Selectivity function scheduler for IEEE 802.11e HCCA access mode

In this paper, we present a scheduling algorithm that enhances the performance of the standard IEEE 802.11e scheduler for the Hybrid Coordination Function Controlled Channel Access mode. The main contribution in designing the proposed scheduler is the ability to accommodate multiple streams with different levels of Quality of Service requirements concurrently running on the same station. This is achieved by dynamically calculating the Transmission Opportunities of each active traffic stream (TS) and the appropriate Service Interval of each active station. The proposed algorithm optimizes the utilization of the scarce bandwidth resources by only polling active stations. The algorithm incorporates a selectivity function to assign polling priorities to the active streams only based on their diverse requirements and their link‐attainable transmission rates. The performance of the proposed Selectivity Function Scheduler (SFS) scheme is evaluated against the standard scheduler. Simulation results show that the SFS outperforms the standard scheduler in terms of enhancing streams' throughput, reducing packet dropping ratio and maintaining high fairness amongst the admitted TS. Copyright © 2011 John Wiley & Sons, Ltd.     

基于IEEE802.11e HCCA的接入控制方案

较传统的IEEE802.11标准的MAC协议,802.11e增强了对QoS的支持力度,主要基于IEEE802.11e的HCCA机制,提出了一套控制接入方案,本方案在全面考虑QoS参数的基础上提出了一个有效的调度算法,从而确保了实时性业务的QoS需要.     

Utilization Model for HCCA EDCA Mixed Mode in IEEE 802.11e

This letter proposes an analytical model to characterize medium utilization in IEEE 802.11e operating in HCCA‐EDCA mixed mode (HEMM). In contrast to existing works which model the backoff process in individual stations, we consider the channel occupancy pattern. Additionally, our work considers the operation of HEMM, which is not widely documented. We show that the proposed model accurately characterizes medium utilization with no more than 5% error.     

An Equal-Spacing-Based Design for QoS Guarantee in IEEE 802.11e HCCA Wireless Networks

IEEE 802.11e standard develops a reference design for a sample scheduler and admission control unit to support the contention-free access. However, the reference design can not efficiently utilize the bandwidth. This paper proposes an equalspacing- based (equal-SP) design to address the problem. In the equal-SP design, which generalizes the reference design, each stream is scheduled with equal-spacing and different streams are scheduled with different spacings. The equal-SP design not only keeps all advantages of the reference design (i.e., it is simple, easy to implement, and can guarantee the delay requirement), but it is compatible with the standard and can also utilize the bandwidth efficiently.     

Enhancement of QoS support of HCCA schedulers using EDCA function in IEEE 802.11e networks

The IEEE 802.11e standard introduces Quality of Service support for wireless local area networks through two MAC functions: Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA). While the former provides prioritized contention-based access to the medium, the latter uses a parameterized contention-free polling scheme. Several studies have proposed enhancements to EDCA or improved scheduling algorithms for HCCA to properly support VBR traffic. However, the cooperation between these functions has only marginally been considered and the solutions vary depending on specific traffic requirements.In this paper we propose a novel approach to address the problem of scheduling VBR traffic streams. Our scheduler, named Overboost, uses HCCA to negotiate a minimum bandwidth and deals with traffic streams that require more bandwidth than the negotiated one by redirecting the excess bandwidth to the EDCA function. An analytical evaluation has been conducted and the results has been corroborated by an extensive set of simulations. They show that the overall scheduler improves the performance with respect to other HCCA schedulers in terms of null rate, throughput, access delay, and queue length.     

A Simple Analytical Model for Expected Frame Waiting Time Evaluation in IEEE 802.11e HCCA Mode

IEEE 802.11e standard defines two access modes to provide Quality of Service support for 802.11-based Wireless LANs: Enhanced Distributed Channel Access and HCF Controlled Channel Access (HCCA). Only HCCA can guarantee bandwidth per flow which is suitable for various multimedia application requirements. However, the reference scheme HCCA is designed without awareness of variable bit rate (VBR) transmission. Several enhancement techniques have been proposed to address the VBR problem, but there are few research results for a model to capture the characteristics of HCCA. In this paper, an analytical model for the expected packet waiting time is proposed. The model can capture the system behavior per session leading to suitable admission control process for VBR support. The proposed model has been validated using the Network Simulator. The results confirm that the reference admission control scheme with mean data rate acceptance cannot guarantee the required bound on waiting time. Using the model, suitable parameters can be investigated for admission control with VBR support. The model can also be applied with polling based technologies, such as WiMAX.     

DPS: An Architecture for VBR Scheduling in IEEE 802.11e HCCA Networks with Multiple Access Points

Recent advances in 802.11 Wireless Local Area Networks (WLANs) have been focused on introducing Quality of Service (QoS) in their performance through the adoption of 802.11e. The Hybrid Controlled Channel Access (HCCA) has been proposed as the mechanism to provide the means for guaranteed QoS in networks controlled by a single Access Point (AP). Moreover, scheduling algorithms have been developed allowing efficient scheduling of Variable Bit Rate (VBR) traffic flows. However, little research may be found regarding the problem of applying HCCA on networks with multiple APs. In this paper, various VBR scheduling mechanisms and methods for multi—AP HCCA are presented and evaluated. In addition, this paper introduces the Dynamic Parallel Scheduler (DPS), a novel HCCA scheduling algorithm for VBR traffic among multiple APs that takes advantage of the rate variability and spatial reuse. DPS’s performance evaluation shows that the proposed scheme achieves improved performance in terms of delay, throughput and packet loss.     

Removing redundant TCP functionalities in wired‐cum‐wireless networks with IEEE 802.11e HCCA support

The TCP was originally designed for wired networks, assuming transmission errors were negligible. Actually, any acknowledgment time‐out unconditionally triggers the congestion control mechanism, even in wireless networks in which this assumption is not valid. Consequently, in wireless networks, TCP performance significantly degrades. To avoid this degradation, this paper proposes the so‐called split TCP and UDP. In this approach, the access point splits the TCP connection and uses a customized and lighter transport protocol for the wireless segment. It takes advantage of the IEEE 802.11e Hybrid Coordination Function Controlled Channel Access (HCCA) mechanisms to remove redundant TCP functionalities. Specifically, the HCCA scheduler allows disabling of the congestion control in the wireless link. Similarly, the IEEE 802.11e error control service makes possible to eliminate TCP acknowledgments, therefore reducing the TCP protocol overhead. Finally, the usage of an HCCA scheduler permits providing fairness among the different data flows. The proposed split scheme is evaluated via extensive simulations. Results show that split TCP and User Datagram Protocol outperforms the analyzed TCP flavors—specifically designed for wireless environments—and the split TCP solution, achieving up to 95% of end‐user throughput gain. Furthermore, the proposed solution is TCP friendly because TCP flows are not degraded by the presence of flows by using this approach. Copyright © 2013 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.     

IEEE 802.11e enhancement for voice service

Motivated by the promising voice over IP technology and the wide service availability of WLANs, the application of voice over WLAN (VoWLAN) is expected to experience dramatic growth in the near future. Originally designed for high-rate data traffic, WLANs may experience bandwidth inefficiency when supporting delay-sensitive and low-rate voice traffic. This article proposes mechanisms to enhance QoS support capability of IEEE 802.11e for voice service. Unnecessary polling of silent voice stations is avoided, and header and control overheads are suppressed significantly. Compared to IEEE 802.11e, our mechanisms can greatly improve the capacity of WLANs to support voice service.     

IEEE802.11e与IEEE802.15.3协议性能对比分析

IEEE802.11e和IEEE802.15.3两个协议在当今无线网络中应用的十分广泛,在详细描述了两者的信道接入机制的基础上,对协议性能进行了分析对比,并指出了各自适用的范围.     

IEEE802．11eWLAN中基于HCCA机制的带宽分配算法的研究

随着使用WLAN（无线局域网）接入因特网的日渐普及,IEEE802．11eWLAN中的HCCA（混合控制信道接入）机制由于在处理实时多媒体业务的高效率受到越来越广泛的关注。在WLAN中为达到高带宽利用率和良好的端到端QoS,介绍了一种基于HCCA机制的带宽分配算法,同时对该算法与802．11PCF（点协调功能）两种接入场景下的网络性能进行仿真比较,其结果验证了该算法可以为WLAN提供良好的QoS保证,对在WLAN中传输语音、视频等实时业务具有一定的指导意义。     

Modeling and performance analysis of an alternative to IEEE 802.11e Hybrid Control Function

Modern wireless networks are offering a wide range of applications that require the efficient integration of multimedia and traditional data traffic along with QoS provision. The IEEE 802.11e workgroup has standardized a new QoS enhanced access scheme for wireless LANs, namely Hybrid Control Function (HCF). HCF consists of the Enhanced Distributed Channel Access (EDCA) and the Hybrid Control Channel Access (HCCA) protocols which manage to ensure QoS support. However, they exhibit specific weaknesses that limit network performance. This work analyzes an alternative protocol, called Priority Oriented Adaptive Polling (POAP). POAP is an integrated channel access mechanism, is collision free, it employs priorities to differentiate traffic in a proportional way, it provides fairness, and generally supports QoS for all types of multimedia applications, while efficiently serving background data traffic. POAP is compared to HCF in order to examine the wireless network performance when serving integrated traffic.     

A Cross-Layer Multi-Hop Simulator for IEEE 802.11e

In this work we simulate the ad hoc mode of IEEE 802.11e for routing optimisation. We simulate the behaviour of routing algorithms at the network layer by using a custom-made cross-layer network simulator developed by our team, which simultaneously considers the physical and Medium Access Control (MAC) layers. Although the simulator also supports the infrastructure mode, in this paper we focus on the ad hoc feature which was introduced by the authors. We opted for the simulator approach over the theoretical analysis, but we also present a mathematical model for IEEE 802.11 ad hoc networks. Some initial tests were performed by using a simple routing algorithm (to evaluate the behaviour of the system in terms of selection of the path between a source and a destination, and the correctness of the calculated metrics, which include end-to-end delay, packets lost, packets delivered), but more advanced cross-layer design solutions were also tested. When information from the physical and MAC layers is used as an input to the routing algorithm, improvements are achieved in the performance of the network. Several functions were compared and the algorithm that privileges shorter links accounting with the metric “collision rate” achieves the best results. When compared with a standard routing solution, this cross-layer approach allows to increase the number of packets delivered, while not significantly affecting the end-to-end delay of the packets.     

A delay model for IEEE 802.11e EDCA

In this paper, we present a model to analyze the delay behavior of the enhanced distributed channel access (EDCA) mechanism of IEEE 802.11e. Simulation results validate the accuracy of the analysis.     

IEEE802.11e中DCF的优先级机制

正在制定过程中的IEEE802.11e标准是802.11WLAN标准的扩展,用以提供所要求的Qos。该文重点阐述了在802.11e中EDCF的优先级机制,并通过仿真数据对优先级机制的性能进行评价。     

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.     

IEEE 802.11协议中分布式协调机制的性能模型

IEEE 802.11采用异步传输方式作为媒体层的主要技术,而基于载波检测碰撞避免的分布式接入机制则是其最大的特点.关于分布式接入机制的研究,目前已经有了许多的模型,但是,大部分的模型都是研究终端所产生的数据包是固定长度,很少有模型来研究终端数据包是可变长度的情况.这种情况下的难点就是不易求得碰撞发生时信道所消耗的时间长度.本文则研究在终端数据包长度的分布函数为f(x)下协议的吞吐量和延迟性能模型.首先本文将原标准协议的退避算法看成是有固定大小的竞争窗口,用以求得站点的发送概率;然后,分析信道的工作状态,给出了性能模型,重点在求解碰撞消耗的信道时间,在文章的最后,我们通过仿真试验来验证了模型的正确性.     

IEEE 802.11e: QoS provisioning at the MAC layer

This article introduces the emerging IEEE 802.11e standard to support quality of service at the medium access control layer. Both the contention-based and contention-free centrally controlled channel access mechanisms are introduced by describing not only the MAC protocol operations and parameters, but also the call admission techniques and scheduling algorithm that have been designed for IEEE 802.11e. Finally, we provide simulation results aimed to highlight the capability of the EDCF to differentiate the traffic classes.