1,807 research outputs found
Performance enhancement solutions in wireless communication networks
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 dizertaÄnĂ prĂĄci je provedena studie novĂœch pĆenosovĂœch protokolĆŻ pro rĆŻznĂ© bezdrĂĄtovĂ© sĂĆ„ovĂ© systĂ©my. S vyuĆŸitĂm matematickĂ© analĂœzy jsme analyzovali a vyhodnotili efektivitu pĆenosu z hlediska pravdÄpodobnosti vĂœpadku pĆes RayleighĆŻv kanĂĄl. TeoretickĂ© analĂœzy jsou ovÄĆeny provedenĂœmi simulacemi metodou Monte Carlo.
Nejprve doĆĄlo ke studii kooperativnĂho pĆenosu ve dvoucestnĂ©m dekĂłduj-a-pĆedej (Two-Way Decode-and-ForwardâTWDF) a vĂcecestnĂ©m DF schĂ©matu s vÄtĆĄĂm poÄtem pĆenosovĂœch uzlĆŻ pro sekundĂĄrnĂ systĂ©m, kdy takto byl zĂskĂĄn pĆĂstup ke spektru spolu s primĂĄrnĂm systĂ©mem. KonkrĂ©tnÄ jsme navrhli dvoucestnĂ© DF schĂ©ma se zĂskĂĄvĂĄnĂm energie a dvoucestnĂ© DF neortogonĂĄlnĂ schĂ©ma s mnohonĂĄsobnĂœm pĆĂstupem (Non-orthogonal Multiple AccessâNOMA) s digitĂĄlnĂm sĂĆ„ovĂœm kĂłdovĂĄnĂm. KromÄ toho rovnÄĆŸ zkoumĂĄme bezdrĂĄtovĂ© systĂ©my s vÄtĆĄĂm poÄtem pĆenosovĂœch uzlĆŻ, kde je pĆĂtomen vĂœbÄr nejlepĆĄĂho pĆenosovĂ©ho uzlu pro optimalizaci efektivnosti navrĆŸenĂ©ho schĂ©matu. PĆenosovĂ© protokoly navrĆŸenĂœch schĂ©mat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou spoleÄnÄ porovnĂĄny v identickĂ©m prostĆedĂ z pohledu pravdÄpodobnosti vĂœpadku. NĂĄslednÄ, na zĂĄkladÄ zĂskanĂœch vĂœsledkĆŻ, jsme dospÄli k zĂĄvÄru, ĆŸe navrĆŸenĂĄ schĂ©mata vylepĆĄujĂ vĂœkonnost bezdrĂĄtovĂœch kooperativnĂch systĂ©mĆŻ, konkrĂ©tnÄ jejich propustnost.
DĂĄle jsme se zamÄĆili na zkoumĂĄnĂ NOMA technologie a navrhli optimĂĄlnĂ ĆeĆĄenĂ (protokoly) pro urychlenĂ datovĂ©ho pĆenosu a zajiĆĄtÄnĂ 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 pĆenosovĂœ uzel napomĂĄhĂĄ dvÄma zdrojovĂœm uzlĆŻm komunikovat mezi sebou. VĂœsledky simulace a analĂœzy ukazujĂ, ĆŸe navrĆŸenĂœ protokol TWNOMA vylepĆĄuje dosaĆŸenou pĆenosovou rychlost v porovnĂĄnĂ s konvenÄnĂm dvoucestnĂœm schĂ©matem pouĆŸĂvajĂcĂm DNC (TWDNC protokol), dvoucestnĂœm schĂ©matem bez pouĆŸitĂ DNC (TWNDNC protokol) a dvoucestnĂœm schĂ©matem v zesil-a-pĆedej (amplify-and-forward) pĆenosovĂœch systĂ©mech (TWANC protokol).
Nakonec jsme zvĂĄĆŸili vyuĆŸitĂ kombinace NOMA a zabezpeÄenĂ fyzickĂ© vrstvy (Physical Layer SecurityâPLS) v podpĆŻrnĂ© kooperativnĂ kognitivnĂ sĂti (Underlay Cooperative Cognitive NetworkâUCCN). Zde je zde zkoumĂĄn vĂœbÄr nejlepĆĄĂho pĆenosovĂ©ho uzlu, kterĂœ uĆŸĂvĂĄ NOMA a bere v Ășvahu PLS pro efektivnÄjĆĄĂ pĆenos a zabezpeÄenĂ novĂ© generace bezdrĂĄtovĂœch sĂtĂ.440 - Katedra telekomunikaÄnĂ technikyvyhovÄ
An Opportunistic-Non Orthogonal Multiple Access based Cooperative Relaying system over Rician Fading Channels
Non-orthogonal Multiple Access (NOMA) has become a salient technology for
improving the spectral efficiency of the next generation 5G wireless
communication networks. In this paper, the achievable average rate of an
Opportunistic Non-Orthogonal Multiple Access (O-NOMA) based Cooperative
Relaying System (CRS) is studied under Rician fading channels with Channel
State Information (CSI) available at the source terminal. Based on CSI, for
opportunistic transmission, the source immediately chooses either the direct
transmission or the cooperative NOMA transmission using the relay, which can
provide better achievable average rate performance than the existing
Conventional-NOMA (C-NOMA) based CRS with no CSI at the source node.
Furthermore, a mathematical expression is also derived for the achievable
average rate and the results are compared with C-NOMA based CRS with no CSI at
the transmitter end, over a range of increasing power allocation coefficients,
transmit Signal-to-Noise Ratios (SNRs) and average channel powers. Numerical
results show that the CRS using O-NOMA with CSI achieves better spectral
efficiency in terms of the achievable average rate than the Conventional-NOMA
based CRS without CSI. To check the consistency of the derived analytical
results, Monte Carlo simulations are performed which verify that the results
are consistent and matched well with the simulation results.Comment: arXiv admin note: substantial text overlap with arXiv:1709.0822
A Simple Cooperative Diversity Method Based on Network Path Selection
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
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
Optimization Framework and Graph-Based Approach for Relay-Assisted Bidirectional OFDMA Cellular Networks
This paper considers a relay-assisted bidirectional cellular network where
the base station (BS) communicates with each mobile station (MS) using OFDMA
for both uplink and downlink. The goal is to improve the overall system
performance by exploring the full potential of the network in various
dimensions including user, subcarrier, relay, and bidirectional traffic. In
this work, we first introduce a novel three-time-slot time-division duplexing
(TDD) transmission protocol. This protocol unifies direct transmission, one-way
relaying and network-coded two-way relaying between the BS and each MS. Using
the proposed three-time-slot TDD protocol, we then propose an optimization
framework for resource allocation to achieve the following gains: cooperative
diversity (via relay selection), network coding gain (via bidirectional
transmission mode selection), and multiuser diversity (via subcarrier
assignment). We formulate the problem as a combinatorial optimization problem,
which is NP-complete. To make it more tractable, we adopt a graph-based
approach. We first establish the equivalence between the original problem and a
maximum weighted clique problem in graph theory. A metaheuristic algorithm
based on any colony optimization (ACO) is then employed to find the solution in
polynomial time. Simulation results demonstrate that the proposed protocol
together with the ACO algorithm significantly enhances the system total
throughput.Comment: 27 pages, 8 figures, 2 table
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