Supporting multimedia streaming and best‐effort data transmission over IEEE 802.11e EDCA

As demand for broadband multimedia wireless services increases, improving quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN (WLAN) has become crucial. To support the QoS required by a wide range of applications, the IEEE 802.11 working group has defined a new standard: IEEE 802.11e. In this paper, we propose a measurement‐based dynamic media time allocation (MBDMTA) scheme combined with a concatenating window scheme to support real‐time variable bit rate (rt‐VBR) video and best‐effort (BE) data transmission using IEEE 802.11e enhanced distributed channel access (EDCA). To provide the QoS guarantee for rt‐VBR video, the proposed MBDMTA scheme dynamically assigns channel time to the rt‐VBR video based on the estimate of the required network resources. On the other hand, the concatenating window scheme controls the contention window (CW) ranges of different priority flows such that real‐time services always have higher channel access probability, thus achieving the capability of preemptive priorities. In addition, the concatenating window scheme preserves fairness among flows of the same class and attains high channel utilization under different network conditions. Simulation results demonstrate that the throughput and delay performance improve significantly for the transmission of rt‐VBR video and BE traffic as compared to those for the 802.11e EDCA specification. It is also revealed that combining the two proposed schemes provides seamless integration and reliable transmission of digital video and data service within the 802.11e EDCA framework. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance Analysis on Coexistence of EDCA and Legacy DCF Stations in IEEE 802.11 Wireless LANs

The distributed coordination function (DCF) scheme of IEEE 802.11 MAC protocol does not support any concepts of quality of service (QoS) but the enhanced distributed channel access (EDCA) scheme in IEEE 802.11e standard provides QoS according to access categories using different access parameters. However, the legacy DCF stations may be used together with EDCA stations. In this letter, we investigate and analyze the performance discrimination when EDCA and DCF stations operate simultaneously     

A fuzzy logic cooperative MAC for MANET

In both wireless local area networks（WLAN） and mobile ad hoc networks（MANET）, the 1EEE 802.11e medium access control （MAC） protocol is proposed for an effective quality of service （QoS） solution. A number of studies have been done to enhance the performance of 802.11e in MANET by independently adjusting contention window （CW） size of each access category （AC） in every node. However, without the cooperation between the high priority flows and lower priority flows, the QoS goal of high priority flows cannot achieve effectively. In this article, a fuzzy logic based cooperative MAC protocol （FLCMAC） is proposed to cooperate amongst network flows and dynamically adjust access probability of each low priority flow affecting the high priority flows to satisfy their QoS requirement. The simulation results indicate that compared to the enhanced distributed channel access （EDCA） scheme of 802.11e, the FLCMAC consistently excels, in terms of throughput and delay under moderate and heavy background traffic both in single-hop and multi-hop scenarios.     

QoS provisioning for large-scale multi-ap WLANs

Large-scale deployment of IEEE 802.11 wireless LANs (WLANs) with a high density of access points (APs) has become commonplace due mainly to its potential for numerous benefits, such as ubiquitous service coverage, seamless handover, and improved link quality. However, the increased AP density can induce significant channel contention among neighboring cells, thus causing severe performance degradation and throughput imbalance between cells. There have been a plethora of research efforts to improve the WLAN performance, but most of them focused only on single WLAN environments without accounting for inter-cell contention. The de facto QoS-provisioning mechanism for WLANs, i.e., the Enhanced Distributed Channel Access (EDCA), is no exception to this. The EDCA focuses only on inter-flow priority distinction and has not considered the effect of inter-cell contention which significantly restricts its efficiency. This paper presents an enhanced QoS provisioning framework that takes into account inter-cell level differentiation as well as inter-flow level priority, which may be viewed as extension of QoS provisioning from a single-WLAN domain to a multi-WLAN domain. We also propose an architecture for managing multi-AP systems in which a central controller regulates the wireless channel occupancy of APs by adaptively configuring the cell-level QoS parameters. Our extensive simulation results show that the proposed inter-AP cooperative QoS scheme overcomes the limit of legacy 802.11e and provides a high level of fairness in large-scale densely-deployed WLANs.     

Exploiting the channel using uninterrupted collision‐free MAC adaptation over IEEE 802.11 WLANs

IEEE 802.11 wireless local area networks (WLANs) have reached an important stage and become a common technology for wireless access due to its low cost, ease of deployment, and mobility support. In parallel with the extensive growth of WLANs, the development of an efficient medium access control protocol that provides both high throughput performance for data traffic and quality of service support for real‐time applications has become a major focus in WLAN research. The IEEE 802.11 Distributed Coordination Functions (DCF/EDCA) provide contention‐based distributed channel access mechanisms for stations to share the wireless medium. However, performance of these mechanisms may drop dramatically because of high collision probabilities as the number of active stations increases. In this paper, we propose an adaptive collision‐free MAC adaptation. The proposed scheme prevents collisions and allows stations to enter the collision‐free state regardless of the traffic load (saturated or unsaturated) and the number of stations on the medium. Simulation results show that the proposed scheme dramatically enhances the overall throughput and supports quality of service for real‐time services over 802.11‐based WLANs. Copyright © 2013 John Wiley & Sons, Ltd.     

Saturation Throughput Analysis of the IEEE 802.11e EDCA Network with Contention Free Burst Under Fading Channel

The 802.11 WLAN legacy standard cannot provide Quality of Service (QoS) support for multimedia applications because the 802.11 was initially developed for Best Effort services. Hence, the 802.11e amendment was published in order to provide the QoS support to WLANs. One of the most important functions in 802.11e is the contention based channel access mechanism called Enhanced Distributed Channel Access (EDCA), which provides a priority scheme by differentiating the Arbitration Inter Frame Space (AIFS), initial window size and Transmission OPportunity limit (TXOPlimit). In this paper, we propose a novel analytical model for the performance analysis of the IEEE 802.11e EDCA network with Contention Free Burst under fading channel and saturated traffic conditions. This new model captures all of the major QoS specific features, namely AIFS, minimum contention window size, maximum contention window size, virtual collision and TXOPlimit. So, we have analyzed the saturation system throughput of the basic access method of the IEEE 802.11e EDCA network.     

Scheme to improve the QoS of MPEG4 over WLAN

IEEE 802.11e is put forward to improve the quality of service (QoS) of WLAN. But how to apply it to different applications is still a problem. This paper focus on apply EDCA to improve the QoS of MPEG4 service over WLAN. The scheme use cross-layer design to map different type of MPEG4 frames to different EDCA AC in order to get better QoS and also proposed an IAEDCF to further improve the QoS. From the NS-2 simulation results, it is proven efficient. This article puts forward two novel user-grouping algorithms for grouped multi-carrier (MC)-code division multiple access (CDMA) systems.     

On the capabilities of IEEE 802.11e for multimedia communications over heterogeneous 802.11/802.11e WLANs

Multimedia communications over WLAN is widely acknowledged as one of the key, emerging applications for wireless LANs. As with any multi-service network, there is the need to provision the WLANs with the QoS mechanisms capable of guaranteeing the requirements of various services. The upcoming IEEE 802.11e (EDCA) standard is a proposal defining the mechanisms for wireless LANs aiming to provide QoS support to time-sensitive applications such as voice and video communications. Due to the fact that the IEEE 802.11e interface cards will take over the WLAN market, replacing the use of legacy IEEE 802.11 interface cards in most WLAN applications, an important number of networking scenarios will consist of a hybrid configuration comprising legacy IEEE 802.11-based stations and IEEE 802.11e-based stations. For this reason, in this paper we carry out a performance analysis on the effectiveness of the IEEE 802.11e (EDCA) upcoming standard when supporting different services, such as, voice, video, best-effort, background and in the presence of traffic generated by legacy 802.11 (DCF) based stations.     

基于Ad hoc网络的新EDCA参数调整方案

IEEE802.11e标准中业务优先级不同的AC（access category）是通过设置不同的竞争窗口最大、最小值CWmax,CWmin和仲裁帧间隔值来体现的,如高优先级AC设置小的CWmin,CWmax和AIFS值.研究表明,EDCA对每个AC指定的默认参数值只适用于中等负载、节点数目少的网络场景,并不适用于负载较重、节点数目较多且链路动态变化的Ad hoc网络环境.提出了一种根据网络状况动态调整IEEE 802.11e EDCA的QoS参数的新方案I-ED-CA,该方案根据网络状态调整竞争窗口CW,并通过修改退避计数器值调整AIFS参数,使I-EDCA适合动态变化的Ad hoc网络环境,采用NS2仿真软件对EDCA改进协议I-EDCA进行仿真.仿真结果表明,随着网络中负载的增加,I-EDCA的吞吐量表现平稳,而EDCA吞吐量是下降的.另外,在业务公平性方面,对优先级不同的业务I-EDCA比EDCA的表现更公平.     

EDCA机制下实时业务多跳传输仿真分析

在AdHoc无线自组织多跳网络中,IEEE802.11e协议采用了增强型分布信道接入机制,用于为实时多媒体业务提供有效的QoS保证机制。简单介绍和对比了802.11分布式协调功能和802.11e增强型分布信道接入机制两种信道接入机制,并通过使用网络仿真软件OPNET,模拟了实时的视、音频业务在802.11分布信道接入机制和802.11e增强型分布信道接入机制信道接入机制下在不同网络负载下的性能并进行了仿真分析。     

Admission control in IEEE 802.11e wireless LANs

Although IEEE 802.11 based wireless local area networks have become more and more popular due to low cost and easy deployment, they can only provide best effort services and do not have quality of service supports for multimedia applications. Recently, a new standard, IEEE 802.11e, has been proposed, which introduces a so-called hybrid coordination function containing two medium access mechanisms: contention-based channel access and controlled channel access. In this article we first give a brief tutorial on the various MAC-layer QoS mechanisms provided by 802.11e. We show that the 802.11e standard provides a very powerful platform for QoS supports in WLANs. Then we provide an extensive survey of recent advances in admission control algorithms/protocols in IEEE 802.11e WLANs. Our survey covers the research work in admission control for both EDCA and HCCA. We show that the new MAC-layer QoS schemes and parameters provided in EDCA and HCCA can be well utilized to fulfill the requirements of admission control so that QoS for multimedia applications can be provided in WLANs. Last, we give a summary of the design of admission control in EDCA and HCCA, and point out the remaining challenges.     

Enhancement of QoS differentiation over IEEE 802.11 WLAN

IQD, a distributed coordination function (DCF) with integrated quality of service (QoS) differentiation, is proposed in this letter to enhance QoS over IEEE 802.11 WLAN. DCF does not support any QoS differentiation. Enhanced DCF (EDCF) only supports delay differentiation. IQD can achieve both delay and packet-loss-rate differentiation by differentiating the initial window size and the retry limit. Simulation results show that IQD performs better than DCF and EDCF in enhancing QoS, and the proposed analytical model is valid.     

Impact of priority differentiation on the bridged WBAN/WLAN healthcare networks

In this work, we develop a prioritized bridging mechanism between the IEEE 802.15.6‐based wireless body area networks (WBANs) and the IEEE 802.11e enhanced distributed channel access (EDCA)‐based wireless local area network (WLAN) to convey the medical data to the medical center. We map the eight WBAN user priorities (UPs) into the four WLAN access categories (ACs) to provide the required quality of service and prioritization for the health variables generated by the WBAN nodes. By assignment of WBAN UPs with default medium access control parameters to eight different medical data streams and under the presence of ordinary nodes, we investigate the impact of WLAN AC differentiation by arbitrary inter‐frame space (AIFS) and contention window (CW) on performance of medical and regular nodes’ data streams. The results of this work indicate that the AC differentiation by AIFS outperforms the differentiation by CW in the sense that it does not deteriorate the end‐to‐end delay of relayed WBAN traffic and ordinary WLAN traffic.Copyright © 2012 John Wiley & Sons, Ltd.     

Performance Analysis of Contention Based Medium Access Control Protocols

This paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that corresponds to the time evolution of the back-off processes at the contending nodes. An extension of the technique is presented to handle the case where service differentiation is provided with the use of heterogeneous protocol parameters, as, for example, in IEEE 802.11e EDCA protocol. Our results provide new insights into the operation of such protocols. The techniques developed in the paper are applicable to a wide variety of contention based MAC protocols.      

Efficient Back-off Mechanism for Multimedia Support in 802.11e EDCA Wireless Ad-Hoc Networks

This paper presents an effective back-off mechanism to improve quality of service (QoS) for multimedia applications over the IEEE 802.11e enhanced distribution channel access (EDCA) standard. It can be done with proposed algorithm called dynamic fast adaptation for contention-based EDCA (DFA-EDCA) mechanism. The main concept of proposed DFA-EDCA mechanism is to use the exponential functions to adaptively tune the back-off parameters in IEEE 802.11e EDCA according to the changes on a network load within a short period. In this proposed mechanism an intra-access category (intra-AC) differentiation mechanism is provided to increase its back-off time randomly and achieve discrimination of same priority traffic on different stations. The performance evaluations have been conducted by using Network Simulator (NS-2). The simulation results show that the proposed DFA-EDCA mechanism has greatly outperformed the previous mechanisms such as non-linear dynamic adaptation scheme of the minimum contention window (CW_min-HA), dynamic adaptation algorithm of the maximum contention window (CW_max-adaptation), adaptive enhanced distributed coordination function and the conventional EDCA in terms of goodput, gain of goodput, packet delay, collision rate and channel utilization ratio (CUR). It has significantly reduced both packet delay and collision rate simultaneously together with an obviously increment in both goodput and CUR, which lead to the improvement in QoS for multimedia applications.     

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs

IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard.     

ACKS: a technique to reduce the impact of legacy stations in 802.11e EDCA WLANs

The EDCA access mechanism of the upcoming 802.11e standard supports legacy DCF stations, but with substantially degraded performance. The reason being that DCF stations typically compete for access with overly small contention windows (CWs). In this letter we propose a new technique that, implemented at the access points (AP's), mitigates the impact of legacy stations on EDCA. The key idea of the technique is that, upon receiving a frame from a legacy station, the AP skips the ACK frame reply with a certain probability. When missing the ACK, the legacy station increases its CW and thus our technique allows us to have some control over the CW's of the legacy stations. We show by means of an example that this technique improves the overall performance of the WLAN.     

Multiservice unicast/multicast communications over IEEE 802.11e networks

Wireless communications are nowadays one of the most active research and development areas in telecommunications. The widespread use of wireless networks and the development of high-rate infrastructure are in turn enabling the introduction and deployment of many new end-user applications. During the past few years, the IEEE 802.11e (EDCA) standard has been working on defining the required QoS mechanisms to be incorporated into the IEEE 802.11 protocol architecture. However, recent studies have shown that EDCA performs poorly when the medium is highly loaded due to the high collision rate. Numerous proposals have been reported in the literature aiming to overcome this main drawback. However, EDCA and the proposed mechanisms continue to have a serious problem with a specific type of application: the multicast traffic. In EDCA (as in DCF) the multicast service is defined as an unreliable service, i.e., it does not include the use of ACK frames. Furthermore, different to the unicast service, the multicast service makes use of a single rate out of the various rates included in the Basic Service Set (BSS) defined by the IEEE 802.11 standard. This situation has led many researchers to design techniques aiming to improve the multicast transmission. In this paper, we analyze the inter-operability of two prominent multicast mechanisms recently reported by the authors and the channel access method defined by the IEEE 802.11e EDCA standard. We further consider the use of B-EDCA: an enhanced version of EDCA recently introduced by the authors. We carried a comparative performance evaluation of the aforementioned mechanisms when supporting unicast and multicast traffic. Our simulation results show the effectiveness of the enhanced protocol architectures when jointly supporting unicast and multicast traffic.     

Study on bandwidth control for multiple transmission rates in IEEE 802.11e EDCAF

IEEE 802.11e supports the guaranteed quality of service (QoS) by providing different transmission priorities. IEEE 802.11e improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function (HCF) controlled channel access (HCCA). Signal quality may affect the available bandwidth and transmission rate, because the characteristic of communication channel in wireless environment is in random time‐variation manner. Generally a station using a lower transmission rate will occupy communication channel for a longer time and degrade system performance, which causes unfairness and cannot provide the guaranteed QoS for the stations with higher transmission rates. We propose a bandwidth control scheme (BCS) by combining the IEEE 802.11e enhanced distributed channel access function (EDCAF) protocol to overcome the guaranteed bandwidth issue in multirate environments. A multirate discrete Markov chain model is analyzed for the multirate transmission system in this paper. According to the obtained results, BCS improves performance especially in throughput and makes the different QoS requirements be processed efficiently and flexibly. Copyright © 2009 John Wiley & Sons, Ltd.     

一种新的用于IEEE 802.11e EDCA中提供QoS的方法

该文提出了一种新的应用于IEEE 802.11e EDCA (Enhanced Distributed Channel Access)中提供QoS(Quality of Service)的方法。这种方法是将几个时隙组合起来构成一个超时隙,每个超时隙的开始分配给不同的业务来进行发包。时隙的分配是根据各种业务的不同优先级来实现的。这种方法可以保证高优先级业务具有较大的吞吐量,较少的MAC延时和较低的丢包率。与802.11e EDCA草案中提出的不同冲突窗口大小的方法相比,这种方法具有可以提高吞吐量,降低丢包率,并能减小站点数目变化对高优先级业务吞吐量的影响等优点。这种新的提供QoS的方法优于不同冲突窗口大小的方法,在IEEE 802.11e EDCA中应用超时隙方法可以大大提高EDCA的性能。