137 research outputs found

    Performance improvement of ad hoc networks using directional antennas and power control

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    Au cours de la derniĂšre dĂ©cennie, un intĂ©rĂȘt remarquable a Ă©tĂ© Ă©prouvĂ© en matiĂšre des rĂ©seaux ad hoc sans fil capables de s'organiser sans soutien des infrastructures. L'utilisation potentielle d'un tel rĂ©seau existe dans de nombreux scĂ©narios, qui vont du gĂ©nie civil et secours en cas de catastrophes aux rĂ©seaux de capteurs et applications militaires. La Fonction de coordination distribuĂ©e (DCF) du standard IEEE 802.11 est le protocole dominant des rĂ©seaux ad hoc sans fil. Cependant, la mĂ©thode DCF n'aide pas Ă  profiter efficacement du canal partagĂ© et Ă©prouve de divers problĂšmes tels que le problĂšme de terminal exposĂ© et de terminal cachĂ©. Par consĂ©quent, au cours des derniĂšres annĂ©es, de diffĂ©rentes mĂ©thodes ont Ă©tĂ© dĂ©veloppĂ©es en vue de rĂ©gler ces problĂšmes, ce qui a entraĂźnĂ© la croissance de dĂ©bits d'ensemble des rĂ©seaux. Ces mĂ©thodes englobent essentiellement la mise au point de seuil de dĂ©tecteur de porteuse, le remplacement des antennes omnidirectionnelles par des antennes directionnelles et le contrĂŽle de puissance pour Ă©mettre des paquets adĂ©quatement. ComparĂ©es avec les antennes omnidirectionnelles, les antennes directionnelles ont de nombreux avantages et peuvent amĂ©liorer la performance des rĂ©seaux ad hoc. Ces antennes ne fixent leurs Ă©nergies qu'envers la direction cible et ont une portĂ©e d'Ă©mission et de rĂ©ception plus large avec la mĂȘme somme de puissance. Cette particularitĂ© peut ĂȘtre exploitĂ©e pour ajuster la puissance d'un transmetteur en cas d'utilisation d'une antenne directionnelle. Certains protocoles de contrĂŽle de puissance directionnel MAC ont Ă©tĂ© proposĂ©s dans les documentations. La majoritĂ© de ces suggestions prennent seulement la transmission directionnelle en considĂ©ration et, dans leurs rĂ©sultats de simulation, ces Ă©tudes ont l'habitude de supposer que la portĂ©e de transmission des antennes omnidirectionnelles et directionnelles est la mĂȘme. Apparemment, cette supposition n'est pas toujours vraie dans les situations rĂ©elles. De surcroĂźt, les recherches prenant l'hĂ©tĂ©rogĂ©nĂ©itĂ© en compte dans les rĂ©seaux ad hoc ne sont pas suffisantes. Le prĂ©sent mĂ©moire est dĂ©diĂ© Ă  proposer un protocole de contrĂŽle de puissance MAC pour les rĂ©seaux ad hoc avec des antennes directionnelles en prenant tous ces problĂšmes en considĂ©ration. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : RĂ©seaux ad hoc, Antennes directives, ContrĂŽle de puissance

    A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

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    In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

    A Millimeter Wave based Sensor Data Broadcasting Scheme for Vehicular Communications

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    In recent years, vehicles are becoming smart with the aid of various onboard sensing, communication and computing capability, which is helpful to improve road safety and driving experiments. With data fusion technique, a vehicle can even increase the driving safety by obtaining sensor data from other vehicles. The millimeter Wave (mmWave) based Vehicle-to-Vehicle (V2V) communication technology has become a promising technology to transmit sensor data in huge size such as video streams. However, the high radio frequency of mmWave makes it vulnerable to obstacles. Furthermore, the directional propagation property is not efficient to broadcast information among vehicles. In this paper, we propose a broadcasting scheme to guarantee each vehicle to get the sensor data of all other vehicles. Head vehicles are selected to gather the information on the environment and decide those transmission vehicles and receiving vehicles in each time slot. A graph-based routing selection algorithm is proposed with relatively low complexity. Moreover, the upper bound of broadcasting delay for one dimensional platoon is analyzed based on the network calculus theory. Simulation results indicate that the proposed scheme has faster delivery rate compared to the traditional First-In-First-Out (FIFO) scheme. The maximum broadcasting delay of the proposed scheme is less than the traditional schemes about 30% in different scenarios

    Edge Artificial Intelligence for Real-Time Target Monitoring

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    The key enabling technology for the exponentially growing cellular communications sector is location-based services. The need for location-aware services has increased along with the number of wireless and mobile devices. Estimation problems, and particularly parameter estimation, have drawn a lot of interest because of its relevance and engineers' ongoing need for higher performance. As applications expanded, a lot of interest was generated in the accurate assessment of temporal and spatial properties. In the thesis, two different approaches to subject monitoring are thoroughly addressed. For military applications, medical tracking, industrial workers, and providing location-based services to the mobile user community, which is always growing, this kind of activity is crucial. In-depth consideration is given to the viability of applying the Angle of Arrival (AoA) and Receiver Signal Strength Indication (RSSI) localization algorithms in real-world situations. We presented two prospective systems, discussed them, and presented specific assessments and tests. These systems were put to the test in diverse contexts (e.g., indoor, outdoor, in water...). The findings showed the localization capability, but because of the low-cost antenna we employed, this method is only practical up to a distance of roughly 150 meters. Consequently, depending on the use-case, this method may or may not be advantageous. An estimation algorithm that enhances the performance of the AoA technique was implemented on an edge device. Another approach was also considered. Radar sensors have shown to be durable in inclement weather and bad lighting conditions. Frequency Modulated Continuous Wave (FMCW) radars are the most frequently employed among the several sorts of radar technologies for these kinds of applications. Actually, this is because they are low-cost and can simultaneously provide range and Doppler data. In comparison to pulse and Ultra Wide Band (UWB) radar sensors, they also need a lower sample rate and a lower peak to average ratio. The system employs a cutting-edge surveillance method based on widely available FMCW radar technology. The data processing approach is built on an ad hoc-chain of different blocks that transforms data, extract features, and make a classification decision before cancelling clutters and leakage using a frame subtraction technique, applying DL algorithms to Range-Doppler (RD) maps, and adding a peak to cluster assignment step before tracking targets. In conclusion, the FMCW radar and DL technique for the RD maps performed well together for indoor use-cases. The aforementioned tests used an edge device and Infineon Technologies' Position2Go FMCW radar tool-set

    Efficient resource allocation for 5G hybrid wireless networks

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    This thesis explores three directions of energy-efficiency(EE) and spectral efficiency(SE) under 5G wireless networks. Firstly, we study the optimization of power control for the small (two-user) interference channel in which the terminals are time-switched between the signal-processing and energy-harvesting phases. Both energy harvesting and signal-processing processes are during the downlink. The objective is to maximize the sum-rate, subject to the minimum data and harvested energy constraints at the receivers, assuming a fixed time-switching coefficient. The key contribution is using a geometric approach that analyzes the feasible region governed by the constraints, which gives rise to the optimal power control solution. Another topic focuses on the performance analysis of two user association schemes for wireless power transfer (WPT) in heterogeneous networks (HetNets) massive multiple-input multiple-output (MIMO) antennas, downlink for the WPT in the first phase and uplink for wireless information transfer (WIT) in the second phase. The two user association schemes considered in the analysis are the Downlink received signal power (DRSP) based approach for maximizing the harvested energy; and the uplink received signal power (URSP) based approach for minimizing the uplink path loss. In the downlink, we adopt a low-complexity approach for massive MIMO power transfer to recharge users. Then we derive the average uplink achievable rate with the harvested energy. The last topic analyses a large-scale mmWave ad hoc network in the randomly located eavesdroppers area, where eavesdroppers can still intercept the confidential messages, since they may reside in the signal beam. This chapter explores the potential of physical layer security in mmWave ad hoc networks. Specifically, we characterize the impact of mmWave channel characteristics, random blockages, and antenna gains on the secrecy performance. For the special case of the uniform linear array (ULA), a tractable approach is proposed to evaluate the average achievable secrecy rate

    Mobile Ad-Hoc Networks

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    Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

    Advanced Trends in Wireless Communications

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    Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics
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