A novel self‐adaptive transmission scheme over an IEEE 802.11 WLAN for supporting multi‐service

The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self‐adaptive transmission scheme to support multi‐service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self‐adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self‐adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright © 2006 John Wiley & Sons, Ltd.     

IEEE 802.11 WLAN支持语音与数据业务的自适应传输方案研究

IEEE 802.11标准中的MAC协议当采用DCF和PCF时是一种随机竞争接入与轮询相结合的协议。该文通过仿真在分析研究此MAC协议对语音、数据业务综合传输性能的基础上,提出了一种支持语音与数据业务的自适应传输方案。仿真结果表明,在满足语音业务最大允许时延的前提下,自适应传输方案通过动态、合理地调整协议参数,可以提高数据业务的传输性能,从而增加网络容量。特别地,本方案不需要改动协议本身,易于实现。     

A Beacon-Based Collision-Free Channel Access Scheme for IEEE 802.11 WLANs

In IEEE 802.11 based WLAN standard, distributed coordination function is the fundamental medium access control (MAC) technique. It employs a CSMA/CA with random binary exponential backoff algorithm and provides contention-based distributed channel access for stations to share the wireless medium. However, performance of this mechanism drops dramatically due to random structure of the backoff process, high collision probability and frame errors. That is why development of an efficient MAC protocol, providing both high throughput for data traffic and quality of service (QoS) support for real-time applications, has become a major focus in WLAN research. In this paper, we propose an adaptive beacon-based collision-free MAC adaptation. The proposed scheme makes use of beacon frames sent periodically by access point, lets stations enter the collision-free state and reduces the number of idle slots regardless of the number of stations and their traffic load (saturated or unsaturated) on the medium. Simulation results indicate that the proposed scheme dramatically enhances the overall throughput and supports QoS by reducing the delay, delay variation and dropping probability of frames.     

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.     

Model-based admission control for IEEE 802.11e enhanced distributed channel access

IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme.     

无线局域网MAC协议分析和仿真研究

随着笔记本电脑、掌上电脑、智能手机等移动终端的普及,无线局域网（WLAN）以其接入灵活、架构和扩展方便等优点得到了迅速发展,WLAN的网络性能（吞吐量、时延等）取决于MAC子层的接入协议。该文从原理上对WLANMAC的实现方式和差异进行了分析,并利用广泛使用的网络仿真软件OPNETITGuru针对差异进行了仿真分析,有助于深入理解MAC接入控制原理和不断演进的相关标准。     

Performance analysis of rate-adaptive cooperative MAC based on wireless local area networks

Bi-dimensional Markov chain model based on cooperative medium access control (MAC) of wireless local area networks (WLAN) is considered to reflect system performance accurately. Two basic factors that affect the analysis results are station retry limits and non-saturated transmit probability. A uniform solution considering both factors is proposed. To prove the theoretical analysis, a cooperative MAC (CoopMAC) topology is established and the simulation model is enhanced by changing the cooperative table to the nodes' memory with more information added. Meanwhile, the three-way handshake scheme is modified and a handshake threshold is set based on the packet size. Simulation results show the performance analytical model is accurate, and the rate-adaptive cooperative MAC protocol significantly improves the network performance in terms of non-saturated system throughput and delay.     

Self-adaptive transmission scheme of integrated services over an IEEE 802.11 WLAN

A novel self-adaptive transmission scheme to support integrated data and voice transmission over an IEEE 802.11 WLAN is proposed. The simulation results show that the scheme can improve the data traffic performance and decrease efficiently the voice traffic delay jitter, and then increase the WLAN capacity. It is easy to realise as no change in the MAC protocol is required.     

Context Aware Inter-BSS Handoff in IEEE 802.11 Networks: Efficient Resource Utilization and Performance Improvement

IEEE 802.11 has become very popular wireless technology to offer high speed Internet access at public places called the ‘Hot-Spots’. This has enabled users to access multimedia and other real time applications using wireless local area networks (WLAN). In IEEE 802.11 WLAN technology, associations between a mobile station and an access point (AP) is controlled by the mobile station, allowing the station to select an AP with the strongest signal in terms of either ‘Received Signal Strength Identifier’ or ‘Signal to Interference and Noise Ratio’. In real time scenarios, the traffic patterns of mobile users are dynamic in nature. This leads to a situation where the traffic loads on the APs are unevenly distributed in the WLAN. Such imbalance in traffic load causes severe degradation in performance of the applications running on the mobile stations associated with the overloaded APs. In this paper, we propose a scheme which dynamically improves the performance of the overloaded APs by handing off some of its associated stations to nearby APs. This handoff decision is taken by an AP in assistance with the mobile stations. The effectiveness of the load distribution through dynamic hand-over in a WLAN is analyzed through theoretical analysis. Simulation results show the overall improvements in terms of delay, throughput and number of stations that an AP can support. The performance improvement in the proposed scheme is also justified through the results obtained from a IEEE 802.11 WLAN testbed.     

A delay based backoff scheme for WLAN with QoS guarantee and its performance

Based on the Distributed Coordination Function (DCF) and the Enhanced DCF (EDCF) mechanisms in IEEE 802.11 and 802.11e, a novel backoff scheme for Wireless Local Area Network (WLAN) is proposed. The scheme is to solve the problem of the packet loss and the decrease of performance due to the increasing Contention Window (CW) when there are continuous collisions. In the proposed scheme, the CW of the packet will change dynamically with different delay for the different traffics. Mathematic formulas are presented to indicate the relationship between the CW and the delay character. The performance of the new scheme is also discussed with simulation results. The results show that it helps WLAN system handle multimedia simultaneously.     

Distributed Medium Access Control Next-Generation CDMA Wireless Networks

The next-generation wireless networks are expected to have a simple infrastructure with distributed control. In this article, we consider a generic distributed network model for future wireless multimedia communications with a code-division multiple access (CDMA) air interface. For the medium access control (MAC) of the network model, we provide an overview of recent research efforts on distributed code assignment and interference control and identify their limitations when applied in next-generation wireless networks supporting multimedia traffic. We also propose a novel distributed MAC scheme to address these limitations, where active receivers determine whether a candidate transmitter should transmit its traffic or defer its transmission to a later time. Simulation results are given to demonstrate the effectiveness of the proposed distributed MAC scheme.     

Decentralised learning MACs for collision-free access in WLANs

By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two schemes that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations.     

DFMAC: DTN-Friendly Medium Access Control for Wireless Local Area Networks Supporting Voice/Data Services

In this paper, we consider a wireless communication network for both local nodes residing in densely populated hot spots and nomadic nodes roaming in a large area. Wireless local area networks (WLANs) are deployed in the hot spots, while a delay/ disruption tolerant network (DTN) provides services to nomadic nodes in the large area with low node density. We investigate the radio resource allocation for a DTN/WLAN integrated network, and propose a DTN-friendly medium access control (DFMAC) scheme for the hot spots supporting voice/data services. Analytical models are established to characterize the interactions between a DTN and WLANs under the proposed DFMAC. Numerical and simulation results demonstrate that our proposed MAC scheme can provide a deterministic delay guarantee for the voice services of local nodes, while achieving an efficient performance tradeoff for the data services between nomadic nodes and local nodes.     

Use of Different Acknowledgement Policies for Burst Transmission in Fiber-fed Wireless LANs

The IEEE 802.11 e medium access control (MAC) for quality-of-service (QoS) support in 802.11 networks defines burst transmission and new acknowledgment (ACK) operations as optional mechanisms for increasing channel utilization. In this paper, we investigate how the performance of these new features is affected by the presence of fiber delay in high speed Wireless LAN (WLAN) over fiber networks. It is shown that the negative effect of the fiber delay on the throughput performance of the 802.11 MAC protocol can be significantly reduced when burst transmission is used with the block or the no ACK policies.     

Optimal Joint Session Admission Control in Integrated WLAN and CDMA Cellular Networks with Vertical Handoff

This paper considers optimizing the utilization of radio resources in a heterogeneous integrated system consisting of two different networks: a wireless local area network (WLAN) and a wideband code division multiple access (CDMA) network. We propose a joint session admission control scheme for multimedia traffic that maximizes overall network revenue with quality of service (QoS) constraints over both the WLAN and the CDMA cellular networks. The WLAN operates under the IEEE 802.11e medium access control (MAC) protocol, which supports QoS for multimedia traffic. A novel concept of effective bandwidth is used in the CDMA network to derive the unified radio resource usage, taking into account both physical layer linear minimum mean square error (LMMSE) receivers and characteristics of the packet traffic. Numerical examples illustrate that the network revenue earned in the proposed joint admission control scheme is significantly larger than that when the individual networks are optimized independently with no vertical handoff between them. The revenue gain is also significant over the scheme in which vertical handoff is supported, but admission control is not done jointly. Furthermore, we show that the optimal joint admission control policy is a randomized policy, i.e., sessions are admitted to the system with probabilities in some states     

Architecture and performance of a MAC protocol for the HFC system

The IEEE 802.14 standard committee is currently working on a project to find a cost-effective means of providing access to integrated networks for people to enjoy multimedia programs and to work at home. An advanced system based on the cable TV system called hybrid fibre coax (HFC) is being studied. Since some properties of the HFC system preclude the possibility of directly using existing medium access control (MAC) protocols for its data link layer, a MAC scheme based on time division is discussed in this paper. This MAC scheme can be extended for wireless networks. © 1997 John Wiley & Sons, Ltd.     

Medium Access Control for QoS Provisioning in Vehicle-to-Infrastructure Communication Networks

The emerging vehicular networks are targeted to provide efficient communications between mobile vehicles and fixed roadside units (RSU), and support mobile multimedia applications and safety services with diverse quality of service (QoS) requirements. In this paper, we propose a busy tone based medium access control (MAC) protocol with enhanced QoS provisioning for life critical safety services. By using busy tone signals for efficient channel preemption in both contention period (CP) and contention free period (CFP), emergency users can access the wireless channel with strict priority when they compete with multimedia users, and thus achieve the minimal access delay. Furthermore, through efficient transmission coordination on the busy tone channel, contention level can be effectively reduced, and the overall network resource utilization can be improved accordingly. We then develop an analytical model to quantify the medium access delay of emergency messages. Extensive simulations with Network Simulator (NS)-2 validate the analysis and demonstrate that the proposed MAC can guarantee reliable and timely emergency message dissemination in a vehicular network.     

Using Chain of Mobile Access Gateway to Reduce Delay for PMIPv6 Protocol Applied in WLAN

Wireless LAN controller (WLC) is used to manage and control Access points (APs) in Wireless local area network (WLAN).Proxy mobile IPv6 (PMIPv6) protocol supports network-layer mobility in WLC based WLAN.However,it introduces extra delay in delivering packets from the APs to the WLC.We use Mobile access gateway (MAG) chain to reduce packet delay.The handoff delay and packet delivery delay under the proposed scheme are derived,based on which we formulate the delay minimization problem whose solution leads to the optimal MAG chain length.Numerical analysis results indicate that the proposed scheme outperforms the existing scheme in terms of delay in the case when the delay between Local mobility anchor (LMA) and WLC is relatively greater than the delay between two neighboring WLCs.The proposed scheme is able to reduce packet loss resulting from the traditional handoff procedure introduced in the PMIPv6 protocol and that due to delay limitation.     

无线局域网QoS机制解析

无线局域网（WLAN）技术的发展带来的多媒体业务流量的剧增,使无线网络的资源管理、服务质量（QoS）保障等问题日益突出,传统的媒体访问控制（MAC）协议需要重新设计才能有效地解决无线网络的QoS问题。本文介绍了无限局域网QoS技术的发展,包括针对IEEE802．11 MAC层协议进行的各种QoS增强技术。通过与传统的802．11标准的MAC层进行对比分析．讨论了IEEE802．11e的2个新策略：增强的分布式协调功能和混合协调功能。通过对受控竞争机制的分析,指出了IEEE802．11e仍存在的不足及未来的发展方向。     

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.