Radio wave propagation measurements provide a way to accurately and reliably characterize environments to assist in the development and optimization of wireless communication systems. As digital radio systems occupy wider bandwidths and use multipath signal combining to enhance quality of service, knowledge of time dispersion and the multipath structure of radio channels become increasingly important. The wideband measurement system presented herein provides a practical means to precisely measure the delays and strengths of individual multipath components which arrive at a radio receiver. Presented in this Thesis are fundamental theory, practical implementation, and simulation models for a sliding correlator measurement system. The sliding correlator technique is explained in detail and large-scale measurement survey is presented. Techniques for statistically quantifying the characteristics of propagation using the sliding correlator measurements are presented and compared. The development of simulations of the sliding correlator system is described, and simulation results are used to test conventional and newly developed post-processing algorithms. This Thesis presents a practical view of the sliding correlator measurement system, but its foundations are rooted in the theoretical results which are explained and derived herein. Propagation researchers and students in the wireless communication field may find this work and the cited references useful for continued study of wideband propagation measurements or for application of the sliding correlator system as a wideband measurement solution. / Master of Science

Current propogation models are no longer sufficient for wireless network planning. They are neither accurate (empirical) nor fast enough (deterministic) to be applicable in the applications of Automated Cell Planning. This thesis focuses on the development of a new method, namely Intelligent Ray Launching Algorithm (IRLA), which is based on a fast, accurate and robust algorithm that is especially suitable for wireless network planning. The infrastructure of IRLA is thoroughly analysed in this thesis and the results are presented. Foster's design methodology has been used to parallelise the new model. Various scenarios for outdoor, indoor, indoor-to-outdoor and outdoor-to-indoor settings have been employed to test the effectiveness and efficiency of IRLA. The field strengths (path loss) and multipath information were calculated, which were used to demonstrate the application of IRLA. The accuracy of IRLA is guaranteed via the use of a meta-based heuristics calibration procedure. In order to achieve a simulation within a realistic time scale, acceleration techniques such as avoid double marking, multi-threading and the use of Parallel Object-Oriented Programming C++ have been employed. Since multipath for a large number of receiver locations can be easily obtained via IRLA, the study of delay spread has been presented. The success of the integration with a wireless network planning platform exemplifies that IRLA is suitable for wireless network planning and optimisation, which is beneficial to relevant academics and industries. Testing demonstrated that depending on various scenarios, IRLA obtains industrially-recognised accuracy ranging from 5 to 8 dB Root-Mean-Square-Error. This model is highly-efficient because its required runtime for most simulations is from a few seconds to a few minutes.

[pt] As variações que ocorrem na estrutura da troposfera ao longo do tempo em relação à sua condição mediana provocam diversos fenômenos que fazem variar aleatoriamente o nível de sinal recebido num enlace rádio. Estas variações aleatórias são denominadas desvanecimentos. Os desvanecimentos são normalmente classificados em rápidos e lentos. Os desvanecimentos rápidos estão geralmente associados ao efeito de multipercurso atmosférico que é fortemente dependente da freqüência, sendo por isto denominados desvanecimentos seletivos, e são a principal causa de degradação do desempenho de enlaces rádio digitais de alta capacidade. Os modelos existentes para a caracterização estatística do desvanecimento por multipercurso são semi-empíricos e baseados em dados experimentais obtidos em regiões de clima temperado, acarretando uma má estimativa quando aplicados a regiões de clima tropical e equatorial. Neste trabalho é apresentada uma avaliação dos métodos existentes para previsão do desempenho de enlaces rádio digitais de alta capacidade, a partir da utilização de dados reais de desempenho extraídos de medidas em um tronco rádio de alta capacidade numa região tropical. / [en] The variations which happen in the troposphere layers throughout the time in relation to the median condition of the signal cause various phenomena that change the received signal level at digital radio relay systems randomly. The random changes are named fading. Fading is normally classified as fast or slow. The former is normally associated with the atmospheric multipath propagation and is strongly dependent on frequency; therefore, this is named selective fading and it is normally the cause of performance degradation in high capacity digital radio relays. The existing models for statistics of multipath fading are semi - empirical and based on experimental data extracts from regions the climate of which is temperate; and this gives a rough estimate with respect to the tropical and equatorial zones. This work presents an evaluation of existing methods of performance prediction for high capacity digital radio relay systems using real performance data obtained from measures of a high capacity digital radio link in operation in the tropical region.

Aujourd'hui, la prolifération de matériel peu coûteux tels que les caméras et les microphones capables de capturer du contenu multimédia de façon ubiquitaire a conduit à l'émergence des réseaux de capteurs sans fil multimédia/vidéo (RCSFM /RCSFV). En conséquence, un grand éventail d'applications peuvent être projetées dans de nombreux domaines de la vie de tous les jours. Par rapport aux réseaux de capteurs traditionnels (RCSF), les RCSFVs présentent des défis uniques principalement en raison de la grande quantité de données à capturer et à transmettre au-dessus d'un réseau contraint en ressources. Dans ce travail, nous avons d'abord proposé un protocole de routage hiérarchique appelé ELPC (Energy Level Passive Clustering) dont l'objectif principal est d'améliorer la durée de vie du réseau en présence de flux vidéo. Ceci est obtenu grâce à l'équilibrage des charges au moment de la construction de la topologie où le rôle de tête de groupe est alterné entre les noeuds candidats en fonction de leur niveau d'énergie. La deuxième contribution consiste en un protocole de routage multichemin qui prend les interférences inter-chemin en considération. Au lieu de supprimer complètement les interférences, notre protocole de routage multichemin tente de les minimiser en se basant sur l'ajout d'informations supplémentaires sur les noeuds voisins dans les messages de construction de la topologie. De plus, nous proposons un schéma de files d'attente à priorités multiples où l'influence des types de données. Les résultats des simulations montrent que l'utilisation de chemins moins interférents combinée à un régime de multipriorité permet une meilleure qualité vidéo / Nowadays, the proliferation of inexpensive hardware such as CMOS cameras and microphones that are able to ubiquitously capture multimedia content has led to the emergence of wireless multimedia/video sensor networks (WMSN/WVSN). As a consequence, a wide spectrum of applications can be projected in many areas and everyday life. Compared to traditional WSNs, WVSNs introduce unique challenges due mainly to the big amount of data to be captured and transmitted over a constrained network. In this work, we first propose a cluster-based (hierarchical) routing protocol called ELPC (Energy Level Passive Clustering) where the main objective is to enhance the network lifetime while handling video applications. This is achieved thanks to a load balancing feature where the role of clusterheads is alternated among candidate nodes depending on their energy level. The second contribution consists in a multipath routing protocol with interference awareness. Instead of completely suppressing interferences, our multipath routing protocol tries to minimize them through a simple algorithm without extra overhead. Multiple paths are built at once while minimizing their inter-path interferences thanks to some additional information on neighboring nodes piggybacked on the route request messages. In addition to interference awareness, we propose a multiqueue multipriority scheme where the influence of data type in a video is considered. Simulation results show that using less interfering paths combined to a multiqueue multipriority scheme allows for better video quality

Este trabalho concentra-se no aumento da robustez à taxa de erros em redes de sensores sem fio industriais (RSSFI). Para alcançar tal objetivo, é preciso, de algum modo, contornar os problemas intrínsecos da comunicação sem fio, que são, o ruído ambiental, interferências e desvanecimento por multipercurso. O multipercurso pode ser considerado um dos principais fatores que tornam as comunicações nas redes de sensores sem fio (RSSF) um verdadeiro desafio quando comparadas com outros meios, como a transmissão em fibra óptica, cabo ou mesmo transmissões de rádio ponto-a-ponto. Nesse sentido, propõe-se a diversidade de antenas como uma solução para minimizar os efeitos do multicaminho, com o objetivo de melhorar a confiabilidade do enlace de rádio para permitir o emprego de RSSF densas. O potencial da diversidade de antenas em RSSF não está totalmente explorado em aplicações industriais. Esta dissertação apresenta ainda, a técnica “Combinação de seleção” para RSSFI através de um algoritmo que seleciona a porta do receptor que apresenta o melhor indicador de qualidade de enlace e realiza a comutação das antenas nos módulos de rádio. Os resultados são analisados para dois tipos de enlaces, isto é, com e sem diversidade de antenas na recepção, e discute-se opções para melhorar o PER (“Packet Error Rate”) com as atuais técnicas de diversidade. / This work concentrates on the increase of reliability and robustness in Industrial Wireless Sensor Networks (IWSNs), decreasing the Packet Error Rate (PER). To achieve this objective, is need to somehow circumvent and reduce the underlying problems of wireless communication, which are: environmental noise, interference, and multipath fading. The multipath can be seen as the main factor which becomes the communications in the Wireless Sensor Networks (WSNs) a real challenge when compared to other types of means such as a transmission in fiber, cable or even point-to-point radio transmissions. In this sense, it is proposed antenna diversity as solution to reduce these effects, with the aim to improve the reliability of the radio link to allow the use of dense WSNs. The potential of antenna diversity in WSN is not fully exploited in industrial applications. In this sense, this dissertation presents the "Combination of selection" technique for IWSNs through an internal algorithm that selects the receiver port that has the highest LQI ("Link Quality Indicator") and performs an antenna switching in the radio modules. Also, options to improve PER using diversity techniques are discussed.

Machine-to-machine (M2M) communication is becoming an important aspect of warehouse management, remote control, robotics, traffic control, supply chain management, fleet management and telemedicine. M2M is expected to become a significant portion of the Industrial Internet and, more broadly, the Internet of Things (IoT). The environments in which M2M systems are expected to operate may be challenging in terms of radio wave propagation due to their cluttered, multipath nature, which can cause deep signal fades and signal depolarization. Polarization diversity in two dimensions is a well-known technique to mitigate such fades. But in the presence of reflectors and retarders where multipath components arrive from any direction, we find the detrimental effects to be three-dimensional and thus consider herein mitigation approaches that are also 3D. The objectives of this dissertation are three. First, to provide a theoretical framework for depolarization in three dimensions. Second, to prepare a tripolar antenna design that meets cost, power consumption, and simplicity requirements of M2M applications and that can mitigate the expected channel effects. Finally, to develop new channel models in three dimensional space for wireless systems. Accordingly, this dissertation presents a complete description of 3D electromagnetic fields, in terms of their polarization characteristics and confirms the advantage of employing tripolar antennas in multipath conditions. Furthermore, the experimental results illustrate that highly variable depolarization occurs across all three spatial dimensions and is dependent on small changes in frequency and space. Motivated by these empirical results, we worked with a collaborating institution to develop a three-dimensional tripolar antenna that can be integrated with a commercially available wireless sensor. This dissertation presents the testing results that show that this design significantly improves channels over traditional 2D approaches. The implications of tripolar antenna integration on M2M systems include reduction in energy use, longer wireless communication link distances, and/or greater link reliability. Similar results are shown for a planar antenna design that enables four different polarization configurations. Finally, the work presents a novel three-dimensional geometry-based stochastic channel model that builds the channel as a sum of shell-like sub-regions, where each sub-region consists of groups of multipath components. The model is validated with empirical data to show the approach may be used for system analyses in indoor environments.

With the proliferation of smart devices that require Internet connectivity anytime, anywhere, and the recent technological advances that make it possible, current networked systems will have to provide a various range of services, such as content distribution, in a wide range of settings, including wireless environments. Wireless links may experience temporary losses, however, TCP, the de facto protocol for robust unicast communications, reacts by reducing the congestion window drastically and injecting less traffic in the network. Consequently the wireless links are underutilized and the overall performance of the TCP protocol in wireless environments is poor. As content delivery (i.e. multicasting) services, such as BBC iPlayer, become popular, the network needs to support the reliable transport of the data at high rates, and with specific delay constraints. A typical approach to deliver content in a scalable way is to rely on peer-to-peer technology (used by BitTorrent, Spotify and PPLive), where users share their resources, including bandwidth, storage space, and processing power. Still, these systems suffer from the lack of incentives for resource sharing and cooperation, and this problem is exacerbated in the presence of heterogenous users, where a tit-for-tat scheme is difficult to implement. Due to the issues highlighted above, current network architectures need to be changed in order to accommodate the users¿ demands for reliable and quality communications. In other words, the emergent need for advanced modes of information transport requires revisiting and improving network components at various levels of the network stack. The innovative paradigm of network coding has been shown as a promising technique to change the design of networked systems, by providing a shift from how data flows traditionally move through the network. This shift implies that data flows are no longer kept separate, according to the ¿store-and-forward¿ model, but they are also processed and mixed in the network. By appropriately combining data by means of network coding, it is expected to obtain significant benefits in several areas of network design and architecture. In this thesis, we set out to show the benefits of including network coding into three communication paradigms, namely point-topoint communications (e.g. unicast), point-to-multipoint communications (e.g. multicast), and multipoint-to-multipoint communications (e.g. peer-to-peer networks). For the first direction, we propose a network coding-based multipath scheme and show that TCP unicast sessions are feasible in highly volatile wireless environments. For point-to-multipoint communications, we give an algorithm to optimally achieve all the rate pairs from the rate region in the case of degraded multicast over the combination network. We also propose a system for live streaming that ensures reliability and quality of service to heterogenous users, even if data transmissions occur over lossy wireless links. Finally, for multipoint-to-multipoint communications, we design a system to provide incentives for live streaming in a peer-to-peer setting, where users have subscribed to different levels of quality. Our work shows that network coding enables a reliable transport of data, even in highly volatile environments, or in delay sensitive scenarios such as live streaming, and facilitates the implementation of an efficient incentive system, even in the presence of heterogenous users. Thus, network coding can solve the challenges faced by next generation networks in order to support advanced information transport.

Orthogonal frequency division multiplexing (OFDM) systems with cyclic prefix (CP) can be used to protect signal from the time-variant multipath channel induced distortions. However, the presence of CP could greatly decrease the effective data rate, thus many recent research works have been focused on the multiple-input multiple-output (MIMO) OFDM systems without CP (CP-free), equipped with the space-time block codes (ST-BC). The constraint of the conventional MIMO-OFDM (without using the ST-BC) system is that the number of receive-antenna has to be greater than the transmit-antenna. In this thesis, we first consider the ST-BC MIMO-OFDM system and show that the above-mentioned constraint can be removed, such that the condition become that the receive antenna should be greater than one, that is the basic requirement for MIMO system. It is particular useful and confirm to the recently specification, e.g., 3GPP LTE (Long Term Evolution) where the system deploy the 2¡Ñ2 or 4¡Ñ4 antennas systems. This thesis also considers the effects of peak-to-average power ratio (PAPR) in the transmitter and In-phase/ Quadrature-phase (IQ) imbalance in the receiver, and solves them by using the adaptive Volterra predistorter and blind adaptive filtering approach of the nonlinear parameters estimation and compensation, along with the power measurement, respectively. After the compensator of IQ imbalance in the receiver, an equalizer under the framework of generalized sidelobe canceller (GSC) is derived for interference suppression. To further reduce the complexity of receiver implementation, the partially adaptive (PA) scheme is applied by exploiting the structural information of the signal and interference signature matrices. As demonstrated from computer simulation results, the performance of the proposed CP-free ST-BC MIMO-OFDM receiver is very similar to that obtained by the conventional CP-based ST-BC MIMO-OFDM system under either the predistortion or compensation scenario.

In this thesis, symbol timing recovery based on matched filtering in Gaussian Minimum Shift Keying (GMSK) with bandwidth-bit period product (BT) of 0.3 is investigated. GMSK is the standard modulation type for GSM. Although GMSK modulation is non-linear, it is approximated to Offset Quadrature Amplitude Modulation (OQAM), which is a linear modulation, so that Maximum Likelihood Sequence Estimation (MLSE) method is possible in the receiver part. In this study Typical Urban (TU) channel model developed in COST 207 is used. Two methods are developed on the construction of the matched filter. In order to obtain timing recovery for GMSK signals, these methods are investigated. The fractional time delays are acquired by using interpolation and an iterative maximum search process. The performance of the proposed symbol timing recovery (STR) scheme is assessed by using computer simulations. It is observed that the STR tracks the variations of the frequency selective multipath fading channels almost the same as the Mazo criterion.

In this thesis, two-dimensional (2-D) direction-of-arrival (DOA) estimation problem is considered. Usually, DOA estimation is considered in one dimension assuming a fixed elevation angle. While this assumption simplifies the problem, both the azimuth and elevation angles, namely, the 2-D DOA estimates are required in practical scenarios. In this thesis, planar array structures are considered for 2-D DOA estimation. In this context, V-shaped arrays are discussed and some of the important features of these arrays are outlined. A new method for the design of V-shaped arrays is presented for both isotropic and directional beam patterns. The design procedure is simple and can be applied for both uniform and nonuniform V-shaped sensor arrays. Closed form expressions are presented for the V-angle in order to obtain isotropic angle performance. While circular arrays have the isotropic characteristics, V-shaped arrays present certain advantages due to their large aperture for the same number of sensors and inter-sensor distance. The comparison of circular and V-shaped arrays is done by considering the azimuth and elevation Cramer-Rao Bounds (CRB). It is shown that V-shaped and circular arrays have similar characteristics for the sensor position errors while the uniform isotropic (UI) V-array performs better when there is mutual coupling and the sources are correlated. In the literature, there are several techniques for 2-D DOA estimation. Usually, fast algorithms are desired for this purpose since a search in two dimensions is a costly process. These algorithms have a major problem, namely, the pairing of the azimuth-elevation couples for multiple sources. In this thesis, a new fast and effective technique for this purpose is proposed. In this technique, a virtual array output is generated such that when the ESPRIT algorithm is used, the eigenvalues of the rotational transformation matrix have the 2-D angle information in both magnitude and phase. This idea is applied in different scenarios and three methods are presented for these cases. In one case, given an arbitrary array structure, array interpolation is used to generate the appropriate virtual arrays. When the antenna mutual coupling is taken into account, a special type of array structure, such as circular, should be used in order to apply the array interpolation. In general, the array mutual coupling matrix (MCM) should have a symmetric Toeplitz form. It is shown that the 2-D DOA performance of the proposed method approaches to the CRB by using minimum number of antennas in case of mutual coupling. This method does not require the estimation of the mutual coupling coefficients. While this technique is effective, it has problems especially when the number of sources increases. In order to improve the performance, MCM is estimated in the third approach. This new approach performs better, but it cannot be used satisfactorily in case of multipath signals. In this thesis, the proposed idea for fast 2-D DOA estimation is further developed in order to solve the problem when mutual coupling and multipath signals jointly exist. In this case, real arrays with some auxiliary sensors are used to generate a structured mutual coupling matrix. It is shown that the problem can be effectively solved when the array structure has a special form. Specifically, parallel uniform linear arrays (PULA) are employed for this purpose. When auxiliary sensors are used, a symmetric banded Toeplitz MCM is obtained for the PULA. This allows the application of spatial smoothing and ESPRIT algorithm for 2-D DOA estimation. The proposed algorithm uses triplets and presents closed form paired 2-D DOA estimates in case of unknown mutual coupling and multipath signals. Several simulations are done and it is shown that the proposed array structure and the method effectively solve the problem.