912 research outputs found
Power allocation in wireless multi-user relay networks
In this paper, we consider an amplify-and-forward wireless relay system where multiple source nodes communicate with their corresponding destination nodes with the help of relay nodes. Conventionally, each relay equally distributes the available resources to its relayed sources. This approach is clearly sub-optimal since each user experiences dissimilar channel conditions, and thus, demands different amount of allocated resources to meet its quality-of-service (QoS) request. Therefore, this paper presents novel power allocation schemes to i) maximize the minimum signal-to-noise ratio among all users; ii) minimize the maximum transmit power over all sources; iii) maximize the network throughput. Moreover, due to limited power, it may be impossible to satisfy the QoS requirement for every user. Consequently, an admission control algorithm should first be carried out to maximize the number of users possibly served. Then, optimal power allocation is performed. Although the joint optimal admission control and power allocation problem is combinatorially hard, we develop an effective heuristic algorithm with significantly reduced complexity. Even though theoretically sub-optimal, it performs remarkably well. The proposed power allocation problems are formulated using geometric programming (GP), a well-studied class of nonlinear and nonconvex optimization. Since a GP problem is readily transformed into an equivalent convex optimization problem, optimal solution can be obtained efficiently. Numerical results demonstrate the effectiveness of our proposed approach
Robust Transmissions in Wireless Powered Multi-Relay Networks with Chance Interference Constraints
In this paper, we consider a wireless powered multi-relay network in which a
multi-antenna hybrid access point underlaying a cellular system transmits
information to distant receivers. Multiple relays capable of energy harvesting
are deployed in the network to assist the information transmission. The hybrid
access point can wirelessly supply energy to the relays, achieving multi-user
gains from signal and energy cooperation. We propose a joint optimization for
signal beamforming of the hybrid access point as well as wireless energy
harvesting and collaborative beamforming strategies of the relays. The
objective is to maximize network throughput subject to probabilistic
interference constraints at the cellular user equipment. We formulate the
throughput maximization with both the time-switching and power-splitting
schemes, which impose very different couplings between the operating parameters
for wireless power and information transfer. Although the optimization problems
are inherently non-convex, they share similar structural properties that can be
leveraged for efficient algorithm design. In particular, by exploiting
monotonicity in the throughput, we maximize it iteratively via customized
polyblock approximation with reduced complexity. The numerical results show
that the proposed algorithms can achieve close to optimal performance in terms
of the energy efficiency and throughput.Comment: 14 pages, 8 figure
Distributed space-time coding for two-way wireless relay networks
In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N,K}(1- (log log P/log P)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding, where the former operates on the unitary group and the latter works on the finite field. Moreover, PDF achieves the diversity order of min{N,K} but the conventional DF can only achieve the diversity order of 1. Finally, we find that two time slots protocols also have advantages over four-time-slot protocols in media access control (MAC) layer
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
Joint Resource Optimization for Multicell Networks with Wireless Energy Harvesting Relays
This paper first considers a multicell network deployment where the base
station (BS) of each cell communicates with its cell-edge user with the
assistance of an amplify-and-forward (AF) relay node. Equipped with a power
splitter and a wireless energy harvester, the self-sustaining relay scavenges
radio frequency (RF) energy from the received signals to process and forward
the information. Our aim is to develop a resource allocation scheme that
jointly optimizes (i) BS transmit powers, (ii) received power splitting factors
for energy harvesting and information processing at the relays, and (iii) relay
transmit powers. In the face of strong intercell interference and limited radio
resources, we formulate three highly-nonconvex problems with the objectives of
sum-rate maximization, max-min throughput fairness and sum-power minimization.
To solve such challenging problems, we propose to apply the successive convex
approximation (SCA) approach and devise iterative algorithms based on geometric
programming and difference-of-convex-functions programming. The proposed
algorithms transform the nonconvex problems into a sequence of convex problems,
each of which is solved very efficiently by the interior-point method. We prove
that our algorithms converge to the locally optimal solutions that satisfy the
Karush-Kuhn-Tucker conditions of the original nonconvex problems. We then
extend our results to the case of decode-and-forward (DF) relaying with
variable timeslot durations. We show that our resource allocation solutions in
this case offer better throughput than that of the AF counterpart with equal
timeslot durations, albeit at a higher computational complexity. Numerical
results confirm that the proposed joint optimization solutions substantially
improve the network performance, compared with cases where the radio resource
parameters are individually optimized
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