On Sustained QoS Guarantees in Operated IEEE 802.11 Wireless LANs

Most of QoS-capable IEEE 802.11 MAC protocols are unable to deliver sustained quality of service while maintaining high network utilization, particularly under congested network conditions. The problem often resides in the fact that flows belonging to the same service class are assigned the same MAC parameters regardless theirs respective bitrate, which leads to throughput fairness rather than perceived QoS fairness. Harmonizing MAC parameters of traffic classes's flows may further lead to sub-optimal situations since certain network configurations (in terms of per class traffic load) can not be accommodated without reassigning the basic MAC parameters. In this paper, we propose a new cross-layer MAC design featuring a delay-sensitive backoff range adaptation along with a distributed flow admission control. By monitoring both MAC queue dynamics and network conditions, each traffic class reacts based on the degree to which application QoS metrics (delay) are satisfied. Besides, we use a distributed admission control mechanism to accept new flows while protecting the active one. Simulation results show that compared to the enhanced distributed coordination function (EDCA) scheme of 802.11e, our protocol consistently excels, in terms of network utilization, bounded delays, and service-level fairness.     

基于跨层的中高速传感器网络多元参数调度与资源自适应分配算法

针对中高速传感器网络中不同业务对QoS(quality of scrvice)的不同要求,跨层考虑物理层和数据链路层参数,提出了一种适合混合业务的多元参数调度算法和资源分配算法。该算法根据不同的业务动态调整时延补偿因子和吞吐量补偿因子两个参数,在满足实时业务QoS约束的前提下,以最大化系统吞吐量为目标建立了相应的优化模模型,对于实时业务能满足时延较小的要求,对于非实时业务能满足吞吐量较大的要求。仿真结果表明,该调度算法可以灵活地在系统功率效率和用户服务质量满意度之间取得折衷,并保证不同类型业务用户间的公平性。     

Enhancing multi-hop communication over multi-radio multi-channel wireless mesh networks: A cross-layer approach

The multi-channel multi-radio technology represents a straightforward approach to expand the capacity of wireless mesh networks (WMNs) in broadband wireless access scenarios. However, the effective leveraging of this technology in WMNs requires (i) enhanced MAC protocols, to coordinate the access to multiple channels with a limited number of radio interfaces, and (ii) efficient channel allocation schemes, to mitigate the impact of co-channel interference. The design of channel assignment schemes and MAC protocols is strictly interrelated, so that joint design should be considered to optimize the mesh network performance. In this paper, a channel assignment and fast MAC architecture (CAFMA) is proposed, which exploits the benefits provided by the multi-channel multi-radio technology to (i) enhance the performance of multi-hop communications, (ii) maximize the resource utilization, and (iii) support differentiation of traffic classes with different quality of service (QoS) requirements. CAFMA is designed with a cross-layer approach and includes (1) a novel MAC scheme, which provides multi-channel coordination and fast data relaying over multi-hop topologies, and (2) a distributed channel allocation scheme, which works in cooperation with the routing protocol. Simulation results confirm the effectiveness of CAFMA when compared with other single-layer and cross-layer solutions for multi-radio multi-channel WMNs.     

WiMAX Mesh网络混合调度下的QoS保障

在WiMAX Mesh网络中,资源分配可由集中式和分布式2种调度机制完成,但多数QoS研究只针对一种调度机制。针对上述情况,提出结合2种调度机制的QoS保障机制CDCSQ,针对不同的服务采用不同的调度机制以改进QoS,其中,集中式调度用于保证实时服务,分布式调度确保Mesh内部节点的直接通信。模拟结果表明,该机制比IEEE 802.16标准中的服务延迟小。     

宽带卫星网络中基于跨层设计的带宽分配研究

传统的带宽分配策略按照分层结构进行设计,集中在链路层解决问题,没有考虑动态变化的信道状态和所承载的数据流的QoS性能。基于跨层设计的思想,针对支持话音业务和Internet数据业务的卫星网络提出了一种基于跨层设计的带宽分配算法。该策略将应用层的业务特性和数据链路层的带宽分配策略以及物理层的信道状态进行跨层优化。主控站通过建立代价函数的方法将所有相关参数综合考虑,利用动态规划算法得到了最佳的带宽分配方案。数值结果表明：跨层设计方式可以适应变化的信道状态,并且同传统带宽分配算法比较,提高了Internet数据的有效吞吐量并且保持了话音业务的QoS要求。     

Dynamic slot assignment protocol for QoS support on TDMA-based mobile networks

An efficient bandwidth allocation scheme in wireless networks should not only guarantee successful data transmission without collisions but also enhance the channel spatial reuse to maximize the system throughput. The design of high-performance wireless Local Area Network (LAN) technologies making use of TDMA/FDD MAC (Time Division Multiple Access/Frequency Division Duplex - Medium Access Control) is a very active area of research and development. Several protocols have been proposed in the literature as TDMA-based bandwidth allocation schemes. However, they do not have a convenient generic parameters or suitable frame repartition for dynamic adjustment. In this work, we undertake the design and performance evaluation of a QoS (Quality of Service)-aware scheme built on top of the underlying signaling and bandwidth allocation mechanisms provided by most wireless LANs standards. The main contribution of this study is the new guarantee-based dynamic adjustment algorithm used in MAC level to provide the required QoS for all traffic types in wireless medium especially Wireless ATM (Asynchronous Transfer Mode). Performance evaluation of this approach consists of improving the bandwidth utilization, supporting different QoS requirements and reducing call reject probability and packet latency.     

一种新的基于HCCA的流量调度算法

IEEE802.11e中MAC协议传送方式采用了混合协调功能(HCF),其中混合式协调控制信道访问(HCCA)是基于集中轮询方式接入业务,它提供了参数化的QoS接入,着重讨论变比特率数据流的接入控制,提出了一种新的根据网络的实际流量、动态调整服务间隔和传输机会,来灵活地分配网络资源的算法.仿真结果表明,该算法能有效提高网络的吞吐量和降低丢包率,大大提高系统性能.     

车用自组网节点主动通告跨层数据传输控制

为提升车用自组网中数据业务的服务质量,改进了车用无线接入技术数据传输控制机制,提出了车用自组网节点数据传输能力主动通告跨层数据传输控制方案(Activc Notify EDCA, AN-EDCA)。仿真实验表明,AN-EDCA跨层数据传输控制机制有效地提升了各种应用环境中车用自组网的数据业务吞吐量,保证了车用自组网中数据业务的服务质量。     

IEEE 802．16协议中上行带宽分配机制研究

802.16是新一代宽带无线接入的标准。标准中明确定义了在MAC层实现QoS的机制,例如:MAC层的通信是基于连接的;将上层业务流根据QoS的要求进行分类等。但是标准对上行带宽的分配机制却未加以定义。我们就这个问题进行了研究,并提出了一种有效的上行带宽分配机制。     

A cross-layer elastic CAC and holistic opportunistic scheduling for QoS support in WiMAX

QoS provisioning is an important issue in the deployment of broadband wireless access networks with real-time and non-real-time traffic integration. An opportunistic MAC (OMAC) combines cross-layer design features with opportunistic scheduling scheme to achieve high system utilization while providing QoS support to various applications. A single scheduling algorithm cannot guarantee all the QoS requirements of traffics without the support of a suitable CAC and vice versa. In this paper, we propose a cross-layer MAC scheduling framework and a corresponding opportunistic scheduling algorithm in tandem with the CAC algorithm to support QoS in WiMAX point-to-multipoint (PMP) networks. Extensive experimental simulations have been carried out to evaluate the performance of our proposal. The simulation results show that our proposed solution can improve the performance of WiMAX networks in terms of packet delay, packet loss rate and throughput. The proposed CAC scheme can guarantee the admitted connections to meet their QoS requirements.     

多小区OFDMA系统一种跨层资源分配方法

正交频分多址(OFDMA)作为一种新的多址接入方式受到了极大关注.多小区系统由于采用频率复用技术会不可避免的产生小区间干扰,严重影响了多小区无线通信系统的性能,针对多小区OFDMA,提出了一种准分布式跨层资源分配方法.分配方法包括无线网络控制器(RNC)的跨层资源分配算法和基站收发系统(BTS)的跨层资源分配算法.RNC将子信道分配给各个小区的BTS,BTS将分配给该小区的子信道分配给该小区的用户.仿真结果表明,相对于传统的资源分配方法,跨层资源分配方法能有效提高多小区OFDMA系统给定服务质量(QoS)下的吞吐率.     

移动Ad Hoc网络中基于能量控制的QoS路由协议

实现QoS路由是保证在移动Ad Hoc网络中进行高效的多媒体业务传输的关键,然而现有的QoS路由协议很少考虑节能的问题,对此提出了一种基于能量控制的QoS路由协议。该协议采用跨层设计思想在MAC层和网络层同时提供能量控制,综合考虑了移动节点的发射功率和剩余能量状况。仿真结果表明该协议具有显著的节能效果,将为多媒体业务的持续传输提供一种有效途径。     

电力线通信系统中跨层的用户调度和资源分配

针对多用户多业务基于正交频分多址的电力线通信系统,提出一种在数据链路控制层进行用户调度和在物理层进行资源分配的多层多目标最优的跨层资源分配算法,其用户调度根据所有用户的服务质量(QoS)满意程度、QoS要求、业务包模型、信道状态信息和队列状态信息,从所有用户中选出要服务的用户和确定这些用户的最优跨层参数;其资源分配则根据所有调度用户的QoS要求、最优跨层参数和信道状态信息,先把功率按地窖注水原理分给每个子载波,再把每个子载波最优地分给调度用户并采用逐比特加载查表算法调整其上分配的功率和比特。最后在典型的电力线信道环境下对算法进行仿真,结果表明新算法在系统资源大范围变化时也能保障用户的服务质量,同时有效地提高系统资源的利用。     

基于IEEE802.11 DCF的QoS机制综述

分布式协调功能（DCF）采用有冲突避免的载波侦听多路访问（CSMA/CA,Carrier Sense Multiple Access with Collision Avoidance）方式访问共享无线媒体,是IEEE802.11媒体访问控制协议的基础。然而,在活动节点数目较大的环境下,这种机制容易造成性能恶化,且难以提供实时业务的服务质量（QoS）保证。概述了IEEE802.11的DCF机制及其性能分析方法,重点剖析了当前基于DCF的各种QoS机制,讨论了它们各自的优缺点,最后得出了优化DCF的一些有益的结论。     

An efficient quality-of-service MAC protocol for infrastructure WLANs

In this paper, we propose a new efficient MAC protocol, named quality-of-service MAC (QMAC), which is an integrated solution for providing QoS guarantees to real-time multimedia applications in infrastructure WLANs. In addition, QMAC has the following attractive features: (i) its reservation scheme ensures that real-time stations enter the polling list in bounded time, (ii) it supports multiple priority levels and guarantees that high-priority stations always join the polling list earlier than low-priority stations, (iii) it employs the distributed pre-check technique such that the access point can admit as many newly flows as possible, while not violating admitted flows' guarantees, (iv) its dynamic bandwidth allocation scheme provides real-time traffic transmission with per-flow probabilistic bandwidth assurances, and (v) it uses a multipoll frame to poll all stations on the polling list at a time, therefore, the bandwidth can be utilized more efficient. Through simulations, we demonstrate the advantage of our QMAC.     

WiMAX系统突发实时业务调度算法的改进

针对现有WiMAX系统MAC层没有提供不同优先级业务具体调度方案的现状,在分析传统分级调度算法的基础上,提出一种针对实时业务突发性的改进DFPQ调度算法实现方案。该方案在带宽分配过程中,通过判断实时业务突发性增多,强制将低优先级业务的一部分带宽分配给实时业务。GloMoSim网络仿真环境下的仿真结果证明,该调度策略在满足各业务QoS要求方面优于传统分级调度策略。     

A cross-layer framework for privacy enhancement in RFID systems

In this paper, we introduce a cross-layer framework for enhancing privacy in RFID systems. The framework relies on mechanisms in the physical (PHY) layer, as well as the medium access control (MAC) layer, to provide flexible protection over the unique identifiers of low-cost RFID tags. Such a framework prevents adversaries and malicious parties from tracking RFID tags through the monitoring of their unique identifiers. More specifically, our framework relies on masking of the identifier at the PHY layer, whereby bit-collisions are induced between the backscattered tag identifier and a protective mask, such that a legitimate reader can be allowed to recover the tag identifier but an illegitimate party would not be able to do so. To strengthen the level of protection provided by the bit-collision masking method, we present the randomized bit encoding scheme that is used in our framework. In addition, we also incorporate mechanisms in the MAC layer, and make use of cross-layer interactions between the MAC and the PHY layers to provide flexible privacy protection. This allows tags that do not require privacy protection to be read conveniently while allowing tags that need to be protected to stay protected.     

Cross Layer QoS Aware Scheduling based on Loss-Based Proportional Fairness with Multihop CRN

As huge users are involved, there is a difficulty in spectrum allocation and scheduling in Cognitive Radio Networks (CRNs). Collision increases when there is no allocation of spectrum and these results in huge drop rate and network performance degradation. To solve these problems and allocate appropriate spectrum, a novel method is introduced termed as Quality of Service (QoS) Improvement Proper Scheduling (QIPS). The major contribution of the work is to design a new cross layer QoS Aware Scheduling based on Loss-based Proportional Fairness with Multihop (QoSAS-LBPFM). In Medium Access Control (MAC) multi-channel network environment mobile nodes practice concurrent broadcast between several channels. Acquiring the advantage of introduced cross layer design, the real-time channel conditions offered by Cognitive Radio (CR) function allows adaptive sub channel choice for every broadcast. To optimize the resources of network, the LBPFM adaptively plans the radio resources for allocating to diverse services without lessening the quality of service. Results obtained from simulation proved that QoSAS-LBPFM provides enhanced QoS guaranteed performance against other existing QIPS algorithm.     

Differentiation, QoS guarantee, and optimization for real-time traffic over one-hop ad hoc networks

Nodes having a self-centrically broadcasting nature of communication form a wireless ad hoc network. Many issues are involved to provide quality of service (QoS) for ad hoc networks, including routing, medium access, resource reservation, mobility management, etc. Previous work mostly focuses on QoS routing with an assumption that the medium access control (MAC) layer can support QoS very well. However, contention-based MAC protocols are adopted in most ad hoc networks since there is no centralized control. QoS support in contention-based MAC layer is a very challenging issue. Carefully designed distributed medium access techniques must be used as foundations for most ad hoc networks. In this paper, we study and enhance distributed medium access techniques for real-time transmissions in the IEEE 802.11 single-hop ad hoc wireless networks. In the IEEE 802.11 MAC, error control adopts positive acknowledgement and retransmission to improve transmission reliability in the wireless medium (WM). However, for real-time multimedia traffic with sensitive delay requirements, retransmitted frames may be too late to be useful due to the fact that the delay of competing the WM is unpredictable. In this paper, we address several MAC issues and QoS issues for delay-sensitive real-time traffic. First, a priority scheme is proposed to differentiate the delay sensitive real-time traffic from the best-effort traffic. In the proposed priority scheme, retransmission is not used for the real-time traffic, and a smaller backoff window size is adopted. Second, we propose several schemes to guarantee QoS requirements. The first scheme is to guarantee frame-dropping probability for the real-time traffic. The second scheme is to guarantee throughput and delay. The last scheme is to guarantee throughput, delay, and frame-dropping probability simultaneously. Finally, we propose adaptive window backoff schemes to optimize throughput with and without QoS constraints.     

Extended EDCA for delay guarantees in wireless local area networks

Despite their very broad diffusion, IEEE 802.11 Wireless Local Area Networks (WLANs) are not able to provide service differentiation and to support real-time multimedia applications, due to their channel access methods. To overcome these limitations, the 802.11e working group has proposed the Enhanced Distributed Coordination Access (EDCA) scheme, which achieves service differentiation on a statistical basis by properly mapping user Quality of Service (QoS) requirements to channel contention parameters. Such a scheme will be included in the emerging 802.11n standard and in the revision of the 802.11 standard. However, it has been widely demonstrated that, especially at high network loads, EDCA does not provide an effective usage of the channel capacity. In particular, it is unable to provide a bounded delay service to all kinds of multimedia flow because flows with lower channel access priorities are starved to advantage only those with the highest priority. To fix this undesired behavior and improve wireless LAN performance, this paper proposes a new Extended EDCA (E²DCA) scheme, that is compliant with 802.11e specifications. By exploiting a closed-loop control algorithm, E²DCA performs a distributed dynamic bandwidth allocation, providing guarantees on average/absolute delays to real-time media flows, regardless of their priorities. Moreover, an innovative Call Admission Control (CAC) procedure has been developed. Using the ns-2 simulator, the effectiveness of the algorithm has been investigated in realistic network scenarios, involving a mix of audio, video, and FTP flows, at several network loads and with random losses. Results have shown that the proposed scheme is able to provide a bounded delay service to multimedia flows in a wide range of network loads and frame loss ratios.