Belaidžio ryšio tinklų terpės prieigos valdymo tyrimas

Over the years, consumer requirements for Quality of Service (QoS) has been growing exponentially. Recently, the ratification process of newly IEEE 802.11ad amendment to IEEE 802.11 was finished. The IEEE 802.11ad is the newly con-sumer wireless communication approach, which will gain high spot on the 5G evolution. Major players in wireless market, such as Qualcomm already are inte-grating solutions from unlicensed band, like IEEE 802.11ac, IEEE 802.11ad into their architecture of LTE PRO (the next evolutionary step for 5G networking) (Qualcomm 2013; Parker et al. 2015). As the demand is growing both in enter-prise wireless networking and home consumer markets. Consumers started to no-tice the performance degradation due to overcrowded unlicensed bands. The un-licensed bands such as 2.4 GHz, 5 GHz are widely used for up-to-date IEEE 802.11n/ac technologies with upcoming IEEE 802.11ax. However, overusage of the available frequency leads to severe interference issue and consequences in to-tal system performance degradation, currently existing wireless medium access method can not sustain the increasing intereference and thus wireless needs a new methods of wireless medium access. The main focal point of this dissertation is to improve wireless performance in dense wireless networks. In dissertation both the conceptual and multi-band wireless medium access methods are considered both from theoretical point of view and experimental usage. The introduction chapter presents the investigated problem and it’s objects of research as well as importance of dissertation and it’s scientific novelty in the unlicensed wireless field. Chapter 1 revises used literature. Existing and up-to-date state-of-the-art so-lution are reviewed, evaluated and key point advantages and disadvantages are analyzed. Conclusions are drawn at the end of the chapter. Chapter 2 describes theoretical analysis of wireless medium access protocols and the new wireless medium access method. During analysis theoretical simula-tions are performed. Conclusions are drawn at the end of the chapter. Chapter 3 is focused on the experimental components evaluation for multi-band system, which would be in line with theoretical concept investigations. The experimental results, showed that components of multi-band system can gain sig-nificant performance increase when compared to the existing IEEE 802.11n/ac wireless systems. General conclusions are drawn after analysis of measurement results

Performance evaluation of channel selection algorithm for multi-channel MAC protocol in ad hoc networks

This thesis aims to provide an approach that is to investigate channel selection algorithm for increasing the performance of ad hoc networks. Although our channel selection algorithms are very simple, multi-channel MAC protocol that employs our channel selection algorithms are effective for increasing the performance of ad hoc networks.学位記番号：工博甲47

Analysis and optimal configuration of distributed opportunistic scheduling techniques in wireless networks

The phenomenon of fading in wireless communications has traditionally been considered as a source of unreliability that needs to be mitigated. In contrast, Opportunistic Scheduling (OS) techniques exploit quick channel quality oscillations in fading links, during the assignment of transmission opportunities, to improve the performance of wireless networks. While centralized mechanisms rely on a central entity with global knowledge, Distributed Opportunistic Scheduling (DOS) techniques have recently been proposed to work in distributed networks, i.e., where either such a central entity is not available, or the communication overhead to feed timely information to this central entity is prohibitive. With DOS, each station contends for the channel with a certain access probability. If a contention is successful, the station measures the channel conditions and transmits if the channel quality is above a certain threshold. Otherwise, the station does not use the transmission opportunity, allowing all stations to recontend. Given the fact that different stations, in different time instances, experience different channel conditions, it is likely that the channel is used by a link with better conditions, improving overall performance. In this thesis we first propose ADOS, an adaptive mechanism that drives the system to an optimal allocation of resources in terms of proportional fairness. We show that this mechanism outperforms previous approaches, particularly in scenarios with non-saturated stations (that do not always have data to transmit). The distributed nature of DOS makes it particularly vulnerable to selfish users that seek to maximize their own performance at the expense of those that cooperate for the common welfare. We thus design a punishing mechanism, namely DOC, that (i) drives the system to the optimal point of operation when all stations follow the protocol, and (ii) removes any potential gain by deviating from it (and thus, the incentive to misbehave). Finally, we propose a novel allocation criterion, namely the EF criterion, to balance between the most energy-eficient configuration (where all resources are given to the most energy e cient devices) and the throughput-optimal allocation (where all devices evenly share the resources regardless of their power consumption). Due to the lack of models that accurately predict the power consumption behavior of wireless devices, we perform a thorough experimental study to devise a power consumption model that completes existing literature. Finally, we apply these findings to design an EF-optimal strategy in DOS networks. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El fenómeno de "fading" o desvanecimiento en comunicaciones inalámbricas se ha considerado tradicionalmente como una fuente de problemas de fiabilidad que debe ser mitigada. En contraste, las técnicas de asignación de recursos oportunistas aprovechan las oscilaciones en la calidad de enlaces para mejorar el rendimiento global. Mientras que los mecanismos centralizados requieren una entidad central con información global, recientemente se han propuesto técnicas oportunistas distribuidas (DOS, por sus siglas en inglés) para operar en redes donde dicha entidad no está disponible, o donde el coste en la comunicación para proporcionarle información puntual es prohibitivo. Con DOS, cada estación contiende por el canal con una cierta probabilidad. Si la contienda resulta exitosa, la estación mide la calidad del canal y transmite si ésta supera un cierto umbral. De lo contrario, la estación no aprovecha esa oportunidad para transmitir, permitiendo a todas las estaciones contender de nuevo. Dado que estaciones diferentes, en distintas instancias de tiempo, experimentan diferentes condiciones de canal, es probable que un enlace con mejores condiciones use el canal, mejorando el rendimiento global. En esta tesis proponemos primero ADOS, un mecanismo adaptativo que lleva al sistema a un reparto óptimo de los recursos en términos de equidad proporcional. Mostramos que este mecanismo supera el rendimiento de trabajos previos, particularmente en escenarios con estaciones no saturados (que no siempre tienen datos que transmitir). La naturaleza distribuida de DOS lo hace particularmente vulnerable a usuarios egoístas que buscan maximizar su rendimiento a expensas de aquellos que cooperan por el bien común. Así, diseñamos un mecanismo, llamado DOC, que (i) optimiza el rendimiento si todos los nodos obedecen el protocolo, y (ii) elimina cualquier posible beneficio por desviarse del mismo (y así, el incentivo a no cooperar). Finalmente, proponemos un nuevo criterio de asignación de recursos, llamado EF, que supone un compromiso entre la configuración más eficiente energéticamente (donde todos los recursos se asignan a los nodos más eficientes) y una asignación donde todos comparten de forma equitativa los recursos sin tener en cuenta su consumo. Dada la falta de modelos para predecir de forma precisa el consumo de dispositivos inalámbricos, llevamos a cabo un estudio experimental que resulta en un modelo energético que completa a la literatura existente. Finalmente, aplicamos lo anterior para diseñar una estrategia que optimiza EF en redes basadas en DOS

Improving aggregate user utilities and providing fairness in multi-rate wireless LANs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 159-166).A distributed medium access control (MAC) protocol is responsible for allocating the shared spectrum efficiently and fairly among competing devices using a wireless local area network. Unfortunately, existing MAC protocols, including 802.11's DCF, achieve neither efficiency nor fairness under many realistic conditions. In this dissertation, we show that both bit and frame-based fairness,the most widely used notions, lead to drastically reduced aggregate throughput and increased average delay in typical environments, in which competing nodes transmit at different data transmission rates. We demonstrate the advantages of time-based fairness, in which each competing node receives an equal share of the wireless channel occupancy time. Through analysis, experiments on a Linux test bed, and simulation, we demonstrate that time-based fairness can lead to significant improvements in aggregate throughput and average delay. Through a game theoretic analysis and simulation, we also show that existing MAC protocols encourage non-cooperative nodes to employ globally inefficient transmission strategies that lead to low aggregate throughput. We show that providing long-term time share guarantees among competing nodes leads rational nodes to employ efficient transmission strategies at equilibriums.(cont.) We describe two novel solutions, TES (Time-fair Efficient and Scalable MAC protocol) and TBR (Time-based Regulator) that provide time-based fairness and long-term time share guarantees among competing nodes. TBR is a backward-compatible centralized solution that runs at the AP,works in conjunction with DCF, and requires no modifications to clients nor to DCF. TBR is appropriate for existing access point based networks, but not effective when nearby non-cooperative nodes fall under different administrative domains. Our evaluation of TBR on an 802.1lb/Linux test bed shows that TBR can improve aggregate TCP throughput by as much as 105% in rate diverse environments. TES is a non-backward compatible distributed contention-based MAC protocol that is effective in any environment, including non-cooperative environments. Furthermore, the aggregate throughputs sustained with increased loads. Through extensive simulation experiments, we demonstrate that TES is significantly more efficient(as much as 140% improvement in aggregate TCP throughput) and fairer than existing MAC protocols including DCF.by Godfrey Tan.Ph.D

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

Optimal Data Scheduling of Clients Serviced using Beamforming Antennas in Mobile Scenarios

The use of beamforming antennas has received significant attention over the last decade. I consider beamforming applied to dynamic operations such as networked UAV hubs which interconnect with users on the ground. The key problem involves understanding how to optimally manage the users' data requirements while considering mobility and a dynamic radio environment serviced by one or more hubs with beamforming antenna capability. In this work I break the problem down into scheduling, tracking and ultimately execution. I develop a regularized linear programming based scheduling algorithm along with developing a very efficient scheduling with uncertainty receding horizon based relaxation and implement them along with a capacity tracking estimation algorithm. Finally I show the results of successfully implementing this system in hardware using Fidelity Comtech's Phocus Array FCI-3100X. This implementation shows that the problem overview presented in this work provides a solid basis and defines the key components needed for a reliable electronic beamforming antenna system able to successfully service dispersed users in a mobile environment. It also shows the tools developed, refined, and integrated with respect to tracking, scheduling, and practical modifications

Design and Evaluation of Flow Mapping Systems for Heterogeneous Wireless Networks

Mobile wireless networks are always challenged by growing application demand. The increasing heterogeneity of both mobile device connection capability and wireless network coverage forms a general heterogeneous wireless network (HetNet). This type of HetNet contains sub-networks of different Radio Access Technologies. How to better coordinate the mappings of flows between Access Points (AP) and User Equipment (UE) inside this type of HetNet to improve system and user-level performance is an interesting research problem. The flow mapping systems used by off-the-shelf mobile devices make policy-based decisions from local information. Several global information based flow mapping systems that use Generalized Proportional Fairness (GPF) as the optimization objectives have been proposed to improve the system-level performance. However, they have not been compared with both the local-policy based approaches and the optimal solution under the same assumptions with variations of system parameters. Therefore, it is still unclear to the community whether it is worthwhile to construct a flow mapping system for HetNets composed by LTE and WiFi networks, even under a simplified assumption of only optimizing throughput related system performance metrics. In this dissertation, we evaluate three types of flow mapping systems: Global Information based Flow Mapping Systems (GIFMS), Local Information based Flow Mapping Systems (LIFMS), and Semi-GIFMS. We evaluate these systems with metrics related to both the spectrum efficiency and flow-level fairness under the following variations of system parameters: 1) topologies of UEs; 2) coverage of APs; 3) number of UEs; 4) number of non-participating UEs; 5) on-off session dynamics; 6) UE mobility. We also discuss options to implement each type of flow mapping systems and any relevant trade-offs. From the evaluations, we find that the currently-in-use WiFi preferred local greedy flow mapping system provides far poorer spectral efficiency and generalized proportional fairness than all the other tested flow mapping systems, including the local greedy flow mapping systems that give LTE and WiFi equal opportunities (local-greedy-equal-chance) in most settings. This finding indicates that the flow mapping system in use has much room for improvement in terms of GPF and aggregate throughput. The performance of local-greedy-equal-chance is close to that of the global and AP-level information based systems under some UE topologies. However, their performance is not as consistent as the global and AP-level based systems when UEs form clusters that produce AP load imbalance. We also derive the incremental evaluations of GPF for both proportional and max-min fair scheduled APs. Based on these derivations, we propose a design for AP-level information based flow mapping system or Semi-GIFMS. It is an event-triggered flow mapping system based on minimum AP-level metrics monitoring and dissemination. From our evaluation and analysis, this flow mapping system performs equivalent to or better than GIFMS in terms of both GPF and aggregate throughput in all the tested scenarios. It also owns the advantages of lower overhead and not requiring an additional scheduling server. We think it is the best choice for the next generation HetNets where APs can be modified to monitor and broadcast the minimum information identified. Furthermore, we find that the number of UEs, number of non-participating UEs, coverage of APs, bandwidth sharing types of APs, on-off session and UE mobility dynamics do not have a major impact on the relative performance difference among various flow mapping systems

Improving Energy Efficiency and Security for Pervasive Computing Systems

Pervasive computing systems are comprised of various personal mobile devices connected by the wireless networks. Pervasive computing systems have gained soaring popularity because of the rapid proliferation of the personal mobile devices. The number of personal mobile devices increased steeply over years and will surpass world population by 2016.;However, the fast development of pervasive computing systems is facing two critical issues, energy efficiency and security assurance. Power consumption of personal mobile devices keeps increasing while the battery capacity has been hardly improved over years. at the same time, a lot of private information is stored on and transmitted from personal mobile devices, which are operating in very risky environment. as such, these devices became favorite targets of malicious attacks. Without proper solutions to address these two challenging problems, concerns will keep rising and slow down the advancement of pervasive computing systems.;We select smartphones as the representative devices in our energy study because they are popular in pervasive computing systems and their energy problem concerns users the most in comparison with other devices. We start with the analysis of the power usage pattern of internal system activities, and then identify energy bugs for improving energy efficiency. We also investigate into the external communication methods employed on smartphones, such as cellular networks and wireless LANs, to reduce energy overhead on transmissions.;As to security, we focus on implantable medical devices (IMDs) that are specialized for medical purposes. Malicious attacks on IMDs may lead to serious damages both in the cyber and physical worlds. Unlike smartphones, simply borrowing existing security solutions does not work on IMDs because of their limited resources and high requirement of accessibility. Thus, we introduce an external device to serve as the security proxy for IMDs and ensure that IMDs remain accessible to save patients\u27 lives in certain emergency situations when security credentials are not available

CROSS-LAYER RESOURCE ALLOCATION ALGORITHMS IN WIRELESS NETWORKS WITH ANTENNA ARRAYS

The application of antenna array is a promising approach to improving the capacity of a wireless network. In this dissertation, we study the application of antenna arrays at the base stations (BSs) in a wireless cellular network. We focus on the downlink transmission. This application requires the BSs be aware of the locations and channel conditions of the mobile users. Towards this end, we propose a family of MAC layer protocols that enable a base station to learn the locations and channel conditions of a number of intended users. Our simulation results demonstrate that the inter-cell interference significantly degrades the system performance of the previously proposed beamforming algorithms in terms of packet loss probability (PLP) in a multi-cell environment. To cope with inter-cell interference, we propose beamforming algorithms that achieve target PLP in the presence of random inter-cell interference. The application of antenna array on the physical layer has great impact on the protocols of higher layers. Novel MAC algorithms and protocols need to be designed to take advantage of the capacity enhancement provided by antenna array on the physical layer. In this dissertation, the issue of designing a downlink scheduling policy with base station antenna arrays is studied. We derive an optimal scheduling policy that achieves the throughput region. Then, based on the structure of the derived optimal policy, we propose two heuristic scheduling algorithms. The interference experienced by each node in an ad-hoc network exhibits stochastic nature similar to the inter-cell interference in a cellular network. We propose a power control algorithm in a distributed scheme to achieve target PLP. Furthermore, the proposed power control algorithm is shown to minimize the aggregate transmission power given the PLP constraint. In the above problems, we mainly consider the non-real-time traffic where throughput is the QoS parameter of concern. On the other hand, delay is an important QoS parameter for real time traffic. In this dissertation, we also consider the scheduling of real time packets by a BS with awareness of physical layer channel conditions of different users