307 research outputs found
A Novel Voice Priority Queue (VPQ) Schedule and Algorithm for VoIP over WLAN Network
The VoIP deployment on Wireless Local Area Networks (WLANs), which is based on IEEE 802.11 standards, is increasing. Currently, many schedulers have been introduced such as Weighted Fair Queueing (WFQ), Strict Priority (SP) General processor sharing (GPS), Deficit Round Robin (DRR), and Contention-Aware Temporally fair Scheduling (CATS). Unfortunately, the current scheduling techniques have some drawbacks on real-time applications and therefore will not be able to handle the VoIP packets in a proper way. The objective of this research is to propose a new scheduler system model for the VoIP application named final stage of Voice Priority Queue (VPQ) scheduler. The scheduler system model is to ensure efficiency by producing a higher throughput and fairness for VoIP packets. In this paper, only the final Stage of the VPQ packet scheduler and its algorithm are presented. Simulation topologies for VoIP traffic were implemented and analyzed using the Network Simulator (NS-2). The results show that this method can achieve a better and more accurate VoIP quality throughput and fairness index over WLANs
Providing Enhanced Framework to support QoS in Open Wireless Architecture
This paper presents a novel approach to support
Quality of Service for Open Wireless Architectures (OWA),
building a suitable framework over the top of the heterogeneous
wireless MACs. It lets to enhance the existing QoS
support provided by standard MAC protocols and it uses
the contract model to guarantee QoS, taking into account
the applications requests. It negotiates dynamically Application
Level Contracts which will be translated seamlessly in
Resource Level Contracts for the underlying network services.
It receives the feedback by underlying network services to
adjust the scheduling algorithms and policies to provide
hard and soft guarantees. The framework comprises QoS
Manager, Admission Control, Enhanced Scheduler, Predictor
and Feedback System. The QoS manager component is able
to dynamically manage available resources under different
load conditions. A IEEE 802.11e Wireless LAN is simulated
to show the benefits of this approach
Coding in 802.11 WLANs
Forward error correction (FEC) coding is widely used in communication systems to correct transmis-
sion errors. In IEEE 802.11a/g transmitters, convolutional codes are used for FEC at the physical
(PHY) layer. As is typical in wireless systems, only a limited choice of pre-speci¯ed coding rates is
supported. These are implemented in hardware and thus di±cult to change, and the coding rates are
selected with point to point operation in mind.
This thesis is concerned with using FEC coding in 802.11 WLANs in more interesting ways that are
better aligned with application requirements. For example, coding to support multicast tra±c rather
than simple point to point tra±c; coding that is cognisant of the multiuser nature of the wireless
channel; and coding which takes account of delay requirements as well as losses. We consider layering
additional coding on top of the existing 802.11 PHY layer coding, and investigate the tradeo® between
higher layer coding and PHY layer modulation and FEC coding as well as MAC layer scheduling.
Firstly we consider the joint multicast performance of higher-layer fountain coding concatenated
with 802.11a/g OFDM PHY modulation/coding. A study on the optimal choice of PHY rates with and
without fountain coding is carried out for standard 802.11 WLANs. We ¯nd that, in contrast to studies
in cellular networks, in 802.11a/g WLANs the PHY rate that optimizes uncoded multicast performance
is also close to optimal for fountain-coded multicast tra±c. This indicates that in 802.11a/g WLANs
cross-layer rate control for higher-layer fountain coding concatenated with physical layer modulation
and FEC would bring few bene¯ts.
Secondly, using experimental measurements taken in an outdoor environment, we model the chan-
nel provided by outdoor 802.11 links as a hybrid binary symmetric/packet erasure channel. This
hybrid channel o®ers capacity increases of more than 100% compared to a conventional packet erasure
channel (PEC) over a wide range of RSSIs. Based upon the established channel model, we further
consider the potential performance gains of adopting a binary symmetric channel (BSC) paradigm for
multi-destination aggregations in 802.11 WLANs. We consider two BSC-based higher-layer coding
approaches, i.e. superposition coding and a simpler time-sharing coding, for multi-destination aggre-
gated packets. The performance results for both unicast and multicast tra±c, taking account of MAC
layer overheads, demonstrate that increases in network throughput of more than 100% are possible
over a wide range of channel conditions, and that the simpler time-sharing approach yields most of
these gains and have minor loss of performance.
Finally, we consider the proportional fair allocation of high-layer coding rates and airtimes in 802.11
WLANs, taking link losses and delay constraints into account. We ¯nd that a layered approach of
separating MAC scheduling and higher-layer coding rate selection is optimal. The proportional fair
coding rate and airtime allocation (i) assigns equal total airtime (i.e. airtime including both successful
and failed transmissions) to every station in a WLAN, (ii) the station airtimes sum to unity (ensuring
operation at the rate region boundary), and (iii) the optimal coding rate is selected to maximise
goodput (treating packets decoded after the delay deadline as losses)
A novel Voice Priority Queue (VPQ) scheduler and algorithm for VOIP over WLAN network
The VoIP deployment on Wireless Local Area Networks (WLANs), which is based on IEEE 802.11 standards, is increasing.Currently, many schedulers have been introduced such as Weighted Fair Queueing (WFQ), Strict Priority (SP) General processor sharing (GPS), Deficit Round Robin (DRR), and Contention-Aware Temporally fair Scheduling(CATS).Unfortunately, the current scheduling
techniques have some drawbacks on real-time applications and therefore will not be able to handle the VoIP packets in a proper way.The objective of this research is to propose
a new scheduler system model for the VoIP application named final stage of Voice Priority Queue (VPQ) scheduler.The scheduler system model is to ensure efficiency by producing
a higher throughput and fairness for VoIP packets.In this paper, only the final Stage of the VPQ packet scheduler and its algorithm are presented.Simulation topologies for VoIP traffic were implemented and analyzed using the Network Simulator (NS-2).The results show that this method can achieve a better and more accurate VoIP quality throughput and fairness index over WLANs
Internet Access and QoS in Ad Hoc Networks
It is likely that the increased popularity of wireless local area networks (WLANs) together with the continuous technological advances in wireless communication, also increase the interest for ad hoc networks. An ad hoc network is a wireless, autonomous, infrastructure-less network composed of stations that communicate with each other directly in a peer-to-peer fashion. When discussing mobile ad hoc networks (MANETs), we often refer to an ad hoc network where the stations cooperate in forwarding packets on behalf of each other to allow communication beyond their transmission range over multi-hop paths. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed quality of service (QoS) guarantees and multi-hop Internet access. This thesis presents conceivable solutions to both of these problems. The first two papers focus on the network layer and consider the provisioning of Internet access to ad hoc networks whereas the last two papers focus on the data link layer and investigate the provisioning of QoS to ad hoc networks. The first paper studies the interconnection between a MANET and the Internet. In addition, it evaluates three approaches for gateway discovery, which can be initiated by the gateway (proactive method), by the mobile station (reactive method) or by mixing these two approaches (hybrid method). The second paper also studies Internet access for MANETs, but with focus on micro mobility, i.e. mobile stations moving from one gateway to another. In particular, it evaluates a solution that allows mobile stations to access the Internet and roam from gateway to gateway. The third paper, gives an overview of the medium access mechanisms in IEEE 802.11 and their QoS limitations. Moreover, it proposes an enhancement to the contention-free medium access mechanism of IEEE 802.11e to provide QoS guarantees in WLANs operating in ad hoc network configuration. The fourth paper continues the work from the third paper by enhancing the scheme and dealing with the problems that occur due to hidden stations. Furthermore, it discusses how to deal with the problems that occur when moving from single-hop ad hoc networks (i.e. WLANs in ad hoc network configuration) to multi-hop ad hoc networks
The VPQ scheduler in access point for VoIP over WLAN
The Voice over Internet Protocol (VoIP) application has observed the fastest growth in the world of telecommunication.VoIP is seen as a short-term and long-trem transmission for voice and audio traffic. Meanwhile, VoIP is moving on Wireless Local Area Networks (WLANs) based on IEEE 802.11 standards.Currently, there are many packet scheduling algorithms for real-time transmission over network.Unfortunately, the current scheduling will not be able to handle the VoIP packets with the proper manner and they have some drawbacks over real-time applications.The objective of this research is to propose a new Voice Priority Queue (VPQ) packet scheduling and algorithm to ensure more throughput, fairness and efficient packet scheduling for VoIP performance of queues and traffics.A new scheduler flexible which is capable of satisfying the VoIP traffic flows.Experimental topologies on NS-2 network simulator were analyzed for voice traffic. Preliminary results show that this can achieve maximum and more accurate VoIP quality throughput and fairness index in access point for VoIP over WLANs.We verified and validated VPQ an extensive experimental simulation study under various traffic flows over WLANs
A quality of service architecture for WLAN-wired networks to enhance multimedia support
Includes abstract.Includes bibliographical references (leaves 77-84).The use of WLAN for the provision of IP multimedia services faces a number of challenges which include quality of service (QoS). Because WLAN users access multimedia services usually over a wired backbone, attention must be paid to QoS over the integrated WLAN-wired network. This research focuses on the provision of QoS to WLAN users accessing multimedia services over a wired backbone. In this thesis, the IEEE 802.11-2007 enhanced data channel access (EDCA) mechanism is used to provide prioritized QoS on the WLAN media access control (MAC) layer, while weighted round robin (WRR) queue scheduling is used to provide prioritized QoS at the IP layer. The inter-working of the EDCA scheme in the WLAN and the WRR scheduling scheme in the wired network provides end-to-end QoS on a WLAN-wired IP network. A mapping module is introduced to enable the inter-working of the EDCA and WRR mechanisms
An improved medium access control protocol for real-time applications in WLANs and its firmware development
The IEEE 802.11 Wireless Local Area Network (WLAN), commonly known as Wi-Fi, has emerged as a popular internet access technology and researchers are continuously working on improvement of the quality of service (QoS) in WLAN by proposing new and efficient schemes. Voice and video over Internet Protocol (VVoIP) applications are becoming very popular in Wi-Fi enabled portable/handheld devices because of recent technological advancements and lower service costs. Different from normal voice and video streaming, these applications demand symmetric throughput for the upstream and downstream. Existing Wi-Fi standards are optimised for generic internet applications and fail to provide symmetric throughput due to traffic bottleneck at access points. Performance analysis and benchmarking is an integral part of WLAN research, and in the majority of the cases, this is done through computer simulation using popular network simulators such as Network Simulator ff 2 (NS-2) or OPNET. While computer simulation is an excellent approach for saving time and money, results generated from computer simulations do not always match practical observations. This is why, for proper assessment of the merits of a proposed system in WLAN, a trial on a practical hardware platform is highly recommended and is often a requirement. In this thesis work, with a view to address the abovementioned challenges for facilitating VoIP and VVoIP services over Wi-Fi, two key contributions are made: i) formulating a suitable medium access control (MAC) protocol to address symmetric traffic scenario and ii) firmware development of this newly devised MAC protocol for real WLAN hardware. The proposed solution shows signifocant improvements over existing standards by supporting higher number of stations with strict QoS criteria. The proposed hardware platform is available off-the-shelf in the market and is a cost effective way of generating and evaluating performance results on a hardware system
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