18,197 research outputs found

    Performance enhancement solutions in wireless communication networks

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    In this dissertation thesis, we study the new relaying protocols for different wireless network systems. We analyze and evaluate an efficiency of the transmission in terms of the outage probability over Rayleigh fading channels by mathematical analyses. The theoretical analyses are verified by performing Monte Carlo simulations. First, we study the cooperative relaying in the Two-Way Decode-and-Forward (DF) and multi-relay DF scheme for a secondary system to obtain spectrum access along with a primary system. In particular, we proposed the Two-Way DF scheme with Energy Harvesting, and the Two-Way DF Non-orthogonal Multiple Access (NOMA) scheme with digital network coding. Besides, we also investigate the wireless systems with multi-relay; the best relay selection is presented to optimize the effect of the proposed scheme. The transmission protocols of the proposed schemes EHAF (Energy Harvesting Amplify and Forward) and EHDF (Energy Harvesting Decode and Forward) are compared together in the same environment and in term of outage probability. Hence, with the obtained results, we conclude that the proposed schemes improve the performance of the wireless cooperative relaying systems, particularly their throughput. Second, we focus on investigating the NOMA technology and proposing the optimal solutions (protocols) to advance the data rate and to ensure the Quality of Service (QoS) for the users in the next generation of wireless communications. In this thesis, we propose a Two-Way DF NOMA scheme (called a TWNOMA protocol) in which an intermediate relay helps two source nodes to communicate with each other. Simulation and analysis results show that the proposed protocol TWNOMA is improving the data rate when comparing with a conventional Two-Way scheme using digital network coding (DNC) (called a TWDNC protocol), Two-Way scheme without using DNC (called a TWNDNC protocol) and Two-Way scheme in amplify-and-forward(AF) relay systems (called a TWANC protocol). Finally, we considered the combination of the NOMA and physical layer security (PLS) in the Underlay Cooperative Cognitive Network (UCCN). The best relay selection strategy is investigated, which uses the NOMA and considers the PLS to enhance the transmission efficiency and secrecy of the new generation wireless networks.V tĂ©to dizertačnĂ­ prĂĄci je provedena studie novĂœch pƙenosovĂœch protokolĆŻ pro rĆŻznĂ© bezdrĂĄtovĂ© sĂ­Ć„ovĂ© systĂ©my. S vyuĆŸitĂ­m matematickĂ© analĂœzy jsme analyzovali a vyhodnotili efektivitu pƙenosu z hlediska pravděpodobnosti vĂœpadku pƙes RayleighĆŻv kanĂĄl. TeoretickĂ© analĂœzy jsou ověƙeny provedenĂœmi simulacemi metodou Monte Carlo. Nejprve doĆĄlo ke studii kooperativnĂ­ho pƙenosu ve dvoucestnĂ©m dekĂłduj-a-pƙedej (Two-Way Decode-and-Forward–TWDF) a vĂ­cecestnĂ©m DF schĂ©matu s větĆĄĂ­m počtem pƙenosovĂœch uzlĆŻ pro sekundĂĄrnĂ­ systĂ©m, kdy takto byl zĂ­skĂĄn pƙístup ke spektru spolu s primĂĄrnĂ­m systĂ©mem. KonkrĂ©tně jsme navrhli dvoucestnĂ© DF schĂ©ma se zĂ­skĂĄvĂĄnĂ­m energie a dvoucestnĂ© DF neortogonĂĄlnĂ­ schĂ©ma s mnohonĂĄsobnĂœm pƙístupem (Non-orthogonal Multiple Access–NOMA) s digitĂĄlnĂ­m sĂ­Ć„ovĂœm kĂłdovĂĄnĂ­m. Kromě toho rovnÄ›ĆŸ zkoumĂĄme bezdrĂĄtovĂ© systĂ©my s větĆĄĂ­m počtem pƙenosovĂœch uzlĆŻ, kde je pƙítomen vĂœběr nejlepĆĄĂ­ho pƙenosovĂ©ho uzlu pro optimalizaci efektivnosti navrĆŸenĂ©ho schĂ©matu. PƙenosovĂ© protokoly navrĆŸenĂœch schĂ©mat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou společně porovnĂĄny v identickĂ©m prostƙedĂ­ z pohledu pravděpodobnosti vĂœpadku. NĂĄsledně, na zĂĄkladě zĂ­skanĂœch vĂœsledkĆŻ, jsme dospěli k zĂĄvěru, ĆŸe navrĆŸenĂĄ schĂ©mata vylepĆĄujĂ­ vĂœkonnost bezdrĂĄtovĂœch kooperativnĂ­ch systĂ©mĆŻ, konkrĂ©tně jejich propustnost. DĂĄle jsme se zaměƙili na zkoumĂĄnĂ­ NOMA technologie a navrhli optimĂĄlnĂ­ ƙeĆĄenĂ­ (protokoly) pro urychlenĂ­ datovĂ©ho pƙenosu a zajiĆĄtěnĂ­ QoS v dalĆĄĂ­ generaci bezdrĂĄtovĂœch komunikacĂ­. V tĂ©to prĂĄci jsme navrhli dvoucestnĂ© DF NOMA schĂ©ma (nazĂœvĂĄno jako TWNOMA protokol), ve kterĂ©m mezilehlĂœ pƙenosovĂœ uzel napomĂĄhĂĄ dvěma zdrojovĂœm uzlĆŻm komunikovat mezi sebou. VĂœsledky simulace a analĂœzy ukazujĂ­, ĆŸe navrĆŸenĂœ protokol TWNOMA vylepĆĄuje dosaĆŸenou pƙenosovou rychlost v porovnĂĄnĂ­ s konvenčnĂ­m dvoucestnĂœm schĂ©matem pouĆŸĂ­vajĂ­cĂ­m DNC (TWDNC protokol), dvoucestnĂœm schĂ©matem bez pouĆŸitĂ­ DNC (TWNDNC protokol) a dvoucestnĂœm schĂ©matem v zesil-a-pƙedej (amplify-and-forward) pƙenosovĂœch systĂ©mech (TWANC protokol). Nakonec jsme zvĂĄĆŸili vyuĆŸitĂ­ kombinace NOMA a zabezpečenĂ­ fyzickĂ© vrstvy (Physical Layer Security–PLS) v podpĆŻrnĂ© kooperativnĂ­ kognitivnĂ­ sĂ­ti (Underlay Cooperative Cognitive Network–UCCN). Zde je zde zkoumĂĄn vĂœběr nejlepĆĄĂ­ho pƙenosovĂ©ho uzlu, kterĂœ uĆŸĂ­vĂĄ NOMA a bere v Ășvahu PLS pro efektivnějĆĄĂ­ pƙenos a zabezpečenĂ­ novĂ© generace bezdrĂĄtovĂœch sĂ­tĂ­.440 - Katedra telekomunikačnĂ­ technikyvyhově

    A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends

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    This paper examines the security vulnerabilities and threats imposed by the inherent open nature of wireless communications and to devise efficient defense mechanisms for improving the wireless network security. We first summarize the security requirements of wireless networks, including their authenticity, confidentiality, integrity and availability issues. Next, a comprehensive overview of security attacks encountered in wireless networks is presented in view of the network protocol architecture, where the potential security threats are discussed at each protocol layer. We also provide a survey of the existing security protocols and algorithms that are adopted in the existing wireless network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term evolution (LTE) systems. Then, we discuss the state-of-the-art in physical-layer security, which is an emerging technique of securing the open communications environment against eavesdropping attacks at the physical layer. We also introduce the family of various jamming attacks and their counter-measures, including the constant jammer, intermittent jammer, reactive jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the integration of physical-layer security into existing authentication and cryptography mechanisms for further securing wireless networks. Finally, some technical challenges which remain unresolved at the time of writing are summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201

    Lifetime Improvement in Wireless Sensor Networks via Collaborative Beamforming and Cooperative Transmission

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    Collaborative beamforming (CB) and cooperative transmission (CT) have recently emerged as communication techniques that can make effective use of collaborative/cooperative nodes to create a virtual multiple-input/multiple-output (MIMO) system. Extending the lifetime of networks composed of battery-operated nodes is a key issue in the design and operation of wireless sensor networks. This paper considers the effects on network lifetime of allowing closely located nodes to use CB/CT to reduce the load or even to avoid packet-forwarding requests to nodes that have critical battery life. First, the effectiveness of CB/CT in improving the signal strength at a faraway destination using energy in nearby nodes is studied. Then, the performance improvement obtained by this technique is analyzed for a special 2D disk case. Further, for general networks in which information-generation rates are fixed, a new routing problem is formulated as a linear programming problem, while for other general networks, the cost for routing is dynamically adjusted according to the amount of energy remaining and the effectiveness of CB/CT. From the analysis and the simulation results, it is seen that the proposed method can reduce the payloads of energy-depleting nodes by about 90% in the special case network considered and improve the lifetimes of general networks by about 10%, compared with existing techniques.Comment: Invited paper to appear in the IEE Proceedings: Microwaves, Antennas and Propagation, Special Issue on Antenna Systems and Propagation for Future Wireless Communication

    Optimum Power Allocation for Cooperative Communications

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    Cooperative communication is a new class of wireless communication techniques in which wireless nodes help each other relay information and realize spatial diversity advantages in a distributed manner. This new transmission technique promises significant performance gains in terms of link reliability, spectral efficiency, system capacity, and transmission range. Analysis and design of cooperative communication wireless systems have been extensively studied over the last few years. The introduction and integration of cooperative communication in next generation wireless standards will lead to the design of an efficient and reliable fully-distributed wireless network. However, there are various technical challenges and open issues to be resolved before this promising concept becomes an integral part of the modern wireless communication devices. A common assumption in the literature on cooperative communications is the equal distribution of power among the cooperating nodes. Optimum power allocation is a key technique to realize the full potentials of relay-assisted transmission promised by the recent information-theoretic results. In this dissertation, we present a comprehensive framework for power allocation problem. We investigate the error rate performance of cooperative communication systems and further devise open-loop optimum power allocation schemes to optimize the performance. By exploiting the information about the location of cooperating nodes, we are able to demonstrate significant improvements in the system performance. In the first part of this dissertation, we consider single-relay systems with amplify-and-forward relaying. We derive upper bounds for bit error rate performance assuming various cooperation protocols and minimize them under total power constraint. In the second part, we consider a multi-relay network with decode-and-forward relaying. We propose a simple relay selection scheme for this multi-relay system to improve the throughput of the system, further optimize its performance through power allocation. Finally, we consider a multi-source multi-relay broadband cooperative network. We derive and optimize approximate symbol error rate of this OFDMA (orthogonal frequency division multiple access) system

    Directional Relays for Multi-Hop Cooperative Cognitive Radio Networks

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    In this paper, we investigate power allocation and beamforming in a relay assisted cognitive radio (CR) network. Our objective is to maximize the performance of the CR network while limiting interference in the direction of the primary users (PUs). In order to achieve these goals, we first consider joint power allocation and beamforming for cognitive nodes in direct links. Then, we propose an optimal power allocation strategy for relay nodes in indirect transmissions. Unlike the conventional cooperative relaying networks, the applied relays are equipped with directional antennas to further reduce the interference to PUs and meet the CR network requirements. The proposed approach employs genetic algorithm (GA) to solve the optimization problems. Numerical simulation results illustrate the quality of service (QoS) satisfaction in both primary and secondary networks. These results also show that notable improvements are achieved in the system performance if the conventional omni-directional relays are replaced with directional ones

    Wireless industrial monitoring and control networks: the journey so far and the road ahead

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    While traditional wired communication technologies have played a crucial role in industrial monitoring and control networks over the past few decades, they are increasingly proving to be inadequate to meet the highly dynamic and stringent demands of today’s industrial applications, primarily due to the very rigid nature of wired infrastructures. Wireless technology, however, through its increased pervasiveness, has the potential to revolutionize the industry, not only by mitigating the problems faced by wired solutions, but also by introducing a completely new class of applications. While present day wireless technologies made some preliminary inroads in the monitoring domain, they still have severe limitations especially when real-time, reliable distributed control operations are concerned. This article provides the reader with an overview of existing wireless technologies commonly used in the monitoring and control industry. It highlights the pros and cons of each technology and assesses the degree to which each technology is able to meet the stringent demands of industrial monitoring and control networks. Additionally, it summarizes mechanisms proposed by academia, especially serving critical applications by addressing the real-time and reliability requirements of industrial process automation. The article also describes certain key research problems from the physical layer communication for sensor networks and the wireless networking perspective that have yet to be addressed to allow the successful use of wireless technologies in industrial monitoring and control networks
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