242 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 této dizertační práci je provedena studie nových přenosových protokolů pro různé bezdrátové síťové systémy. S využitím matematické analýzy jsme analyzovali a vyhodnotili efektivitu přenosu z hlediska pravděpodobnosti výpadku přes Rayleighův kanál. Teoretické analýzy jsou ověřeny provedenými simulacemi metodou Monte Carlo.
Nejprve došlo ke studii kooperativního přenosu ve dvoucestném dekóduj-a-předej (Two-Way Decode-and-Forward–TWDF) a vícecestném DF schématu s větším počtem přenosových uzlů pro sekundární systém, kdy takto byl získán přístup ke spektru spolu s primárním systémem. Konkrétně jsme navrhli dvoucestné DF schéma se získáváním energie a dvoucestné DF neortogonální schéma s mnohonásobným přístupem (Non-orthogonal Multiple Access–NOMA) s digitálním síťovým kódováním. Kromě toho rovněž zkoumáme bezdrátové systémy s větším počtem přenosových uzlů, kde je přítomen výběr nejlepšího přenosového uzlu pro optimalizaci efektivnosti navrženého schématu. Přenosové protokoly navržených schémat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou společně porovnány v identickém prostředí z pohledu pravděpodobnosti výpadku. Následně, na základě získaných výsledků, jsme dospěli k závěru, že navržená schémata vylepšují výkonnost bezdrátových kooperativních systémů, konkrétně jejich propustnost.
Dále jsme se zaměřili na zkoumání NOMA technologie a navrhli optimální řešení (protokoly) pro urychlení datového přenosu a zajištění QoS v další generaci bezdrátových komunikací. V této práci jsme navrhli dvoucestné DF NOMA schéma (nazýváno jako TWNOMA protokol), ve kterém mezilehlý přenosový uzel napomáhá dvěma zdrojovým uzlům komunikovat mezi sebou. Výsledky simulace a analýzy ukazují, že navržený protokol TWNOMA vylepšuje dosaženou přenosovou rychlost v porovnání s konvenčním dvoucestným schématem používajícím DNC (TWDNC protokol), dvoucestným schématem bez použití DNC (TWNDNC protokol) a dvoucestným schématem v zesil-a-předej (amplify-and-forward) přenosových systémech (TWANC protokol).
Nakonec jsme zvážili využití kombinace NOMA a zabezpečení fyzické vrstvy (Physical Layer Security–PLS) v podpůrné kooperativní kognitivní síti (Underlay Cooperative Cognitive Network–UCCN). Zde je zde zkoumán výběr nejlepšího přenosového uzlu, který užívá NOMA a bere v úvahu PLS pro efektivnější přenos a zabezpečení nové generace bezdrátových sítí.440 - Katedra telekomunikační technikyvyhově
Opportunistic Relaying in Time Division Broadcast Protocol with Incremental Relaying
In this paper, we investigate the performance of time division broadcast protocol (TDBC) with incremental relaying (IR) when there are multiple available relays. Opportunistic relaying (OR), i.e., the “best” relay is select for transmission to minimize the system’s outage probability, is proposed. Two OR schemes are presented. The first scheme, termed TDBC-OIR-I, selects the “best” relay from the set of relays that can decode both flows of signal from the two sources successfully. The second one, termed TDBC-OIR-II, selects two “best” relays from two respective sets of relays that can decode successfully each flow of signal. The performance, in terms of outage probability, expected rate (ER), and diversity-multiplexing tradeoff (DMT), of the two schemes are analyzed and compared with two TDBC schemes that have no IR but OR (termed TDBC-OR-I and TDBC-OR-II accordingly) and two other benchmark OR schemes that have no direct link transmission between the two sources
Modeling and Analysis of Two-Way Relay Non-Orthogonal Multiple Access Systems
A two-way relay non-orthogonal multiple access (TWR-NOMA) system is
investigated, where two groups of NOMA users exchange messages with the aid of
one half-duplex (HD) decode-and-forward (DF) relay. Since the
signal-plus-interference-to-noise ratios (SINRs) of NOMA signals mainly depend
on effective successive interference cancellation (SIC) schemes, imperfect SIC
(ipSIC) and perfect SIC (pSIC) are taken into account. In order to characterize
the performance of TWR-NOMA systems, we first derive closed-form expressions
for both exact and asymptotic outage probabilities of NOMA users' signals with
ipSIC/pSIC. Based on the derived results, the diversity order and throughput of
the system are examined. Then we study the ergodic rates of users' signals by
providing the asymptotic analysis in high SNR regimes. Lastly, numerical
simulations are provided to verify the analytical results and show that: 1)
TWR-NOMA is superior to TWR-OMA in terms of outage probability in low SNR
regimes; 2) Due to the impact of interference signal (IS) at the relay, error
floors and throughput ceilings exist in outage probabilities and ergodic rates
for TWR-NOMA, respectively; and 3) In delay-limited transmission mode, TWR-NOMA
with ipSIC and pSIC have almost the same energy efficiency. However, in
delay-tolerant transmission mode, TWR-NOMA with pSIC is capable of achieving
larger energy efficiency compared to TWR-NOMA with ipSIC.Comment: 12 pages, 8 figures. arXiv admin note: substantial text overlap with
arXiv:1801.0817
A Review- Proposed Bidirectional Relaying for Improved Channel Estimation Error and Co-Channel Interference
Wireless Communication has gained a lot of interest as future generation requires higher data rates and more suitable transmission with adequate quality of service. Wireless communication suffers from various problems like Co-Channel Interference (CCI) and Channel Estimation Error (CEE). Cooperative communication is an efficient technique to deal with these types of problems by offering significant multiplexing and diversity gains without increasing power and bandwidth. Our proposed two way relaying helps to improve the overall system performance in wireless networks. Cooperative communications also deals with the various problems like fading and shadowing. It is further investigated that proposed two way relaying is spectrally efficient technique which provides a way to surmount half duplexing loss in one way relay channel
A Study Of Cooperative Spectrum Sharing Schemes For Internet Of Things Systems
The Internet of Things (IoT) has gained much attention in recent years with the massive increase in the number of connected devices. Cognitive Machine-to-Machine (CM2M) communications is a hot research topic in which a cognitive dimension allows M2M networks to overcome the challenges of spectrum scarcity, interference, and green requirements. In this paper, we propose a Generalized Cooperative Spectrum Sharing (GCSS) scheme for M2M communication. Cooperation extends the coverage of wireless networks as well as increasing their throughput while reducing the energy consumption of the connected low power devices. We study the outage performance of the proposed GCSS scheme for M2M system and derive exact expressions for the outage probability. We also analyze the effect of varying transmission powers on the performance of the system
On Green Energy Powered Cognitive Radio Networks
Green energy powered cognitive radio (CR) network is capable of liberating
the wireless access networks from spectral and energy constraints. The
limitation of the spectrum is alleviated by exploiting cognitive networking in
which wireless nodes sense and utilize the spare spectrum for data
communications, while dependence on the traditional unsustainable energy is
assuaged by adopting energy harvesting (EH) through which green energy can be
harnessed to power wireless networks. Green energy powered CR increases the
network availability and thus extends emerging network applications. Designing
green CR networks is challenging. It requires not only the optimization of
dynamic spectrum access but also the optimal utilization of green energy. This
paper surveys the energy efficient cognitive radio techniques and the
optimization of green energy powered wireless networks. Existing works on
energy aware spectrum sensing, management, and sharing are investigated in
detail. The state of the art of the energy efficient CR based wireless access
network is discussed in various aspects such as relay and cooperative radio and
small cells. Envisioning green energy as an important energy resource in the
future, network performance highly depends on the dynamics of the available
spectrum and green energy. As compared with the traditional energy source, the
arrival rate of green energy, which highly depends on the environment of the
energy harvesters, is rather random and intermittent. To optimize and adapt the
usage of green energy according to the opportunistic spectrum availability, we
discuss research challenges in designing cognitive radio networks which are
powered by energy harvesters
Cooperation in 5G HetNets: Advanced Spectrum Access and D2D Assisted Communications
The evolution of conventional wireless communication networks to the fifth
generation (5G) is driven by an explosive increase in the number of wireless
mobile devices and services, as well as their demand for all-time and
everywhere connectivity, high data rates, low latency, high energy-efficiency
and improved quality of service. To address these challenges, 5G relies on key
technologies, such as full duplex (FD), device-to-device (D2D) communications,
and network densification. In this article, a heterogeneous networking
architecture is envisioned, where cells of different sizes and radio access
technologies coexist. Specifically, collaboration for spectrum access is
explored for both FD- and cognitive-based approaches, and cooperation among
devices is discussed in the context of the state-of-the-art D2D assisted
communication paradigm. The presented cooperative framework is expected to
advance the understandings of the critical technical issues towards dynamic
spectrum management for 5G heterogeneous networks.Comment: to appear in IEEE Wireless Communication
Secure Communications in NOMA System: Subcarrier Assignment and Power Allocation
Secure communication is a promising technology for wireless networks because
it ensures secure transmission of information. In this paper, we investigate
the joint subcarrier (SC) assignment and power allocation problem for
non-orthogonal multiple access (NOMA) amplify-and-forward two-way relay
wireless networks, in the presence of eavesdroppers. By exploiting cooperative
jamming (CJ) to enhance the security of the communication link, we aim to
maximize the achievable secrecy energy efficiency by jointly designing the SC
assignment, user pair scheduling and power allocation. Assuming the perfect
knowledge of the channel state information (CSI) at the relay station, we
propose a low-complexity subcarrier assignment scheme (SCAS-1), which is
equivalent to many-to-many matching games, and then SCAS-2 is formulated as a
secrecy energy efficiency maximization problem. The secure power allocation
problem is modeled as a convex geometric programming problem, and then solved
by interior point methods. Simulation results demonstrate that the
effectiveness of the proposed SSPA algorithms under scenarios of using and not
using CJ, respectively
Resource Allocation and Fairness in Wireless Powered Cooperative Cognitive Radio Networks
We integrate a wireless powered communication network with a cooperative
cognitive radio network, where multiple secondary users (SUs) powered
wirelessly by a hybrid access point (HAP) help a primary user relay the data.
As a reward for the cooperation, the secondary network gains the spectrum
access where SUs transmit to HAP using time division multiple access. To
maximize the sum-throughput of SUs, we present a secondary sum-throughput
optimal resource allocation (STORA) scheme. Under the constraint of meeting
target primary rate, the STORA scheme chooses the optimal set of relaying SUs
and jointly performs the time and energy allocation for SUs. Specifically, by
exploiting the structure of the optimal solution, we find the order in which
SUs are prioritized to relay primary data. Since the STORA scheme focuses on
the sum-throughput, it becomes inconsiderate towards individual SU throughput,
resulting in low fairness. To enhance fairness, we investigate three resource
allocation schemes, which are (i) equal time allocation, (ii) minimum
throughput maximization, and (iii) proportional time allocation. Simulation
results reveal the trade-off between sum-throughput and fairness. The minimum
throughput maximization scheme is the fairest one as each SU gets the same
throughput, but yields the least SU sum-throughput.Comment: Accepted in IEEE Transactions on Communication
A Survey of Optimization Approaches for Wireless Physical Layer Security
Due to the malicious attacks in wireless networks, physical layer security
has attracted increasing concerns from both academia and industry. The research
on physical layer security mainly focuses either on the secrecy
capacity/achievable secrecy rate/capacity-equivocation region from the
perspective of information theory, or on the security designs from the
viewpoints of optimization and signal processing. Because of its importance in
security designs, the latter research direction is surveyed in a comprehensive
way in this paper. The survey begins with typical wiretap channel models to
cover common scenarios and systems. The topics on physical-layer security
designs are then summarized from resource allocation, beamforming/precoding,
and antenna/node selection and cooperation. Based on the aforementioned
schemes, the performance metrics and fundamental optimization problems are
discussed, which are generally adopted in security designs. Thereafter, the
state of the art of optimization approaches on each research topic of physical
layer security is reviewed from four categories of optimization problems, such
as secrecy rate maximization, secrecy outrage probability minimization, power
consumption minimization, and secure energy efficiency maximization.
Furthermore, the impacts of channel state information on optimization and
design are discussed. Finally, the survey concludes with the observations on
potential future directions and open challenges.Comment: to appear in IEEE Communications Surveys & Tutorial
- …