Incomplete cooperation‐based service differentiation in WLANs

In 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 & 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.     

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.     

A novel QoS‐aware MAC protocol for voice services over IEEE 802.11‐based WLANs

With the pervasive growth in the popularity of IEEE 802.11‐based wireless local area networks (WLANs) worldwide, the demand to support delay‐sensitive services such as voice has increased very rapidly. This paper provides a comprehensive survey on the medium access control (MAC) architectures and quality of service (QoS) provisioning issues for WLANs. The major challenges in providing QoS to voice services through WLAN MAC protocols are outlined and the solution approaches proposed in the literature are reviewed. To this end, a novel QoS‐aware wireless MAC protocol, called hybrid contention‐free access (H‐CFA) protocol and a call admission control technique, called traffic stream admission control (TS‐AC) algorithm, are presented. The H‐CFA protocol is based on a novel idea that combines two contention‐free wireless medium access approaches, that is, round‐robin polling and time‐division multiple access (TDMA)‐like time slot assignment, and it increases the capacity of WLANs through efficient silence suppression. The TS‐AC algorithm ensures efficient admission control for consistent delay‐bound guarantees and further maximizes the capacity through exploiting the voice characteristic that it can tolerate some level of inconsecutive packet loss. The benefits of the proposed schemes are demonstrated in the simulations results. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

A MAC-Layer QoS Provisioning Protocol for Cognitive Radio Networks

Due to the proliferation of diverse network devices with multimedia capabilities, there is an increasing need for Quality of Service (QoS) provisioning in wireless networks. The MAC layer protocol with enhanced distributed channel access (EDCA) in the IEEE 802.11-2007 is able to provide differentiated QoS for different traffic types in wireless networks through varying the Arbitration Inter-Frame Spaces (AIFS) and contention window sizes. However, the performance of high priority traffic can be seriously degraded in the presence of strong noise over the wireless channels. Schemes utilizing adaptive modulation and coding (AMC) technique have also been proposed for the provisioning of QoS. They can provide limited protection in the presence of noise but are ineffective in a high noise scenario. Although multiple non-overlapped channels exist in the 2.4 and 5?GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel at anytime. As a result, these networks cannot fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. By identifying vacant channels through the use of cognitive radios technique, the noise problem can be mitigated by distributing network traffic across multiple vacant channels to reduce the node density per transmission channel. In this paper, we propose the MAC-Layer QoS Provisioning Protocol (MQPP) for 802.11-based cognitive radio networks (CRNs) which combines adaptive modulation and coding with dynamic spectrum access. Simulation results demonstrate that MQPP can achieve better performance in terms of lower delay and higher throughput.     

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.     

A practical QoS solution to voice over IP in IEEE 802.11 WLANs - [topics in design & implentation]

In this article we study the behavior of voice over IP traffic in IEEE 802.11 wireless networks. Specifically, we design a QoS provisioning mechanism for VoIP traffic, and propose a practical solution of configuring the 802.11e enhanced distributed control access parameter sets for different types of traffic. We show that media access control layer only methods may be insufficient, but the demonstrated cross-layer (layers 2, 3, and 4) method works simply and efficiently. We find that the EDCA parameter sets of the access point are not always necessarily set more aggressively than those of wireless stations even though the traffic load of AP is much heavier than the stations. With our mechanism, the EDCA parameter sets can be easily configured via software interface for off-theshelf WiFi phone products, and there is no need to modify the operations of APs or 802.11 MAC layer protocols. The performance of our mechanism is evaluated via ns-2 simulations and via laboratory experiments over Quanta?s O2 dual mode handsets. The results show our mechanism can provide effective and efficient QoS provisioning for VoIP traffic in IEEE 802.11 WLANs. Since the configuration may be readily configured in the field and the performance is robust across a wide range of environments, we believe that organizations deploying and operating WiFi networks for VoIP may benefit from our work and reduce or eliminate post-deployment tuning and debugging.     

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.     

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。     

Multiple preemptive EDCA for emergency medium access control in distributed WLANs

The increasingly use of wireless local area networks (WLANs) in public safety and emergency network services demands for a strict quality of service (QoS) guarantee especially a large number of users report an emergency for immediate channel access. Unfortunately, the traditional IEEE 802.11e-based enhanced distributed channel access (EDCA) does not support a strict QoS guarantee for life saving emergency traffic under high loads. Previous studies have attempted to enhance the performance of EDCA called the Channel Preemtive EDCA (CP-EDCA) which is a promising idea to support emergency traffic in WLANs. However, CP-EDCA supports a single emergency traffic only (i.e. no emergency service differentiation) with high delays for increased traffic loads. To overcome this problem, we propose a class of EDCA protocol called Multiple Preemption EDCA (MP-EDCA) as a candidate to support multiple emergency traffics under high loads. Each MP-EDCA node can support up to four emergency traffics (life, health, property and environment) with different priorities in addition to support background (non-emergency) traffic. The proposed protocol privileged the high priority life-saving emergency traffic to preempt the services of low priority ones without much starvation in the network to maintain a strict QoS guarantee. The paper evaluates the performance of MP-EDCA through an extensive analysis of simulation outcome. The results obtained show that MP-EDCA outperforms CP-EDCA in achieving lower medium access control and emergency node delays.     

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.     

Provisioning QoS controlled media access in vehicular to infrastructure communications

The emerging IEEE 802.11p standard adopts the enhanced distributed channel access (EDCA) mechanism as its Media Access Control (MAC) scheme to support quality-of-service (QoS) in the rapidly changing vehicular environment. While the IEEE 802.11 protocol family represents the dominant solutions for wireless local area networks, its QoS performance in terms of throughput and delay, in the highly mobile vehicular networks, is still unclear. To explore an in-depth understanding on this issue, in this paper, we develop a comprehensive analytical model that takes into account both the QoS features of EDCA and the vehicle mobility (velocity and moving directions). Based on the model, we analyze the throughput performance and mean transmission delay of differentiated service traffic, and seek solutions to optimally adjust the parameters of EDCA towards the controllable QoS provision to vehicles. Analytical and simulation results are given to demonstrate the accuracy of the proposed model for varying EDCA parameters and vehicle velocity and density.     

A unified model for the performance analysis of IEEE 802.11e EDCA

Rapid deployment of IEEE 802.11 wireless local area networks (WLANs) and their increasing quality of service (QoS) requirements motivate extensive performance evaluations of the upcoming 802.11e QoS-aware enhanced distributed coordination function (EDCA). Most of the analytical studies up-to-date have been based on one of the three major performance models in legacy distributed coordination function analysis, requiring a large degree of complexity in solving multidimensional Markov chains. Here, we expose the common guiding principle behind these three seemingly different models. Subsequently, by abstracting, unifying, and extending this common principle, we propose a new unified performance model and analysis method to study the saturation throughput and delay performance of EDCA, under the assumption of a finite number of stations and ideal channel conditions in a single-hop WLAN. This unified model combines the strengths of all three models, and thus, is easy to understand and apply; on the other hand, it helps increase the understanding of the existing performance analysis. Despite its appealing simplicity, our unified model and analysis are validated very well by simulation results. Ultimately, by means of the proposed model, we are able to precisely evaluate the differentiation effects of EDCA parameters on WLAN performance in very broad settings, a feature which is essential for network design.     

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.     

Arbitration Interframe Space‐controlled Medium Access Control: a medium access control protocol guaranteeing absolute priority in wireless local area networks

The demand for multimedia services, such as voice over Internet Protocol, video on demand, information dissemination, and ?le sharing, is increasing explosively in wireless local area networks. These multimedia services require a certain level of QoS. Thus, it is important to provide QoS for multimedia applications. IEEE 802.11e tries to meet the QoS requirement of multimedia services by using Enhanced Distributed Channel Access. This gives more weights to high‐priority tra?c than low‐priority tra?c in accessing the wireless channel. However, Enhanced Distributed Channel Access suffers from many problems such as low aggregate throughput, high collision rates, and ineffective QoS differentiation among priority classes. In this paper, we propose a new medium access scheme, the Arbitration Interframe Space‐controlled Medium Access Control (AC‐MAC), that guarantees absolute priority in 802.11 wireless networks. In AC‐MAC, the AIFS and contention window values are controlled, so that a higher‐priority tra?c can preferentially access and effectively utilize the channel. Extensive simulations show that AC‐MAC can perfectly provide absolute priority and good throughput performance regardless of the number of contending nodes. In the simulation of voice over Internet Protocol service, AC‐MAC provides effective QoS differentiation among services and also meets the high level of QoS requirements. AC‐MAC also adapts quickly in a dynamic environment and provides good fairness among the nodes belonging to the same priority class. Copyright © 2011 John Wiley & Sons, Ltd.     

MCCA: a high-throughput MAC strategy for next-generation WLANs [medium access control protocols for wireless LANs]

Wireless LAN technology has been shown to he a revolutionary development during the last decade. Recently popularized IEEE 802.11a/g-based products can support up to 54 Mb/s physical layer rate and provide wireless access to the Internet. However, in order to deal robustly with the unreliable wireless nature, the 802.11 medium access control protocol has a relatively large overhead and hence, the throughput performance is much worse than the underlying physical layer rate. Moreover, along with many emerging applications and services over WLANs, such as voice over WLAN and audio/video streaming, the demand lor faster and higher- capacity WLANs has been growing recently. In this article, we propose a new medium access control protocol for the next-generation high-speed WLANs. The proposed medium access control, called multi-user polling controlled channel access, is composed of two components: multi-layer frame aggregation, which performs aggregation at both the medium access control and the physical layers; and multi-user polling, used to reduce the contention overhead and in turn, achieve higher network utilization. Multi-user polling controlled channel access is compared with the 802.11e-enhanced distributed channel access medium access control. Highly enhanced medium access control efficiency can be achieved by applying multi-user polling controlled channel access. We show the improved medium access control performance in terms of the aggregate throughput of non-QoS Hows with relevant QoS requirements.     

Busy tone contention protocol: a new high‐throughput and energy‐efficient wireless local area network medium access control protocol using busy tone

Design of an efficient wireless medium access control (MAC) protocol is a challenging task due to the time‐varying characteristics of wireless communication channel and different delay requirements in diverse applications. To support variable number of active stations and varying network load conditions, random access MAC protocols are employed. Existing wireless local area network (WLAN) protocol (IEEE 802.11) is found to be inefficient at high data rates because of the overhead associated with the contention resolution mechanism employed. The new amendments of IEEE 802.11 that support multimedia traffic (IEEE 802.11e) are at the expense of reduced data traffic network efficiency. In this paper, we propose a random access MAC protocol called busy tone contention protocol (BTCP) that uses out‐of‐band signals for contention resolution in WLANs. A few variants of this protocol are also proposed to meet the challenges in WLAN environments and application requirements. The proposed BTCP isolate multimedia traffics from background data transmissions and gives high throughput irrespective of the number of contending stations in the network. As a result, in BTCP, admission control of multimedia flows becomes simple and well defined. Studies of the protocol, both analytically and through simulations under various network conditions, have shown to give better performance in comparison with the IEEE 802.11 distributed coordination function. Copyright © 2011 John Wiley & Sons, Ltd.     

A call admission control framework for voice over WLANs

In this article a call admission control framework is presented for voice over wireless local area networks (WLANs). The framework, called WLAN voice manager, manages admission control for voice over IP (VoIP) calls with WLANs as the access networks. WLAN voice manager interacts with WLAN medium access control (MAC) layer protocols, soft-switches (VoIP call agents), routers, and other network devices to perform end-to-end (ETE) quality of service (QoS) provisioning and control for VoIP calls originated from WLANs. By implementing the proposed WLAN voice manager in the WLAN access network, a two-level ETE VoIP QoS control mechanism can be achieved: level 1 QoS for voice traffic over WLAN medium access and level 2 QoS for ETE VoIP services in the networks with WLANs as the local access. The implementation challenges of this framework are discussed for both level 1 and level 2. Possible solutions to the implementation issues are proposed and other remaining open issues are also addressed.     

Improving DL-MU-MIMO performance in IEEE 802.11ac networks through decoupled scheduling

The IEEE 802.11ac standard introduces new downlink multi-user MIMO (DL-MU-MIMO) transmissions to up to four users in order to increase spatial reuse in wireless local area networks (WLANs). We argue that even better WLAN performance can be achieved by slightly modifying the DL-MU-MIMO scheduling. To this end we propose a new queuing mechanism based on the decoupling of EDCA and DL-MU-MIMO scheduling (DEMS) to avoid head-of-line blocking. We show that DEMS outperforms traditional 802.11ac scheduling based on first in, first out transmission queues. The improvement is shown in terms throughput achieved with: (a) more efficient channel usage, (b) increased probability of transmission of high priority traffic, and (c) decreased competition between frames destined to distinct users.