Advanced Wireless LAN

The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN

A fair access mechanism based on TXOP in IEEE 802.11e wireless networks

IEEE 802.11e is an extension of IEEE 802.11 that provides Quality of Service (QoS) for the applications with different service requirements. This standard makes use of several parameters such as contention window; inter frame space time and transmission opportunity to create service differentiation in the network. Transmission opportunity (TXOP), that is the focus point of this paper, is the time interval, during which a station is allowed to transmit packets without any contention. As the fixed amounts of TXOPs are allocated to different stations, unfairness appears in the network. And when users with different data rates exist, IEEE 802.11e WLANs face the lack of fairness in the network. Because the higher data rate stations transfer more data than the lower rate ones. Several mechanisms have been proposed to solve this problem by generating new TXOPs adaptive to the network's traffic condition. In this paper, some proposed mechanisms are evaluated and according to their evaluated strengths and weaknesses, a new mechanism is proposed for TXOP determination in IEEE 802.11e wireless networks. Our new algorithm considers data rate, channel error rate and data packet lengths to calculate adaptive TXOPs for the stations. The simulation results show that the proposed algorithm leads to better fairness and also higher throughput and lower delays in the network.

Adaptive Segregation-Based MAC Protocol for Real-Time Multimedia Traffic in WLANs

Wireless local area networks (WLANs) have become very popular both in private and public sectors. Despite the fast expansion of WLANs in various environments, quality of service (QoS) issues for multimedia applications in WLANs are not yet resolved. Multimedia applications contain traffic that are sensitive to delay and jitter and therefore a best-effort protocol such as the legacy IEEE 802.11 is not suitable. The 802.11e protocol provides prioritization and classification of traffic to offer better QoS for real-time services. However, it leaves the design and implementation of many important optimization features to vendors. In this paper we introduce a mechanism to improve the delay and jitter of real-time traffic in WLAN nodes supporting multimedia applications. In our proposed mechanism, we segregate voice and video traffic from the best-effort traffic. We create a scheduler that schedules the access of real-time traffic and non real-time traffic to the medium with centralized polling and distributed contention respectively. We show that our proposed protocol performs better in terms of delay and jitter than the legacy 802.11 and 802.11e in a scenario where all wireless nodes carry multimedia traffic simultaneously

Quality Of Service Improvement With 802.11e Edca Scheme Using Enhanced Adaptive Contention Window Algorithm

Currently users of data services is growing exponentially and the content accessed by the users are browsing, social media, video streaming and VOIP. Real time and multimedia communications with Quality of Service (QoS) support are important in wireless networks of any nature due to network limited capacity. This QoS is to support the growing demand of services like VoIP, streaming and video conferencing. The most connection commonly used is wireless LAN IEEe 802.11. Wireless Local Area Networks (WLANs) have emerged as one of the prevailing technologies for the broadband wireless access. However, there is a constraint on Wi-Fi network for media sharing method that relies on the CSMA/CA. There is a mechanism requirement to improve the Quality of Service in a Wi-Fi network with a certain method that delivering good Wi-Fi service for real-time and non-real time traffic. The introduction in the IEEE 802.11e standard of a new contention access scheme called Enhanced Distributed Channel Access (EDCA) has provided a new mechanisms for QoS support compared with previous method called Distributed Coordination Function (DCF) used in the widely deployed 802.11 WLANs. EDCA scheme provide four traffic type (voice, video, best effor and background task) which is called Access Category (AC) to define the priority. Real time traffic such as VoIP requires good throughput and delay so the priority is the highest. There are three parameters in EDCA to improve Quality of Service i.e TXOP (Transmission Opportunity), AIFS (Arbitrary Inter Frame Space) and CW (Contention Windows). Based on the main reference for throughput and delay improvement, this research will adjust contention window value adaptively. Adjustment is based on number of station involved in the network and collision probability. The more number of stations or the lower contention window value will result higher collision probability. Different Access Category will have different adjustment to get optimum throughput and delay improvement. To validate the result of contention window adjustment, simulation using NS-2 is applied. Simulation is done during low traffic (non-saturated) and high traffic (saturated) network. The algorithm avoids saturation and protects the admitted traffics from being degraded, through a continuous monitoring of the available resources. The proposed algorithm leads the throughput improvement by 2.29% and delay improvement by 3.32% in average for all traffic category. VOIP traffic gets the highest improvement for all condition of traffic. Best effort traffic gets very small improvement during low traffic and considered no improvement during saturated traffic

Study of QoS Management In IEEE 802.11 and 802.11e MAC Layer Protocols

Wireless networks have become increasingly popular in recent times and it has become a pressing need to ensure that the various applications using it get the necessary Quality of service. Wireless networks being inherently different from wired networks and pose a unique set of challenges . Quality of Service(QoS) is dened as the performance oered by a network to its users in terms of providing resource assurance and service dierentiation to dierent kinds of trac ows .Due to scarcity of bandwidth and high rate of packet loss in wireless networks providing QoS to time critical applications is a challeng- ing task .In this thesis we attempt to study the QoS management strategies applied by the wireless networks at the MAC layer .The most common QoS provisioning strategy is to prioritize the dierent classes of trac and make sure that the high priority trac gets preferential access to the channel .In this thesis ,a study of the binary exponential back-o algorithm which is used by the wireless MAC protocols has been done and an improvement has been proposed in which the Contention Window(CW) is varied in a non-uniform manner for dierent access categories with an aim to improve the performance parameters. The CW denes the range[0,CW] from which a random no of slots are chosen by a station in case of a failure in transmission for backing o before attempt- ing to transmit again. To demonstrate the eect of the modied contention window variation scheme simulations have been carried out using the Qualnet Simulator designed by Scalable Network Technologies, Inc. After implementing the proposed modication a performance comparison has been carried out for parameters such as packet delivery ratio, throughput and jitter

Towards End-to-End QoS in Ad Hoc Networks

http://citi.insa-lyon.fr/wons2006/index.htmlIn this paper, we address the problem of supporting adaptive QoS resource management in mobile ad hoc networks, by proposing an efficient model for providing proportional endto- end QoS between classes. The effectiveness of our proposed solution in meeting desired QoS differentiation at a specific node and from end-to-end are assessed by simulation using a queueing network model implemented in QNAP. The experiments results show that the proposed solution provides consistent proportional differentiation for any service class and validates our claim even under bursty traffic and fading channel conditions

Control-theoretic approaches for efficient transmission on IEEE 802.11e wireless networks

With the increasing use of multimedia applications on the wireless network, the functionalities of the IEEE 802.11 WLAN was extended to allow traffic differentiation so that priority traffic gets quicker service time depending on their Quality of Service (QoS) requirements. The extended functionalities contained in the IEEE Medium Access Control (MAC) and Physical Layer (PHY) Specifications, i.e. the IEEE 802.11e specifications, are recommended values for channel access parameters along traffic lines and the channel access parameters are: the Minimum Contention Window CWmin, Maximum Contention Window CWmax, Arbitration inter-frame space number, (AIFSN) and the Transmission Opportunity (TXOP). These default Enhanced Distributed Channel Access (EDCA) contention values used by each traffic type in accessing the wireless medium are only recommended values which could be adjusted or changed based on the condition of number of associated nodes on the network. In particular, we focus on the Contention Window (CW) parameter and it has been shown that when the number of nodes on the network is small, a smaller value of CWmin should be used for channel access in order to avoid underutilization of channel time and when the number of associated nodes is large, a larger value of CWmin should be used in order to avoid large collisions and retransmissions on the network. Fortunately, allowance was made for these default values to be adjusted or changed but the challenge has been in designing an algorithm that constantly and automatically tunes the CWmin value so that the Access Point (AP) gives out the right CWmin value to be used on the WLAN and this value should be derived based on the level of activity experienced on the network or predefined QoS constraints while considering the dynamic nature of the WLAN. In this thesis, we propose the use of feedback based control and we design a controller for wireless medium access. The controller will give an output which will be the EDCA CWmin value to be used by contending stations/nodes in accessing the medium and this value will be based on current WLAN conditions. We propose the use of feedback control due to its established mathematical concepts particularly for single-input-single-output systems and multi-variable systems which are scenarios that apply to the WLAN

A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs

In this paper we expose a dynamic traffic-classification scheme to support multimedia applications such as voice and broadband video transmissions over IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link and to better serve these applications - which normally have strict bounded transmission delay or minimum link rate requirement - a service differentiation technique can be applied to the media traffic transmitted by the same mobile node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA) protocol. However, the given EDCA mode does not offer user differentiation, which can be viewed as a deficiency in multi-access wireless networks. Accordingly, we propose a new inter-node priority access scheme for IEEE 802.11e networks which is compatible with the EDCA scheme. The proposed scheme joins a dynamic user-weight to each mobile station depending on its outgoing data, and therefore deploys inter-node priority for the channel access to complement the existing EDCA inter-frame priority. This provides efficient quality of service control across multiple users within the same coverage area of an access point. We provide performance evaluations to compare the proposed access model with the basic EDCA 802.11 MAC protocol mode to elucidate the quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer Networks & Communications (IJCNC