一种支持服务类别的无线公平调度算法

本文提出了一种支持服务类别的无线公平调度算法:CoSB－WFS(基于服务类别的无线公平调度).算法区分不同的服务类别并可根据其业务需要进行不同的调度.考虑到无线信道的特殊性,算法引入了补偿和再分配模式.在仿真工具OPNET上模拟了算法并得到了性能改良的结果.     

一种按比例补偿的无线公平调度算法

该文提出了一种按比例补偿的无线公平调度算法,算法区分不同的服务类别并可根据其业务需要进行不同的调度。考虑到无线信道的特殊性,算法引入了补偿和再分配模式。其中补偿模式采用了针对滞后流按照其预约速率的固定比例进行补偿的方式。     

一种适用于宽带无线IP网络的分组调度算法

自适应调制技术在许多新型的无线分组网络如WCDMA HSDPA、HiperLAN/2中得到广泛采用.本文在充分考虑自适应调制系统链路带宽随时隙呈不平均分布特点的基础上,提出一种全新的调度算法,自适应区分补偿公平队列(ADCFQ).该算法采用了基于工作量的分析方法,设计了不同功能的多个子队列,可以为系统所有待发流提供基本的QoS保证,为各个流公平共享剩余带宽,并能够通过合理的补偿机制克服无线环境中突发错误影响.分析和仿真结果表明,这一算法可以满足目标要求.此外,仿真中,针对自适应链路的特点,本文还提出了一种基于多状态Markov链的信道建模方法.     

区分服务中AF类的一种调度算法

该文根据区分服务中确保转发(Assured Forwarding,AF)类的特点,设计了一种新的调度算法公平加权轮循(Fair、Weighted Round Robin,FWRR)算法。 FWRR是一种基于轮循、工作保持型、适于变长分组的调度算法.它的实现简单,算法复杂度为O(1).仿真实验和数学分析表明,FWRR算法不仅能够提供保证最小带宽的服务,而且能够按比例分配剩余带宽,适合用来调度区分服务中的AF类.     

区分服务网络中自适应加权调度方案的研究

针对现有区分服务网络中多服务间带宽公平性问题，提出了一种自适应加权调度方案。该方案通过对本地节点缓存区指标的定期测量，计算得到在各队列间公平分配剩余带宽的调度权值。仿真结果表明，该方案可以在网络负载变化时自适应的快速调整到理想调度值，有效改进了带宽分配的公平性。     

变长分组变公平调度的算法与实现

提出并实现了一种应用于路由器的公平排队算法－补偿型轮询调度算法。该算法在逐包调度的基础上采用补偿措施,在处理一个包仅需O（1）的运算量条件下,获得了输出带宽的近似公平共享。性能分析表明,该算法能够有效地实现公平调度,阻止个别违约用户过度占用输出带宽。该算法应用于国家863计划重大课题核心路由器－OmniRouter880的研制中,样机验收测试结果表明,补偿型轮询调度算法具有良好的性能。     

基于块对角化和服务公平性的次最优用户选择方案

该文基于块对角化的思想提出了一种次最优用户选择方案。首先推导出一个和速率容量的上界公式,将其作为该文提出算法的选择准则;然后用此上界公式代替瞬时和容量公式作为自适应准则,得到了所提出算法的简化算法;最后考虑到用户之间服务公平性的因素,把该文的提出算法与比例公平调度机制相结合,使得系统既能获得一定的信道容量增益又能让所有用户均得到公平的服务。仿真结果表明,该文所提出算法具有接近最优的性能,与比例公平调度机制相结合后可以达到系统和容量与服务公平性的折衷。     

基于优先级的分组公平调度算法研究

为了在光突发交换网络中支持区分服务,提出了一种新颖的控制分组调度算法,即基于优先级权重的公平队列调度算法.近似的调度分析模型用来简化对不同级别的调度权重的求解.:同时定义了一种参数来评估分析模型的有效性和调度算法的公平性.仿真试验结果证实了该分析模型在负载较高时是非常有效的,而且调度算法能提供很好的公平性.     

一种改善IP网络中基于类的数据服务QoS的调度方法

IP网络中基于类的数据服务QoS支持一般包括包的延时、吞吐量和丢失率,目前的研究成果大都集中于对其中某一个指标的确保或支持。该文提出一种在IP网络中一个网络路由器节点上同时考虑类间流量带宽、包丢失和延时区分的队列管理调度算法,称为动态比例自适应算法(Dynamic Proportional Adaptive Algorithm,DPAA)。该算法是针对比例区分服务PDS(Proportional Differentiated Services)中流量负载频繁变化的情况提出的。仿真实验通过与前人提出的基于比例区分服务模型的调度算法比较,证明了DPAA 算法的有效性。     

E-UTRA中一种多业务两步比率公平调度算法

符合3GPP多业务处理原则的子信道调度方案是影响E-UTRA系统性能的关键技术。为减少填充和提高多用户分集效应,提出了一种多业务两步比率公平调度算法。在不区分用户业务优先级的情况下,先采用实际缓存量替代传统比率公平算法中的传输速率来分配子信道;业务优先级高的未分配用户再按比率公平算法确认的优先权重从低到高来挤占业务优先级低的用户所分配的子信道,从而确保符合3GPP提出的服务完高优先级业务后再服务低优先级业务的多业务处理原则。仿真结果表明,该算法能在保证用户公平的基础上提高系统吞吐量。     

An Internet‐style approach to wireless link errors

Wireless links differ from traditional ‘wired’ links in two ways that challenge the existing Internet. On wireless links packet loss or corruption due to transmission errors is not rare, which calls into question the standard Internet assumptions that transmission errors should be corrected by transport‐level protocols at end systems and that end‐to‐end packet loss typically indicates network congestion. Also, the severity and location‐ dependent nature of these errors calls into question the meaning of ‘fair’ scheduling, per‐flow quality of service, and even looser notions such as service level agreements, when applied to wireless links. An important question is whether the two unique problems posed by wireless links can be successfully addressed within the standard Internet architecture, as opposed to requiring new transport protocols designed specifically for wireless links or requiring wireless links to ‘fix up’ the operation of specific end‐to‐end protocols. We provide experimental evidence that a combination of protocol‐blind link‐level local error control, which lessens the damage, and error‐sensitive link scheduling, which ensures sensible outcomes in response to link capacity loss, provides a good operating environment while adhering to traditional Internet design practices. Copyright © 2001 John Wiley & Sons, Ltd.     

Temporal fairness guarantee in multi-rate wireless LANs for per-flow protection

Wireless LAN technologies such as IEEE 802.11a and 802.11b support high bandwidth and multi-rate data transmission to match the channel condition (i.e., signal to noise ratio). While some wireless packet fair queuing algorithms to achieve the per-flow throughput fairness have been proposed, they are not appropriate for guaranteeing QoS in multi-rate wireless LAN environments. We propose a wireless packet scheduling algorithm that uses the multi-state (multi-rate) wireless channel model and performs packet scheduling by taking into account the channel usage time of each flow. The proposed algorithm aims at per-flow protection by providing equal channel usage time for each flow. To achieve the per-flow protection, we propose a temporally fair scheduling algorithm called Contention-Aware Temporally fair Scheduling (CATS) which provides equal channel usage time for each flow. Channel usage time is defined as the sum of the packet transmission time and the contention overhead time due to the CSMA/CA mechanism. The CATS algorithm provides per-flow protection in wireless LAN environments where the channel qualities of mobile stations are dynamic over time, and where the packet sizes are application-dependent. We also extend CATS to Decentralized-CATS (D-CATS) to provide per-flow protection in the uplink transmission. Using an NS-2 simulation, we evaluate the fairness property of both CATS and D-CATS in various scenarios. Simulation results show that the throughput of mobile stations with stable link conditions is not degraded by the mobility (or link instability) of other stations or by packet size variations. D-CATS also shows less delay and less delay jitter than FIFO. In addition, since D-CATS can coordinate the number of contending mobile stations, the overall throughput is not degraded as the number of mobile stations increases. This work was supported in part by the Brain Korea 21 project of Ministry of Education and in part by the National Research Laboratory project of Ministry of Science and Technology, 2004, Korea.     

无线网络中的分组调度算法

探讨了将有线网络的分组调度算法引入无线网络需要改进的事项,分析了公平排队算法,建立了一个基本的无线分组调度模型,并综述了一些目前存在的无线分组调度算法。     

Wireless Packet Scheduling Algorithm for OFDMA System Based on Time‐Utility and Channel State

In this paper, we propose an urgency‐ and efficiencybased wireless packet scheduling (UEPS) algorithm that is able to schedule real‐time (RT) and non‐real‐time (NRT) traffics at the same time while supporting multiple users simultaneously at any given scheduling time instant. The UEPS algorithm is designed to support wireless downlink packet scheduling in an orthogonal frequency division multiple access (OFDMA) system, which is a strong candidate as a wireless access method for the next generation of wireless communications. The UEPS algorithm uses the time‐utility function as a scheduling urgency factor and the relative status of the current channel to the average channel status as an efficiency indicator of radio resource usage. The design goal of the UEPS algorithm is to maximize throughput of NRT traffics while satisfying quality‐of‐service (QoS) requirements of RT traffics. The simulation study shows that the UEPS algorithm is able to give better throughput performance than existing wireless packet scheduling algorithms such as proportional fair (PF) and modifiedlargest weighted delay first (M‐LWDF), while satisfying the QoS requirements of RT traffics such as average delay and packet loss rate under various traffic loads.     

一种具有小尺度公平的无线分组调度算法

本文在调度判决时考虑到用户的访问时延限制,比例公平调度算法基础上提出了M-PF算法。本文建立了无线分组调度系统模型,通过仿真对新算法在小尺度服务时间保证、大尺度服务时间公平和系统吞吐量等方面的性能进行分析,研究了系统参数对算法性能的影响。结果证明,新算法在保证系统吞吐量和大尺度公平性的同时可以提供更好的小尺度服务时间保证。     

Soft QoS provisioning using the token bank fair queuing scheduling algorithm

Future-generation wireless packet networks will support multimedia applications with diverse QoS requirements. Much of the research on scheduling algorithms has been focused on hard QoS provisioning of integrated services. Although these algorithms give hard delay bounds, their stringent requirements sacrifice the potential statistical multiplexing performance and flexibility of the packet-switched network. Furthermore, the complexities of the algorithms often make them impractical for wireless networks. There is a need to develop a packet scheduling scheme for wireless packet-switched networks that provides soft QoS guarantees for heterogeneous traffic, and is also simple to implement and manage. This article proposes token bank fair queuing (TBFQ), a soft scheduling algorithm that possesses these qualities. This algorithm is work-conserving and has a complexity of O(1). We focus on packet scheduling on a reservation-based TDMA/TDD wireless channel to service integrated real-time traffic. The TBFQ scheduling mechanism integrates the policing and servicing functions, and keeps track of the usage of each connection. We address the impact of TBFQ on mean packet delay, violation probability, and bandwidth utilization. We also demonstrate that due to its soft provisioning capabilities, the TBFQ performs rather well even when traffic conditions deviate from the established contracts.     

QoS-oriented access control for 4G mobile multimedia CDMAcommunications

An efficient medium access control protocol with fair packet loss sharing packet scheduling is proposed for wireless code-division multiple access communications. The proposed MAC protocol exploits both time-division and code-division statistical multiplexing. The FPLS scheduler uses the information of traffic rate distribution and quality of service requirements to assign priorities to the users and determines an efficient combination of the packets for transmission in the time slots of each frame, so the number of the served users is maximized under the QoS constraints. Simulation results demonstrate the effectiveness of the FPLS scheduler, in comparison with other previously proposed scheduling algorithms     

Improving Quality of Service and Assuring Fairness in WLAN Access Networks

As public deployment of wireless local area networks (WLANs) has increased and various applications with different service requirements have emerged, fairness and quality of service (QoS) are two imperative issues in allocating wireless channels. This study proposes a fair QoS agent (FQA) to simultaneously provide per-class QoS enhancement and per-station fair channel sharing in WLAN access networks. FQA implements two additional components above the 802.11 MAC: a dual service differentiator and a service level manager. The former is intended to improve QoS for different service classes by differentiating service with appropriate scheduling and queue management algorithms, while the latter is to assure fair channel sharing by estimating the fair share for each station and dynamically adjusting the service levels of packets. FQA assures (weighted) fairness among stations in terms of channel access time without decreasing channel utilization. Furthermore, it can provide quantitative service assurance in terms of queuing delay and packet loss rate. FQA neither resorts to any complex fair scheduling algorithm nor requires maintaining per-station queues. Since the FQA algorithm is an add-on scheme above the 802.11 MAC, it does not require any modification of the standard MAC protocol. Extensive ns-2 simulations confirm the effectiveness of the FQA algorithm with respect to the per class QoS enhancement and per-station fair channel sharing     

一种适用于W-CDMA系统的多业务无线资源调度算法

3G系统将以分组交换方式提供语音、数据、视频等具有不同QoS要求的多种业务，资源调度对保证系统服务质量和提高资源利用效率起关键作用．本文提出了一种基于业务类型、当前待发送负荷以及剩余延时限的时间调度策略和基于资源优化的资源调度策略，并使无线链路的传输质量与业务的优先级水平一致．通过系统仿真评价了算法的性能．     

Using channel state dependent packet scheduling to improve TCPthroughput over wireless LANs

In recent years, a variety of mobile computers equipped with wireless communication devices have become popular. These computers use applications and protocols, originally developed for wired desktop hosts, to communicate over wireless channels. Unlike wired networks, packets transmitted on wireless channels are often subject to burst errors which cause back to back packet losses. In this paper we study the effect of burst packet errors and error recovery mechanisms employed in wireless MAC protocols on the performance of transport protocols such as TCP. Most wireless LAN link layer protocols recover from packet losses by retransmitting lost segments. When the wireless channel is in a burst error state, most retransmission attempts fail, thereby causing poor utilization of the wireless channel. Furthermore, in the event of multiple sessions sharing a wireless link, FIFO packet scheduling can cause the HOL blocking effect, resulting in unfair sharing of the bandwidth. This observation leads to a new class of packet dispatching methods which explicitly take wireless channel characteristics into consideration in making packet dispatching decisions. We compare a variety of channel state dependent packet (CSDP) scheduling methods with a view towards enhancing the performance of transport layer sessions. Our results indicate that by employing a CSDP scheduler at the wireless LAN device driver level, significant improvement in channel utilization can be achieved in typical wireless LAN configurations. This revised version was published online in July 2006 with corrections to the Cover Date.