Emna Charfi

PHY/MAC Enhancements and QoS Mechanisms for Very High Throughput WLANs: A Survey

Wireless local area networking has experienced tremendous growth in the last years with the proliferation of IEEE 802.11 devices in order to improve wireless technology. The first generation of high throughput networks known as IEEE 802.11n was developed in 2009 to reach 130 Mbps. Furthermore, to enhance the throughput, two new amendments for IEEE 802.11 are under developments which are IEEE 802.11ad and IEEE 802.11ac. The first one aims to reach 1Gbps with supporting multi-user access techniques. The second amendment aims to enable up to 7Gbp with the possibility of transmitting in the 60GHz band that provides the opportunity for much wider band channels. Another WLAN is already finalized called IEEE 802.11aa in the goal to provide a reliable multicast transport for video streaming. In this survey, we examine the different PHY and MAC enhancements introduced by all these WLAN specifications. Particularly, we focus on the characteristics of each amendment as well as the main MAC mechanisms that lead to improve the network performance. Based on the fact that all recent MAC mechanisms aim to increase QoS guarantee for real time multimedia applications, we have studied different schemes and mechanisms that provide QoS satisfaction for real time multimedia flows transport over WLANs. Namely, we investigate the scheduling mechanisms, the call admission control algorithms, and the anticipated MAC enhancement which are proposed for WLANs networks to support real time applications with QoS satisfaction.

Upcoming WLANs MAC access mechanisms: An overview

This paper gives an overview of the recent medium access control (MAC) mechanisms which are rising today. We focus on the already existing IEEE 802.11 and IEEE 802.11e MAC mechanisms, as well as those which are under development such as IEEE 802.11ac, IEEE 802.11ad, and IEEE 802.11aa. We describe the 802.11ac access mechanisms which support the multi-user access techniques in the form of sharing the transmit opportunity TXOP period. For the 802.11ad, we explain protocols that enable up to 7 Gigabit. We detail 802.11aa access mechanisms that guarantee more reliable multicast transport for video streaming.

Fairness of the IEEE 802.11n aggregation scheme for real time application in unsaturated condition

One of the challenges in todays wireless networks is to provide appropriate throughput and delay for data and multimedia application. Although IEEE802.11e (EDCA) standard is concerned to support QoS in wireless networks, it cannot provide strict QoS required by real-time and multimedia services without proper network control mechanisms. The recent standard 802.11n introduced new MAC access mechanism based on aggregation scheme. In this paper, we aim to develop an analytical model for throughput and end-to-end delay under unsaturated 802.11n network taking in consideration the different Access Categories (AC) priorities. Based on simulation results, we demonstrate that even with aggregation mechanism, 802.11n is not able to guarantee QoS for high priority traffics.

Priority consideration in inter-WBAN data scheduling and aggregation for monitoring systems

Wireless body area networks WBANs are composed of small intelligent tiny wireless sensors; these sensors are responsible for collecting information of a patients vital signs and transmitting vital information. WBAN offers mobility to patients and flexibility to medical staff. An increase of the deployment of monitoring systems on patients promotes researchers and developers to focus on issues related to WBAN. Quality of service QoS has been always treated as a major issue in WBAN technology, and scheduling as a packet prioritizing mechanism contributes to QoS guarantee provisioning significantly. In this paper, two novel inter-WBAN data scheduling and aggregation are developed for monitoring systems in order to satisfy QoS requirements in WBAN networks. We introduced a novel parameter called critical delay to serve packets taking into account their priorities and classify them into an aggregated frame to be further transmitted to medical server. The proposed scheme provides QoS-guaranteed service for the applications running on the sensor nodes in all the three aspects of QoS, that is, delay, throughput and packet loss. Copyright

New adaptive frame aggregation call admission control AFA-CAC for high throughput WLANs

The major enhancements introduced by the very high throughput wireless local area network, cannot provide quality of service QoS satisfaction for real time and multimedia applications. The recent standard IEEE 802.11n introduced new Medium Access Control MAC mechanisms based on aggregation scheme to enhance throughput. Besides that, functional modules for QoS provisioning such as call admission control and bandwidth management should be implemented in the access point. Hence, an efficient call admission control CAC algorithm is required for 802.11n network to satisfy QoS requirements of strict multimedia services. In this paper, we propose a new model-based call admission control algorithm, called adaptation of frame aggregation AFA-CAC to be implemented within the QoS access point in IEEE 802.11n standard in a way to provide QoS satisfaction to real time services. We first propose an accurate analytical model to estimate the achieved QoS metrics of a new flow entering in the network. Then, we detailed the AFA-CAC algorithm that supports IEEE 802.11n aggregation schemes aggregated MAC service data unit and aggregated MAC protocol data unit and consider the IEEE 802.11e enhanced distributed channel access. AFA-CAC is based on both predicting the QoS constraints of the already active flows and the new flow, and adjusting the number of aggregated subframes of each flow. Conducted simulations illustrate the performance of our proposed AFA-CAC in terms of satisfying QoS throughput and end-to-end delay requirements of voice and video traffics. Copyright

QoS support of voice/video services under IEEE 802.11n WLANs

IEEE 802.11n WLAN was mainly developed to support a high data transmission rate toward 600Mbps based on the aggregation scheme that accumulates several sub-frames to transmit them into a larger frame. This concept reduces overheads and increases efficiency and throughput. Nevertheless, it cannot provide QoS satisfaction for delay sensitive application since it badly affects the delay. To outperform this inefficiency, we have proposed an admission control mechanism named Adaptation of Frame Aggregation AFA-CAC. In this paper, we further investigate the performance of our proposed QoS mechanism on supporting real time applications particularly on audio and video services.

Dynamic Frame Aggregation Scheduler for Multimedia applications in IEEE 802.11n Networks

Providing Quality of Service (QoS) to real time applications over Wireless Local Area Networks (WLANs) is becoming a very challenging task due to the diversity of multimedia applications. Concurrently, there are numerous WLANs devices that are rising recently. Mainly, we focus on IEEE 802.11n since it was designed to support a high data transmission rate (toward 600 Mbps) based on frame aggregation schemes. The aggregation mechanism accumulates many frames before transmitting them into a single larger frame, thus reducing overhead and increasing efficiency and throughput. Yet, this scheme cannot provide QoS satisfaction for delay sensitive application even if it supports higher throughputs. Indeed, aggregation headers cause supplementary delays particularly when aggregating unfrequent packets with small sizes. To overcome this limitation, we propose in this paper a new Dynamic Frame Aggregation (DFA) scheduler to provide QoS satisfaction to real time services. To achieve this goal, we defined new scheduling parameters such as QoS delays to avoid accumulation of non-scheduled packets. Hence, the DFA scheduler serves packets and dynamically adjusts the aggregated frame size based on these QoS delays. Conducted simulations illustrate the performance of our proposed DFA scheduler in term of satisfying QoS, throughput, loss and delay requirements of voice and video traffics.

Analytical analysis of applying aggregation with fragment retransmission on IEEE 802.11e EDCA network in saturated conditions

Wireless local area networking has experienced tremendous growth in the last ten years with the proliferation of IEEE 802.11 devices. The first IEEE 802.11 Medium Access Control (MAC) technique of 802.11 is called Distributed Coordination Function (DCF. In order to enhance the throughput, new mechanism access control techniques are developed by TGn group of IEEE 802.11n. The main purpose of AFR mechanism is to retransmit only the corrupted fragment from large frame including multiple aggregated packets that leads to overhead reduction. This paper investigates a theoretical analysis of Aggregation with fragment retransmission, based on computing saturation throughput for DCF and AFR mechanisms. We provide a simple and accurate analytical model to calculate the Maximum MAC throughput to evaluate performances of AFR. We study the application of AFR on differentiated IEEE 802.11EDCA services.

Multi-user access mechanism with intra-access categories differentiation for IEEE 802.11ac wireless local area networks

To cope with the increasing demand of multimedia applications, new IEEE 802.11 wireless local area networks devices have been defined such as IEEE 802.11aa and IEEE 802.11ac. The former proposes new intra-access categories (AC) differentiation based on stream classification service (SCS) scheme. The latter standard allows simultaneous downlink transmissions thanks to downlink multi-user MIMO technology and sharing transmission opportunity (TXOP) period scheme. In this paper, we focus on the basis of this technique and the behavior of the access point (AP) to manage the multi-user access. Then, we propose a hybrid access mechanism entitled multi-user multi-cast access mechanism (MUMAM) that supports downlink multi-user transmissions while considering intra-AC differentiation. MUMAN considers SCS scheme to prioritize between multicast and unicast flows of an AC and follows transmissions based on IEEE 802.11ac TXOP sharing technique. Extensive simulation and analysis show that MUMAM has a significant positive impact on delay and throughput performance of different AC(s).

Performance analysis of correlation filters used for face recognition

There are many approaches for designing filters to be used with optical correlation techniques that presents a good method to carry out instantly a decision on the target form. In this paper, we are interested on filters designs since their important role for target tracking and identification. Considering a Vanderlugt correlator (VLC), we discuss the basis of existing filters in the literature, and we carry out a performance analysis of the above filters in terms of Receiver Operating Characteristic (ROC) and peak-to-correlation energy (PCE). Simulation results prove that POF is more appropriate for optical correlator to be used for face recognition.