LTE系统中提高TCP性能的资源调度算法研究

LTE可以提供真正无处不在基于IP的移动宽带业务,但随着承载网的IP化,网络拥塞、丢包、抖动、延时等质量问题将影响到LTE业务层的QoS质量.作为LTE无线资源管理的核心,研究并设计一个良好的资源调度算法是提高数据业务的性能和终端用户的体验是一个亟待解决的重要任务.本文通过借鉴LTE对VoIP数据分组的半持续调度算法的思想,提出了一种LTE的无线资源调度的改进方案.方案将TCP确认包映射到具有更高优先级的空闲逻辑信道,从而降低了ACK包在无线信道中发生丢弃和拥塞的概率,避免了TCP拥塞控制机制的频繁开启.仿真结果表明,本文提出的TCP确认包映射转换方案在RTT时延、吞吐量等方面均有一定的提升,具有一定的稳定性和性能优势.     

OFDMA系统中基于遗传算法的资源分配

资源分配是OFDMA系统中保证用户QoS和提高系统容量的一种重要手段.在传统的OFDMA资源分配算法中,分组调度和子载波分配两部分是独立进行优化的.为了进一步提高系统的整体性能,提出一种基于遗传算法的分组调度和子载波分配联合优化的资源分配算法.资源分配算法中,利用随机逼近的方法来更新调度算法中的控制参数,在保证用户公平性的前提下最大化系统吞吐量;利用遗传算法来求解联合优化中的子载波分配.仿真结果表明,无论是在系统的吞吐量、丢包率,数据包等待时延还是用户公平性方面,都具有良好的性能.     

网络控制系统的一种变采样周期动态调度策略

提出一种基于网络运行状态的网络控制系统动态调度器的设计方法．首先利用监测器在线获取当前的网络利用率、网络诱导误差和数据包执行时间，基于获取的网络状态，预测下一监测周期内的网络利用率和数据包执行时间．然后按照网络运行性能和控制性能的需求，基于网络利用率和数据包执行时间的预估值分配网络资源，计算控制系统新的采样周期．当数据包传输发生冲突时，采用MEF（Maximum Error First）作为辅助调度策略，确定数据包的发送优先级．最后通过一组仿真结果验证了所设计的动态调度器的有效性．     

A traffic-class burst-polling based delta DBA scheme for QoS in distributed EPONs

Ethernet passive optical network (EPON) preserves the merits of traditional Ethernet network while reducing complexities and improving quality of service (QoS). In this paper, a traffic-class burst-polling based delta dynamic bandwidth allocation (TCBP-DDBA) scheme is presented to provide better QoS to expedited forwarding packet and maximize channel utilization service to assure forwarding and best effort packets. The network resources are efficiently utilized and adaptively allocated to the three traffic classes by guaranteeing the requested QoS. Simulation results using OPNET show that the TCBP-DDBA scheme performs well in comparison to the conventional allocation scheme for a set of given parameters such as: packet delay, queue size, packet delay variation and channel utilization. This work considers system-wide DBA development in contrast to unit-based approach. It is concluded that the algorithm can be used for many types of EPON-based practical distributed networks.     

带有扩散程度估计的机会网络分组调度机制

根据数据分组扩散程度与投递状态具有直接关系的特点,提出一种带有数据分组扩散程度估计的机会网络分组调度机制。通过机会网传输机制估计每个数据分组的扩散程度,利用动态效用函数估算其效用值。在分组调度时删除效用值小的数据分组,以节点之间的相遇概率作为数据分组优先转发的依据。仿真结果显示,该机制能够提高数据分组的成功投递率,降低网络负载率及数据分组的传输时延。     

TEMPEST: a new Test EnvironMent for Performance Evaluation of the Scheduling of packeTs

The packet scheduling problem has been deeply studied for lot of years by researchers in the computer science and telecommunications fields as an important solution that decides the order in which packets are sent over a link in order to provide QoS on a network. Recently, the packet scheduling has become again a challenging topic due to the massive use of wireless technologies (e.g. WiFi, LTE, 4G/5G) with which to provide high QoS guarantees is still an open problem. Unfortunately, it is difficult to compare different solutions and actually test them in order to select the most proper packet scheduler for each particular environment. In this paper we present TEMPEST, a new Test EnvironMent for Performance Evaluation of the Scheduling of packeTs, which is a novel tool able to help the research in the packet scheduling field. TEMPEST is able to measure the actual performance of a packet scheduler in several environments, both wired or wireless, like the execution time, QoS metrics and throughput, giving prompt feedback about the quality of the solution studied. The goal of this paper is to present in detail the current features of TEMPEST, showing how it is easy to add, configure, test and evaluate several scheduling solutions in multiple scenarios.     

基于TDMA的空中自组网MAC层资源调度算法研究

空中移动无线自组织网络是一种拓扑结构快速变化,有自组织性的多跳无中心网络;针对传统时隙分配算法资源利用率低、吞吐量不足、通信距离近等问题,采用引入分配系数的混合时隙分配模式,通过节点业务优先级和流量预测相结合,设计了一种基于TDMA定向分布式资源动态调度算法（M-TDMA）;对比分析了节点数量、传输速率、分配系数以及不同拓扑等多个维度对算法传输时延、吞吐量以及丢包率的影响;最后通过仿真实验对资源调度算法进行验证;仿真结果表明,在20个网络节点时,网络的最大传输时延小于600 ms,网络吞吐量可以达到4.5 Mbps以上, M-TDMA算法通过高效的资源调度,有效降低了网络传输时延并提高了网络吞吐量;     

OFDMA 协同网络中基于QoS 保证的资源分配算法

针对正交频分多址(OFDMA)协作通信系统,为了解决数据传输速率最大化并提供尽力而为业务与实时业务的服务质量(QoS)保证问题,提出新型资源分配算法.通过以总功率受限为约束条件,定义基于数据速率、时延和丢包率的效用函数,并以在协作传输中以最大化效用函数为目标进行中继选择和子载波分配.通过中继和用户上的子载波和功率分配方案的设计,从而最大化网络数据传输速率并最小化时延与丢包率,为多种业务提供服务质量保证.采用最优化理论与方法求解效用函数,得到了资源分配结果.仿真结果验证了算法收敛,并给出功率分配结果,以及网络吞吐量和时延性能指标情况,验证了算法的有效性.     

基于HSDPA的增强型分组调度算法研究

从系统吞吐量、用户公平性等方面分析研究了HSDPA系统中支持非实时业务的三种经典分组调度算法RR、Max C/I和PF。针对PF算法重传时延过长问题,提出了一种结合混合自动请求重传HARQ的增强分组调度算法。该算法通过提高重传分组的优先级降低重传时延,有效地避免系统资源的浪费。MATLAB仿真结果表明,该算法在降低单用户重传时延的同时,仍能保证用户间的公平性和系统的吞吐量。     

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.     

基于电网的采样感知加权循环调度算法

针对智能电网相量测量设备竞争使用有限的网络通信资源时，会因资源分配不均而导致数据包延时或丢失，进而影响电力系统状态估计的精度这一问题，提出了一种采样感知加权循环（SAWRR）调度算法。首先根据电网相量测量单元（PMU）采样频率和数据包大小的特性，提出了基于PMU业务流均方差的权重定义方法；然后设计了相应的PMU采样感知迭代循环调度算法；最后将该算法运用到PMU采样传输模型中。该算法能自适应地感知PMU的采样变化，及时调整数据包的传输。仿真结果表明，与原始的加权循环调度算法相比，SAWRR算法减少了95%的PMU采样数据包的调度时延，降低了一半的丢包率，增加了两倍的吞吐量。将SAWRR算法运用到PMU数据传输中有利于保证智能电网的稳定性。     

Integrated connection-level and packet-level QoS controls over wireless mesh networks

This paper focuses on integrating connection-level and packet-level QoS controls over wireless mesh network (WMN) to support applications with diverse QoS performance requirements. At the connection-level, the dynamic guard based prioritized connection admission control (DG-PCAC) provides prioritized admission with relative connection blocking probabilities and end-to-end deterministic minimum bandwidth allocation guarantees. DG-PCAC is enabled by dynamic guard based logical link configuration controls (LCCs), which provides relative differentiated capacity limits for prioritized admission classes. At the packet-level, the optimal rate delay scheduler (ORDS) dynamically allocates link bandwidth to the admitted flows of prioritized traffic classes; with the objective to minimize deviation from relative delay targets with minimum bandwidth guarantees according to traffic classes. Two realizations of the ORDS are presented, namely optimal scheduling policy via dynamic programming (DP) algorithm, and neural network (NN) based heuristic to alleviate computational complexity. Performance results show that the DG-PCAC enables consistent performance guarantees under non-stationary arrivals of connection requests. Performance results also show that the performance of the NN based scheduling heuristic approaches to that of the DP based optimal ORDS scheme.     

图书馆多媒体业务流的短时公平分组反馈调度方法

研究了一种新的基于短时公平的分组调度算法的问题. 基于短时公平性的分组反馈调度算法改进了WF2Q＋算法在短期内无法为新加入客户端提供公平服务的缺陷,增强了调度算法的适应性和公平性. 在本算法中,调度器中的各个客户端权值能够根据其获得的实际服务量状况在线调整,增强了系统的鲁棒性和自适应性,同时提高了系统实现短期公平性的能力,对各个客户端提供更为公平的服务质量（Quality of Service,QoS）.     

Flubber: Two-level disk scheduling in virtualized environment

While virtualization enables multiple virtual machines (VMs)—with multiple operating systems and applications—to run within a physical server, it also complicates resource allocations trying to guarantee Quality of Service (QoS) requirements of the diverse applications running within these VMs. As QoS is crucial in the cloud, considerable research efforts have been directed towards CPU, memory and network allocations to provide effective QoS to VMs, but little attention has been devoted to disk resource allocation.This paper presents the design and implementation of Flubber, a two-level scheduling framework that decouples throughput and latency allocation to provide QoS guarantees to VMs while maintaining high disk utilization. The high-level throughput control regulates the pending requests from the VMs with an adaptive credit-rate controller, in order to meet the throughput requirements of different VMs and ensure performance isolation. Meanwhile, the low-level latency control, by the virtue of the batch and delay earliest deadline first mechanism (BD-EDF), re-orders all pending requests from VMs based on their deadlines, and batches them to disk devices taking into account the locality of accesses across VMs. We have implemented Flubber and made extensive evaluations on a Xen-based host. The results show that Flubber can simultaneously meet the different service requirements of VMs while improving the efficiency of the physical disk. The results also show improvement of up to 25% in the VM performance over state-of-art approaches: for example, in contract to the default Xen disk I/O scheduler—Completely Fair Queueing (CFQ)—besides achieving the desired QoS of each VM, Flubber speeds up the sequential and random reads by 17% and 25%, respectively, due to the efficient physical disk utilization.     

Delivering relative differentiated services in future high-speed networks using hierarchical dynamic deficit round robin

With the increasing deployment of real-time audio/video services over the Internet, provision of quality of service (QoS) has attracted much attention. When the line rate of future networks upgrades to multi-terabits per second, if routers/switches intend to deliver differentiated services through packet scheduling, the reduction of computational overhead and elimination of bottleneck resulting from memory latency will both become important factors. In addition, the decrease of average queueing delay and provision of small delays for short packets are two further critical factors influencing the delivery of better QoS for real-time applications. The advanced waiting time priority (AWTP) is a timestamp-based packet scheduler which is enhanced from the well-known WTP. Although AWTP considers the effect of packet size, the latency resulting from timestamp access and a great quantity of computational overhead may result in bottlenecks for AWTP being deployed over high-speed links. Many existing schedulers have the same problems. We propose a multi-level hierarchical dynamic deficit round-robin (MLHDDRR) scheduling scheme which is enhanced from the existing dynamic deficit round-robin scheduler. The new scheme can resolve these issues and efficiently provide relative differentiated services under a variety of load conditions. Besides, MLHDDRR can also protect the highest priority traffic from significant performance degradation due to bursts of low-priority traffic. We compare the performance of AWTP with the proposed scheme. Extensive simulation results and complexity analysis are presented to illustrate the effectiveness and efficiency of MLHDDRR.     

WiMAX网络中基于优先级的视频分组调度算法

无线视频传输是网络传输的研究热点,在WiMAX网络中,实时轮询业务(rtPS)的典型应用是实时视频传输,当前使用较多的是先进先出(FIFO)和最早到达期限数据优先(EDF)队列调度算法,其中EDF算法多用于多业务之间的资源分配,而非单个业务流队列的出对调度。在视频优先级以及WiMAX网络为单个视频流分配带宽限定的条件下进行调度算法的研究,以期待在带宽有限的情况下得到更高的视频服务质量。     

GAME based dynamic resource scheduling in QoS aware radio access networks

Radio resource management and QoS are finally inseparable in wideband CDMA networks. In this paper, we propose a novel wireless resource scheduler, called GAME-C, that integrates our genetic algorithm for mobiles equilibrium (GAME) with the standard CDMA transmitter closed loop power control (CLPC). GAME assigns optimally both transmitting power and bit rate to every mobile station. Optimal allocation is in the sense that every user gets only enough resources necessary for meeting or exceeding its QoS requirements while minimizing interference to other users. Having done that, we gain further benefits as well. In addition to QoS provisioning, lower transmitting power extends a mobile station battery life. Moreover, the base station coverage efficiency is improved by decreasing the probability of blocking new connections or dropping current ones. In short, GAME-C expands the number of QoS-satisfied mobile stations in a cell. Various simulations show improvements achieved over the established (CLPC) basic scheme.     

Bandwidth guaranteed multicast scheduling for virtual output queued packet switches

Multicast enables efficient data transmission from one source to multiple destinations, and has been playing an important role in Internet multimedia applications. Although several multicast scheduling schemes for packet switches have been proposed in the literature, they usually aim to achieve only short multicast latency and high throughput without considering bandwidth guarantees. However, fair bandwidth allocation is critical for the quality of service (QoS) of the network, and is necessary to support multicast applications requiring guaranteed performance services, such as online audio and video streaming. This paper addresses the issue of bandwidth guaranteed multicast scheduling on virtual output queued (VOQ) switches. We propose the Credit based Multicast Fair scheduling (CMF) algorithm, which aims at achieving not only short multicast latency but also fair bandwidth allocation. CMF uses a credit based strategy to guarantee the reserved bandwidth of an input port on each output port of the switch. It keeps track of the difference between the reserved bandwidth and actually received bandwidth, and minimizes the difference to ensure fairness. Moreover, in order to fully utilize the multicast capability provided by the switch, CMF lets a multicast packet simultaneously send transmission requests to multiple output ports. In this way, a multicast packet has more chances to be delivered to multiple destination output ports in the same time slot and thus to achieve short multicast latency. Extensive simulations are conducted to evaluate the performance of CMF, and the results demonstrate that CMF achieves the two design goals: fair bandwidth allocation and short multicast latency.     

Load-balanced three-stage switch

A load-balanced two-stage switch is scalable and can provide close to 100% throughput. Its major problem is that packets can be mis-sequenced when they arrive at outputs. In a recent work, the packet mis-sequencing problem is elegantly solved by a feedback-based switch architecture. In this paper, we extend the feedback-based switch from two-stage to three-stage for further cutting down average packet delay while still ensuring in-order packet delivery and close to 100% throughput. The basic idea is to use the third stage switch to map heavy flows to experience less middle-stage delays. To identity heavy flows, an adaptive traffic estimation algorithm is proposed. To ensure max-min fairness in bandwidth allocation under any inadmissible traffic pattern, an efficient fair scheduler is devised.     

IEEE802.16e的实时上行链路调度服务优化算法

深入分析了IEEE802.16e建议的三种实时调度服务算法：UGS、rtPS、ertPS，并在此基础上提出了一种优化的实时调度服务算法：irtPS。该优化的调度服务算法在保证变化数据率实时上行链路的延时性能基础上，最大限度地提高了实时上行链路的资源利用率。数学建模分析结果显示，在保证延时性能的前提下，该优化的调度服务算法的系统容量较IEEE802.16e建议算法的系统容量有显著增加。