Cognitive Radio Systems

Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems

Joint design of PAPR, PICR and OBP in OFDM systems

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

Physical Layer Techniques for OFDM-Based Cognitive Radios

Cognitive radio has recently been proposed as a promising approach for efficient utilization of radio spectrum. However, there are several challenges to be addressed across all layers of a cognitive radio system design, from application to hardware implementation. From the physical layer point-of-view, two key challenges are spectrum sensing and an appropriate signaling scheme for data transmission. The modulation techniques used in cognitive radio not only should be efficient and flexible but also must not cause (harmful) interference to the primary (licensed) users. Among all the proposed signaling schemes for cognitive radio, orthogonal frequency division multiplexing (OFDM) has emerged as a promising one due to its robustness against multipath fading, high spectral efficiency, and capacity for dynamic spectrum use. However, OFDM suffers from high out-of-band radiation which is due to high sidelobes of subcarriers. In this thesis, we consider spectral shaping in OFDM-based cognitive radio systems with focus on reducing interference to primary users created by by out-of-band radiation of secondary users' OFDM signal. In the first part of this research, we first study the trade-o between time-based and frequency-based methods proposed for sidelobe suppression in OFDM. To this end, two recently proposed techniques, active interference cancellation (AIC) and adaptive symbol transition (AST), are considered and a new joint time-frequency scheme is developed for both single-antenna and multi-antenna systems. Furthermore, knowledge of wireless channel is used in the setting of the proposed joint scheme to better minimize interference to the primary user. This scheme enables us to evaluate the trade-o between the degrees of freedom provided by each of the two aforementioned methods. In the second part of this research, a novel low-complexity technique for reducing out-of-band radiation power of OFDM subcarriers for both single-antenna and multi-antenna systems is proposed. In the new technique, referred to as a phase adjustment technique, each OFDM symbol is rotated in the complex plane by an optimal phase such that the interference to primary users is minimized. It is shown that the phase adjustment technique neither reduces the system throughput, nor does increase the bit-error-rate of the system. Moreover, the performance of the technique in interference reduction is evaluated analytically in some special cases and is verified using numerical simulations. Due to high sensitivity of OFDM systems to time and frequency synchronization errors, performance of spectral shaping techniques in OFDM is significantly affected by timing jitter in practical systems. In the last part of this research, we investigate the impact of timing jitter on sidelobe suppression techniques. Considering AIC as the base method of sidelobe suppression, we first propose a mathematical model for OFDM spectrum in presence of timing jitter and evaluate the performance degradation to AIC due to timing jitter. Then, a precautionary scheme based on a minimax approach is proposed to make the technique robust against random timing jitter.4 month

Orthogonal frequency division multiplexing multiple-input multiple-output automotive radar with novel signal processing algorithms

Advanced driver assistance systems that actively assist the driver based on environment perception achieved significant advances in recent years. Along with this development, autonomous driving became a major research topic that aims ultimately at development of fully automated, driverless vehicles. Since such applications rely on environment perception, their ever increasing sophistication imposes growing demands on environmental sensors. Specifically, the need for reliable environment sensing necessitates the development of more sophisticated, high-performance radar sensors. A further vital challenge in terms of increased radar interference arises with the growing market penetration of the vehicular radar technology. To address these challenges, in many respects novel approaches and radar concepts are required. As the modulation is one of the key factors determining the radar performance, the research of new modulation schemes for automotive radar becomes essential. A topic that emerged in the last years is the radar operating with digitally generated waveforms based on orthogonal frequency division multiplexing (OFDM). Initially, the use of OFDM for radar was motivated by the combination of radar with communication via modulation of the radar waveform with communication data. Some subsequent works studied the use of OFDM as a modulation scheme in many different radar applications - from adaptive radar processing to synthetic aperture radar. This suggests that the flexibility provided by OFDM based digital generation of radar waveforms can potentially enable novel radar concepts that are well suited for future automotive radar systems. This thesis aims to explore the perspectives of OFDM as a modulation scheme for high-performance, robust and adaptive automotive radar. To this end, novel signal processing algorithms and OFDM based radar concepts are introduced in this work. The main focus of the thesis is on high-end automotive radar applications, while the applicability for real time implementation is of primary concern. The first part of this thesis focuses on signal processing algorithms for distance-velocity estimation. As a foundation for the algorithms presented in this thesis, a novel and rigorous signal model for OFDM radar is introduced. Based on this signal model, the limitations of the state-of-the-art OFDM radar signal processing are pointed out. To overcome these limitations, we propose two novel signal processing algorithms that build upon the conventional processing and extend it by more sophisticated modeling of the radar signal. The first method named all-cell Doppler compensation (ACDC) overcomes the Doppler sensitivity problem of OFDM radar. The core idea of this algorithm is the scenario-independent correction of Doppler shifts for the entire measurement signal. Since Doppler effect is a major concern for OFDM radar and influences the radar parametrization, its complete compensation opens new perspectives for OFDM radar. It not only achieves an improved, Doppler-independent performance, it also enables more favorable system parametrization. The second distance-velocity estimation algorithm introduced in this thesis addresses the issue of range and Doppler frequency migration due to the target’s motion during the measurement. For the conventional radar signal processing, these migration effects set an upper limit on the simultaneously achievable distance and velocity resolution. The proposed method named all-cell migration compensation (ACMC) extends the underlying OFDM radar signal model to account for the target motion. As a result, the effect of migration is compensated implicitly for the entire radar measurement, which leads to an improved distance and velocity resolution. Simulations show the effectiveness of the proposed algorithms in overcoming the two major limitations of the conventional OFDM radar signal processing. As multiple-input multiple-output (MIMO) radar is a well-established technology for improving the direction-of-arrival (DOA) estimation, the second part of this work studies the multiplexing methods for OFDM radar that enable simultaneous use of multiple transmit antennas for MIMO radar processing. After discussing the drawbacks of known multiplexing methods, we introduce two advanced multiplexing schemes for OFDM-MIMO radar based on non-equidistant interleaving of OFDM subcarriers. These multiplexing approaches exploit the multicarrier structure of OFDM for generation of orthogonal waveforms that enable a simultaneous operation of multiple MIMO channels occupying the same bandwidth. The primary advantage of these methods is that despite multiplexing they maintain all original radar parameters (resolution and unambiguous range in distance and velocity) for each individual MIMO channel. To obtain favorable interleaving patterns with low sidelobes, we propose an optimization approach based on genetic algorithms. Furthermore, to overcome the drawback of increased sidelobes due to subcarrier interleaving, we study the applicability of sparse processing methods for the distance-velocity estimation from measurements of non-equidistantly interleaved OFDM-MIMO radar. We introduce a novel sparsity based frequency estimation algorithm designed for this purpose. The third topic addressed in this work is the robustness of OFDM radar to interference from other radar sensors. In this part of the work we study the interference robustness of OFDM radar and propose novel interference mitigation techniques. The first interference suppression algorithm we introduce exploits the robustness of OFDM to narrowband interference by dropping subcarriers strongly corrupted by interference from evaluation. To avoid increase of sidelobes due to missing subcarriers, their values are reconstructed from the neighboring ones based on linear prediction methods. As a further measure for increasing the interference robustness in a more universal manner, we propose the extension of OFDM radar with cognitive features. We introduce the general concept of cognitive radar that is capable of adapting to the current spectral situation for avoiding interference. Our work focuses mainly on waveform adaptation techniques; we propose adaptation methods that allow dynamic interference avoidance without affecting adversely the estimation performance. The final part of this work focuses on prototypical implementation of OFDM-MIMO radar. With the constructed prototype, the feasibility of OFDM for high-performance radar applications is demonstrated. Furthermore, based on this radar prototype the algorithms presented in this thesis are validated experimentally. The measurements confirm the applicability of the proposed algorithms and concepts for real world automotive radar implementations

Sidelobe Suppression and Agile Transmission Techniques for Multicarrier-based Cognitive Radio Systems

With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing spectrum allocation policies of the Federal Communications Commission (FCC) prohibits unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interference-prone frequency bands, which causes spectrum scarcity. However, it has been shown by several spectrum measurement campaigns that the current licensed spectrum usage across time and frequency is inefficient. Therefore, a concept of unlicensed users temporarily ``borrowing spectrum from incumbent license holders to improve the spectrum utilization, called ``spectrum pooling , which is based on dynamic spectrum access (DSA), is proposed. Cognitive radio is a communication paradigm that employs software-defined radio technology in order to perform DSA and offers versatile, powerful and portable wireless transceivers. Orthogonal frequency division multiplexing (OFDM) is a promising candidate for cognitive radio transmission. OFDM supports high data rates that are robust to channel impairments. In addition, some subcarriers can be deactivated which constitutes a non-contiguous OFDM (NC-OFDM) transmission. However, one of the biggest problems for OFDM transmission is high out-of-band (OOB) radiation, which is caused by sinc-type function representing the symbols during one time constant. Thus, high sidelobe may occur that will interfere with neighboring transmissions. This thesis presents two novel techniques for NC-OFDM sidelobe suppression. Another concern about cognitive radio systems is that the influence of frequency-selective fading channel. Consequently, this thesis also presents a combined approach employing power loading, bit allocation and sidelobe suppression for OFDM-based cognitive radio systems optimization

PAPR Reduction of OFDM Signals Using Clipping and Coding

The problem of the high peak to average ratio (PAPR) in OFDM signals is investigated with a brief presentation of the various methods used to reduce the PAPR with special attention to the clipping method. An alternative approach of clipping is presented, where the clipping is performed right after the IFFT stage unlike the conventional clipping that is performed in the power amplifier stage, which causes undesirable out of signal band spectral growth. In the proposed method, there is clipping of samples not clipping of wave, therefore, the spectral distortion is avoided. Coding is required to correct the errors introduced by the clipping and the overall system is tested for two types of modulations, the QPSK as a constant amplitude modulation and 16QAM as a varying amplitude modulation

Conformação de pulso de formas de onda OFDM para a interface aérea 5G

Orientador: Luís Geraldo Pedroso MeloniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: As formas de onda com multiplexação ortogonal por divisão de freqüência (OFDM) foram utilizadas com sucesso na interface aérea 3GPP LTE para superar a seletividade do canal e proporcionar uma boa eficiência espectral e altas taxas de transmissão de dados. O próximo sistema de comunicações 5G tem como objetivo oferecer suporte a mais serviços do que o antecessor, como comunicações de banda larga móveis, comunicações de tipo máquina e comunicações de baixa latência, e considera muitos outros cenários de aplicação, como o uso de espectro fragmentado. Esta diversidade de serviços com diferentes requisitos não pode ser suportada pela OFDM convencional, pois OFDM configura toda a largura de banda com parâmetros que atendem a um serviço em particular. Além disso, pode ocorrer interferência interportadora (ICI) quando a OFDM convencional é usada com multiplexação assíncrona de múltiplos usuários e isso é devido às altas emissões fora de banda (OOB) das subportadoras e à violação da condição de ortogonalidade do sinal. Portanto, para atender aos requisitos das futuras aplicações sem fio 5G, o desenvolvimento de uma interface aérea inovadora com novas capacidades torna-se necessário, em particular, uma nova forma de onda mais espectralmente ágil do que OFDM capaz de suportar múltiplas configurações, suprimindo efetivamente a interferência entre usuários, e com integração direta com as camadas superiores. Este trabalho centra-se em duas técnicas de conformação de pulsos para reduzir a emissões fora de banda e melhorar o desempenho de formas de onda baseadas em OFDM. A conformação de pulsos pode permitir o uso de parametrizações múltiplas dentro da forma de onda e abandonar os paradigmas rígidos de ortogonalidade e sincronismo com uma degradação de desempenho causada por interferência intersymbol (ISI) e ICI relativamente baixa. A primeira parte aborda um método de modelagem de pulso baseado na filtragem por subportadora para reduzir a emissão fora de banda no transmissor e interferência de canal adjacente (ACI) no receptor. Ele pode ser implementado usando funções de janela e alguns formatos de janela são apresentados nesta parte. O primeiro usa o prefixo cíclico (CP) existente dos símbolos para suavizar as transições abruptas do sinal, portanto, os grandes lóbulos espectrais sinc causados pelos filtros retangulares. Isso garante a compatibilidade retroativa em sistemas que usam OFDM com prefixo cíclico (CP-OFDM). O formato da segunda janela estende o comprimento do CP para reter a capacidade da forma de onda para combater a propagação do atraso do canal. Os efeitos no desempenho do ISI e ICI são estudados em termos de relação de sinal para interferência (SIR) e taxa de erro de bit (BER) usando formas de onda LTE em um cenário de espectro fragmentado multi-usuário. A segunda parte deste trabalho aborda o desenho e análise de filtros para a contenção espectral flexível em transceptores com filtragem baseada em sub-banda. Este filtro, chamado aqui semi-equiripple, exibe melhor atenuação na banda de rejeição para reduzir as interferências entre subbandas do que os filtros equiripple e filtros sinc baseados em janelamento e também possui boas características de resposta ao impulso para reduzir o ISI. O projeto de filtros baseia-se no algoritmo Parks-McClellan para obter diferentes taxas de decaimento da banda de parada e atende a especificações arbitrárias de máscaras de emissão de espectro (SEM) com baixa distorção dentro da banda. Portanto, pode ser útil para obter baixas emissões fora da banda e configurar sub-bandas com parâmetros independentes, uma vez que a interferência assíncrona é contida pelos filtros. São estudadas três distorções de ISI no filtro: espalhamento de símbolos relacionado à causalidade do filtro, ecos de símbolos devido a ondulações na banda e amplificação de ISI devido a amostras de valores anômalas nas caudas de sua resposta de impulso. O desempenho do filtro é avaliado em termos de densidade de espectro de potência (PSD) e conformidade com SEMs, taxa de erro de modulação (MER) e operação em um esquema assíncrono multi-serviço usando uma única forma de onda. O SIR e o efeito da filtragem na precisão da modulação são avaliados usando formas de onda OFDM ISDB-T e LTE. Estruturas de hardware flexíveis também são propostas para implementações reais. Os resultados mostram que esses métodos de conformação de pulso permitem que a forma de onda explore os fragmentos de espectro disponíveis e ofereça suporte a múltiplos serviços sem uma penalidade de desempenho significativa, o que pode permitir uma interface aérea mais flexívelAbstract: Orthogonal frequency division multiplexing (OFDM) waveforms have been used successfully in the 3GPP Long Term Evolution (LTE) air interface to overcome the channel selectivity and to provide good spectrum efficiency and high transmission data rates. The forthcoming 5G communication system aims to support more services than its predecessor, such as enhanced mobile broadband, machine-type communications and low latency communications, and considers many other application scenarios such as the fragmented spectrum use. This diversity of services with different requirements cannot be supported by conventional OFDM since OFDM configures the entire bandwidth with parameters attending one service in particular. Also, substantial intercarrier interference (ICI) can occur when conventional OFDM is used with asynchronous multiuser multiplexing and this is due to the high out-of-band (OOB) emissions of the subcarriers and the violation of the signal orthogonality constraint. Therefore, to meet the requirements of future 5G wireless applications, the development of an innovative air interface with new capabilities becomes necessary, in particular, a new waveform more spectrally agile than OFDM capable of supporting multiple configurations, suppressing the inter-user interference effectively, and with straightforward integration with the upper layers. This work focuses on two pulse shaping techniques to reduce the OOB emission and improve the in-band and OOB performances of OFDM-based waveforms. Pulse shaping can enable the use of multiple parameterizations within the waveform and abandon the strict paradigms of orthogonality and synchronism with relatively low performance degradation caused by intersymbol interference (ISI) and ICI. The first part addresses a pulse shaping method based on per-subcarrier filtering to reduce both OOB emission in the transmitter and adjacent channel interference (ACI) in the receiver. It can be implemented using window functions and some window formats are presented in this part. The first uses the existing cyclic prefix (CP) of OFDM symbols to smooth abrupt transitions of the signal, thus the large sinc spectral sidelobes caused by the rectangular filters. This guarantees backwards compatibility in systems using conventional cyclic prefixed OFDM (CP-OFDM). The second window format extends the CP length to retain the waveform ability to combat channel delay spread. The effects on performance of ISI and ICI are studied in terms of the signal to interference ratio (SIR) and bit error rate (BER) using LTE waveforms in a multi-user fragmented spectrum scenario. The second part of this work addresses the design and analysis of a filters for flexible spectral containment in subband-based filtering transceivers. This filter, called here semi-equiripple, exhibits better stopband attenuation to reduce the inter-subband interferences than equiripple and windowed truncated sinc filters and also has good impulse response characteristics to reduce ISI. The design is based on the Parks-McClellan algorithm to obtain different stopband decay rates and meet arbitrary spectrum emission masks (SEM) specifications with low in-band distortion. Therefore, it can be useful to achieve low OOB emission and configure subbands with independent parameters since the asynchronous interference is contained by the filters. Three ISI distortions in the filter are studied: symbol spreading related to the filter causality, symbol echoes due to in-band ripples, and ISI amplification due to outlier samples in the tails of its impulse response. The performance of the filter is assessed in terms of the power spectrum density (PSD) and compliance with tight SEMs, modulation error rate (MER) and operation in a multi-service asynchronous scheme using a single waveform. The SIR and the effect of filtering on the modulation accuracy are evaluated using OFDM ISDB-T and LTE waveforms. Flexible hardware structures are also proposed for actual implementations. The results show that these pulse shaping methods enable the waveform to exploit the available spectrum fragments and support multiple services without significant performance penalty, which can allow a more flexible air interfaceMestradoTelecomunicações e TelemáticaMestre em Engenharia ElétricaCAPE

Resource Management in Multicarrier Based Cognitive Radio Systems

The ever-increasing growth of the wireless application and services affirms the importance of the effective usage of the limited radio spectrum. Existing spectrum management policies have led to significant spectrum under-utilization. Recent measurements showed that large range of the spectrum is sparsely used in both temporal and spatial manner. This conflict between the inefficient usage of the spectrum and the continuous evolution in the wireless communication calls upon the development of more flexible management policies. Cognitive radio (CR) with the dynamic spectrum access (DSA) is considered to be a key technology in making the best solution of this conflict by allowing a group of secondary users (SUs) to share the radio spectrum originally allocated to the primary user (PUs). The operation of CR should not negatively alter the performance of the PUs. Therefore, the interference control along with the highly dynamic nature of PUs activities open up new resource allocation problems in CR systems. The resource allocation algorithms should ensure an effective share of the temporarily available frequency bands and deliver the solutions in timely fashion to cope with quick changes in the network. In this dissertation, the resource management problem in multicarrier based CR systems is considered. The dissertation focuses on three main issues: 1) design of efficient resource allocation algorithms to allocate subcarriers and powers between SUs such that no harmful interference is introduced to PUs, 2) compare the spectral efficiency of using different multicarrier schemes in the CR physical layer, specifically, orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC) schemes, 3) investigate the impact of the different constraints values on the overall performance of the CR system. Three different scenarios are considered in this dissertation, namely downlink transmission, uplink transmission, and relayed transmission. For every scenario, the optimal solution is examined and efficient sub-optimal algorithms are proposed to reduce the computational burden of obtaining the optimal solution. The suboptimal algorithms are developed by separate the subcarrier and power allocation into two steps in downlink and uplink scenarios. In the relayed scenario, dual decomposition technique is used to obtain an asymptotically optimal solution, and a joint heuristic algorithm is proposed to find the suboptimal solution. Numerical simulations show that the proposed suboptimal algorithms achieve a near optimal performance and perform better than the existing algorithms designed for cognitive and non-cognitive systems. Eventually, the ability of FBMC to overcome the OFDM drawbacks and achieve more spectral efficiency is verified which recommends the consideration of FBMC in the future CR systems.El crecimiento continuo de las aplicaciones y servicios en sistemas inal´ambricos, indica la importancia y necesidad de una utilizaci´on eficaz del espectro radio. Las pol´ıticas actuales de gesti´on del espectro han conducido a una infrautilizaci´on del propio espectro radioel´ectrico. Recientes mediciones en diferentes entornos han mostrado que gran parte del espectro queda poco utilizado en sus ambas vertientes, la temporal, y la espacial. El permanente conflicto entre el uso ineficiente del espectro y la evoluci´on continua de los sistemas de comunicaci´on inal´ambrica, hace que sea urgente y necesario el desarrollo de esquemas de gesti´on del espectro m´as flexibles. Se considera el acceso din´amico (DSA) al espectro en los sistemas cognitivos como una tecnolog´ıa clave para resolver este conflicto al permitir que un grupo de usuarios secundarios (SUs) puedan compartir y acceder al espectro asignado inicialmente a uno o varios usuarios primarios (PUs). Las operaciones de comunicaci´on llevadas a cabo por los sistemas radio cognitivos no deben en ning´un caso alterar (interferir) los sistemas primarios. Por tanto, el control de la interferencia junto al gran dinamismo de los sistemas primarios implica nuevos retos en el control y asignaci´on de los recursos radio en los sistemas de comunicaci´on CR. Los algoritmos de gesti´on y asignaci´on de recursos (Radio Resource Management-RRM) deben garantizar una participaci´on efectiva de las bandas con frecuencias disponibles temporalmente, y ofrecer en cada momento oportunas soluciones para hacer frente a los distintos cambios r´apidos que influyen en la misma red. En esta tesis doctoral, se analiza el problema de la gesti´on de los recursos radio en sistemas multiportadoras CR, proponiendo varias soluciones para su uso eficaz y coexistencia con los PUs. La tesis en s´ı, se centra en tres l´ıneas principales: 1) el dise˜no de algoritmos eficientes de gesti´on de recursos para la asignaci´on de sub-portadoras y distribuci´on de la potencia en sistemas segundarios, evitando asi cualquier interferencia que pueda ser perjudicial para el funcionamiento normal de los usuarios de la red primaria, 2) analizar y comparar la eficiencia espectral alcanzada a la hora de utilizar diferentes esquema de transmisi´on multiportadora en la capa f´ısica del sistema CR, espec´ıficamente en sistemas basados en OFDM y los basados en banco de filtros multiportadoras (Filter bank Multicarrier-FBMC), 3) investigar el impacto de las diferentes limitaciones en el rendimiento total del sistema de CR. Los escenarios considerados en esta tesis son tres, es decir; modo de transmisi´on descendente (downlink), modo de transmisi´on ascendente (uplink), y el modo de transmisi´on ”Relay”. En cada escenario, la soluci´on ´optima es examinada y comparada con algoritmos sub- ´optimos que tienen como objetivo principal reducir la carga computacional. Los algoritmos sub-´optimos son llevados a cabo en dos fases mediante la separaci´on del propio proceso de distribuci´on de subportadoras y la asignaci´on de la potencia en los modos de comunicaci´on descendente (downlink), y ascendente (uplink). Para los entornos de tipo ”Relay”, se ha utilizado la t´ecnica de doble descomposici´on (dual decomposition) para obtener una soluci´on asint´oticamente ´optima. Adem´as, se ha desarrollado un algoritmo heur´ıstico para poder obtener la soluci´on ´optima con un reducido coste computacional. Los resultados obtenidos mediante simulaciones num´ericas muestran que los algoritmos sub-´optimos desarrollados logran acercarse a la soluci´on ´optima en cada uno de los entornos analizados, logrando as´ı un mayor rendimiento que los ya existentes y utilizados tanto en entornos cognitivos como no-cognitivos. Se puede comprobar en varios resultados obtenidos en la tesis la superioridad del esquema multiportadora FBMC sobre los sistemas basados en OFDM para los entornos cognitivos, causando una menor interferencia que el OFDM en los sistemas primarios, y logrando una mayor eficiencia espectral. Finalmente, en base a lo analizado en esta tesis, podemos recomendar al esquema multiportadora FBMC como una id´onea y potente forma de comunicaci´on para las futuras redes cognitivas

Wavelet-based multi-carrier code division multiple access systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

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