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Ishaq, Muhammad Irfan, Yasir Ali Khan, and Muhammad Talha Gul. "Precoding in MIMO, OFDM to reduce PAPR (Peak to Average Power Ratio)." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-18621.
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One of the critical issues of systems utilizing Orthogonal Frequency Division Multiplexing (OFDM) is the high peak to the average power ratio of OFDM signals. We have used Precoding as a way to mitigate the PAPR problem. Furthermore the performance of Precoded OFDM in fading multi-path channels has been studied. This thesis is based on an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is data-independent and thus, does not require new processing and optimization for each transmitted OFDM block. The reduction in PAPR of the OFDM signal is obtained through a proper selection of a Precoding scheme that distributes the power of each modulated symbol over the OFDM block. The obtained results show that this Precoding scheme is an attractive solution to the PAPR problem of OFDM signals.
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Hussain, Sajjad. "PEAK TO AVERAGE POWER RATIO ANALYSIS AND REDUCTION OF COGNITIVE RADIO SIGNALS." Phd thesis, Université Rennes 1, 2009. http://tel.archives-ouvertes.fr/tel-00426930.
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* La multiplication des standards de télécommunications fait apparaître la nécessité de disposer de terminaux multistandard et reconfigurables. Ces nouvelles fonctionnalités trouvent leurs réponses dans le domaine de la radio logicielle. De tels terminaux ne sont pas encore réalisables pour des raisons technologiques liées à la complexité nécessaire à leur réalisation (convertisseurs ultra rapides, processeurs reconfigurables, antennes et amplificateurs très large bande, ....). En se basant alors sur une véritable technologie radio logicielle, la radio intelligente va encore plus loin dans la prospective en dotant le terminal de capteurs qui lui permettront de s'adapter et de réagir vis à vis de son environnement. La radio devient alors décentralisée et flexible se détachant de la notion de standards et transmettant de façon opportuniste une communication dans une bande qui aura été détectée comme libre. Cette présentation s'inscrit dans le contexte présenté ci-dessus en se focalisant sur les conséquences de l'amplification de puissance d'un signal multistandard. En effet, l'amplication de puissance est un étage fondamental de tout système radio et certaines précautions doivent être prises avant d'amplifier un signal. En effet, les amplificateurs ont des caractéristiques non linéaires et de faibles rendements nécessitant un traitement du signal à amplifier afin de limiter d'une part les distorsions non linéaires et d'autre part la consommation des terminaux. Les signaux caractérisant les systèmes multistandard ayant des caractéristiques proches de celle d'un signal OFDM (connu pour les problèmes liés à l'amplification de puissance), ce travail apporte des réponses sur : * les niveaux de puissance d'un signal multistandard * les méthodes à développer pour en minimiser les fluctuations de puissance * les conséquences de l'accès opportuniste au spectre sur les fluctuations de puissance dans un contexte de radio intelligente
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Kwak, Yongjun. "Near Shannon Limit and Reduced Peak to Average Power Ratio Channel Coded OFDM." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10176.
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Solutions to the problem of large peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems are proposed. Although the design of PAPR reduction codewords has been extensively studied and the existence of asymptotically good codes with low PAPR has been proved, still no reduced PAPR capacity achieving code has been constructed. This is the topic of the current thesis.This goal is achieved by implementing a time-frequency turbo block coded OFDM.
In this scheme, we design the frequency domain component code to have a PAPR bounded by a small number. The time domain component code is designed to obtain good performance while the decoding algorithm has reasonable complexity. Through comparative numerical evaluation we show that our method achieves considerable improvement in terms of PAPR with slight performance degradation compared to capacity achieving codes with similar block lengths. For the frequency domain component code, we used the realization of Golay sequences as cosets of the fi rst order Reed-Muller code and the modi cation of dual BCH code. A simple MAP decoding algorithm for the modi ed dual BCH code is also provided. Finally, we provide a flexible and practical scheme based on probabilistic approach to a PAPR problem. This approach decreases the PAPR without any signi cant
performance loss and without any adverse impact or required change to the system.Engineering and Applied Sciences
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Mazin, Asim Mohamed. "REDUCING THE PEAK TO AVERAGE POWER RATIO OF MIMO-OFDM USING Particle SWARM OPTIMIZATION BASED PTS." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1130.
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Asim M. Mazin, for the Master of Science degree in Electrical and Computer Engineering, presented on Mar 27, 2013, at Southern Illinois University Carbondale. TITLE: REDUCING THE PEAK TO AVERAGE POWER RATIO OF MIMO-OFDM USING PSO BASED PTS. MAJOR PROFESSOR: Dr. Garth V. Crosby, In this thesis we proposed PSO based PTS to accomplish the lowest Peak-to-Average Power Ratio of MIMO-OFDM system. We applied the PSO based PTS on each antenna of the system in order to find the optimal phase factors which is a straightforward method to get the minimum PAPR in such a system. The performance of PSO based PTS algorithm in MIMO-OFDM with a wide range of phase factor tends to give a high performance according to the simulation results. In addition, there is no need to increase the number of particles of the PSO algorithm to enhance the performance of the system, which keeps the complexity of finding the minimum PAPR reasonable.
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Luo, Jun. "Peak-to-Average Power Ratio Reduced Parallel Interference Cancellation Multicarrier-Code Division Multiple Access System with Anti-Interference Property." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/20.
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Orthogonal Frequency-Division Multiplexing (OFDM) has been proved to be a promising technology that enables the transmission of higher data rate. Multicarrier Code-Division Multiple Access (MC-CDMA) is a transmission technique which combines the advantages of both OFDM and Code-Division Multiplexing Access (CDMA), so as to allow high transmission rates over severe time-dispersive multi-path channels without the need of a complex receiver implementation. Also MC-CDMA exploits frequency diversity via the different subcarriers, and therefore allows the high code rates systems to achieve good Bit Error Rate (BER) performances. Furthermore, the spreading in the frequency domain makes the time synchronization requirement much lower than traditional direct sequence CDMA schemes. There are still some problems when we use MC-CDMA. One is the high Peak-to-Average Power Ratio (PAPR) of the transmit signal. High PAPR leads to nonlinear distortion of the amplifier and results in inter-carrier self-interference plus out-of-band radiation. On the other hand, suppressing the Multiple Access Interference (MAI) is another crucial problem in the MC-CDMA system. Imperfect cross-correlation characteristics of the spreading codes and the multipath fading destroy the orthogonality among the users, and then cause MAI, which produces serious BER degradation in the system. Moreover, in uplink system the received signals at a base station are always asynchronous. This also destroys the orthogonality among the users, and hence, generates MAI which degrades the system performance. Besides those two problems, the interference should always be considered seriously for any communication system. In this dissertation, we design a novel MC-CDMA system, which has low PAPR and mitigated MAI. The new Semi-blind channel estimation and multi-user data detection based on Parallel Interference Cancellation (PIC) have been applied in the system. The Low Density Parity Codes (LDPC) has also been introduced into the system to improve the performance. Different interference models are analyzed in multi-carrier communication systems and then the effective interference suppression for MC-CDMA systems is employed in this dissertation. The experimental results indicate that our system not only significantly reduces the PAPR and MAI but also effectively suppresses the outside interference with low complexity. Finally, we present a practical cognitive application of the proposed system over the software defined radio platform.
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Baxley, Robert John. "Analyzing Selected Mapping for Peak-to-Average Power Reduction in OFDM." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6922.
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Orthogonal frequency division multiplexing (OFDM) has become a popular modulation method in high-speed wireless communications. By partitioning a wideband fading channel into flat narrowband channels, OFDM is able to mitigate the detrimental effects of multipath fading using a simple one-tap equalizer. However, in the time domain OFDM signals suffer from large envelope variations, which are often characterized by the peak-to-average ratio (PAR). High PAR signals, like OFDM, require that transmission amplifiers operate at very low power efficiencies to avoid clipping.
In this thesis we review the most popular OFDM PAR-reduction techniques and demonstrate that selected mapping (SLM) is a particularly promising reduction technique. In a SLM system, an OFDM symbol is mapped to a set of quasi-independent equivalent symbols and then the lowest-PAR symbol is selected for transmission. The tradeoff for PAR reduction in SLM is computational complexity as each mapping requires an additional inverse fast fourier transform (IFFT) operation in the
transmitter.
In additional to an overview of current SLM work, we present a thorough analysis of SLM as well as several novel SLM proposals. First, we derive the closed-form expression for the expected PAR in an SLM system. The expected PAR can be thought of as a metric of PAR reduction capability. Second, we provide a power analysis of SLM to determine if the computational power costs outweigh the power saved through PAR reduction. Through this analysis, we show that SLM is capable of several Watts of net power savings when used in a wireless transmission system. Third, we propose that a PAR threshold should be set in SLM. Such thresholding leads to significant complexity decreases. Fourth, we derive the maximum likelihood (ML) and maximum extit{a posteriori} (MAP) detection metrics for blind SLM (BSLM) and threshold BSLM respectively. Lastly, we demonstrate that by using monomial phase sequences in SLM blind phase sequence detection is possible with a single FFT operation in the receiver.
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McCarthy, Stephen J. "Investigation of Power Reduction Methods for Multi-User MIMO WLAN Applications." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1416778581.
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Prieto, Alberto Pastor. "Simulation and evaluation of a DVB System using Simulink (Vol. II)." Thesis, Linköping University, Department of Electrical Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2723.
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DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content.
The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers.
This thesis talks about the improvement of the PAPR problem using the soft compression method.
The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.
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Bulusu, Sri Satish Krishna Chaitanya. "Performance Analysis and PAPR Reduction Techniques for Filter-Bank based Multi-Carrier Systems with Non-Linear Power Amplifiers." Thesis, Paris, CNAM, 2016. http://www.theses.fr/2016CNAM1042/document.
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Cette thèse a été effectuée dans le cadre du projet européen FP7 EMPHATIC (Enhanced Multicarrier Techniques for Professional Ad-Hoc and Cell-Based Communications). Plusieurs universités européennes et deux partenaires industriels: THALES Communications Security et CASSIDIAN ont participé à ce projet. L'objectif de ce projet est de développer, d'évaluer et de démontrer les apports des techniques multi-porteuses avancées, permettant une meilleure utilisation des bandes de fréquences radio existantes en fournissant des services de données à large bande, en coexistence avec les services traditionnels à bande étroite. Le projet porte sur l'application de radiocommunications mobiles professionnelles (Professional Mobile Radio : PMR). L'idée principale de ce projet est d'analyser la viabilité des systèmes à large bande utilisant des bancs de filtres (Filter Bank Multi Carrier : FBMC) conjointement avec une modulation d'amplitude en quadrature avec décalage (Offset Quadrature Amplitude Modulation : OQAM) dans le cadre de la 5ème génération (5G) des systèmes radio-mobiles. La modulation FBMC-OQAM se positionne comme candidate potentielle pour les futurs systèmes de communication. Cette modulation avancée offre de nombreux avantages tels que l’excellente localisation fréquentielle de sa densité spectrale de puissance (DSP), une robustesse au bruit de phase, aux décalages de fréquence ainsi qu’à l’asynchronisme entre les utilisateurs. Ces atouts, la rendent plus attrayant qu’OFDM pour l’application PMR, la radio cognitive (CR) et la 5G. Cependant, comme toute autre technique de modulation muti-porteuses, FBMC-OQAM souffre d’un facteur de crête ou d’un PAPR (pour Peak to Average Power Ratio) élevé. Lorsque l'amplificateur de puissance (AP), utilisé au niveau de l’émetteur, est opéré proche de sa zone non-linéaire (NL), ce qui est le cas dans la pratique, la bonne localisation fréquentielle de la DSP du système FBMC/OQAM est sérieusement compromise, en raison des remontées spectrales. Le premier objectif de cette thèse est de prédire l'étendue des remontées spectrales dans les systèmes FBMC-OQAM, introduites par la non-linéarité AP. Le deuxième objectif de ce travail est de proposer des techniques, pour les systèmes FBMC-OQAM, permettant la réduction du PAPR et la linéarisation de l’AP, afin d'atténuer les effets NL. L’utilisation des cumulants, a permis de prédire les remontées spectrales pour les signaux FBMC-OQAM après amplification NL. En outre, certains algorithmes de réduction du PAPR, basées sur des approches probabilistes et des techniques d'ajout de signaux, ont été proposés. La capacité de coexistence du système à large bande utilisant FBMC-OQAM avec des systèmes PMR à bande étroite en présence de PA a été analysée et il a été démontré que la coexistence est possible, à condition qu'il y est une bonne combinaison entre le recul du signal à l’entrée de l’AP (Input Back-Off : IBO), la réduction du PAPR et la linéarisation de l’AP. Enfin, une nouvelle technique de linéarisation de l’AP a été proposée pour le système FBMC-OQAMThis thesis is part of the European FP7 EMPHATIC project (Enhanced Multicarrier Techniques for Professional Ad-Hoc and Cell-Based Communications) including various European universities and two main industrial partners: THALES Communications Security and CASSIDIAN. The EMPHATIC objective is to develop, evaluate and demonstrate the capability of enhanced multi-carrier techniques to make better use of the existing radio frequency bands in providing broadband data services in coexistence with narrowband legacy services. The project addresses the Professional Mobile Radio (PMR) application. The main idea is to analyze the viability of broadband systems based on filter-bank multi-carrier (FBMC) clubbed with o ffset quadrature amplitude modulation (OQAM) in the context of the future 5th Generation (5G) radio access technology (RAT). Increasingly, the FBMC-OQAM systems are gaining appeal in the probe for advanced multi-carrier modulation (MCM) waveforms for future communication systems. This advanced modulation scheme o ers numerous advantages such as excellent frequency localization in its power spectral density (PSD), a robustness to phase noise, frequency off sets and also to the multi-user asynchronism; making it more appealing than OFDM for PMR, cognitive radio (CR) and 5G RAT. However, like any other MCM technique, FBMC-OQAM suff ers from high PAPR. When the power amplifi er (PA) non-linearity, which is realistic radio-frequency impairment, is taken into account; the good frequency localization property is severely compromised, due to the spectral regrowth. The first objective of this PhD thesis is, to predict the extent of the spectral regrowth in FBMC-OQAM systems, due to the PA non-linearity. The second objective is to probe techniques for FBMC-OQAM systems, such as PAPR reduction and PA linearization, in order to mitigate the NL eff ects of PA. By cumulant analysis, spectral regrowth prediction has been done for FBMC-OQAM systems. Also, some algorithms for PAPR reduction, which are based on probabilistic approach and adding signal methods, have been proposed. The coexistence capability of the FBMC-OQAM based broadband system with the narrowband PMR systems in the presence of PA has been analyzed and it has been found that coexistence is possible, provided there is a symbiotic combination of PA Input Back-off (IBO), PAPR reduction and PA linearization. Finally, a novel PA linearization technique has been proposed for FBMC-OQAM
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Déjardin, Romain. "Récepteurs itératifs dédiés à la correction de saturation pour les systèmes OFDM." Reims, 2010. http://theses.univ-reims.fr/sciences/2010REIMS005.pdf.
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Malgré la difficulté d’amplifier les systèmes mutli-porteuses à haut rendement, étant donnée la dynamique des signaux concernés, la modulation orthogonal frequency division multiplexing (OFDM) est aujourd’hui devenue incontournable dans les systèmes de communication. Elle est d’ailleurs de plus en plus utilisée dans les normes de transmission filaires ou non. Pourtant, le high peak-to-average power ratio (PAPR) reste le principal inconvénient de l’OFDM. Différentes techniques ont été proposées pour contraindre la dynamique des signaux à l’émission. Cependant, elles sont le plus souvent très compliquées à mettre en oeuvre et nécessitent des procédés particuliers au récepteur et la transmission d’une information supplémentaire dédiée. Contraindre volontairement l’amplitude du signal est une technique efficace et simple pour réduire le PAPR des signaux OFDM. Si le bruit hors-bande résultant peut être facilement réduit par filtrage, les dégradations subies au sein de la bande utile obligent le récepteur à adopter une stratégie de recouvrement de la performance de la transmission. Cette thèse propose une revue complète du PAPR des signaux OFDM et de la méthode de clipping des signaux d’émission. Nous proposons également d’établir la performance analytique des systèmes OFDM avec clipping au regard de la capacité de canal et de la fiabilité de l’information binaire. Aussi, les techniques au récepteur permettant de recouvrer la performance dégradée par le clipping sont étudiées. Nous portons particulièrement notre attention aux approches par annulation du bruit de clipping et reconstruction d’amplitude en proposant leur comparaison exhaustive ainsi qu’une méthode dérivée de la première. Finalement, nous posons la description d’un nouveau récepteur proposant une information a posteriori corrigée des bits du mot de code. Cette information souple est en fait basée sur une décision sous-optimale par maximum de vraisemblance (SML). L’étude de l’algorithme montre son efficacité aussi bien sur canal blanc que sélectif en fréquence ; scénarios pour lesquels il permet de s’approcher très prés du cas sans clippingDespite the fact that multi-carrier signals amplification is pratically difficult due to their Gaussian-like distribution and the non-linear behaviour of power amplifiers, the orthogonal frequency division multiplexing (OFDM) modulation has been successfully brought in many communication standards for wired and wireless tranmsissions. However, the high peak-to-average power ratio (PAPR) of OFDM signals stands for the OFDM major drawback. Several strategies can be cited to manage the PAPR at transmitter side. However, most of them are computationally expensive and need a dedicated process at receiver relying on side information transmission. The deliberate amplitude clipping and filtering before amplification is an easy way to restrain PAPR at a desired level. If the out-of-band noise caused by clipping can be easilly discarded by filtering, the in-band distortion noise, also refered as clipping noise, must be mitigated at receiver side in order to restore the transmission performance. In this Thesis, we propose a wide review of both PAPR and clipping. We also give an analytical performance analysis of OFDM systems running under clipping constraint. Channel capacity and bit error rate are derived and conclusions are given. Afterwards, dedicated techniques mitigating clipping effects are studied. Clipping noise cancellation and decision aided reconstruction are especially reviewed. We also propose a complete comparison of these techniques and give an increased performance version of the first one. Finally, we propose a new scheme dealing with code word bits a posteriori probability enhancement. This soft decision is based on a suboptimal maximum likelihood (SML) detection using a limited neighbour signals to perform the transmitted code word detection. Actually, the receiver performance study shows that the algorithm can operate under severe clipping ratio constraint and is able to perform close to the non-clipped transmission case over both AWGN and frequencyselective channels
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Bibi, Nargis. "Mitigating the effect of soft-limiting for OFDM peak reduction." Thesis, University of Manchester, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618002.
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Digital communication systems which use Orthogonal Frequency Division Multiplexing (OFDM) are now widely used and have many advantages. The main disadvantage is the requirement for highly linear analogue electronics including the high power amplifier (HPA). This requirement cannot be met in all circumstances because of the occurrence of symbols with high peak to average power ratio (PAPR). Such symbols may be non-linearly distorted by limiting. Approaches to solve this problem have been either to reduce the PAPR at the transmitter or to try to mitigate the effect of the non-linearity at the receiver. Soft-limiting, i.e. applying limiting in software prior to the HPA is a simple way to reduce the PAPR. It produces non-linear distortion which will cause an increase in the bit-error-rate (BER) at the receiver. This thesis surveys existing alternatives ways of reducing the effect of non-linearity and proposes some new ones. Two iterative receiver techniques, based on statistical analysis of the nature of the non-linearity, have been implemented and investigated. These are the ‘Bussgang Noise Cancellation’ (BNC) technique and the ‘Decision Aided Reconstruction’ (DAR) techniques. As these techniques are valid for any memory-less nonlinearity, an alternative form of limiting, named as Inverted-Wraparound (IWRAP) has been included in the BNC investigation. A new method is proposed which is capable of correcting the received time-domain samples that are clipped, once they have been identified. This is named the ‘Equation-Method’ and it works by identifying constellation symbols that are likely to be correct at the receiver. If there are a sufficient number of these and they are correctly identified, the FFT may be partitioned to produce a set of equations that may be solved for the clipped time-domain samples. The thesis proposes four enhancements to this new method which improve its effectiveness. It is shown that the best form of this method outperforms conventional techniques especially for severe clipping levels. The performance of these four enhancements is evaluated over channels with additive white Gaussian noise (AWGN) in addition to clipping distortion. A technique based on a ‘margin factor’ is designed to make these methods work more effectively in the presence of AWGN noise. A new combining algorithm referred as ‘HARQ for Clipping’ is presented where soft bit decisions are combined from multiple transmissions. ‘HARQ for Clipping’ has been combined with the best version of the Equation-Method, and the performance of this approach is evaluated in terms of the BER with different levels of AWGN. It has been compared to other approaches from the literature and was found to out-perform the BNC iterative receiver by 3dB at signal to noise ratios around 10dB. Without HARQ, the best version of the Equation-Method performs better than the BNC receiver, at signal-to-nose ratios above about 17dB.
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Dhuness, Kahesh. "An offset modulation method used to control the PAPR of an OFDM transmission." Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/27258.
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Orthogonal frequency division multiplexing (OFDM) has become a very popular method for high-data-rate communication. However, it is well known that OFDM is plagued by a large peak-to-average power ratio (PAPR) problem. This high PAPR results in overdesigned power amplifiers, which amongst other things leads to inefficient amplifier usage, which is undesirable. Various methods have been recommended to reduce the PAPR of an OFDM transmission; however, all these methods result in a number of drawbacks. In this thesis, a novel method called offset modulation (OM-OFDM) is proposed to control the PAPR of an OFDM signal. The proposed OM-OFDM method does not result in a number of the drawbacks being experienced by current methods in the field. The theoretical bandwidth occupancy and theoretical bit error rate (BER) expression for an OM-OFDM transmission is derived. A newly applied power performance decision metric is also introduced, which can be utilised throughout the PAPR field, in order to compare various methods. The proposed OM-OFDM method appears to be similar to a well-known constant envelope OFDM (CE-OFDM) transmission. The modulation, structural and performance differences between an OM-OFDM and a CE-OFDM method are discussed. By applying the power performance decision metric, the OM-OFDM method is shown to offer significant performance gains when compared to CE-OFDM and traditional OFDM transmissions. In addition, the OM-OFDM method is able to accurately control the PAPR of a transmission for a targeted BER. By applying the power performance decision metric and complementary cumulative distribution function (CCDF), the proposed OM-OFDM method is shown to offer further performance gains when compared to existing PAPR methods, under frequency selective fading conditions. In this thesis, the OM-OFDM method has been combined with an existing active constellation extended (ACE) PAPR reduction method. To introduce a novel method called offset modulation with active constellation extension (OM-ACE), to control the PAPR of an OFDM signal. The theoretical BER expression for an OM-ACE transmission is presented and validated. Thereafter, by applying the decision metric and CCDF, the OM-ACE method is shown to offer performance improvements when compared to various PAPR methods. The use of OM-OFDM for cognitive radio applications is also investigated. Cognitive radio applications require transmissions that are easily detectable. The detection characteristics of an OM-OFDM and OFDM transmission are studied by using receiver operating characteristic curves. A derivation of a simplified theoretical closed-form expression, which relates the probability of a missed detection to the probability of a false alarm, for an unknown deterministic signal, at various signal-to-noise ratio (SNR) values is derived and validated. Previous expressions have been derived, which relate the probability of a missed detection to the probability of a false alarm. However, they have not been presented in such a generic closed-form expression that can be used for any unknown deterministic signal (for instance OFDM and OM-OFDM). Thereafter, an examination of the spectrum characteristics of an OM-OFDM transmission indicates its attractive detection characteristics. The proposed OM-OFDM method is further shown to operate at a significantly lower SNR value than an OFDM transmission, while still offering better detection characteristics than that of an OFDM transmission under Rician, Rayleigh and frequency selective fading channel conditions. In addition to its attractive PAPR properties, OM-OFDM also offers good detection characteristics for cognitive radio applications. These aspects make OM-OFDM a promising candidate for future deployment.Thesis (PhD)--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
unrestricted
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BAIG, CLEMENT RANJITH ANTHIKKAD & IRFAN AHMED. "PERFORMANCE ENHANCEMENT OF OFDM IN PAPR REDUCTION USING NEW COMPANDING TRANSFORM AND ADAPTIVE AC EXTENSION ALGORITHM FOR NEXT GENERATION NETWORKSPERFORMANCE ENHANCEMENT OF OFDM IN PAPR REDUCTION USING NEW COMPANDING TRANSFORM AND ADAPTIVE AC EXTENSION ALGORITHM FOR NEXT GENERATION NETWORKS." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6011.
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This paper presents a new hybrid PAPR reduction technique for the OFDM signal, which combines a multiple symbol representations method with a signal clipping method. The clipping method is a nonlinear PAPR reduction scheme, where the amplitude of the signal is limited to a given threshold. Considering the fact that the signal must be interpolated before A/D conversion, a variety of clipping methods has been proposed. Some methods suggest the clipping before interpolation, having the disadvantage of the peaks re-growth. Other methods contributed that the clipping after interpolation, having the disadvantage of out-of-band power production. In order to overcome this problem different filtering techniques have been proposed. Filtering can also cause peak re-growth, but less than the clipping before interpolation. Another clipping technique supposes that only subcarriers having the highest phase difference between the original signal and its clipped variant will be changed. This is the case of the partial clipping method. To further reduce the PAPR, the dynamic of the clipped signal can be compressed. Linear methods like partial transmit sequence or selective mapping has been proposed for the reduction of PAPR as well. Another PAPR reduction method is the tone reservation. It uses tones on which no data is sent to reduce the transmitted signal peaks. Derivatives of this method with lower computation complexity and improved performance have been proposed: One-Tone One-Peak and one by-one iteration. A similar PAPR reduction method is the multiple symbol representations, where alternative signalling points are used to represent one symbol. The simulation results highlight the advantages of the proposed PAPR reduction method.The proposed technique namely Adaptive Active Constellation Extension (Adaptive ACE) Algorithm reduced the high Peak-to-Average Power Ratio (PAPR) of the Orthogonal Frequency Division Multiplexing (OFDM) systems. The Peak-to-Average Power Ratio (PAPR) is equal to 6.8 dB for the target clipping ratios of 4 dB, 2 dB and 0 dB by using Adaptive Active Constellation Extension (Adaptive ACE) Algorithm. Thus, the minimum PAPR can be achieved for low target clipping ratios. The Signal-to-Noise Ratio (SNR) of the Orthogonal Frequency Division Multiplexing (OFDM) signal obtained by the Adaptive Active Constellation Extension (Adaptive ACE) algorithm is equal to 1.2 dB at a Bit Error Rate (BER) of 10-0..4 for different constellation orders like 4-Quadrature Amplitude Modulation (4-QAM), 16-Quadrature Amplitude Modulation (16-QAM) and 64-Quadrature Amplitude Modulation (16-QAM). Here, the Bit Error Rate of 10-0.4 or 0.398, that means a total of 398-bits are in error when 1000-bits are transmitted via a communication channel or approximately 4-bits are in error when 10-bits are transmitted via a communication channel, which is high when compared to that of the original Orthogonal Frequency Division Multiplexing (OFDM) signal. The other problems faced by the Adaptive Active Constellation Extension (Adaptive ACE) algorithm are Out-of-Band Interference (OBI) and peak regrowth. Here, the Out-of-Band Interference (OBI) is a form of noise or an unwanted signal, which is caused when the original Orthogonal Frequency Division Multiplexing (OFDM) signal is clipped for reducing the peak signals which are outside of the predetermined area and the peak regrowth is obtained after filtering the clipped signal. The peak regrowth results to, increase in the computational time and computational complexity. In this paper, we have proposed a PAPR reduction scheme to improve the bit error rate performance by applying companding transform technique. Hence, 1-1.5 dB reduction in PAPR with this Non-companding technique is achieved. In Future, We can accept to implement the same on Rician and Rayleigh channels.
Clement Ranjith Anthikkad (E-mail: clement.ranjith@gmail.com / clan11@bth.se) & Irfan Ahmed Baig (E-mail: baig.irfanahmed@gmail.com / ir-a11@bth.se )
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Yu, Zhenhua. "Optical wireless communications with optical power and dynamic range constraints." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51784.
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Along with the rapidly increasing demand for wireless data while more and more crowded radio frequency (RF) spectrum, optical wireless communications (OWC) become a promising candidate to complement conventional RF communications, especially for indoor short and medium range data transmissions. Orthogonal frequency division multiplexing (OFDM) is considered for OWC due to its ability to boost data rates. However, the average emitted optical power and dynamic range of driving signals of LEDs are two major constraints in OWC. OFDM waveforms exhibits high upper and lower peak-to-average power ratios (PAPRs), which make OFDM signals optical power inefficient and easy to violate the dynamic range of LEDs, resulting clipping and nonlinear distortions. In this dissertation, we analyze and design optical power and dynamic range constrained OWC systems, for which OFDM is our major subject. We first derive distributions of upper PAPR and lower PAPR of OWC-OFDM signals. Then we analyze the clipped OFDM signals in term of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both optical power and dynamic range constraints. The next part of this dissertation is the OFDM system design for visible light communications (VLC) considering illumination requirement. We investigate the illumination-to-communication efficiency (ICE) in VLC-OFDM, and design the brightness control and flickering mitigation schemes for VLC-OFDM. In the end, to reduce the complexity of driving circuits of LEDs , we propose using delta-sigma modulators in VLC-OFDM systems to convert continuous magnitude OFDM symbols into two-level LED driver signals without loss of the communication theory advantages of OFDM.
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NOBILET, Stéphane. "Etude et optimisation des techniques MC-CDMA pour les futures générations de systèmes de communications hertziennes." Phd thesis, INSA de Rennes, 2003. http://tel.archives-ouvertes.fr/tel-00004081.
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Les futurs systèmes de radiocommunications devront proposer des services nécessitant des transferts de données à haut débit, tout en garantissant une grande mobilité aux utilisateurs. Pour y parvenir, de nouvelles techniques de traitement de signal doivent être mises en oeuvre. Une de ces approches constituant actuellement un axe important de la recherche dans ce domaine est la technique MC-CDMA. Cette dernière repose sur la combinaison de deux techniques : les modulations à porteuses multiples et l'étalement de spectre. Les travaux de recherche présentés dans cette thèse ont pour buts l'étude et l'optimisation des systèmes de communications mettant en oeuvre cette technique MC-CDMA.Après une présentation générale des différentes façons de combiner les techniques de modulations à porteuses multiples et d'étalement de spectre, les performances des systèmes MC-CDMA sont présentées sur des canaux de Rayleigh et BRAN dans le cas de détection mono-utilisateur et multi-utilisateur.
Puis, l'influence des codes d'étalement sur la variation de la dynamique de l'enveloppe du signal émis, et sur l'interférence produite par la cohabitation des données de plusieurs utilisateurs sur les mêmes ressources fréquentielles et temporelles est étudiée. Pour cela, nous nous sommes intéressés aux variations de l'enveloppe des sisgnaux MC-CDMA à travers l'étude du facteur de crête et du facteur de crête global. Ces quantités permettent d'estimer les fluctuations du signal transmis respectivement en voie montante et descendante. En ce qui concerne la minimisation de l'interférence d'accès multiple, une technique reposant sur l'allocation des séquences d'étalement est décrite et plusieurs critères de sélection des codes d'étalement sont proposés.
Enfin, une attention particulière est portée à l'optimisation de la voie montante des systèmes MC-CDMA. Afin d'éviter l'insertion de Nu jeux de sous-porteuses pilotes servant à estimer les Nu canaux de la voie montante, une solution reposant sur le principe de la réciprocité du canal radiomobile est ici proposée. Cette alternative consiste à effectuer une prédistorsion du signal utile dans le terminal avant son émission. Deux variantes sont envisagées, la première repose sur un multiplexage temporel des voies montante et descendante alors que la seconde repose sur un multiplexage fréquentiel de ces deux voies.
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Khoo, Boon Kien. "Constellation Shaping and Peak-to-Average Power Ratio Reduction Algorithms for Wireless Communications." Thesis, University of Newcastle upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484815.
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Wireless communication technologies have undergone an explosive growth over the last two decades. High reliable transmission, high data rate, bandwidth and power-efficient communications are however major concerns for future wireless application designs. In the first part of this thesis, a bandwidth as well as power-efficient coded modulation system is proposed. Bit-interleaved coded modulation (BICM) system is a well-known bandwidth-efficient coded modulation scheme that concatenates channel codi!1g, interleaver and modulation block. The concatenation makes the BICM system similar to a serial concatenated convolutional code, and thus suggests that, in the receiver, the demodulation block and decoder can operate in an iterative manner resulting in turbo-like performance. Such system, known as bit-interleaved coded modulation with iterative decoding (BICM-ID), is well suited to additive white Gaussian noise channel. In the proposed technique, the BICM-ID system is modified by inserting a single short-length binary shaping block code for constellation shaping purpose. The corresponding receiver structure is then made up of four main blocks exchanging extrinsic information. By combining constellation shaping and BICM-ID system, the average transmitted power can be reduced and thus resulting bandwidth as well as power-efficient coded modulation system. In the second part of the thesis, high peak-to-average power ratio· (PAPR) of orthogonal-frequency division multiplexing (OFDM) for high data rate communication systems is focused. To date, there are a number of existing techniques for PAPR reduction. Among these techniques, selected mapping (SLM) technique is one of the well-known method to overcome the PAPR problem. However, the implementation of SLM technique required side information transmission. To this end, a simple SLM technique for PAPR reduction in OFDM that does not require the explicit transmission of side information is proposed.
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Deumal, Herraiz Marc. "Multicarrier communication systems with low sensibility to nonlinear amplification." Doctoral thesis, Universitat Ramon Llull, 2008. http://hdl.handle.net/10803/9137.
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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.
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Alharbi, Faisal Shaji. "Digital signal processing techniques for peak-to-average power ratio mitigation in MIMO-OFDM systems." Thesis, Loughborough University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510322.
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Alsamahi, Samer Saif. "Design of Peak-to-Average-Power-Ratio Reduction Scheme for Bandwith Efficient Wireless OFDM Systems." Thesis, University of Newcastle upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512163.
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Spalding, David Ian. "A Phase-Time Modulation Scheme for Peak-to-Average Power Mitigation in Multi-Carrier Wireless Transmission." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1116.
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An explosive growth in demand for broadband mobile wireless services is currently being fuelled by cellular telephone users who, encouraged by service providers, are no longer content with voice transmission only but are demanding real-time video services, including multi-user, interactive games and 'movie' programmes. As these applications develop, expectations mount in other mobile user markets, especially the public safety arena, for comparable user features but with greater emphasis on reliability and robustness of the equipment and supporting network in adverse propagation conditions, remote locations and emergencies. These applications all have in common the requirements for efficient use of wireless bandwidth and of battery power, as well as seamless operation when moving, sometimes at high vehicle speeds, from one type of environment to another in a multi-user scenario. Orthogonal frequency-division multiplexed (OFDM) signals have been found to compare favourably with other modulation systems in these applications, the multi-carrier format being more tolerant of delay spread. It has been used in both code-division (MC-CDMA) and frequency-division (OFDMA) multi-user schemes, the latter having the advantage of maintaining orthogonality among users in fading-signal environments, with consequent simplification of signal processing. The major drawback of OFDM has been the high peak-to-average power ratio (PAPR) that is characteristic of signals with multiple sub-carriers. A result of this is that the transmitter requires a linear power amplifier (PA) that generally has to be 'backed off' to accommodate the high PAPR. Additional back-off is required to achieve linearity, as well as sometimes-complex linearisation circuitry. The power usage and cost of such a transmitter is more acceptable in a base station, tending to limit the application of OFDM to downlinks. The potential application to hand-portable terminals has severe constraints of size, cost and battery life, exacerbated by the use of video-capable LCD displays, increasing motivation for the use of MIMO (multi-antenna) technology and the development of mobile ad-hoc networks, the latter being particularly applicable in the public safety arena. Previous efforts to ameliorate the PAPR problem have been principally directed at two areas, the reduction of signal PAPR, by block coding, clipping or other techniques, and methods of achieving PA linearisation with improved power efficiency. The first object of the present research was to establish, as far as practicable, the current state of the art in these areas, to set a performance baseline. The next step was to develop an improved transmitter modulation scheme that would not only be able to take advantage of any existing peak reduction methods but would transmit a signal that would be compatible with existing OFDM receivers. A novel modulation technique is now presented, termed Quadrature Phase-Time Modulation (QPTM), that has been found to meet the requirements for linearity, simplicity and low cost, whilst being able to take advantage of constant-envelope PA technology, with its attendant power efficiency. After final amplification, the signal is restored by a passive narrow-band filter to standard OFDM form, having both phase and amplitude modulation. The QPTM system of modulation relies on a dual baseband pulse-width modulation process, performed at a substantially-higher rate than the upper baseband frequency, followed by direct quadrature modulation of a carrier signal. The work undertaken has been in the nature of a feasibility study, commencing with the theoretical basis of the technique, from which a behavioural system model was designed and simulated. After the system was simulated successfully, in several forms, a model was designed for realisation with available high-frequency integrated circuits. From this design, prototypes were constructed and tested. The prototype circuit boards also included an experimental UHF Class-D PA circuit, excluding the output filter, to facilitate ongoing development of the PA and filter subsystem as a separate project. This type of PA was seen as a potential complement to the QPTM modulator, although the technology was at an early stage of development. The prototype PA has a novel push-pull arrangement of GaAs FETs that employs a broadside-coupled tapered-stripline balun instead of the usual transformer. Preliminary measurements were made on the PA using both a spectrum analyser and a newly-available 8GHz-bandwidth digital oscilloscope to confirm basic operating characteristics. The performance of the QPTM technique at frequencies needed for broadband operation is dependent on its practical implementation, which has therefore been a major focus. The inherent difficulties in realising a highly-linear 40MHz triangle-wave reference generator, with a precise ultra-high-speed comparator and modulator system, have been overcome with the chosen design techniques and attention to several critical aspects. The result has been the successful demonstration of QPTM as an efficient PA modulation technique that is equally applicable to either narrow-band, high-capacity UHF or broadband OFDM microwave systems.
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Aimer, Younes. "Étude des performances d'un système de communication sans fil à haut débit." Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2269.
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La demande des usagers en termes de débit, de couverture et de qualité de service croît exponentiellement, avec une demande de plus en plus accrue en énergie électrique pour assurer les liaisons entre les réseaux. Dans ce contexte, les nouvelles formes d’ondes basées sur la modulation OFDM se sont répandues et sont utilisées dans les récentes architectures de radiocommunications. Cependant, ces signaux sont très sensibles aux non-linéarités des amplificateurs de puissance à cause des fortes fluctuations d’enveloppe caractérisées par un fort PAPR qui dégrade le bilan énergétique et le rendement de l’émetteur. Dans ce travail de thèse, nous avons tout d’abord dressé un état de l’art des techniques de réduction du PAPR. Cette présentation nous a permis de proposer une nouvelle méthodologie basée sur les techniques d’entrelacement et de codage. Cette première contribution consiste en l’utilisation de la technique d’entrelacement, en faisant appel aux sous porteuses nulles pour la transmission des informations auxiliaires, tout en respectant les spécifications fréquentielles du standard utilisé. La deuxième contribution est basée sur la combinaison des deux techniques de Shaping et de Transformée en Cosinus Discrète DCT, dans l’objectif d’améliorer davantage les performances du système. Les résultats de simulation ont montré que l’utilisation de ces deux techniques permet un gain significatif en termes de réduction du PAPR, qui se traduit par l’amélioration du rendement. Enfin, nous avons présenté une étude expérimentale pour l’ensemble des techniques proposées afin de confirmer les résultats obtenus en simulation. Ces évaluations sont réalisées avec un banc d'essais de radiocommunications pour le test d'un amplificateur de puissance commercial de technologie LDMOS de 20W, fonctionnant à 3.7 GHz en classe AB. Les résultats obtenus pour les standards IEEE 802.11 montrent que ces nouvelles approches permettent de garantir la robustesse de transmission, d’améliorer la qualité des liaisons et d’optimiser la consommation électriqueThe request of the users in terms of rate, coverage and quality of service is growing exponentially, with increasing demand for electrical energy, to ensure networks link. In this context, new waveforms based on the OFDM modulation become widely popular and used intensively in recent radio communications architectures. However, these signals are sensitive to the power amplifier nonlinearities because of their high envelope fluctuations characterized by a high PAPR, which degrades the energy consumption and the transmitter efficiency.In this thesis, we first began by a state art of the PAPR reduction techniques. This presentation allowed us to propose a new method based on interleaving and coding techniques. The first contribution consists on the use of the interleaving technique using null-subcarriers for the transmission of the side information, while respecting the frequency specifications of the used standard. The second one is based on the conjunction of the Shaping technique and the Discrete Cosine Transform (DCT), with the aim of improving the performance of the system. Simulation results show that the use of these two techniques allows a significant gain in terms of PAPR reduction, which results in the improvement of the system efficiency. Finally, we presented an experimental study of the proposed techniques using an RF test bench with a commercial LDMOS 20 W PA, class AB operating at 3.7 GHz. The results obtained for the IEEE 802.11 standards show that the proposed approaches allow the transmission robustness and quality, while optimizing the power consumption
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Siegl, Christian [Verfasser]. "Peak-to-Average Power Ratio Reduction in Multi-Antenna OFDM via Multiple Signal Representation / Christian Siegl." Aachen : Shaker, 2010. http://d-nb.info/1084536188/34.
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Bendig, Rudi Matthew. "AC Power Combining Strategy with Application to Efficient Linear Power Amplifiers." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1220.
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With the ongoing push for wireless systems to accommodate more users and support higher data rates more efficient modulation schemes have been created that are more advanced than simple FM and AM modulation used for radio broadcasting. These modulation schemes, such as orthogonal frequency division multiplexing (OFDM), suffer from high peak to average power ratios. Standard Class A and Class AB amplifiers cannot simultaneously achieve good linearity and efficiency, and therefore there has been an increase in the development of new topologies to combat this issue. Common features to these circuits is power combining of two or more separate transistors.
In this work, we consider various ways of two-source power combining and identify four topologies of interest. We notice that linear power-efficient amplifiers reported to date are based upon two of the identified combining strategies. We believe that no amplifiers have been reported that leverage the other two alternatives. This work produces a fully-functional amplifier based on one of these alternatives. The prototypes are intended to serve as concept verification of the architecture and hence are implemented at lower (1 MHz) frequencies.
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Buzid, Tufik. "Frequency domain equalization of modulation formats with low peak to average power ratio = Frequenzbereichsentzerrung von Modulationsverfahren mit niedrigem Spitzen- zu Mittelwert-Verhältnis." kostenfrei, 2009. http://d-nb.info/1000376435/34.
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Thiagarajan, Thenappan T. "A Simple and Effective Peak-To-Average Power Ratio Reduction Approach Based on Iterative Companding Transform and Filtering Framework of Orthogonal Frequency Division Multiplexing Signal." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10604995.
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The peak-to-average power ratio (PAPR) reduction in OFDM is an unresolved issue. Intense research has been carried out to solve the issue of peak power and to reduce the impact on overall system performance. PAPR can negatively affect system performance by inducing spectral regrowth and degrading detection efficiency. The purpose of this study is to show how the iterative companding transform and filtering (ICTF) framework can solve the PAPR issue in a redefined way. ICTF is able to obtain low out-of-band interference (OBI) and improved bit error rate (BER) while reducing PAPR significantly. Simulation results show good performance, low complexity, and reliable efficiency over traditional state of methods such as the iterative clipping and filtering technique.
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Dasgupta, Abhijeet. "High efficiency S-Band vector power modulator design using GaN technology." Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0021/document.
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L’évolution des systèmes de télécommunications, liée à une demande sans cesse croissante en termes de débit et de volume de données, se concrétise par le développement de systèmes proposant des bandes passantes très larges, des modulations à très hautes efficacités spectrales, de la flexibilité en puissance et en fréquence d’émission. Par ailleurs, la mise en œuvre de ces dispositifs doit se faire avec un souci permanent d’économie d’énergie d’où la problématique récurrente de l’amplification de puissance RF qui consiste à allier au mieux rendement, linéarité et bande passante. L’architecture conventionnelle d’une chaine d’émission RF consiste dans une première étape à réaliser l’opération de modulation-conversion de fréquence (Modulateur IQ) puis dans une deuxième étape l’opération de conversion d’énergie DC-RF (Amplificateur de Puissance), ces deux étapes étant traditionnellement traitées de manière indépendante. L’objectif de ces travaux de thèse est de proposer une approche alternative qui consiste à combiner ces deux opérations dans une seule et même fonction : le modulateur vectoriel de puissance à haute efficacité énergétique. Le cœur du dispositif, conçu en technologie GaN, repose sur un circuit à deux étages de transistors HEMT permettant d’obtenir un gain en puissance variable en régime de saturation. Il est associé à un modulateur de polarisation multi-niveaux spécifique également en technologie GaN. Le dispositif réalisé a permis de générer directement, à une fréquence de 2.5 GHz, une modulation vectorielle 16QAM (100Msymb/s) de puissance moyenne 13 W, de puissance crête 25W avec un rendement global de 40% et une linéarité mesurée par un EVM à 5%The evolution of telecommunications systems, linked to a constantly increasing demand in terms of data rate and volume, leads to the development of systems offering very wide bandwidths, modulations with very high spectral efficiencies, increased power and frequency flexibilities in transmitters. Moreover, the implementation of such systems must be done with a permanent concern for energy saving, hence the recurring goal of the RF power amplification which is to combine the best efficiency, linearity and bandwidth. Conventional architectures of RF emitter front-ends consist in a first step in performing the frequency modulation-conversion operation (IQ Modulator) and then in a second step the DC-RF energy conversion operation (Power Amplifier), these two steps being usually managed independently. The aim of this thesis is to propose an alternative approach that consists in combining these two operations in only one function: a high efficiency vector power modulator. The core of the proposed system is based on a two-stage GaN HEMT circuit to obtain a variable power gain operating at saturation. It is associated with a specific multi-level bias modulator also design using GaN technology. The fabricated device generates, at a frequency of 2.5 GHz, a 16QAM modulation (100Msymb/s) with 13W average power, 25W peak power, with an overall efficiency of 40% and 5% EVM
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Ajo, Jr Amos V. "Design and Implementation of a Constant Envelope OFDM Waveform in a Software-Defined Radio Platform." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71689.
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This thesis examines the high peak-to-average-power ratio (PAPR) problem of OFDM and other spectrally-efficient multicarrier modulation schemes, specifically their stringent requirements for highly linear, power-inefficient amplification. The thesis then presents a most intriguing answer to the PAPR-problem in the form of a constant-envelope OFDM (CE-OFDM) waveform, a waveform which employs phase modulation to transform the high-PAPR OFDM signal into a constant envelope signal, like FSK or GMSK, which can be amplified with non-linear power amplifiers at near saturation levels of efficiency. A brief analytical description of CE-OFDM and its suboptimal receiver architecture is provided in order to define and analyze the key parameters of the waveform and their performance impacts.
The primary contribution of this thesis is a highly tunable software-defined radio (SDR) implementation of the waveform which enables rapid-prototyping and testing of CE-OFDM systems. The digital baseband processing of the waveform is executed on a general purpose processor (GPP) in the Linux Ubuntu 14.04 operating system, and programmed using the GNU Radio SDR software framework with a mixture of Python and C++ routines. A detailed description of the software implementation is provided, and baseband simulations of the SDR CE-OFDM receiver in additive white Gaussian noise (AWGN) validate the performance of the implemented signal processing.
A fully-functional CE-OFDM radio system is proposed in which GPPs executing the software defined transmitter and receiver routines are interfaced with Ettus Universal Software Radio Peripheral (USRP) transceiver front ends. A software testbench is created to enable rapid configuration and testing of the CE-OFDM waveform over all permutations of its parameters, over both simulated and physical RF channels, to draw deeper insights into the characteristics of the waveform and the necessary design considerations and improvements for further development and deployment of CE-OFDM systems.Master of Science
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Tsuda, Hirofumi. "Study on Communication System From the Perspective of Improving Signal-to-Noise Ratio." Kyoto University, 2019. http://hdl.handle.net/2433/242440.
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Neslen, Cody R. "Negative Conductance Load Modulation RF Power Amplifier." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/312.
Full textAbstract:
The number of mobile wireless devices on the market has increased substantially over the last decade. The frequency spectrum has become crowded due to the number of devices demanding radio traffic and new modulation schemes have been developed to accommodate the number of users. These new modulation schemes have caused very poor efficiencies in power amplifiers for wireless transmission systems due to high peak-to-average power ratios (PAPR). This thesis first presents the issue with classical power amplifiers in modern modulation systems. A brief overview of current attempts to mitigate this issue is provided. A new RF power amplifier topology is then presented with supporting simulations.
The presented amplifier topology utilizes the concept of negative conductance and load modulation. The amplifier operates in two stages, a low power stage and a high power stage. A negative conductance amplifier is utilized during peak power transmission to modulate the load presented to the input amplifier. This topology is shown to greatly improve the power added efficiency of power amplifiers in systems with high PAPR.
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Tom, Anas. "Physical Layer Algorithms for Interference Reduction in OFDM-Based Cognitive Radio Systems." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5872.
Full textAbstract:
Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier transmission scheme used in most of the existing wireless standards such as LTE, WiFi and WiMAX. The popularity of OFDM stems from the multitude of benefits it offers in terms of providing high data rate transmission, robustness against multipath fading and ease of implementation. Additionally, OFDM signals are agile in the sense that any subcarrier can be switched on or off to fit the available transmission bandwidth, which makes it well suited for systems with dynamic spectrum access such as cognitive radio systems. Nonetheless, and despite all the aforementioned advantages, OFDM signals have high spectral sidelobes outside the designated band of transmission, that can create severe interference to users in adjacent transmission bands, particularly when there is no synchronization between users. The focus of this dissertation is to propose baseband solutions at the Physical Layer (PHY) of the communications system to address the interference resulting from the high out-of-band (OOB) emissions of OFDM.
In the first part of this dissertation, we propose a precoder capable of generating mask compliant OFDM signals with low OOB emissions that are always contained under a given spectrum emission mask (SEM) specified by the OFDM standard. The proposed precoder generates transmitted signals with bit error rate (BER) performance similar to that of classical OFDM and does not reduce the spectral efficiency of the system.
In the second part of this dissertation, we introduce a novel and elegant approach, called suppressing alignment (SA), to jointly reduce the OOB interference and peak-to-average power ratio (PAPR) of OFDM systems. SA exploits the unavoidable redundancy provided by the CP as well as the wireless communications channel to generate an OOB/PAPR suppressing signal at the OFDM transmitter. Furthermore, after passing through the wireless channel, the suppressing signal is aligned with the CP duration at the OFDM receiver, essentially causing no interference to the data portion of the OFDM symbol. The proposed approach improves the PAPR of the transmitted OFDM signal and reduces the OOB interference by tens of decibels. Additionally, the proposed approach maintains an error performance similar to that of plain OFDM without requiring any change in the receiver structure of legacy OFDM.
In order to reduce the spectral emissions of OFDM, additional blocks, such as linear precoders, are usually introduced in the transmitter leading to a transmitted signal that is drastically different than that of a classical OFDM signal. This distortion is typically quantified by the error vector magnitude (EVM), a widely used metric specified by the wireless standard and is directly related to the BER performance of the system. The receiver can usually decode the information data with acceptable error probabilities if the distortion introduced to the transmitted signal is below the EVM values specified in the OFDM standard. Linear precoders, while capable of achieving significant reduction in the OOB interference, they typically introduce large distortion to the transmitted signal. As such, the receiver needs to know the precoding done at the transmitter to be able to recover the data which usually entails sending large amount of side information that can greatly reduce the spectral efficiency of the system. In the last part of this dissertation, we target the design of precoders for the purpose reducing the OOB interference, in a transparent manner where the receiver does not need to know the changes introduced in the transmitter. We present two precoders capable of significantly reducing the OOB emissions while producing transmitted signals with EVM values below those specified by the wireless standard, thereby guaranteeing acceptable error performance.
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Arraño, Scharager Hernán Felipe. "Performance enhancement of OFDM-Based systems using Nyquist-I pulses." Tesis, Universidad de Chile, 2015. http://repositorio.uchile.cl/handle/2250/136267.
Full textAbstract:
Ingeniero Civil EléctricoLos constantes y cada vez más acelerados avances tecnológicos, han generado que los sistemas de comunicación se optimicen considerablemente con el transcurso de los años. Dentro de los cambios más importantes que se han visto en el último tiempo, destaca la disminución del uso de los clásicos sistemas de telecomunicaciones basados en portadoras únicas, dándose paso a sistemas más complejos en donde la información se transmite utilizando múltiples portadoras. Dentro de este último grupo de técnicas, uno de los que más sobresale es orthogonal frequency division multiplexing (OFDM), el cual ha sido y es, ampliamente utilizado en múltiples aplicaciones o estándares de comunicación. El uso extensivo de OFDM se debe a varias ventajas que esta técnica posee, tales como: alcanzar altas tasas de transmisión de datos, generar señales robustas ante canales inalámbricos, tener una alta eficiencia espectral, entre otros. Pero, aun cuando éstos exhiben múltiples ventajas, también presentan ciertos inconvenientes que deben ser tratados como lo son: los altos niveles de peak-to-average power ratio (PAPR) que caracterizan a las señales OFDM y la sensibilidad a errores originados por la desincronización entre el transmisor y receptor. Esto último, facilita la generación de interferencia entre portadoras (inter-carrier interference, ICI) y, por ende, un aumento en la probabilidad de error. En este trabajo se examina el funcionamiento de los sistemas basados en OFDM, partiendo desde la generación de la señal, hasta su comportamiento espectral. Pero por otro lado, también se analiza como la implementación de pulsos que cumplen con el primer criterio de Nyquist (Nyquist-I), favorece al rendimiento de esta clase de sistemas. El uso de pulsos Nyquist-I para combatir los inconvenientes típicos mostrados por los sistemas basados en OFDM ha sido propuesto por múltiples investigadores. En este trabajo se estudia en detalle una nueva familia de pulsos Nyquist-I llamada improved parametric linear combination pulses (IPLCP), la cual se propone para combatir un completo listado de aspectos perjudiciales mostrados por sistemas OFDM reales, a diferencia de otros pulsos que solamente buscan solucionar uno de ellos. Para analizar el rendimiento de la nueva familia de pulsos, se le compara con otras ya conocidas en términos del ICI, la razón señal a interferencia (signal-to-interference ratio, SIR), el PAPR y la tasa de probabilidad de error de bit (bit error rate, BER). Finalmente, el análisis demuestra que la nueva familia es la que mejor se desempeña en promedio en términos de los parámetros de estudio recién mencionados, dejando en claro que la implementación del IPLCP favorece al rendimiento de los sistemas de comunicación basados en la tecnología OFDM.
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Mollén, Christopher. "On Massive MIMO Base Stations with Low-End Hardware." Licentiate thesis, Linköpings universitet, Kommunikationssystem, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-130516.
Full textAbstract:
Massive MIMO (Multiple-Input Multiple-Output) base stations have proven, both in theory and in practice, to possess many of the qualities that future wireless communication systems will require. They can provide equally high data rates throughout their coverage area and can concurrently serve multiple low-end handsets without requiring wider spectrum, denser base station deployment or significantly more power than current base stations. The main challenge of massive MIMO is the immense hardware complexity and cost of the base station—each element in the large antenna array needs to be individually controllable and therefore requires its own radio chain. To make massive MIMO commercially viable, the base station has to be built from inexpensive simple hardware. In this thesis, it is investigated how the use of low-end power amplifiers and analog-to-digital converters (ADCs) affects the performance of massive MIMO. In the study of the signal distortion from low-end amplifiers, it is shown that in-band distortion is negligible in massive MIMO and that out-of-band radiation is the limiting factor that decides what power efficiency the amplifiers can be operated at. A precoder that produces transmit signals for the downlink with constant envelope in continuous time is presented to allow for highly power efficient low-end amplifiers. Further, it is found that the out-of-band radiation is isotropic when the channel is frequency selective and when multiple users are served; and that it can be beamformed when the channel is frequency flat and when few users are served. Since a massive MIMO base station radiates less power than today's base stations, isotropic out-of-band radiation means that low-end hardware with poorer linearity than required today can be used in massive MIMO. It is also shown that using one-bit ADCs—the simplest and least power-hungry ADCs—at the base station only degrades the signal-to-interference-and-noise ratio of the system by approximately 4 dB when proper power allocation among users is done, which indicates that massive MIMO is resistant against coarse quantization and that low-end ADCs can be used.Massiv-MIMO-basstationer (eng: Multiple-Input Multiple-Output) har visats, både i teori och praktik, besitta många av de egenskaper som framtida trådlösa kommunikationssystem kommer att behöva. De kan tillhandahålla enhetligt höga datatakter i hela täckningsområdet och simultant betjäna flera enkla mobilenheter utan att använda bredare spektrum, tätare basstationsplacering eller betydligt mer effekt än dagens basstationer. Huvudutmaningen med massiv MIMO är basstationens enorma hårdvarukomplexitet och -kostnad – varje element i den stora gruppantennen skall kunna kontrolleras individuellt och kräver sålunda sin egen radiokedja. För att massiv MIMO skall bli kommersiellt attraktiv, måste basstationen byggas av billig, enkel hårdvara. I denna avhandling undersöks hur enkla effektförstärkare och analog-till-digital-omvandlare (AD-omvandlare) påverkar massiv-MIMO-systemets prestanda. I studien av signaldistorsionen från enkla förstärkare visas det att inband-distorsionen är försumbar i massiv MIMO och att utombandsstrålningen är den begränsande faktorn som bestämmer vid vilken verkningsgrad förstärkarna kan arbeta. En förkodare som åstadkommer nerlänks-sändsignaler som har konstant envelopp i kontinuerlig tid presenteras för att möjliggöra användandet av enkla förstärkare med hög verkningsgrad. Vidare konstateras det att utombandsstrålningen är isotrop när kanalen är frekvensselektiv och när flera användare betjänas; och att den kan lobformas när kanalen är frekvensflat och när få användare betjänas. Eftersom en massiv-MIMO-basstation utstrålar mindre effekt än dagens basstationer, betyder isotrop utombandsstrålning att enkel hårdvara med sämre linearitet än vad som krävs idag kan användas i massiv MIMO. Det visas även att användandet av enbits-AD-omvandlare – de enklaste och mest strömsnåla AD-omvandlarna – i basstationen endast minskar signal-till-interferens-och-brus-förhållandet med 4 dB när tillbörlig effektallokering mellan användarna utförs, vilket indikerar att massiv MIMO är motståndskraftig mot grov kvantisering och att enkla AD-omvandlare kan användas.
大規模多輸入多輸出基站，無論從理論上或實際上，皆已經證明具有許多未來無線通訊系統所需的特質。比如：在其整個覆蓋區域均一地提供高數據傳輸速率、在同一時間頻率資源上服務多個簡單的終端設備，而無需佔用更多頻譜資源或更密集地部署基站，亦無需提高基站的功耗。實現大規模多入多出系统的主要挑戰在於硬件複雜度及基站成本——大規模天線陣列中的每一個天線元必須單獨可控，因此需要其自身的射頻鏈路。爲使大規模多入多出基站有商業吸引力，基站必須以簡單低成本的硬件來建造。本論文探討簡單的功率放大器與模擬數字轉換器對大規模多入多出性能的影響。對低端功放信號失真的研究表明，帶內失真對大規模多入多出的性能影響幾乎可以忽略，而帶外泄露是限制功放效率的決定因素。爲使用高功率效率低端功放，本文提出能產生具有恆定包絡連續時間信號的預編碼。本文指出，在頻率選擇性衰落信道上服務多個用戶時，帶外泄露呈現各向同性；而在平坦衰落信道上服務少數用戶時，帶外泄露可呈現波束賦形。由於大規模多入多出基站比現用基站輻射較少功率，帶外泄露各向同性意味著大規模多入多出基站可使用低端硬件，其線性要求不比現有基站的高。另外表明，如果進行合理的多用戶功率分配，基站使用單比特模擬數字轉換器——最簡單低耗的轉換器——僅使系統的信干噪比降低約４分貝。以此可見，大規模多入多出系統對非精確量比較穩定，低端模擬數字轉換器可於此類系統中使用。
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Qian, Hua. "Power Efficiency Improvements for Wireless Transmissions." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/11649.
Full textAbstract:
Many communications signal formats are not power efficient because of their large peak-to-average power ratios (PARs). Moreover, in the presence of nonlinear devices such as power amplifiers (PAs) or mixers, the non-constant-modulus signals may generate both in-band distortion and out-of-band interference. Backing off the signal to the linear region of the device further reduces the system power efficiency. To improve the power efficiency of the communication system, one can pursue two approaches: i) linearize the PA; ii) reduce the high PAR of the input signal.
In this dissertation, we first explore the optimal nonlinearity under the peak power constraint. We show that the optimal nonlinearity is a soft limiter with a specific gain calculated based on the peak power limit, noise variance, and the probability density function of the input amplitude. The result is also extended to the fading channel case.
Next, we focus on digital baseband predistortion linearization for power amplifiers with memory effects. We build a high-speed wireless test-bed and carry out digital baseband predistortion linearization experiments. To implement adaptive PA linearization in wireless handsets, we propose an adaptive digital predistortion linearization architecture that utilizes existing components of the wireless transceiver to fulfill the adaptive predistorter training functionality.
We then investigate the topic of PAR reduction for OFDM signals and forward link CDMA signals. To reduce the PAR of the OFDM signal, we propose a dynamic selected mapping (DSLM) algorithm with a two-buffer structure to reduce the computational requirement of the SLM method without sacrificing the PAR reduction capability. To reduce the PAR of the forward link CDMA signal, we propose a new PAR reduction algorithm by introducing a relative offset between the in-phase branch and the quadrature branch of the transmission system.
34
King, Matthew E. "Linear Power-Efficient RF Amplifier with Partial Positive Feedback." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/811.
Full textAbstract:
Over the last decade, the number of mobile wireless devices on the market has increased substantially. New “multi-carrier” modulation schemes, such as OFDM, WCDMA, and WiMAX, have been developed to accommodate the increasing number of wireless subscribers and the demand for faster data rates within the limited commercial frequency spectrum. These complex modulation schemes create signals with high peak-to-average power ratios (PAPR), exhibiting rapid changes in the signal magnitude. To accommodate these high-PAPR signals, RF power amplifiers in mobile devices must operate under backed-off gain conditions, resulting in poor power efficiency. Various efficiency-enhancement solutions have been realized for backed-off devices to combat this issue.
A brief overview of one of the more extensively researched solutions, the Doherty amplifier, is given, and its inherent limitations are discussed. A recently proposed amplifier topology that provides the efficiency benefits of the Doherty amplifier, while overcoming some of the fundamental problems that plague the standard Doherty architecture, is investigated. A step-by-step design methodology is presented and confirmed by extensive simulation in Agilent ADS. A design example, tuned for maximum efficiency at peak output power, is implemented on a PCB and tested to verify the validity of the proposed circuit configuration.
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Yazici, Ayhan. "Block Transmissions On Orthogonal Carriers." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606516/index.pdf.
Full textAbstract:
Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier
Block Transmissions (SCBT) are located at the two opposite edges of block
transmission concept. In this thesis a system which lies between OFDM
and SCBT is proposed. The new system, namely Block Transmissions on
Orthogonal Carriers (BTOC), can be considered as a hybrid form of OFDM
and SCBT. BTOC system is investigated under the redundant filterbank
precoders and equalizers framework. Peak to average power ratio (PAPR) of
BTOC is formulated and compared with the PAPRs of OFDM and SCBT.
Effect of frequency offset for BTOC is investigated and comparison between
OFDM, SCBT, and BTOC is presented. Simulation results of Zero Padded
OFDM (ZP-OFDM), SCBT, and BTOC are included.
36
Hou, Xin-Anne, and 侯信安. "An Efficient Peak-to-Average Power Ratio (PAPR) Reduction Method in OFDM." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/06326511381186668784.
Full textAbstract:
碩士國立交通大學
電子工程系
90
Orthogonal Frequency Division Multiplexing (OFDM) is a promising transmission technique which satisfy the requirement of high data rate communication. However, OFDM has two main disadvantages: high PAPR and sensitivity to frequency offset. High PAPR reduces the power amplifier efficiency and degrades the performance of the system. Consequently, high PAPR makes implementation of OFDM difficult. This thesis reviews several PAPR reduction methods and provides computer simulations to evaluate these methods. The basic algorithms of PAPR reduction methods, including signal distortion, coding, and multiple signal representation, are described in this thesis. Furthermore, the modified algorithms are also investigated. Finally, we propose an efficient PAPR reduction method, attenuation, in OFDM based on the simulation result.
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Yu, Yao-Chun, and 游曜駿. "A study on Peak-to-Average Power Ratio (PAPR) Reduction in OFDM Systems." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/62457643720352134831.
Full textAbstract:
碩士國立中正大學
電機工程研究所
90
Orthogonal frequency division multiplexing (OFDM) is a promising transmission technology for future high data rate communications. OFDM has been used in wide varieties of applications, such as digital television video system (DTV), digital audio broadcasting system (DVB) and wireless local area network (WLAN). In this thesis, the issue of Peak-to-average power ratio (PAPR) of OFDM systems is investigated. Optimal output backoff (OBO) with minimum total power degradation (TPD) is obtained with the effects of nonlinear power amplifiers being taken into account. Several PAPR reduction methods, including clipping, complementary code and companding in combination of practical nonlinear power amplifiers such as Traveling-Wave Tube Amplifier (TWTA) and Solid-State Power Amplifier (SSPA) have been considered. Computer simulations based on IEEE 802.11a are employed to compare different PAPR reduction methods and to evaluate the effects of nonlinear amplifiers.
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Wei, Yi-De, and 魏羿得. "Peak-to-average power ratio (PAPR) reduction by pulse shaping using the K-exponential filter." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/98878927891923350199.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
97
The K-exponential filter is designed for peak to average power ratio (PAPR) reduction without intersymbol interference (ISI). The key point is that the frequency responses of the filter which keeps the same bandwidth can vary with different designing parameter, the origin for the name. There is a minimum PAPR corresponding to an appropriate when roll-off factor α is fixed. The simulated result shows that the maximum PAPR reduction by the filters is about 0.25 dB in OFDM system and 1 dB in IFDMA system compared with the raised cosine filter. Besides, the K-exponential filter has almost equal performance in IFDMA system but better performance in OFDM system compared with the same kind of the versatile filter.
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Paul, Prabal. "On The Peak-To-Average-Power-Ratio Of Affine Linear Codes." Thesis, 2006. http://hdl.handle.net/2005/350.
Full textAbstract:
Employing an error control code is one of the techniques to reduce the Peak-to-Average Power Ratio (PAPR) in an Orthogonal Frequency Division Multiplexing system; a well known class of such codes being the cosets of Reed-Muller codes. In this thesis, classes of such coset-codes of arbitrary linear codes are considered. It has been proved that the size of such a code can be doubled with marginal/no increase in the PAPR. Conditions for employing this method iteratively have been enunciated. In fact this method has enabled to get the optimal coset-codes. The PAPR of the coset-codes of the extended codes is obtained from the PAPR of the corresponding coset-codes of the parent code. Utility of a special type of lengthening is established in PAPR studies
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Bae, Ki-taek. "New signal processing approaches to peak-to-average power ratio reduction in multicarrier systems." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1649.
Full textAbstract:
Multi-carrier systems based on orthogonal frequency division multiplexing (OFDM) are efficient technologies for the implementation of broadband
wireless communication systems. OFDM is widely used and has been adopted for current mobile broadband wireless communication systems such as IEEE 802.a/g wireless LANs, WiMAX, 3GPP LTE, and DVB-T/H digital video broadcasting systems. Despite their many advantages, however, OFDM-based systems suffer from potentially high peak-to-average power ratio (PAR). Since communication systems typically include nonlinear devices such as RF power amplifiers (PA) and digital-to-analog converters (DAC), high PAR results in increased symbol error rates and spectral radiation. To mitigate these nonlinear effects and to avoid nonlinear saturation effects of the PA, the operating point of a signal with high peak power must be backed off into the linear
region of the PA. This so-called output backoff (OBO) results in a reduced power conversion efficiency which limits the battery life for mobile applications, reduces the coverage range, and increases both the cost of the PA and power consumption in the cellular base station. With the increasing demand for high energy efficiency, low power consumption, and greenhouse gas emission reduction, PAR reduction is a key technique in the design of practical OFDM systems.
Motivated by the PAR reduction problem associated with multi-carrier systems, such as OFDM, this research explores the state of the art of PAR reduction techniques and develops new signal processing techniques that can
achieve a minimum PAR for given system parameters and that are compatible with the appropriate standards. The following are the three principal contributions of this dissertation research.
First, we present and derive the semi-analytical results for the output of asymptotic iterative clipping and filtering. This work provides expressions and analytical techniques for estimating the attenuation factor, error vector magnitude, and bit-error-rate (BER), using a noise enhancement factor that
is obtained by simulation. With these semi-analytical results, we obtain a relationship between the BER and the target clipping level for asymptotic iterative
clipping and filtering. These results serve as a performance benchmark for designing PAR reduction techniques using iterative clipping and filtering
in OFDM systems.
Second, we analyze the impact of the selected mapping (SLM) technique on BER performance of OFDM systems in an additive white Gaussian noise channel in the presence of nonlinearity. We first derive a closed-form expression
for the envelope power distribution in an OFDM system with SLM. Then, using this derived envelope power distribution, we investigate the BER performance and the total degradation (TD) of OFDM systems with SLM under
the existence of nonlinearity. As a result, we obtain the TD-minimizing peak backoff (PBO) and clipping ratio as functions of the number of candidate signals in SLM.
Third, we propose an adaptive clipping control algorithm and pilotaided algorithm to address a fundamental issue associated with two lowcomplexity PAR reduction techniques, namely, tone reservation (TR) and active constellation extension (ACE). Specifically, we discovered that the existing low-complexity algorithms have a low clipping ratio problem in that they can not achieve the minimum PAR when the target clipping level is set
below the initially unknown optimum value. Using our proposed algorithms, we overcome this problem and demonstrate that additional PAR reduction is
obtained for any low value of the initial target clipping ratio.text
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Viegas, Pedro Miguel Germano. "Amplificação linear quantizada de sinais multi-portadora." Master's thesis, 2017. http://hdl.handle.net/10362/74801.
Full textAbstract:
A constante evolução dos dispositivos móveis e das aplicações, acarreta a transmissão de dados com maior velocidade, tanto ao nível da transmissão guiada como da transmissão sem fios. O advento da quarta geração de redes móveis (4G) resultou num crescimento do número de smartphones e tablets e consequentemente do volume de dados transmitidos. Este último, por sua vez, levou à necessidade de desenvolvimento de técnicas multi-portadora, como o OFDM (Orthogonal Frequency Division Multiplexing), espectralmente eficientes para a transmissão de dados digitais, de forma a suportar os ritmos exigidos. Contudo, o aumento do ritmo é conseguido à custa de um sacrifício da eficiência de potência, dado o nível de flutuações de envolvente característica destas técnicas. Com o advento da quinta geração de telefonia móvel (5G), estimam-se ritmos de transmissão 10 a 20 vezes superiores ao 4G e uma maior penetração quer dos dispositivos móveis e células nas quais são empregues este tipo de modulações, que torna crítica uma melhor gestão energética. Consequentemente, é necessária uma maior eficiência energética quer a nível dos dispositivos móveis quer a nível da rede, que pode ser atingida mediante uma amplificação de potência com maior rendimento. Esta pode ser conseguida através de uma amplificação linear, como a proposta nesta tese, com recurso a amplificadores não lineares, na qual o sinal de envolvente variável é decomposto em componentes de envolvente constante, que são amplificadas independentemente por amplificadores saturados. Desta forma consegue-se melhorar o rendimento da amplificação, permitindo uma maior eficiência energética, independentemente do nível da PAPR (Peak to Average Power Ratio) apresentado pelos sinais à entrada do andar de amplificação.
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Das, Smarajit. "Low-PAPR, Low-delay, High-Rate Space-Time Block Codes From Orthogonal Designs." Thesis, 2009. http://hdl.handle.net/2005/1046.
Full textAbstract:
It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. Some of the design criteria of the space-time block codes (STBCs) for multiple input multiple output (MIMO)communication system are that these codes should attain large transmit diversity, high data-rate, low decoding-complexity, low decoding –delay and low peak-to-average power ratio (PAPR). STBCs based on real orthogonal designs (RODs) and complex orthogonal designs (CODs) achieve full transmit diversity and in addition, these codes are single-symbol maximum-likelihood (ML) decodable. It has been observed that the data-rate (in number of information symbols per channel use) of the square CODs falls exponentially with increase in number of antennas and it has led to the construction of rectangular CODs with high rate.
We have constructed a class of maximal-rate CODs for n transmit antennas with rate if n is even and if n is odd. The novelty of the above construction is that they 2n+1 are constructed from square CODs. Though these codes have a high rate, this is achieved at the expense of large decoding delay especially when the number of antennas is 5or more. Moreover the rate also converges to half as the number of transmit antennas increases. We give a construction of rate-1/2 CODs with a substantial reduction in decoding delay when compared with the maximal- rate codes.
Though there is a significant improvement in the rate of the codes mentioned above when compared with square CODs for the same number of antennas, the decoding delay of these codes is still considerably high. For certain applications, it is desirable to construct codes which are balanced with respect to both rate and decoding delay. To this end, we have constructed high rate and low decoding-delay RODs and CODs from Cayley-Dickson Algebra.
Apart from the rate and decoding delay of orthogonal designs, peak-to-average power ratio (PAPR) of STBC is very important from implementation point of view. The standard constructions of square complex orthogonal designs contain a large number of zeros in the matrix result in gin high PAPR. We have given a construction for square complex orthogonal designs with lesser number of zero entries than the known constructions. When a + 1 is a power of 2, we get codes with no zero entries. Further more, we get complex orthogonal designs with no zero entry for any power of 2 antennas by introducing co- ordinate interleaved variables in the design matrix. These codes have significant advantage over the existing codes in term of PAPR. The only sacrifice that is made in the construction of these codes is that the signaling complexity (of these codes) is marginally greater than the existing codes (with zero entries) for some of the entries in the matrix consist of co-ordinate interleaved variables. Also a class of maximal-rate CODs
(For mathematical equations pl see the pdf file)
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Correia, Pedro Gonçalves. "Amplificação de potência energeticamente eficiente para sinais mono portadora e multi portadora." Master's thesis, 2018. http://hdl.handle.net/10362/121789.
Full textAbstract:
Os recentes avanços tecnológicos, permitiram não só o desenvolvimento da rede móvel, como também permitiram a massificação de dispositivos móveis. Com o crescimento exponencial de utilizadores da rede celular, é necessário garantir ritmos de transmissão elevados e uma redução no consumo energético por parte dos dipositivos. Para garantir ritmos de transmissão elevados, são utilizados sinais multi-portadora como o OFDM (Orthogonal Frequency Division Multiplexing) ou sinais SC-FDE (Single Carrier Frequency Domain Equalization). No entanto, estes sinais são caracterizados por elevada PAPR (Peak-to-AveragePower Ratio) levando a que seja necessário sobre dimensionar os amplificadores de acordo com a gama dinâmica do sinal, sacrificando assim a eficiência energética. Neste trabalho, é proposto um transmissor que realiza uma quantização da envolvente complexa de sinal com elevada PAPR, dividindo-a num somatório de componentes com envolvente constante, permitindo assim utilizar amplificadores a operar na zona de saturação ou próximo desta, minimizando os efeitos não lineares por parte dos amplificadores ao mesmo tempo que se maximiza a eficiência energética do transmissor.The recent technological advances enabled not only the development of the mobile communication systems, but also led to the massification of mobile devices. While the increase number of users of the cellular network, it is necessary to guarantee high transmis-sion rates and reduced energy consumption by the devices. Signals like OFDM (Orthog-onal Frequency Division Multiplexing) or SC-FDE (Single Carrier Frequency Domain Equalization) can be used to maintain high transmission rates, however, these signals are characterized by high PAPR (Peak-to-Mean Power Ratio) which require linear amplifiers that can amplify the signals accordingly with their dynamic range, thus sacrificing the power efficiency of the amplifiers. In this work, it is proposed a transmitter that performs a signal processing that allows to divide a signal with a high PAPR into a sum of components that have constant envelope. Since the components have constant envelope, it allows the use of amplifiers operating near the saturation zone, minimizing the effects of nonlinear effects of the amplifier while maximizing the power efficiency of the transmitter.
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Hung, Kuen-Ming, and 洪崑銘. "Study on Peak-to-Average Power Ratio of OFDM Systems." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/75901412828179664477.
Full textAbstract:
碩士國立中山大學
電機工程學系研究所
92
In recent years, the development of OFDM system has received a lot of attention. Some examples of existing systems where OFDM system is used are digital audio broadcasting, high-definition television terrestrial broadcasting, asymmetric digital subcarrier lines and so on. There are several reasons for using OFDM systems. First, OFDM system is an efficient way to deal with multipath effect. Under a fixed amount of delay spread, the implementation complexity of OFDM system is much less than that of single-carrier system. The reason is that OFDM system can simply use guard time to process delay spread without a complex equalizer. Second, OFDM system can achieve high data rate to transmit by using large number of subcarriers. Third, OFDM system can also efficiently combat with narrow band interference. On the other hand, OFDM system also has two main drawbacks. One is more sensitive to frequency offset, the other is higher PAPR. This thesis focuses on the PAPR problem. Pulse shaping method is an effective way to solve this problem. It can be used for any number of subcarriers of OFDM systems, so it is very flexible. It doesn’t have any additional IFFTs in comparison to the selected mapping or partial transmit sequence method. Its implementation is simpler. And because it also doesn’t distort the OFDM symbols, its bit error performance should be better than the clipping method. According to the pulse shaping method, we get a better waveform that can make the PAPR of OFDM symbols do not exceed about 2.
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Chung, Albert I.-Chou, and 鍾翼州. "Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/12764655199023481437.
Full textAbstract:
碩士國立交通大學
電子工程系
89
Orthogonal Frequency Division Multiplexing (OFDM) is a very promising technique for high-speed data transmission. It can effectively take care of the inter-symbol interference induced by multipath propagation over radio channels. One of the major drawbacks of OFDM is the high peak-to-average power ratio (PAPR). Thus, the nonlinearity between transmitter modulator and receiver demodulator will degrade the overall system performance because of the large dynamic range of the OFDM signal. In this thesis, the peak power problem in OFDM is discussed. PAPR reduction techniques in the literature are reviewed. Also, we investigate several schemes to take care of this issue. An approach termed “deliberate signal distortion with interleaved error-control coding” can be used to deal with this problem. This approach also can be combined with multiple signal representation techniques to achieve more improvement in PAPR reduction.
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Chen, Kevin, and 陳鉉文. "Peak-to-Average Power Ratio Reduction of OFDM Based on Adaptive Peak Reduction Carriers." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/77855769115768485417.
Full textAbstract:
碩士國立交通大學
電信工程系所
95
Due to the large dynamic range of the OFDM signal, the peak-to- average power ratio (PAPR) can be very high. This large PAPR value will lead to severe nonlinear distortion, resulting in reduced efficiency of the RF power amplifier and increased complexity of the analog-to-digital and digital-to-analog converters. To reduce the PAPR, several techniques have been proposed, among them Tone Reservation is a technique which lowers the PAPR without distorting the signal. In this thesis, we investigate the technique of Tone Reservation and consider the effect of channel condition. Base on the channel condition, we adaptively choose the subcarrier with the worst channel condition to be our peak reduction carrier to effectively lower the signal PAPR and increase the efficiency of subcarrier transmission. In searching the proper value of the peak reduction carriers, we modified Wang’s algorithm to recursively adjust the percentage (β) we wanted to lower the peak value, so that each of the adaptive peak reduction carriers can effectively reduce the signal PAPR while avoiding the circumstance of wasting them if failed to reduce signal PAPR.
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Liu, Peng. "New peak-to-average power ratio reduction schemes for OFDM systems." Thesis, 2004. http://spectrum.library.concordia.ca/7937/1/MQ91071.pdf.
Full textAbstract:
It is known that the orthogonal frequency division multiplexing (OFDM) modulation is very suitable for high-speed wireless transmission systems due to its bandwidth efficiency and ability in coping with multipath fading. However, the large peak-to-average power ratio (PAPR) of an OFDM signal limits the application of OFDM to a certain degree. The research focus of this thesis is on the study of some new PAPR reduction schemes for OFDM systems. In the first part of the thesis, we investigate the peak windowing method, the clipping method, and a combination of the two techniques with an emphasis on the performance assessment of the transmitted OFDM signal using the combination scheme. We start with the review of the two typical signal distortion techniques and point out their advantages and shortcomings. We then propose a combination scheme for the two techniques in order to overcome their drawbacks. In the proposed combination scheme, a weighting function is used to remove instantaneous signal peaks and then a hard-limiting is utilized for the reduction of the overall peak powers. A modified IDFT interpolation is developed and employed in the combination scheme to improve the interpolation precision of the time-domain OFDM signal. (Abstract shortened by UMI.)
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Tung, Yuan-Hao, and 董原豪. "Studies of Peak-to-Average Power Ratio Reduction for OFDM Signals." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/89647820959131044676.
Full textAbstract:
碩士國立交通大學
電信工程研究所
98
In this thesis we propose several approaches for reducing peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. The conventional clipping approach clips the magnitude of a time-domain OFDM waveform while leaving its phase intact. We present a novel time-domain clipping method with hybrid frequency domain constraint by independently clipping both real and imaginary parts of a complex time-domain OFDM waveform and using linear pro- gramming (LP) to obtain the optimal clipped signal. Selective mapping (SLM) often requires that side information about the mapping sequence used be sent along with the desired data sequence. Maximum likelihood de- tection without side information is realized at the cost of much higher complexity. We proposed a novel SLM sequences design which enable a receiver to use a simple detector without side information, leading to bandwidth e±ciency and capacity improvement. The proposed design also has the advantages of simple encoding implementation and low memory requirement. When SLM side information is needed for signal detection, it is often protected with a low rate forward error-correcting code. We propose an SLM scheme with embedded side information. Active constellation extension (ACE) and projection onto convex set (POCS) techniques are used to adjust side information for both reducing PAPR and achieving better SLM index detection probability.
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hung, Kuang-cheng, and 洪光政. "A Simulation Study of SC-FDMA Peak-to-Average Power Ratio." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/11537190932358238976.
Full textAbstract:
碩士國立中央大學
通訊工程研究所碩士在職專班
98
In this paper, we compare the PAPR with different parameters at Single carrier frequency division multiple access (SC-FDMA) system. We also try to reduce the PAPR to avoid signal distortion and improve the efficiency of amplifier. In the paper, we change the precode, subcarrier mapping method and modulation method to compare the PAPR. We use Matlab to simulator the SC-FDMA system and analysis the PAPR result.
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Kuo, Yen-Chih, and 郭彥志. "On Peak-to-Average Power Ratio Reduction in the OFDM system." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/14757805190422151293.
Full textAbstract:
碩士國立交通大學
電子工程系所
95
This thesis considers the Orthogonal Frequency Division Multiplexing (OFDM) system’s undesirable feature of a large peak-to-average power ratio (PAPR) of the transmitted signal. In the MIMO-OFDM system, a low complexity structure to deal with PAPR problem is important because multiple transmitter. In the various PAPR reduction methods, the method selected mapping has high PAPR reduction capability but also high complexity and needs to transmit additional side information. In this thesis, we combine low complexity SLM structure and transmitting the side information, simulation display this method can reduce PAPR effectively. And implement to DSP board using 802.11n which is MIMO-OFDM system, profiling that this structure has low complexity and doesn’t engage much time in the system.