-linéarités, des effets mémoires et des critères visuels permettant d'évaluer la qualité des transmissions de données multimédias.Le développement d'architectures entièrement numérique, reconfigurables est traité en dernière partie de ce cette HDR. Pour cette large thématique, nous proposons des améliorations pour des coefficients des modulateurs afin d'obtenir une fonction de transfert du bruit respectant un gabarit fréquentiel donné. La correction des erreurs de calcul dus aux coefficients du type 1/$2^L$. Cette correction est basée sur la ré-injection de l'erreur au sein de la boucle directe à travers un filtre numérique

Design and implementation of low complexity adaptive optical OFDM systems for software-defined transmission in elastic optical networks

Due to the increasing global IP traffic and the exponential growing demand for broadband services, optical networks are experimenting significant changes. Advanced modulation formats are being implemented at the Digital Signal Processing (DSP) level as key enablers for high data rate transmission. Whereas in the network layer, flexi Dense Wavelength-Division Multiplexing (DWDM) grids are being investigated in order to efficiently use the optical spectrum according to the traffic demand. Enabling these capabilities makes high data rate transmission more feasible. Hence, introducing flexibility in the system is one of the main goals of this thesis. Furthermore, minimizing the cost and enhancing the Spectral Efficiency (SE) of the system are two crucial issues to consider in the transceiver design. This dissertation investigates the use of Optical Orthogonal Frequency Division Multiplexing (O-OFDM) based either on the Fast Fourier Transform (FFT) or the Fast Hartley Transform (FHT) and flexi-grid technology to allow high data rate transmission over the fiber. Different cost-effective solutions for Elastic Optical Networks (EON) are provided. On the one hand, Direct Detection (DD) systems are investigated and proposed to cope with present and future traffic demand. After an introduction to the principles of OFDM and its application in optical systems, the main problems of such modulation is introduced. In particular, Peak-to-Average Power Ratio (PAPR) is presented as a limitation in OFDM systems, as well as clipping and quantization noise. Hence, PAPR reduction techniques are proposed to mitigate these impairments. Additionally, Low Complexity (LC) PAPR reduction techniques based on the FHT have also been presented with a simplified DSP. On the other hand, loading schemes have also been introduced in the analyzed system to combat Chromatic Dispersion (CD) when transmitting over the optical link. Moreover, thanks to Bit Loading (BL) and Power Loading (PL), flexible and software-defined transceivers can be implemented maximizing the spectral efficiency by adapting the data rate to the current demand and the actual network conditions. Specifically, OFDM symbols are created by mapping the different subcarriers with different modulation formats according to the channel profile. Experimental validation of the proposed flexible transceivers is also provided in this dissertation. The benefits of including loading capabilities in the design, such as enabling high data rate and software-defined transmission, are highlighted.Degut al creixement del tràfic IP i de la demanda de serveis de banda ampla, les xarxes òptiques estan experimentant canvis significatius. Els formats avançats de modulació, implementats a nivell de processat del senyal digital, habiliten la transmissió a alta velocitat. Mentre que a la capa de xarxa, l'espectre òptic es dividit en ranures flexibles ocupant l'ample de banda necessari segons la demanda de tràfic. La transmissió a alta velocitat és fa més tangible un cop habilitades totes aquestes funcionalitats. D'aquesta manera un dels principals objectius d'aquesta tesis es introduir flexibilitat al sistema. A demés, minimitzar el cost i maximitzar l'eficiència espectral del sistema són també dos aspectes crucials a considerar en el disseny del transmissor i receptor. Aquesta tesis investiga l'ús de la tecnologia Optical Orthogonal Frequency Division Multiplexing (OFDM) basada en la transformada de Fourier (FFT) i la de Hartley (FHT) per tal de dissenyar un sistema flexible i capaç de transmetre a alta velocitat a través de la fibra òptica. Per tant, es proposen diferent solucions de baix cost vàlides per a utilitzar en xarxes òptiques elàstiques. En primer lloc, s'investiguen i es proposen sistemes basats en detecció directa per tal de suportar la present i futura demanda. Després d'una introducció dels principis d' OFDM i la seva aplicació als sistemes òptics, s'introdueixen alguns dels problemes d'aquesta modulació. En particular, es presenten el Peak-to-Average Power Ratio (PAPR) i els sorolls de clipping i de quantizació com a limitació dels sistemes OFDM. S'analitzen tècniques de reducció de PAPR per tal de reduir l'impacte d'aquests impediments. També es proposen tècniques de baixa complexitat per a reduir el PAPR basades en la FHT. Finalment, s'utilitzen algoritmes d'assignació de bits i de potència, Bit Loading (BL) i Power Loading (PL), per tal de combatre la dispersió cromàtica quan es transmet pel canal òptic. Amb la implementació dels algoritmes de BL i PL, es poden dissenyar transmissors i receptors flexibles adaptant la velocitat a la demanda del moment i a les actuals condicions de la xarxa. En particular, els símbols OFDM es creen mapejant cada portadora amb un format de modulació diferent segons el perfil del canal. El sistema és validat experimentalment mostrant les prestacions i els beneficis d'incloure flexibilitat per tal de facilitar la transmissió a alta velocitat i cobrir les necessitats de l'Internet del futurDebido al crecimiento del tráfico IP y de la demanda de servicios de banda ancha, las redes ópticas están experimentando cambios significativos. Los formatos avanzados de modulación, implementados a nivel de procesado de la señal digital, habilitan la transmisión a alta velocidad. Mientras que en la capa de red, el espectro óptico se divide en ranuras flexibles ocupando el ancho de banda necesario según la demanda de tráfico. La transmisión a alta velocidad es más tangible una vez habilitadas todas estas funcionalidades. De este modo uno de los principales objetivos de esta tesis es introducir flexibilidad en el sistema. Además, minimizar el coste y maximizar la eficiencia espectral del sistema son también dos aspectos cruciales a considerar en el diseño del transmisor y receptor. Esta tesis investiga el uso de la tecnologia Optical Orthogonal Frequency Division Multiplexing (OFDM) basada en la transformada de Fourier (FFT) y en la de Hartley (FHT) con tal de diseñar un sistema flexible y capaz de transmitir a alta velocidad a través de la fibra óptica. Por lo tanto, se proponen distintas soluciones de bajo coste válidas para utilizar en redes ópticas elásticas. En primer lugar, se investigan y se proponen sistemas basados en detección directa con tal de soportar la presente y futura demanda. Después de una introducción de los principios de OFDM y su aplicación en los sistemas ópticos, se introduce el principal problema de esta modulación. En particular se presentan el Peak-to-Average Power Ratio (PAPR) y los ruidos de clipping y cuantización como limitaciones de los sistemas OFDM. Se analizan técnicas de reducción de PAPR con tal de reducir el impacto de estos impedimentos. También se proponen técnicas de baja complejidad para reducir el PAPR basadas en la FHT. Finalmente, se utilizan algoritmos de asignación de bits y potencia, Bit Loading (BL) y Power Loading (PL), con tal de combatir la dispersión cromática cuando se transmite por el canal óptico. Con la implementación de los algoritmos de BL y PL, se pueden diseñar transmisores y receptores flexibles adaptando la velocidad a la demanda del momento y a las actuales condiciones de la red. En particular, los símbolos OFDM se crean mapeando cada portadora con un formato de modulaci_on distinto según el perfil del canal. El sistema se valida experimentalmente mostrando las prestaciones y los beneficios de incluir flexibilidad con tal de facilitar la transmisión a alta velocidad y cubrir las necesidades de Internet del futuro