Recent studies on operational wireless LANs (WLANs) have shown that user load is often unevenly distributed among wireless access points (APs). This unbalanced load results in unfair bandwidth allocation among users. We observe that the unbalanced load and unfair bandwidth allocation can be greatly alleviated by intelligently associating users to APs, termed association control, rather than having users greedily associate APs of best received signal strength.In this study, we present an efficient algorithmic solution to determine the user-AP associations that ensure max-min fair bandwidth allocation. We provide a rigorous formulation of the association control problem that considers bandwidth constraints of both the wireless and backhaul links. Our formulation indicates the strong correlation between fairness and load balancing, which enables us to use load balancing techniques for obtaining near optimal max-min fair bandwidth allocation. Since this problem is NP-hard, we present algorithms that achieve a constant-factor approximate max-min fair bandwidth allocation. First, we calculate a fractional load balancing solution, where users can be associated with multiple APs simultaneously. This solution guarantees the fairest bandwidth allocation in terms of max-min fairness. Then, by utilizing a rounding method we obtain an efficient integral association. In particular, we provide a 2-approximation algorithm for unweighted greedy users and a 3-approximation algorithm for weighted and bounded-demand users. In addition to bandwidth fairness, we also consider time fairness and we show it can be solved optimally. We further extend our schemes for the on-line case where users may join and leave. Our simulations demonstrate that the proposed algorithms achieve close to optimal load balancing and max-min fairness and they outperform commonly used heuristic approaches.

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Fairness and load balancing in wireless LANs using association control

This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach, called adaptive enhanced distributed coordination function (AEDCF), is derived from the new EDCF introduced in the upcoming IEEE 802.11e standard. Our scheme aims to share the transmission channel efficiently. Relative priorities are provisioned by adjusting the size of the contention window (CW) of each traffic class taking into account both applications requirements and network conditions. We evaluate through simulations the performance of AEDCF and compare it with the EDCF scheme proposed in the 802.11e. Results show that AEDCF outperforms the basic EDCF, especially at high traffic load conditions. Indeed, our scheme increases the medium utilization ratio and reduces for more than 50% the collision rate. While achieving delay differentiation, the overall goodput obtained is up to 25% higher than EDCF. Moreover, the complexity of AEDCF remains similar to the EDCF scheme, enabling the design of cheap implementations.

/pdf/adaptive-edcf-enhanced-service-differentiation-for-ieee-802-4o0ijgslp2.pdf

Adaptive EDCF: enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks

One key usage of VANET is to support vehicle safety applications. This use case is characterized by the prominence of broadcasts in scaled settings. In this context, we try to answer the following questions: i) what is the probability of reception of a broadcast message by another car depending on its distance to the sender, ii) how to give priority access and an improved reception rate for important warnings, e.g., sent out in an emergency situation, and iii) how are the above two results affected by signal strength fluctuations caused by radio channel fading? We quantify via simulation the probability of reception for the two-ray-ground propagation model as well as for the Nakagami distribution in saturated environments. By making use of some IEEE 802.11e EDCA mechanisms for priority access, we do not only quantify how channel access times can be reduced but also demonstrate how improved reception rates can be achieved. Our results show that the mechanisms for priority access are successful under the two-way-ground model. However, with a non-deterministic radio propagation model like Nakagami's distribution the benefit is still obvious but the general level of probability of reception is much smaller compared to two-ray-ground model. The results indicate that -- particularly for safety-critical and sensor network type of applications -- the proper design of repetition or multi-hop retransmission strategies represents an important aspect of future work for robustness and network stability of vehicular ad hoc networks.

/pdf/broadcast-reception-rates-and-effects-of-priority-access-in-48wnv4dy84.pdf

Broadcast reception rates and effects of priority access in 802.11-based vehicular ad-hoc networks

*Summary Quality of service (QoS) is a key problem of today’s IP networks. Many frameworks (IntServ, DiffServ, MPLS, etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time-varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. Although IEEE 802.11 wireless LAN (WLAN) is the most widely used WLAN standard today, it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This paper summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail.

/pdf/a-survey-of-qos-enhancements-for-ieee-802-11-wireless-lan-5d2t9i0lu3.pdf

A survey of QoS enhancements for IEEE 802.11 wireless LAN

Survey A survey of routing protocols for smart grid communications

Quality of Service (QoS) is a key problem of today's IP networks. Many frameworks (IntServ, DiffServ, MPLS, Traffic engineering, etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time-varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. IEEE 802.11 wireless LAN (WLAN) is the most widely used WLAN standard today, but it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This report summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail.

https://hal.inria.fr/inria-00071973/document

QoS Issues and Enhancements for IEEE 802.11 Wireless LAN

Quality-of-service (QoS) is a key problem of today's IP networks. Many frameworks (IntServ, DiffServ, MPLS etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time-varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. Although IEEE 802.11 wireless LAN (WLAN) is the most widely used IEEE 802.11 wireless LAN (WLAN) standard today, it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This paper summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail. Copyright © 2004 John Wiley & Sons, Ltd.

A survey of QoS enhancements for IEEE 802.11 wireless LAN: Research Articles

Nowadays, the cross-layer design approach is an important concept in mobile ad-hoc networks which is adopted to solve several open issues. It aims to overcome MANET performance problems by allowing protocols belonging to different layers to cooperate and share network status information while still maintaining separated layers. Indeed, the mechanisms on how to access the radio channel are extremely important in order to guarantee QoS and improve application performance. In this work, we present a cross layer routing protocol called CLAE which is based on the cooperation between the on-demand AODV routing protocol and the new IEEE 802.11e MAC protocol (EDCA). This proposal aims to find the best path according to application requirements in terms of delay, bandwidth, route stability, etc. Without loss of generality, this paper focuses only on determining the path with the lowest delay. Each node periodically estimates the average transmission delay for each class of service defined by 802.11e. This information is injected into routing requests and replies crossing each node. The sender is then able to select the best path which fits its delay requirement. Furthermore, in order to overcome transient network characteristics due to new communications set up and mobility, we develop a new buffer management scheme for the audio class of service that aims to discriminate audio packets according to their tolerated end-to-end transfer delay and their current experienced delay. The simulation results demonstrate that our proposal improves the performance of delay-sensitive applications while maintaining a good packet delivery ratio of other traffics

Lamia Romdhani

Papers

Adaptive EDCF: enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks

A survey of QoS enhancements for IEEE 802.11 wireless LAN

QoS Issues and Enhancements for IEEE 802.11 Wireless LAN

A survey of QoS enhancements for IEEE 802.11 wireless LAN: Research Articles

A cross-layer on-demand routing protocol for delay-sensitive applications