The transmitting of video content over Vehicular Ad Hoc Networks (VANETs) faces a great number of challenges caused by strict QoS (Quality of Service) requirements and highly dynamic network topology. In order to tackle these challenges, multipath forwarding schemes can be regarded as potential solutions. However, route coupling effect and the path length growth severely impair the performance of multipath schemes. In this thesis, the current research status about video streaming over VANETs as well as multipath transmissions are reviewed. With the demand to discover a more suitable solution, we propose the Location-Aware Multipath Video Streaming (LIAITHON+) protocol to address video streaming over urban VANETs. LIAITHON+ uses location information to discover relatively short paths with minimal route coupling effect. The performance results have shown it outperforms the underlying single path solution as well as the node-disjoint multipath solution. In addition, the impact of added redundancy on the multipath solution is investigated through LIAITHON+. According to the results, added redundancy has a different impact depending on the data rate.

Till recently, no significant attempts have been made of developing Aircraft Based Augmentation System (ABAS) architectures capable of generating integrity signals suitable for safety-critical GNSS applications and no commercial ABAS products are available at present. The aim of this research is to support the design a system that generates integrity signals suitable for GNSS application. The conceptual design and key mathematical models were recently developed by the Italian Air Force Experimental Flight Test Centre (CSV-RSV) [1, 2]. Such a system, would be able to provide steering information to the pilot, allowing for real-time and continuous integrity monitoring, avoidance of safety/mission-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. The key elements addressed in this thesis are the development of a CATIA model for military and civil aircraft, supporting antenna obscuration and multipath analysis. This is to allow the ABAS system to generate suitable integrity flags when satellites signals are lost. In order to analyse the GNSS signal loss causes, the GNSS constellation models, the flight dynamics models, fading models, multipath models, Doppler shift models, and GNSS receiver tracking technology previously developed by CSV-RSV, are considered in this research.

In this thesis, a blind symbol timing synchronization algorithm based on cyclic prefix for OFDM systems in multipath fading channels is proposed. It finds the starting point of symbol timing for using appropriate weights which are designed from channel delay spread characteristics. In multipath fading channels, the conventional ML (maximum likelihood) algorithm estimate is biased and has a large variance due to the effect of channel delay spread. The proposed exponential weighting methods not only solve the above problems but also improve the accuracy of symbol timing. Particularly, the proposed method does not require the information of SNR and channel length. From computer simulation results, the proposed method outperforms the other conventional algorithms and is also robust against the effect of multipath fading channels.

Ultra-wideband systems can be used in indoor wireless personal area network (WPAN) or short-range wireless local area network (WLAN) transmission. Yet owing to the effects of indoor dense multipath, it will cause more power consumption. We usually use Rake receiver to improve system performance. However, we should do some compromise between system performance and the design complexity. Thus, the concept of Selective Rake can be used to substitute for the conventional Rake receiver. Selective Rake receiver uses fewer but more powerful paths instead of using all the paths to raise system performance. Hence, we have to precisely detect the multipath components for best performance. Earlier we use CLEAN algorithm to estimate the multipath components. The CLEAN algorithm can be used in selecting the paths with relatively high energy. But as the impact of frequency selective fading makes the transmitted signal distorted, the CLEAN algorithm no longer applies to this situation. Thus, we use Multiscale CLEAN algorithm instead. Multiscale CLEAN algorithm calculate the value of cross-correlation between the received signal and a set of waveforms, and then choose the higher one as the waveform transmitted. Besides, we use Maximal Ratio Combining to weigh the different paths to get the signal with more power. We represent the signal affected by frequency selective fading by using the second derivatives of Gaussian waveform function with different effective widths of pulse. The waveforms corresponding different effective widths have different spectra which represent the different effects of fading. It is seen that that the multiscale CLEAN has better performance than the CLEAN algorithm with more precise estimation of multipath components. In simulation result, we can figure out path searching using Multiscale CLEAN algorithm is more accurate than using CLEAN algorithm. Even the path with smaller energy gain, using multiscale CLEAN algorithm can search successfully, while CLEAN algorithm cannot do.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 94-101).

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / The goal of this paper is to implement a model of multipath fading in a radio channel simulator for aeronautical applications. When developing a wireless communications system, it is useful to perform simulations of the radio context in which the system has to operate. A radio link is substantially composed by three parts: transmitting segment, transmission channel and receiving segment. We focus our attention on the radio channel propagation. We proposed two geometrical models of a territory corresponding to a determined flight area and, after importing the data needed to estimate our parameters, we compared our results with the channel soundings in literature, obtaining comparable values.

Many computers and devices such as smart phones, laptops and tablet devices are now equipped with multiple network interfaces, enabling them to use multiple paths to access content over the network. If the resources could be used concurrently, end user experience can be greatly improved. The recent studies in MPTCP suggest that improved reliability, load balancing and mobility are feasible. The thesis presents a new multipath delay based algorithm, MPPERT (Multipath Probabilistic Early response TCP), which provides high throughput and efficient load balancing. In all-PERT environment, MPPERT suffers no packet loss and maintains much smaller queue sizes compared to existing MPTCP, making it suitable for real time data transfer. MP-PERT is suitable for incremental deployment in a heterogeneous environment. It also presents a parametrized approach to tune the amount of traffic shift off the congested path. Multipath approach is benefited from having multiple connections between end hosts. However, it is desired to keep the connection set minimal as increasing number of paths may not always provide significant increase in the performance. Moreover, higher number of paths unnecessarily increase computational requirement. Ideally, we should suppress paths with low throughputs and avoid paths with shared bottlenecks. In case of MPTCP, there is no efficient way to detect a common bottleneck between subflows. MPTCP applies a constraint of best single-path TCP throughput, to ensure fair share at a common bottleneck link. The best path throughput constraint along with traffic shift, from more congested to less congested paths, provide better opportunity for the competing flows to achieve higher throughput. However, the disadvantage is that even if there are no shared links, the same constraint would decrease the overall achievable throughput of a multipath flow. PERT, being a delay based TCP protocol, has continuous information about the state of the queue. This information is valuable in enabling MPPERT to detect subflows sharing a common bottleneck and obtain a smaller set of disjoint subflows. This information can even be used to switch from coupled (a set of subflows having interdependent increase/decrease of congestion windows) to uncoupled (independent increase/decrease of congestion windows) subflows, yielding higher throughput when best single-path TCP constraint is relaxed. The ns-2 simulations support MPPERT as a highly competitive multipath approach, suitable for real time data transfer, which is capable of offering higher throughput and improved reliability.

[pt] Uma solução simples, de baixo custo e robusta, para o problema de multipercursos na comunicação acústica submarina em águas profundas, é apresentada. Inicialmente, uma caracterização do perfil de atrasos e do nível de ruído, em ambientes de exploração de petróleo Offshore é feita, com o objetivo de definir as características do canal de comunicação em questão. A técnica de modulação, considerada mais adequada pela sua simplicidade e robustez, é a FSK. A inadequação de um sistema FSK-2 não coerente, sem nenhuma medida contra o multipercurso é comprovada em resultados experimentais. Duas possíveis soluções para o problema de demodulação de sinais FSK-2 com multipercurso são apresentadas. Uma muito simples, baseada na inserção de tempos de guarda entre dois bits, suficientes para o desaparecimento dos multipercursos, que foi implementada e testada. A outra, mais elaborada, baseada na estimação dos parâmetros do canal, através do algoritmo EM, e da análise de particularidades do problema para o caso de três raios. Essa segunda solução é analisada e simulada em computador. Os resultados para as duas soluções são analisados. / [en] A simple, low-cost and robust for the problem of multipath in underwater acoustic communication in deep water, is presented. Initially, a delay profile and noise level characterization, in offshore oil exploitation environments is done, with the objective of defining the communication channel of interest. The modulation techique, considered adequate by means of its simplicity and robustness is FSK. The non adequacy of an non-coherent FSK-2 system, without any contermeasure againt multipath is showed in experimental results. Two possible solutions to the problem of the demodulation of FSK-2 signals with multipath are presented. One very simple, based on the insertion of guard times between the bits, sufficient to the vanishing of the multipaths, that have been implemented and tested. The other, more elaborated, based in the estimation of the channel parameters, with the EM algorithm, and the analysis of some particularities of the problem, for the case of three rays. The second solution is analyzed and simulated in a computer. The results for both solutions are analyzed.

Submitted by Diogo Barreiros (diogo.barreiros@ufba.br) on 2017-06-02T16:07:58Z No. of bitstreams: 1 Dissertação_Cleber_Final.pdf: 7551475 bytes, checksum: 81ec53d1cfbee023ecc28745db6472a1 (MD5) / Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2017-06-06T14:17:04Z (GMT) No. of bitstreams: 1 Dissertação_Cleber_Final.pdf: 7551475 bytes, checksum: 81ec53d1cfbee023ecc28745db6472a1 (MD5) / Made available in DSpace on 2017-06-06T14:17:04Z (GMT). No. of bitstreams: 1 Dissertação_Cleber_Final.pdf: 7551475 bytes, checksum: 81ec53d1cfbee023ecc28745db6472a1 (MD5) / Os grandes centros de dados atuais tipicamente adotam redund^ancia de servidores e equipamentos de comunica c~ao para aumento de sua con abilidade e disponibilidade. Infraestrutura altamente redundante, contudo, consiste num dos desa os da area devido ao alto consumo de energia. Esta disserta c~ao apresenta a BEEP, uma estrat egia energeticamente e ciente para redes de centro de dados de nidas por software, baseadas na topologia Fat-Tree. Nossa estrat egia, implementada atrav es de uma rede OpenFlow faz uso de m ultiplos caminhos, atrav es do MultiPath TCP { MPTCP e da vis~ao global oferecida por controladores de uma rede de nida por software, para equilibrar e ci^encia energ etica, n vel de redund^ancia dos equipamentos e ganho de desempenho no atendimento as demandas de tr afego. Para alcan car este equil brio, a BEEP procura fazer com que o tr afego de comunica c~ao seja enviado o mais r apido poss vel, utilizando-se da maior quantidade poss vel de caminhos distintos existentes entre a origem o destino de uma comunica c~ao. Desta forma, as interfaces dos comutadores permanecem em estado ocioso na maior parte do tempo e, assim, o consumo energ etico e reduzido. Resultados experimentais em variantes da topologia Fat-Tree demonstraram ganhos de e ci^encia energ etica com a estrat egia na ordem de 21% a 47%, em compara c~ao a outras estrat egias (ECO-RP e GreenCloud), al em de melhoria na utiliza c~ao da largura de banda dispon vel, conforme haja mais caminhos alternativos dispon veis em todos os cen arios avaliados. Al em de construir a BEEP, as demais contribui c~oes trazidas por esta disserta c~ao s~ao: i) o desenvolvimento de um ambiente de prototipa c~ao de aplica c~oes de TCP de m ultiplos caminhos em redes de nidas por software, capaz de mensurar e validar novas propostas para economia de energia baseada em elementos de uma rede de centro de dados; e ii) uma avalia c~ao experimental do TCP de m ultiplos caminhos implementado atrav es de redes de nidas por software para redes de centro de dados.

Multipath TCP (MPTCP) is a new modification of TCP protocol which enables a client to transfer data over multiple paths simultaneously under a single TCP connection, for improved throughput and fault resilience. However, MPTCP is susceptible to some major drawbacks when applied in a wireless network. We found several cases where, despite improving individual MPTCP clients throughput, MPTCP reduces the capacity of the overall wireless network due to the mac level fairness and contention-based access schemes. Additionally, even if the bandwidth improves, employing Multipath TCP (MPTCP) in wireless networks can be energy inecient due to additional energy consumption by multiple interfaces. This creates a dilemma between bandwidth improvement and energy efficiency. This thesis research aims to solve these important issues for MPTCP in the wireless environment. We analyzed the root cause of these drawbacks and identified instances where they can arise. Two novel schemes denoted MPWiFi and kMPTCP, are developed to solve the bandwidth degradation and energy efficiency issues respectively, while maintaining the promised benefitts of MPTCP. The MPWiFi assigns dierent priorities to the subflows and aggressively suppresses some of them based on some design logic. Similarly, kMPTCP adds an additional multipath subflow only if the bandwidth requirement can't be fulllled by single path and the new subflow meets the data rate and signal strength condition. Moreover, kMPTCP keeps additional subflows as long as the signal strength remains in good range and this subflow remain mandatory to provide the necessary bandwidth to the application. These two schemes have been implemented along with Linux Kernel MPTCP implementation. Extensive real-world deployment and NS3 simulation show that the proposed schemes can eectively alleviate the adverse impacts of the MPTCP based multipath access in Wireless networks.