2,523 research outputs found

    Cooperative Symbol-Based Signaling for Networks with Multiple Relays

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    Wireless channels suffer from severe inherent impairments and hence reliable and high data rate wireless transmission is particularly challenging to achieve. Fortunately, using multiple antennae improves performance in wireless transmission by providing space diversity, spatial multiplexing, and power gains. However, in wireless ad-hoc networks multiple antennae may not be acceptable due to limitations in size, cost, and hardware complexity. As a result, cooperative relaying strategies have attracted considerable attention because of their abilities to take advantage of multi-antenna by using multiple single-antenna relays. This study is to explore cooperative signaling for different relay networks, such as multi-hop relay networks formed by multiple single-antenna relays and multi-stage relay networks formed by multiple relaying stages with each stage holding several single-antenna relays. The main contribution of this study is the development of a new relaying scheme for networks using symbol-level modulation, such as binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). We also analyze effects of this newly developed scheme when it is used with space-time coding in a multi-stage relay network. Simulation results demonstrate that the new scheme outperforms previously proposed schemes: amplify-and-forward (AF) scheme and decode-and-forward (DF) scheme

    Cooperative Relaying in Wireless Networks under Spatially and Temporally Correlated Interference

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    We analyze the performance of an interference-limited, decode-and-forward, cooperative relaying system that comprises a source, a destination, and NN relays, placed arbitrarily on the plane and suffering from interference by a set of interferers placed according to a spatial Poisson process. In each transmission attempt, first the transmitter sends a packet; subsequently, a single one of the relays that received the packet correctly, if such a relay exists, retransmits it. We consider both selection combining and maximal ratio combining at the destination, Rayleigh fading, and interferer mobility. We derive expressions for the probability that a single transmission attempt is successful, as well as for the distribution of the transmission attempts until a packet is transmitted successfully. Results provide design guidelines applicable to a wide range of systems. Overall, the temporal and spatial characteristics of the interference play a significant role in shaping the system performance. Maximal ratio combining is only helpful when relays are close to the destination; in harsh environments, having many relays is especially helpful, and relay placement is critical; the performance improves when interferer mobility increases; and a tradeoff exists between energy efficiency and throughput

    A Simple Cooperative Diversity Method Based on Network Path Selection

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    Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However most of the proposed solutions require distributed space-time coding algorithms, the careful design of which is left for future investigation if there is more than one cooperative relay. We propose a novel scheme, that alleviates these problems and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this best relay for cooperation between the source and the destination. We develop and analyze a distributed method to select the best relay that requires no topology information and is based on local measurements of the instantaneous channel conditions. This method also requires no explicit communication among the relays. The success (or failure) to select the best available path depends on the statistics of the wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M nodes is required, such as those proposed in [7]. The simplicity of the technique, allows for immediate implementation in existing radio hardware and its adoption could provide for improved flexibility, reliability and efficiency in future 4G wireless systems.Comment: To appear, IEEE JSAC, special issue on 4

    Dispensing with channel estimation: differentially modulated cooperative wireless communications

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    As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective

    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
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