275 research outputs found
Cross-Layer Optimization of Two-Way Relaying for Statistical QoS Guarantees
Two-way relaying promises considerable improvements on spectral efficiency in
wireless relay networks. While most existing works focus on physical layer
approaches to exploit its capacity gain, the benefits of two-way relaying on
upper layers are much less investigated. In this paper, we study the
cross-layer design and optimization for delay quality-of-service (QoS)
provisioning in two-way relay systems. Our goal is to find the optimal
transmission policy to maximize the weighted sum throughput of the two users in
the physical layer while guaranteeing the individual statistical delay-QoS
requirement for each user in the datalink layer. This statistical delay-QoS
requirement is characterized by the QoS exponent. By integrating the concept of
effective capacity, the cross-layer optimization problem is equivalent to a
weighted sum effective capacity maximization problem. We derive the jointly
optimal power and rate adaptation policies for both three-phase and two-phase
two-way relay protocols. Numerical results show that the proposed adaptive
transmission policies can efficiently provide QoS guarantees and improve the
performance. In addition, the throughput gain obtained by the considered
three-phase and two-phase protocols over direct transmission is significant
when the delay-QoS requirements are loose, but the gain diminishes at tight
delay requirements. It is also found that, in the two-phase protocol, the relay
node should be placed closer to the source with more stringent delay
requirement.Comment: 14 pages, 9 figures, accepted for publicatio
Reconfigurable Wireless Networks
Driven by the advent of sophisticated and ubiquitous applications, and the
ever-growing need for information, wireless networks are without a doubt
steadily evolving into profoundly more complex and dynamic systems. The user
demands are progressively rampant, while application requirements continue to
expand in both range and diversity. Future wireless networks, therefore, must
be equipped with the ability to handle numerous, albeit challenging
requirements. Network reconfiguration, considered as a prominent network
paradigm, is envisioned to play a key role in leveraging future network
performance and considerably advancing current user experiences. This paper
presents a comprehensive overview of reconfigurable wireless networks and an
in-depth analysis of reconfiguration at all layers of the protocol stack. Such
networks characteristically possess the ability to reconfigure and adapt their
hardware and software components and architectures, thus enabling flexible
delivery of broad services, as well as sustaining robust operation under highly
dynamic conditions. The paper offers a unifying framework for research in
reconfigurable wireless networks. This should provide the reader with a
holistic view of concepts, methods, and strategies in reconfigurable wireless
networks. Focus is given to reconfigurable systems in relatively new and
emerging research areas such as cognitive radio networks, cross-layer
reconfiguration and software-defined networks. In addition, modern networks
have to be intelligent and capable of self-organization. Thus, this paper
discusses the concept of network intelligence as a means to enable
reconfiguration in highly complex and dynamic networks. Finally, the paper is
supported with several examples and case studies showing the tremendous impact
of reconfiguration on wireless networks.Comment: 28 pages, 26 figures; Submitted to the Proceedings of the IEEE (a
special issue on Reconfigurable Systems
Survey of Cognitive Radio Techniques in Wireless Network
In this report, I surveyed the cognitive radio technique in wireless
networks. Researched several kinds of cognitive techniques about their
advantages and disadvantages
QoS based Radio Resource Management Techniques for Next Generation MU-MIMO WLANs: A Survey
IEEE 802.11 based Wireless Local Area Networks (WLANs) have emerged as a popular candidate that offers Internet services for wireless users. The demand of data traffic is increasing every day due to the increase in the use of multimedia applications, such as digital audio, video, and online gaming. With the inclusion of Physical Layer (PHY) technologies, such as the OFDM and MIMO, the current 802.11ac WLANs are claiming Gigabit speeds. Hence, the existing Medium Access Control (MAC) must be in a suitable position to convert the offered PHY data rates for efficient throughput. Further, the integration of cellular networks with WLANs requires unique changes at MAC layer. It is highly required to preserve the Quality of Service (QoS) in these scenarios. Fundamentally, many QoS issues arise from the problem of effective Radio Resource Management (RRM). Although IEEE 802.11 has lifted PHY layer aspects, there is a necessity to investigate MAC layer issues, such as resource utilization, scheduling, admission control and congestion control. In this survey, a literature overview of these techniques, namely the resource allocation and scheduling algorithms are briefly discussed in connection with the QoS at MAC layer. Further, some anticipated enhancements proposed for Multi-User Multiple-Input and Multiple-Output (MU-MIMO) WLANs are discussed
Five Facets of 6G: Research Challenges and Opportunities
Whilst the fifth-generation (5G) systems are being rolled out across the
globe, researchers have turned their attention to the exploration of radical
next-generation solutions. At this early evolutionary stage we survey five main
research facets of this field, namely {\em Facet~1: next-generation
architectures, spectrum and services, Facet~2: next-generation networking,
Facet~3: Internet of Things (IoT), Facet~4: wireless positioning and sensing,
as well as Facet~5: applications of deep learning in 6G networks.} In this
paper, we have provided a critical appraisal of the literature of promising
techniques ranging from the associated architectures, networking, applications
as well as designs. We have portrayed a plethora of heterogeneous architectures
relying on cooperative hybrid networks supported by diverse access and
transmission mechanisms. The vulnerabilities of these techniques are also
addressed and carefully considered for highlighting the most of promising
future research directions. Additionally, we have listed a rich suite of
learning-driven optimization techniques. We conclude by observing the
evolutionary paradigm-shift that has taken place from pure single-component
bandwidth-efficiency, power-efficiency or delay-optimization towards
multi-component designs, as exemplified by the twin-component ultra-reliable
low-latency mode of the 5G system. We advocate a further evolutionary step
towards multi-component Pareto optimization, which requires the exploration of
the entire Pareto front of all optiomal solutions, where none of the components
of the objective function may be improved without degrading at least one of the
other components
Multi-Element VLC Networks: LED Assignment, Power Control, and Optimum Combining
Visible light communications (VLC) is a promising technology to address the
spectrum crunch problem in radio frequency (RF) networks. A major advantage of
VLC networks is that they can use the existing lighting infrastructure in
indoor environments, which may have large number of LEDs for illumination.
While LEDs used for lighting typically have limited bandwidth, presence of many
LEDs can be exploited for indoor VLC networks, to serve each user by multiple
LEDs for improving link quality and throughput. In this paper, LEDs are grouped
and assigned to the users based on received signal strength from each LED, for
which different solutions are proposed to achieve maximum throughput,
proportional fairness and quality of service (QoS). Additionally, power
optimization of LEDs for a given assignment is investigated, and Jacobian and
Hessian matrices of the corresponding optimization problem are derived.
Moreover, for multi-element receivers with LED grouping at the transmitter, an
improved optimal combining method is proposed. This method suppresses
interference caused by simultaneous data transfer of LEDs and improves the
overall signal-to-interference-plus-noise-ratio (SINR) by 2 dB to 5 dB. Lastly,
an efficient calculation of channel response is presented to simulate multipath
VLC channel with low computational complexity.Comment: Submitted to J. Select. Areas Commun. (JSAC
Resource management in QoS-aware wireless cellular networks
2011 Summer.Includes bibliographical references.Emerging broadband wireless networks that support high speed packet data with heterogeneous quality of service (QoS) requirements demand more flexible and efficient use of the scarce spectral resource. Opportunistic scheduling exploits the time-varying, location-dependent channel conditions to achieve multiuser diversity. In this work, we study two types of resource allocation problems in QoS-aware wireless cellular networks. First, we develop a rigorous framework to study opportunistic scheduling in multiuser OFDM systems. We derive optimal opportunistic scheduling policies under three common QoS/fairness constraints for multiuser OFDM systems--temporal fairness, utilitarian fairness, and minimum-performance guarantees. To implement these optimal policies efficiently, we provide a modified Hungarian algorithm and a simple suboptimal algorithm. We then propose a generalized opportunistic scheduling framework that incorporates multiple mixed QoS/fairness constraints, including providing both lower and upper bound constraints. Next, taking input queues and channel memory into consideration, we reformulate the transmission scheduling problem as a new class of Markov decision processes (MDPs) with fairness constraints. We investigate the throughput maximization and the delay minimization problems in this context. We study two categories of fairness constraints, namely temporal fairness and utilitarian fairness. We consider two criteria: infinite horizon expected total discounted reward and expected average reward. We derive and prove explicit dynamic programming equations for the above constrained MDPs, and characterize optimal scheduling policies based on those equations. An attractive feature of our proposed schemes is that they can easily be extended to fit different objective functions and other fairness measures. Although we only focus on uplink scheduling, the scheme is equally applicable to the downlink case. Furthermore, we develop an efficient approximation method--temporal fair rollout--to reduce the computational cost
Quality of service in WiMAX networks
Mestrado em Engenharia ElectrĆ³nica e TelecomunicaƧƵesO acesso Ć banda larga Ć© um requisito importante na actualidade para satisfazer os utilizadores em termos de novas aplicaƧƵes e serviƧos em tempo
real. O WiMAX, como tecnologia sem fios para Ć”reas metropolitanas, prometendo cobrir uma maior superfĆcie e com maior dĆ©bito, Ć© uma tecnologia
promissora para as redes de prĆ³xima geraĆ§Ć£o. No entanto um requisito importante para a instalaĆ§Ć£o e massificaĆ§Ć£o desta tecnologia Ć© o seu comportamento a nĆvel de qualidade de serviƧos e garantia aos utilizadores do cumprimento eficiente dos requisitos de QoS.
Esta tese aborda e estuda o suporte de qualidade de serviƧos para redes WiMAX presente em diferentes modelos de simulaĆ§Ć£o, implementados na ferramenta de simulaĆ§Ć£o ns-2. Para alĆ©m da validaĆ§Ć£o e comparaĆ§Ć£o entre os modelos existentes, tambĆ©m Ć© efectuada a especificaĆ§Ć£o e implementaĆ§Ć£o de uma soluĆ§Ć£o de QoS composta por um classificador e escalonador, e Ć©
proposto e avaliado um algoritmo de escalonamento que utiliza prioritizaĆ§Ć£o de
classes de serviƧo e informaĆ§Ć£o fĆsica dinĆ¢mica ācross layerā para decisƵes de escalonamento no simulador.
Para validar e avaliar as soluƧƵes propostas e desenvolvidas, um conjunto de cenĆ”rios orientados para a utilizaĆ§Ć£o de vĆ”rios serviƧos e aferiĆ§Ć£o de mĆ©tricas de QoS foram simulados. Os resultados obtidos mostram a diferenciaĆ§Ć£o entre distintas classes de trĆ”fego. O mecanismo proposto apresenta um pequeno ganho em dĆ©bito e latĆŖncia comparativamente Ć s soluƧƵes previamente
analisadas/implementadas.
ABSTRACT: Broadband access is an important requirement to satisfy user demands and support a new set of real time services and applications. WiMAX, as a
Broadband Wireless Access solution for Wireless Metropolitan Area Networks, covering large distances with high throughputs, is a promising technology for Next Generation Networks. Nevertheless, for the successful deployment and
massification of WiMAX based solutions, Quality of Service (QoS) is a mandatory feature that must be supported.
In this thesis , the QoS support for WiMAX in ns-2 simulation software is addressed. A QoS framework, composed by a packet classification mechanism
and a scheduler, has been specified and implemented on the simulator, providing service differentiation over WiMAX networks. Furthermore, validation and comparison of different IEEE 802.16 simulation models is provided. Finally a scheduling solution is proposed and evaluated that uses prioritization and dynamic cross layer information for schedulling decisions in WiMAX networks.
In order to validate the developed solutions, a set of QoS oriented scenarios have been simulated and the obtained results show that the implemented
schedullers are able to efficiently differentiate between the different traffic classes and achieve gains in throughput and delay
Resource Allocation in 4G and 5G Networks: A Review
The advent of 4G and 5G broadband wireless networks brings several challenges with respect to resource allocation in the networks. In an interconnected network of wireless devices, users, and devices, all compete for scarce resources which further emphasizes the fair and efficient allocation of those resources for the proper functioning of the networks. The purpose of this study is to discover the different factors that are involved in resource allocation in 4G and 5G networks. The methodology used was an empirical study using qualitative techniques by performing literature reviews on the state of art in 4G and 5G networks, analyze their respective architectures and resource allocation mechanisms, discover parameters, criteria and provide recommendations. It was observed that resource allocation is primarily done with radio resource in 4G and 5G networks, owing to their wireless nature, and resource allocation is measured in terms of delay, fairness, packet loss ratio, spectral efficiency, and throughput. Minimal consideration is given to other resources along the end-to-end 4G and 5G network architectures. This paper defines more types of resources, such as electrical energy, processor cycles and memory space, along end-to-end architectures, whose allocation processes need to be emphasized owing to the inclusion of software defined networking and network function virtualization in 5G network architectures. Thus, more criteria, such as electrical energy usage, processor cycle, and memory to evaluate resource allocation have been proposed.Ā Finally, ten recommendations have been made to enhance resource allocation along the whole 5G network architecture
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