This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach is called Dynamic Age-Dependent Backoff (DADB) which is derived from the ADB scheme and aims to improve the ADB scheme when the traffic load is high. Improvement of our scheme are provisioned by adjusting the size of the persistent factor of high traffic categories taking into account both age time of frame and network conditions. We evaluate the performance of DADB through simulations and compare it with the ADB scheme proposed in the 802.11e. Results show that our scheme DADB is similar to ADB scheme which can improve the delay and jitter in wireless network. Especially at high traffic load conditions, DADB outperforms the basic ADB: our scheme improve the throughput of high priority traffic category and decrease collision rate when traffic load is heavy.

We propose a novel medium access control scheme which borrows ideas from the dual busy tone approach and the IEEE 802.11e standard for improving quality of services in wireless networks. In the field of medium access control in Wireless LAN, there are two notorious problems, which have been studied for a long time. They are the hidden terminal problem and the exposed terminal problem. To avoid the collisions caused by hidden terminals, the RTS/CTS approach is widely adopted. However, RTS and CTS frames themselves are still subject to collisions. The Transmit Busy Tone and the Receive Busy Tone were proposed to further mitigate the hidden terminal problem and the exposed terminal problem. The transmit busy tone provides protection for the RTS packets and thus, increase the probability of successful RTS reception at the intended receiver. The receive busy tone acknowledges the RTS packet and provide continuous protection for the subsequent data packets. We use computer simulations to justify the usage of our proposal. We show that the proposed scheme outperforms the IEEE 802.11e standard.

Thèse de doctorat : Physiopathologie : Paris 12 : 2007. / Titre provenant de l'écran-titre. Bibliogr. : 189 réf.

In this thesis we have focused in the wireless environment and how to run voice application over it. Conducive environment that makes it possible for the voice services to run in wireless is necessary. As we know this well that wireless is a contemporary technology due to it low cost and its effectiveness, and one major advantage of it is the mobility that is one fell free to move anywhere but have the access to the resource. So this makes wireless networks of great value, we in this thesis have focused on wireless LAN’s. In second part of the thesis we have shed some light on the VoIP showing how it works in the wireless environment. Analysis phase is relatively more important phase then the previous section which shows issues or hindrances in carrying voice over wireless environment. This analysis shows that these issues still prevails and should be addresses and the corresponding results are also discussed and by looking at those results we have derived a summery out of it. Next chapter we firstly tried to explain why we have chosen specific protocols and then showing some graphical representation measurements that are to address the problem based on the work done. We tried to evaluate EDCF and DCF as these play important role in handling real time applications like voice. After that we proposed a scheme through which these effects can be minimized and to enhance the method is necessary to avoid the issues still in effect. / Thesis is Part for Master program in Electrical Engineering with Emphasis on Telecommunication(2007-2009).We have had a very nice time doing this thesis as there was alot of learning. Our examinator was allways there to help us, we are thankfull to Richard for his endless support.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / IEEE 802.11e is an amendment of the medium-access control (MAC) layer of the standard for wireless local area networking IEEE 802.11. The goal of 802.11e is to provide 802.11 networks with Quality of Service (QoS). 802.11 has three physical layers (PHY) of practical importance: 802.11b, 802.11a, and 802.11g. 802.11a and 802.11g provide data rates between 6 and 54 Mbps, and 802.11b provides data rates of 5.5 Mbps and 11 Mbps. However these data rates are not the actual throughput. The actual throughput that a user will experience will be lower. The throughput depends on both the PHY and MAC layers. It is important to estimate what exactly is the throughput when the physical layer is 802.11a, 802.11b, or 802.11g, and the MAC layer is 802.11e. In other words, how does providing QoS change the throughput for each of the three physical layers? In this paper we provide answers to this problem. Analytic formulae are derived. The maximum achievable throughput and minimum delay involved in data transfers are determined. The obtained results have further significance for the design of high-throughput wireless protocols.

IEEE 802.11 has become the standard of medium access control (MAC) in wireless ad hoc networks. However, due to the embedded binary exponential backoff algorithm, the packet delay and jitter incurred by access collisions and frame retransmissions may grow drastically. The lack of time-constraint considerations in IEEE 802.11 makes it very difficult to provide QoS (Quality of Service) guarantees for multimedia services. Therefore, a lot of research works focusing on priority-based MAC protocols for wireless ad hoc networks have been proposed. Yet, no standards come out until now. This thesis presents a priority-based MAC scheme in wireless ad hoc networks, which not only provides differentiated services, but also improves the QoS limitations of the previously proposed schemes. The main idea of the proposed JMAC (jamming-based MAC) mechanism is that traffic flows with different priorities can be differentiated by transmitting jamming noises of different lengths to interfere with one another. The one with the longest length of jamming noise can start data transmission. Besides, in our design, priority can be dynamically adjusted to allow each MH to change its contention priority and the length of jamming noise in accordance with network congestions. To implement the proposed JMAC, three modules are developed in this thesis: Collision Avoidance, Starvation Prevention, and Deadlock Prevention. For the purpose of evaluation, we perform simulations on the well-known network simulator, NS-2. Our scheme is compared with the EDCF (enhanced distributed coordination function) of IEEE 802.11e¡]draft¡^and one of the existing works. The simulation results demonstrate the effectiveness and superiority of our scheme.

<p>IEEE 802.11 [1]is the standard that has emerged as a prevailing technology for the wireless local area networks. It can be considered the wireless version of Ethernet, which supports best-effortservice. IEEE is developing a new standard called 802.11e to be able to provide quality of service (QoS) in WLANs. Two possible methods have been proposed in [3]in order to improve the performance of service differentiation in the MAC layer. They are called PCWA (Practical Contention Window Adjustment) and AIPM (Adaptive Initiative Polling Machine). In this thesis, I will analyse both methods and propose new ideas to improve their performance, simulating the ideas concerning PCWA. Simulations show better general performance, especially for highest priorities flows, although the behaviour of the lowest priority one is reduced.</p>

<p>Nowadays Wireless LAN is playing a more and more important role in network systems. After 1999, in which the IEEE organization published its Wireless Local Network standard 802.11[1], many people saw the advantages of the standard but also the lack of support for multimedia streaming. A lot of research work has been done on the proposed IEEE 802.11e standard draft during the past 4 years. It is supposed to be able to fully support Quality of Service. The final version will be published early in 2004. In my thesis, I propose two possible methods to improve the performance of service differentiation in the MAC layer. The first one is calledPCWA (Practical Contention Window Adjustment). It is a method with which the station finds a best size of its contention window when running the EDCF (Enhanced Distributed Coordination Function) access method. It helps to improve the total system throughput, the jitter and the delay of traffics with different priorities. The second method is called AIPM (Adaptive Initiative Polling Machine). It uses the polling mechanism for differential service, intelligently arranging the polling time to reduce the delay as much as possible, achieving large improvement in performance. This method significantly increases the total system throughput, while the delay and jitter of the traffics are very much small in comparison to EDCF.</p>

IEEE 802.11 has become the standard in wireless LAN. Originally, 802.11 is designed for the best-effort services only. To support the increasing demand of delay-sensitive applications, IEEE 802.11 Task Group E is developing a QoS-aware MAC protocol, EDCF, for differentiated services. However, when the network becomes congested, there exists unexpected packet delay due to collisions and retransmissions. This thesis proposes a dynamic contention control (DCC) scheme to reduce packet delay and increase the percentage of packets arriving in time. DCC estimates per-hop delay, denoted as Mrtt, and end-to-end delay, denoted as Sigma_t, based on either the received MAC-layer ACK or the control packets of a reactive routing protocol. Then, Mrtt and Sigma_t are used to dynamically adjust the associated contention window for each priority. Besides, when a frame is retransmitted, the backoff time is determined according to the remaining end-to-end delay instead of a uniformly distributed random number. For the propose of evaluation, we perform simulations on the well-known network simulator, NS-2. DCC is compared with the EDCF and one previously proposed scheme, AEDCF. The simulation results demonstrate the effectiveness and superiority of DCC.

IEEE 802.11 [1]is the standard that has emerged as a prevailing technology for the wireless local area networks. It can be considered the wireless version of Ethernet, which supports best-effortservice. IEEE is developing a new standard called 802.11e to be able to provide quality of service (QoS) in WLANs. Two possible methods have been proposed in [3]in order to improve the performance of service differentiation in the MAC layer. They are called PCWA (Practical Contention Window Adjustment) and AIPM (Adaptive Initiative Polling Machine). In this thesis, I will analyse both methods and propose new ideas to improve their performance, simulating the ideas concerning PCWA. Simulations show better general performance, especially for highest priorities flows, although the behaviour of the lowest priority one is reduced.