Running Multiple Instances of the Distributed Coordination Function for Air-time Fairness in Multi-Rate WLANs

Cataloged from PDF version of article.Conventional multi-rate IEEE 802.11 Wireless LANs (WLANs) are associated with the so-called performance anomaly to describe the phenomenon of high bit rate nodes being dragged down by slower nodes. This anomaly is known to be an impediment to obtaining high cumulative throughputs despite the employment of effective link adaptation mechanisms. To cope with the performance anomaly, air-time fairness has been proposed as an alternative to throughput fairness, the latter being a main characteristic of the IEEE 802.11 Distributed Coordination Function (DCF). In this paper, we propose a novel distributed air-time fair MAC (Medium Access Control) without having to change the operation of the conventional DCF. In the proposed MAC, each node in the system runs multiple instances of the conventional DCF back-off algorithm where the number of DCF instances for the nodes can be chosen in a distributed manner. Both analytical and simulation-based results are provided to validate the effectiveness of the proposed air-time fair MAC. © 2013 IEEE

Cross-layer design and optimization of medium access control protocols for wlans

This thesis provides a contribution to the field of Medium Access Control (MAC) layer protocol design for wireless networks by proposing and evaluating mechanisms that enhance different aspects of the network performance. These enhancements are achieved through the exchange of information between different layers of the traditional protocol stack, a concept known as Cross-Layer (CL) design. The main thesis contributions are divided into two parts. The first part of the thesis introduces a novel MAC layer protocol named Distributed Queuing Collision Avoidance (DQCA). DQCA behaves as a reservation scheme that ensures collision-free data transmissions at the majority of the time and switches automatically to an Aloha-like random access mechanism when the traffic load is low. DQCA can be enriched by more advanced scheduling algorithms based on a CL dialogue between the MAC and other protocol layers, to provide higher throughput and Quality of Service (QoS) guarantees. The second part of the thesis explores a different challenge in MAC layer design, related to the ability of multiple antenna systems to offer point-to-multipoint communications. Some modifications to the recently approved IEEE 802.11n standard are proposed in order to handle simultaneous multiuser downlink transmissions. A number of multiuser MAC schemes that handle channel access and scheduling issues and provide mechanisms for feedback acquisition have been presented and evaluated. The obtained performance enhancements have been demonstrated with the help of both theoretical analysis and simulation obtained results

Mobile ad hoc networks for intelligent systems

Advances in wireless technology and portable computing along with demands for high user mobility have provided a major promotion toward the development of ad hoc networks. Mobile ad hoc networks feature dynamic topology, self-organization, limited bandwidth and battery power of a node. They do not rely on specialized routers for path discovery and traffic routing. Research on ad hoc networks has been extensively investigated in the past few years and related work has focused on many of the layers of the communications architecture. This research intends to investigate applications of MANET for intelligent systems, including intelligent transportation system (ITS), sensor network and mobile intelligent robot network, and propose some approaches to topology management, link layer multiple access and routing algorithms. Their performance is evaluated by theoretical analysis and off-the-shelf simulation tools. Most current research on ad hoc networks assumes the availability of IEEE 802.11. However, the RTS/CTS protocol of 802.11 still leads to packet collision which in turn decreases the network throughput and lifetime. For sensor networks, sensors are mostly battery operated. Hence, resolving packet collision may improve network lifetime by saving valuable power. Using space and network diversity combination, this work proposes a new packet separation approach to packet collision caused by masked nodes. Inter-vehicle communication is a key component of ITS and it is also called vehicular ad hoc network. VANET has many features different from regular MANETs in terms of mobility, network size and connectivity. Given rapid topology changes and network partitioning, this work studies how to organize the numerous vehicular nodes and establish message paths between any pair of vehicular nodes if they are not apart too far away. In urban areas, the inter-vehicle communication has different requirements and constraints than highway environments. The proposed position-based routing strategy for VANETs utilizes the traffic pattern in city environments. Packets are forwarded based on traffic lights timing sequence and the moving direction of relaying vehicles. A multicast protocol is also introduced to visualize the real time road traffic with customized scale. Only vehicles related to a source node\u27s planned trajectory will reply the query packet. The visualized real time traffic information therefore helps the driver make better decision in route planning when traffic congestion happens. Nowadays robots become more and more powerful and intelligent. They can take part in operations in a cooperative manner which makes distributed control necessary. Ad hoc robot communication network is still fresh field for researchers working on networking technology. This work investigates some key issues in robot ad hoc network and evaluate the challenges while establishing robot ad hoc networks

Enabling Dynamic Spectrum Allocation in Cognitive Radio Networks

The last decade has witnessed the proliferation of innovative wireless technologies, such asWi-Fi, wireless mesh networks, operating in unlicensed bands. Due to the increasing popularity and the wide deployments of these technologies, the unlicensed bands become overcrowded. The wireless devices operating in these bands interfere with each other and hurt the overall performance. To support fast growths of wireless technologies, more spectrums are required. However, as most "prime" spectrum has been allocated, there is no spectrum available to expand these innovative wireless services. Despite the general perception that there is an actual spectral shortage, the recent measurement results released by the FCC (Federal Communications Commission) show that on average only 5% of the spectrum from 30MHz to 30 GHz is used in the US. This indicates that the inefficient spectrum usage is the root cause of the spectral shortage problem. Therefore, this dissertation is focused on improving spectrum utilization and efficiency in tackling the spectral shortage problem to support ever-growing user demands for wireless applications. This dissertation proposes a novel concept of dynamic spectrum allocation, which adaptively divides available spectrum into non-overlapping frequency segments of different bandwidth considering the number of potentially interfering transmissions and the distribution of traffic load in a local environment. The goals are (1) to maximize spectrum efficiency by increasing parallel transmissions and reducing co-channel interferences, and (2) to improve fairness across a network by balancing spectrum assignments. Since existing radio systems offer very limited flexibility, cognitive radios, which can sense and adapt to radio environments, are exploited to support such a dynamic concept. We explore two directions to improve spectrum efficiency by adopting the proposed dynamic allocation concept. First, we build a cognitive wireless system called KNOWS to exploit unoccupied frequencies in the licensed TV bands. KNOWS is a hardware-software platform that includes new radio hardware, a spectrum-aware MAC (medium access control) protocol and an algorithm for implementing the dynamic spectrum allocation. We show that KNOWS accomplishes a remarkable 200% throughput gain over systems based on fixed allocations in common cases. Second, we enhance Wireless LANs (WLANs), the most popular network setting in unlicensed bands, by proposing a dynamic channelization structure and a scalable MAC design. Through analysis and extensive simulations, we show that the new channelization structure and the scalable MAC design improve not only network capacity but per-client fairness by allocating channels of variable width for access points in a WLAN. As a conclusion, we believe that our proposed concept of dynamic spectrum allocation lays down a solid foundation for building systems to efficiently use the invaluable spectrum resource

Traffic Steering in Radio Level Integration of LTE and Wi-Fi Networks

A smartphone generates approximately 1, 614 MB of data per month which is 48 times of the data generated by a typical basic-feature cell phone. Cisco forecasts that the mobile data traffic growth will remain to increase and reach 49 Exabytes per month by 2021. However, the telecommunication service providers/operators face many challenges in order to improve cellular network capacity to match these ever-increasing data demands due to low, almost flat Average Revenue Per User (ARPU) and low Return on Investment (RoI). Spectrum resource crunch and licensing requirement for operation in cellular bands further complicate the procedure to support and manage the network. In order to deal with the aforementioned challenges, one of the most vital solutions is to leverage the integration benefits of cellular networks with unlicensed operation of Wi-Fi networks. A closer level of cellular and Wi-Fi coupling/interworking improves Quality of Service (QoS) by unified connection management to user devices (UEs). It also offloads a significant portion of user traffic from cellular Base Station (BS) to Wi-Fi Access Point (AP). In this thesis, we have considered the cellular network to be Long Term Evolution (LTE) popularly known as 4G-LTE for interworking with Wi-Fi. Third Generation Partnership Project (3GPP) defined various LTE and Wi-Fi interworking architectures from Rel-8 to Rel-11. Because of the limitations in these legacy LTE Wi-Fi interworking solutions, 3GPP proposed Radio Level Integration (RLI) architectures to enhance flow mobility and to react fast to channel dynamics. RLI node encompasses link level connection between Small cell deployments, (ii) Meeting Guaranteed Bit Rate (GBR) requirements of the users including those experiencing poor Signal to Interference plus Noise Ratio (SINR), and (iii) Dynamic steering of the flows across LTE and Wi-Fi links to maximize the system throughput. The second important problem addressed is the uplink traffic steering. To enable efficient uplink traffic steering in LWIP system, in this thesis, Network Coordination Function (NCF) is proposed. NCF is realized at the LWIP node by implementing various uplink traffic steering algorithms. NCF encompasses four different uplink traffic steering algorithms for efficient utilization of Wi-Fi resources in LWIP system. NCF facilitates the network to take intelligent decisions rather than individual UEs deciding to steer the uplink traffic onto LTE link or Wi-Fi link. The NCF algorithms work by leveraging the availability of LTE as the anchor to improvise the channel utilization of Wi-Fi. The third most important problem is to enable packet level steering in LWIP. When data rates of LTE and Wi-Fi links are incomparable, steering packets across the links create problems for TCP traffic. When the packets are received Out-of-Order (OOO) at the TCP receiver due to variation in delay experienced on each link, it leads to the generation of DUPlicate ACKnowledgements (DUP-ACK). These unnecessary DUP-ACKs adversely affect the TCP congestion window growth and thereby lead to poor TCP performance. This thesis addresses this problem by proposing a virtual congestion control mechanism (VIrtual congeStion control wIth Boost acknowLedgEment -VISIBLE). The proposed mechanism not only improves the throughput of a flow by reducing the number of unnecessary DUPACKs delivered to the TCP sender but also sends Boost ACKs in order to rapidly grow the congestion window to reap in aggregation benefits of heterogeneous links. The fourth problem considered is the placement of LWIP nodes. In this thesis, we have addressed problems pertaining to the dense deployment of LWIP nodes. LWIP deployment can be realized in colocated and non-colocated fashion. The placement of LWIP nodes is done with the following objectives: (i) Minimizing the number of LWIP nodes deployed without any coverage holes, (ii) Maximizing SINR in every sub-region of a building, and (iii) Minimizing the energy spent by UEs and LWIP nodes. Finally, prototypes of RLI architectures are presented (i.e., LWIP and LWA testbeds). The prototypes are developed using open source LTE platform OpenAirInterface (OAI) and commercial-off-the-shelf hardware components. The developed LWIP prototype is made to work with commercial UE (Nexus 5). The LWA prototype requires modification at the UE protocol stack, hence it is realized using OAI-UE. The developed prototypes are coupled with the legacy multipath protocol such as MPTCP to investigate the coupling benefits

Comunicações cooperativas em redes IEEE 802.11 multi-débito

Doutoramento em TelecomunicaçõesEsta tese apresenta um estudo sobre alguns dos protocolos de cooperação MAC para redes sem fios utilizando o sistema IEEE 802.11 multi-débito. É proposto um novo modelo de arquitetura para a categorização e análise da cooperação em redes sem fios, tendo este modelo sido aplicado a protocolos cooperativos existentes para camada MAC. É investigado como as características do meio físico, assim como os requisitos de níveis superiores podem ser aplicados ao processo de cooperação, com vista a melhorar as características de funcionamento da rede de comunicações. Para este propósito são exploradas as métricas mais relevantes para o processo de cooperação. São igualmente estudados os limites impostos pelos protocolos da camada MAC e as limitações práticas impostas por protocolos da família de normas que compõem o IEEE 802.11. Neste trabalho foi criada uma métrica multicamada, que permite considerar os requisitos aplicacionais de performance e o tipo de tráfego, assim como a mobilidade dos dispositivos, no funcionamento dos mecanismos de cooperação. Como forma de validação, e para corretamente avaliar o impacto da métrica, um novo protocolo de cooperação foi desenvolvido e implementado. O seu funcionamento é descrito de forma analítica assim como validado através de a um ambiente de simulação. Os resultados obtidos mostram que a utilização de uma métrica multicamada é uma técnica robusta, fornecendo melhorias consistentes no contexto de redes IEEE 802.11. São igualmente demonstradas várias outras características de funcionamento com impacto para as comunicações. Estes dados fornecem uma visão real e encorajadora para a realização de mais pesquisas para a melhoria da performance dos protocolos cooperativos, assim como a sua utilização num variado número de aplicações futuras. No final do documento são apresentados alguns desafios para a continuação da investigação deste tópico.This thesis presents a study on cooperative MAC protocols in Multi-rate IEEE 802.11 wireless networks. We proposed a novel architectural framework for cooperation algorithms in wireless network. This behavior model was considered for existing cooperative MAC protocols. A classification of these protocols was presented based on their cooperation objectives. We investigate how physical layer specifications and higher layer requirements can be applied in cooperation MAC protocols to enhance the overall network performance. For this purpose, we exploit the appropriate metrics which are consistent to the cooperation objectives. Performance bounds provided by MAC protocols and practical limitations posed by IEEE 802.11 standards have been also studied. A cross layer metric was achieved in cooperative MAC protocols to adapt cooperation performance to traffic service requirements and mobility scenario. In order to realize the impact of this metric, a new cooperative MAC protocol is designed and implemented. Analytical and simulation of this protocol was performed in different scenarios and environments. The obtained results have shown a robust technique in providing consistent cross layer optimization in context of IEEE 802.11 networks. A number of findings was experienced which are illustrated at the end. These observations would enhance and encourage potential research in the area and optimize the performance of cooperative protocols for a number of interesting applications in future. A summary of future research challenges is presented at the end