E Enhanced Distributed Channel Access Research Articles

A fuzzy-based QoS Maximization protocol for WiFi Multimedia (IEEE 802.11e) Ad hoc Networks

The Quality of Service (QoS) management within a multiple-traffic Wi-Fi MultiMedia (WMM) ad hoc network is a tedious task, since each traffic type requires a well determined QoS-level. For this reason, the IEEE Working Group has proposed the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol at the MAC layer of WMM ad hoc networks. However, several studies have shown that EDCA must be further improved for three main reasons. The first reason is the poor performance of EDCA under high traffic conditions due to the high collision rate. The second reason is the need to maximize the traffic performance (delay, throughput, etc.) guaranteed by EDCA, seen the rapid evolution of the applications (multimedia, real time, etc.). The third reason is the need to maximize the energy efficiency of the EDCA, seen its use in battery constrained devices (e.g. Laptop, Smart phone, Tablet computers, etc.). For these three reasons, we propose in this paper a Three-in-One solution MAC protocol called QoS Maximization of EDCA (QM-EDCA), which is an enhanced version of EDCA. Based on the fuzzy logic mathematic theory, QM-EDCA incorporates a dynamic MAC parameters fuzzy logic system, in order to adapt dynamically the Arbitration inter frame Spaces according to the network state and remaining energy. Simulation results show that QM-EDCA outperforms EDCA by reducing significantly the collision rate, and maximizing traffic performance and energy-efficiency. In addition our solution is fully distributed.

Preemptive admission control mechanism for strict QoS guarantee to life-saving emergency traffic in wireless LANs

The increasing usage of distributed emergency services (e.g. natural disaster or disaster caused by humans) in wireless local area networks requires the support of immediate channel access with strict quality of service (QoS) guarantee from a medium access control (MAC) protocol. The IEEE 802.11e/enhanced distributed channel access (EDCA) standard is the MAC enhancement for QoS. Unfortunately, 802.11e (EDCA) neither supports emergency traffic nor provides a strict QoS guarantee especially for a large number of users who report an emergency. To address this problem of achieving a strict QoS guarantee for emergency traffic, we previously developed and reported a multi-preemptive EDCA (MP-EDCA) protocol suitable for operating under low to medium traffic loads. However, MP-EDCA does not provide a strict QoS guarantee to life-saving emergency traffic (e.g. ambulance calls) in highly loaded networks. In this paper, we provide a solution to the problem of achieving a strict QoS guarantee to life-saving emergency traffic under high traffic loads. To this end, we propose a preemptive admission control (PAC) mechanism for MP-EDCA called PAC-MP-EDCA. The proposed PAC-MP-EDCA protects ongoing life-saving emergency traffic flows by giving high priority; thus, assures a QoS guarantee (in terms of lower packet delays) to life-saving emergency traffic when a high number of nodes require immediate channel access during emergency time. The priorities are set by carefully adjusting the short inter-frame space and slot-time in the emergency frames. The performance of PAC-MP-EDCA is evaluated by Riverbed Modeler simulation. Results obtained show that the proposed PAC-MP-EDCA achieved up to 98% lower MAC delays for life-saving emergency nodes and about 15% higher throughput than MP-EDCA under high traffic loads.

A survey on 802.11 MAC industrial standards, architecture, security & supporting emergency traffic: Future directions

The IEEE 802.11-based Wireless Local Area Network (WLAN) has become a ubiquitous networking technology deployed around the world. IEEE 802.11 WLAN are now widely used for real-time multimedia applications (e.g. voice and video streaming) and distributed emergency services such as telemedicine, healthcare, and disaster recovery. Both time-sensitive applications and emergency traffic are not only characterized by their high bandwidth requirements, but also impose severe restrictions on end-to-end packet delays (i.e. response time), jitter (i.e. delay variance) and packet losses. In other words, time-sensitive applications and emergency services require a strict Quality of Service (QoS) guarantee. Medium Access Control (MAC) protocol is one of the key factors that influence the performance of WLANs. The IEEE 802.11e working group enhanced the 802.11 MAC to provide QoS support in WLANs. However, recent studies have shown that 802.11e Enhanced Distributed Channel Access (EDCA) standard has limitations and it neither supports strict QoS guarantee nor emergency traffic. Providing a strict QoS guarantee as well as supporting emergency traffic under high traffic loads is really a challenging task in WLANs. A thorough review of literature on QoS MAC protocols reveals that most QoS schemes have focused on either network throughput enhancement or service differentiation by adjusting Contention Window (CW) or Inter-Frame Spaces (IFS). Therefore, a research on developing techniques to provide a strict QoS guarantee as well as support for emergency traffic is required in such systems. To achieve this objective, a general understanding of WLANs is required. This paper aims introduce various key concepts of WLANs that are necessary for design, model and develop such framework. Our main contribution in this paper is the QoS for IEEE 802.11 WLAN and MAC protocols for supporting industrial emergency traffic over network and future directions.

Performance analysis of IEEE802.11e EDCA wireless networks under finite load

In the majority of IEEE 802.11 series wireless networks, the quality of service (QoS) requirements are related to the queueing behavior of buffers in mobile stations, e.g., the buffer stability, overflow probability and packet delay, etc. Thus, it is important to accurately evaluate the performance of such networks in non-saturation environments. In this paper, we analyze the IEEE 802.11e enhanced distributed channel access (EDCA) wireless network under finite load. We develop an analysis model by a 3-dimensional Markov chain and derive its steady state distribution using the spectral method. We present a variety of performance measures including the buffer stability, the collision probability, the non-saturation throughput and the probability generating function of head-of-line delay (HoL-delay). For IEEE 802.11e EDCA wireless networks, these results are very useful in optimizing the network architecture and system parameters under the given QoS requirements.

Joint Optimization of Message Transmissions With Adaptive Selection of CCH Interval in VANETs

In vehicular networks, the safety-related messages (emergency and periodic messages) and non-safety message (RFS: request for service message) should share the scarce wireless resource. Emergency messages deliver time-critical information with guaranteed reliability, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> road-safety information, whereas periodic ones convey normal status update information, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> vehicular positions, show that is less time- and loss-critical. The RFS message is used for reserving Internet data service through the infrastructure on the road. In the channel access for vehicles, the synchronization interval (SI) is repeated every 100 ms and each SI is divided by one control channel interval (CCHI) for the transmission of safety-related messages and RFS message and by one service channel interval (SCHI) for the Internet service from the roadside infrastructure. It is crucial to set the length of CCHI appropriately in the SI because of the dynamic environment of VANETs. In this paper, we consider two optimization problems of message transmissions depending on whether the length of CCHI is flexible or not: 1) a fixed CCHI (non-adaptive) and 2) a variable CCHI (adaptive), respectively, and obtain the optimal MAC parameters where we adopt the IEEE 802.11e enhanced distributed channel access (EDCA) protocol with a “strict” priority for the emergency message. Finally, we conduct extensive simulations to validate our analytical findings.

Optimal joint load balancing and EDCA configuration of IEEE 802.11 wireless hotspots

SummaryWireless hotspots, ie, infrastructures composed of several IEEE 802.11 access points (APs), are today the most common solution in providing Internet access to a wide and rapidly changing population of users. According to common device implementation, stations establish associations with APs based on the measured strongest Received Signal Strength Indicator level. This usually leads to an uneven distribution of users to APs, increasing the chances of local network congestion. Load balancing (LB) solutions aim at mitigating this problem controlling the distribution of users. The LB algorithms enforce stations to associate with APs that manage a low number of users and/or that have a low traffic load. Usually, LB solutions do not consider traffic priorities or they assume some a priori quality of service (QoS) configuration for users.In this study, we propose a QoS‐LB solution based on the cell breathing technique with the goal of balancing the load in IEEE 802.11e Enhanced Distributed Channel Access (EDCA) Hotspots. The proposed algorithm explores the space of possible power/EDCA configurations by using a branch and bound approach that reduces the number of analyzed configurations and, hence, the time required to find the global optimal solution. The algorithm has been analytically defined and its performance evaluated through simulations and tests in a real test bed. The results prove that the proposed solution is effective in solving the optimal QoS‐LB configuration problem in WiFi hotspots of average size.

A Routing Optimization Based on Cross-Layer Design for Wireless Multimedia Sensor Networks (WMSNs)

Multimedia applications are routed from source nodes via neighboring nodes to a sink in Wireless Multimedia Sensor Networks (WMSNs). However, the existing routing protocols in the WMSNs do not fulfill the quality of service (QoS) constraint yet for multimedia transmission. The WMSNs have specific characteristics such as multi-hop way, limited node capability and varying bandwidth, which can affect the quality of service of multimedia applications during the routing process. The best quality of service (QoS) is required by the multimedia applications consisting of high throughput, low end-to-end delay and low packet drop rate. A routing optimization based on the cross-layer design is proposed for multimedia transmission in the WMSNs. The cross-layer design utilizes H.264/Scalable Video Coding (SVC) and IEEE 802.11e Enhanced Distributed Channel Access (EDCA) and has been implemented in Network Simulator 2 (NS2) simulation. The NS2 simulation indicates that the H.264/SVC video application has an average delay of 0.02 sec. Thus, the routing optimization has accomplished to deliver multimedia application successfully via Wireless Multimedia Sensor Network (WMSN).

D2D: Delay-Aware Distributed Dynamic Adaptation of Contention Window in Wireless Networks

The IEEE 802.11e enhanced distributed channel access (EDCA) protocol follows class-based service differentiation for providing differentiated quality-of-service (QoS). However, its collision avoidance mechanism using backoff algorithm can be inefficient for providing improved performance with respect to throughput and channel access delay, especially in a high network configuration (i.e. number of stations) with imperfect wireless channel. The existing and emerging works have devoted considerable attention on tuning the backoff parameters for achieving optimal throughput only. The prior works do not consider the channel access delay and throughput metrics altogether for performance improvement. Additionally, in most of the cases, the optimal configuration of backoff parameters are performed by a centralized controller. In this paper, we propose a delay-aware distributed dynamic adaptation of contention window scheme, namely D2D , for the cumulative improvement of both the throughput and the channel access delay at runtime. The D2D scheme requires two ad-hoc, distributed, and easy-to-obtain estimates— delay deviation ratio and channel busyness ratio —of the present delay level and channel congestion status of the network, respectively. A key advantage of the D2D scheme is that it is compliant with the IEEE 802.11 standard, and, thus, can be seamlessly integrable with the existing wireless card. We show the integrated model of the medium access control protocol, namely D2D Channel Access ( D2DCA ), for the IEEE 802.11e networks. We further propose a two-dimensional Markov chain model of the D2DCA protocol for analyzing its theoretical performance in saturated networks with imperfect wireless channel. Theoretical comparison with the benchmark protocols establishes the effectiveness of the D2DCA protocol.

End-to-end throughput analysis for IEEE 802.11e EDCA string-topology wireless multi-hop networks

This paper proposes analytical expressions of end-to-end throughput for IEEE 802.11e Enhanced Distributed Channel Access (EDCA) wireless string-topology multi-hop net- works. For obtaining the IEEE 802.11e EDCA performance, internal collisions between Access Categories (ACs) in a node, frame collisions with external nodes, and frame-existence probabil- ities of buffers at each AC are expressed as functions of EDCA access parameters. Therefore, it is possible to obtain the effects of the EDCA access parameters to Quality of Service (QoS) support in the EDCA. It is possible to obtain the end-to-end throughput at any offered load with respect to each AC because the buffer states can be expressed according to ACs. The obtained analytical expressions are verified by showing the quantitative agreements with sim- ulation results.

Dual Probability Selection Mapping Algorithm for Video Transmission over Wireless Sensor Networks

The video stream transmission over wireless sensor networks is specially required to consider the Quality of Service (QoS), such as low packet loss, low latency and high Peak Signal-to-Noise Ratio (PSNR). In order to improve the performance above, we propose a novel video transmission solution, named Dual Probability Selection Mapping Algorithm (DPSMA). In this solution, by analyzing different video frames for the importance of decoding and combining with the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) mechanism, the DPSMA allocates different mapping probabilities for different video frames. In addition, the DPSMA could be able to perceive the congestion of the queue and could be able to ensure the transmission of high priority data. By simulating with the NS2 tool, the DPSMA shows better performance than the 802.11e and other mapping algorithms. Index Terms—Video stream transmission, QoS, PSNR, wireless sensor networks

Achieving VoIP Guarantee in Wireless Local Area Networks

Recently, voice over Internet Protocol (VoIP) has gained much attention in wireless local area networks (WLANs). Although IEEE 802.11e enhanced distributed channel access (EDCA) has been standardized to provide voice traffic with quality of service (QoS) support, the voice quality could still be severely degraded by the traffic transmitted from low-priority stations (LP-STAs). Like 802.11b, the 802.11e EDCA also has the performance anomaly problem. Therefore, the voice quality of the high-rate stations (HR-STAs) could be severely degraded by the traffic transmitted from low-rate stations (LR-STAs). In fact, the LP-STAs and LR-STAs can be present simultaneously in practical WLAN environments. In this paper, we consider the effects of LP-STAs and/or LR-STAs on voice traffic and propose an extended EDCA scheme called voice differentiation-EDCA (VD-EDCA) to protect voice traffic from LP-STAs and/or LR-STAs. With VD-EDCA, the voice AC in a HR-STA has an absolute priority over LP-STAs and LR-STAs when they are notified that the wireless delay of a voice frame at the QoS access point (QAP) is larger than or equal to the predefined maximal delay threshold. We evaluate the performance of the proposed VD-EDCA scheme through extensive simulations. The simulation results show that, with appropriate maximal delay threshold settings, the proposed scheme well protects all of the VoIP calls transmitted by HR-STAs from LP-STAs and/or LR-STAs

A fuzzy-based QoS Maximization protocol for WiFi Multimedia (IEEE 802.11e) Ad hoc Networks

The Quality of Service (QoS) management within a multiple-traffic Wi-Fi MultiMedia (WMM) ad hoc network is a tedious task, since each traffic type requires a well determined QoS-level. For this reason, the IEEE Working Group has proposed the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol at the MAC layer of WMM ad hoc networks. However, several studies have shown that EDCA must be further improved for three main reasons. The first reason is the poor performance of EDCA under high traffic conditions due to the high collision rate. The second reason is the need to maximize the traffic performance (delay, throughput, etc.) guaranteed by EDCA, seen the rapid evolution of the applications (multimedia, real time, etc.). The third reason is the need to maximize the energy efficiency of the EDCA, seen its use in battery constrained devices (e.g. Laptop, Smart phone, Tablet computers, etc.). For these three reasons, we propose in this paper a Three-in-One solution MAC protocol called QoS Maximization of EDCA (QM-EDCA), which is an enhanced version of EDCA. Based on the fuzzy logic mathematic theory, QM-EDCA incorporates a dynamic MAC parameters fuzzy logic system, in order to adapt dynamically the Arbitration inter frame Spaces according to the network state and remaining energy. Simulation results show that QM-EDCA outperforms EDCA by reducing significantly the collision rate, and maximizing traffic performance and energy-efficiency. In addition our solution is fully distributed.

Pareto Optimized EDCA Parameter Control for Wireless Local Area Networks

The performance of IEEE 802.11e enhanced distributed channel access (EDCA) is influenced by several interactive parameters that make quality of service (QoS) control complex and difficult. In EDCA, the most critical performance influencing parameters are the arbitration interframe space (AIFS) and contention window size (CW) of each access category (AC). The objective of this paper is to provide a scheme for parameter control such that the throughput per station as well as the overall system throughput of the network is maximized and controllable. For this purpose, a simple and accurate analytical model describing the throughput behavior of EDCA networks is presented in this paper. Based on this model, the paper further provides a scheme in which a Pareto optimal system configuration is obtained via an appropriate CW control for a given AIFS value, which is a different approach compared to relevant papers in the literature that deal with CW control only. The simulation results confirm the effectiveness of the proposed method which shows significant performance improvements compared to other existing algorithms.

Modeling and performance study of the packet fragmentation in an IEEE 802.11e-EDCA network over fading channel

Mathematical modeling and performance analysis of the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) has been the subject of several research papers published in the literature. However, the Packet Fragmentation (PF) which has been proposed by the IEEE work group in the legacy IEEE 802.11 standard, has never been taken into account in the mathematical models available in the literature, in order to analyze the performance of the IEEE 802.11e-EDCA network under the influence of the Packet Error Rate (PER). Yet, the Packet Fragmentation is the only existing solution since 1999, which allows reducing the influence of the PER on the performance of IEEE 802.11 networks. In this paper, we aim at showing for the first time, how the Packet Fragmentation developed in the legacy IEEE 802.11 standard can be used to enhance the current IEEE 802.11e Quality of Service (QoS). Therefore, we propose an extension of the existing Markov chain models of the IEEE 802.11e EDCA function, in order to take into account the Packet Error Rate and Packet Fragmentation. Furthermore, we develop a mathematical model to derive the saturation throughput of a given Access Category (AC), namely: Voice (VO), Video (VI), Best Effort (BE) and Background (BK). The obtained analytical results show that, applying the Packet Fragmentation on the IEEE 802.11e-EDCA network, allows improving the utilization of the scarce wireless bandwidth under the impact of PER parameters, namely: Bit Error Rate (BER) and packet length.

Performance analysis of a threshold-based dynamic TXOP scheme for intra-AC QoS in wireless LANs

The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has been proposed for provisioning of differentiated Quality-of-Service (QoS) between various Access Categories (ACs), i.e., inter-AC QoS, in Wireless Local Area Networks (WLANs). However, the EDCA lacks the support of the intra-AC QoS provisioning, which is indispensable in practical WLANs since the network loads are always asymmetric between traffic flows of ACs with the same priority. To address the intra-AC QoS issue, this paper proposes a Threshold-Based Dynamic Transmission Opportunity (TBD-TXOP) scheme which sets the TXOP limits adaptive to the current status of the transmission queue based on the pre-setting threshold. An analytical model is further developed to evaluate the QoS performance of this scheme in terms of throughput, end-to-end delay, and frame loss probability. NS-2 simulation experiments validate the accuracy of the proposed analytical model. The performance results demonstrate the efficacy of TBD-TXOP for the intra-AC QoS differentiation.

A weighted fairness guarantee scheme based on node cooperation for multimedia WLAN mesh networks

In this paper, we focus on weighted fairness in multimedia WLAN mesh networks. Based on the analysis of the fairness problem of IEEE 802.11e Enhanced Distributed Channel Access (EDCA) scheme in WLAN mesh networks, we propose a weighted fairness guarantee scheme (WFGS), which provides weighted fairness for multimedia flows with different QoS requirements through node cooperation. WFGS piggybacks extra field in RTS/CTS frames to declare the channel occupation ratio of each flow. Accordingly, the transmitters can get the neighboring flows' channel occupation ratio via overhearing the RTS/CTS frames from its neighbors, and cooperatively adjust the contention window size to achieve weighted fairness among the flows. Also, to reliably reserve transmissions, an adaptive power control based RTS/CTS handshake mechanism is introduced. Simulation results show that compared with EDCA scheme, WFGS can effectively resolve the collisions induced by the carrier interference and thereby guarantee both the short-term and long-term weighted fairness among multimedia flows.

Throughput Analysis of IEEE 802.11e Enhanced Distributed Channel Access (EDCA) under Unsaturated Condition in One-Hop Ad Hoc Networks

With the previous proposed G/G/1 model, this paper analyzed the throughput expression in an unsaturated 802.11e one-hop ad hoc network. The expression is validated and the throughput performance is discussed by the simulations. The throughput expression derived in this paper will provide a way to analyze the impact of major QoS specific features on the throughput and hence can improve the performance of the network.

Opportunistic Retransmission in WLANs

This paper presents an efficient opportunistic retransmission protocol (PRO, Protocol for Retransmitting Opportunistically) to improve the performance of IEEE 802.11 WLANs. PRO is a link-layer protocol that allows overhearing nodes to function as relays that retransmit on behalf of a source after they learn about a failed transmission. Relays with better connectivity to the destination have a higher chance of delivering the packet than the source, thereby resulting in a more efficient use of the channel. PRO has four main features. First, channel reciprocity coupled with a runtime calibration process is used to estimate the instantaneous link quality to the destination. Second, a local qualification process filters out poor relays early. Third, a distributed relay selection algorithm chooses the best set of eligible relays among all qualified relays and prioritizes them. Finally, 802.11e Enhanced Distributed Channel Access (EDCA) is leveraged to make sure high-quality relays transmit with higher probability. PRO is designed to coexist with legacy 802.11 stations. Our extensive evaluation on both a controlled testbed and in the real world shows that PRO can improve throughput in diverse wireless environments. PRO helps the most when there is significant contention for the ether, under fading, and with user mobility.

Incomplete cooperation‐based service differentiation in WLANs

AbstractIn the IEEE 802.11 wireless LAN (WLAN), the fundamental medium access control (MAC) mechanism—distributed coordination function (DCF), only supports best‐effort service, and is unaware of the quality‐of‐service (QoS). IEEE 802.11e enhanced distributed channel access (EDCA) supports service differentiation by differentiating contention parameters. This may introduce the problem of non‐cooperative service differentiation. Hence, an incompletely cooperative EDCA (IC‐EDCA) is proposed in this paper to solve the problem. In IC‐EDCA, each node that is cooperative a priori adjusts its contention parameters (e.g., the contention window (CW)) adaptively to the estimated system state (e.g., the number of competing nodes of each service priority). To implement IC‐EDCA in current WLAN nodes, a frame‐analytic estimation algorithm is presented. Moreover, an analytical model is proposed to analyze the performance of IC‐EDCA under saturation cases. Extensive simulations are also carried out to compare the performances of DCF, EDCA, incompletely cooperative game, and IC‐EDCA, and to evaluate the accuracy of the proposed performance model. The simulation results show that IC‐EDCA performs better than DCF, EDCA, and incompletely cooperative game in terms of system throughput or QoS, and that the proposed analytical model is valid. Copyright © 2010 John Wiley &amp; Sons, Ltd.

A novel cross-layer design using comb-shaped quadratic packet mapping for video delivery over 802.11e wireless ad hoc networks

Cross-layer design is a promising direction and challenging issue for quality delivery of multimedia over wireless networks. This article proposes a cross-layer design which can substantially enhance the transmission quality of video streaming over 802.11e ad hoc networks. The proposed design consists of two parts: a dispersive video frame importance (DVFI) scheme in the application layer that can correctly label the priorities of video packets, and a comb-shaped quadratic mapping (CQM) algorithm in the medium access control (MAC) layer that can provide a better congestion control mechanism among the multiple access category (AC) queues than 802.11e Enhanced Distributed Channel Access (EDCA) for wireless video delivery. The DVFI value of a video frame is measured from its own transmission loss and the accompanied impact to other coding-dependent video frames, and is accordingly adopted to prioritize the video frame associated packets. When these prioritized video packets arrive at the reserved AC queue in the MAC layer, the CQM algorithm can accordingly provide multi-branched service differentiation among them by dynamically downward mapping less significant video packets to lower-priority ACs based on the instant congestion level of the reserved AC queue, which can thus offer a better channel access resource to those video packets of higher priorities. In addition, the minimum-delay-time rule embedded in the CQM will select a better destiny for those downward mapped video packets among the lower-priority AC queues. Under various video-input-rate and cross-traffic tests, the simulation results show that this study outperforms the existing works, including EDCA, Adaptive Mapping, and Enhanced Adaptive Mapping.