双服务器分组调度算法

分组调度算法对于确保分组交换系统的QoS具有重要意义。时延,公平性,计算复杂度是微量分组度算法的主要指标。本文提出了一种双服务器分组调度算法,该算法在两种不同的工作状态下分别采用两种服务规则决定分组的服务次序。其中一种服务规则用来确保分组的时延,另一种服务规则在时延得到保障的情况下对系统的公平性进行改善,这两种规则计算都不复杂。因此本文提出的算法具有时延低,公平性较好,计算复杂度低的特点。     

LTE系统上行链路调度算法研究

长期演进(Long Term Evolution,LTE)已经成为4G无线技术标准。目前,LTE分组调度的下行链路调度被大多数研究者研究,上行链路的研究相对较少。针对上行链路调度无法保证实时业务分组在延迟期限内传输,存在公平性较差、分组丢弃多的问题。因此,提出了一种新的上行链路调度算法。该算法根据实时业务的延迟约束条件建立目标整数线性规划模型,再根据目标整数线性规划模型进行调度。实验结果表明,该算法能保证实时业务分组在延迟期限内传输,适用于实时业务,能确保公平性,最小化分组丢弃,具有较好的适用性。     

阵列天线波束成形技术在宽带CDMA下行链路中的应用

本文利用自适应天线阵列上行链路信号到达角估计信息,并结合导频辅助下行链路信道矩阵估计值,在前人提出的具有反馈特性的自适应发送阵列原理基础上,提出一种简单可行的宽带CDMA下行链路天线阵列波束成形权重计算方法,并进一步分析了到达角估计误差和信道信息反馈时延对权重计算的影响,最后给出系统误码率性能的计算机仿真结果。     

LL-DRR:一种有效的用于高速分组网络的调度算法

该文在亏空轮循(Deficit Round Robin,DRR)算法的基础上提出了一种新的适用于变长分组的调度算法低时延亏空轮循(Low Latency Deficit Round Robin,LL-DRR)。仿真和理论分析表明,在时延性能上LL-DRR比DRR有显著的改善,并具有连接的最大时延与连接数无关的特性,可以支待实时业务。LL-DRR继承了DRR在平均吞吐率上的公平性。LL-DRR易于实现且适用于高速网络。     

一类基于调度表的公平轮循调度算法

本文研究了一类利用时标在调度表中安排信元发送时隙的公平轮循(Fair Round Robin,FRR)调度算法.对其中三种算法的性能进行了分析比较.FRR能够保证连接的带宽和时延,同时实现复杂性低于一些分组公平排队算法,例如WF²Q+.     

CoMP上行链路基于属性的自适应分组算法

针对传统协作多点传输技术(Co MP)系统的上行链路用户配对算法在实际系统中存在系统整体效率不高的问题,提出了一种基于用户属性的自适应分组算法。该算法以可量化的用户属性为参数,通过最小最大原则确定分组数量,利用k-means方法进行用户聚类,实现了对小区中用户的按属性自适应分组,增加了同时传输的用户数量,将基站侧多天线的数量优势转化为上行传输性能,提高了系统上行和容量。仿真结果表明,所提算法能够有效提高系统的上行和容量,且在低信噪比(SNR)条件下仍可以获得预期的性能提升。     

一种基于紧急程度的自时钟开始时间公平排队分组调度算法

为了克服目前GPS (Generalized Processor Sharing)类调度算法中实时应用分组的排队时延较大且不稳定的局限性,该文提出一种新的分组排队调度算法,该调度算法在计算分组服务标签时添加了一个紧急程度函数,调整了到达分组间的竞争关系,从而可以按照实时性应用的要求来调整到达分组的转发先优级,由此显著降低了实时性应用分组的排队时延和抖动幅度。分析和仿真实验表明,与GPS类其它调度算法相比,该调度算法对于实时应用的分组能提供较低的、更稳定的排队时延保证,同时还继承了GPS类算法的公平性和排队时延有界等特性,而且对系统虚拟时间的跟踪计算更为简捷高效。     

基于相继干扰消除和跨层并发传输的物联网数据聚合调度

近年来物联网在许多军事和民用领域(灾后恢复、环境监控和军事对抗等)展现出蓬勃的应用前景,而在实际应用中,为了维护终端数据的新鲜度,必须以尽可能低的时延来完成数据聚合调度,从而为用户提供及时准确的数据服务.但是,受信号干扰的影响,最低时延数据聚合调度问题已被证明是NP(Non-deterministic Polynomial)难问题,而如何设计低时延的数据聚合调度算法是物联网领域的研究热点.现有面向传统物联网(如无线传感网)的解决方案通常采用逐层调度方法和干扰避免技术来实现,减少了可并发传输的链路数目,不利于降低数据聚合时延.值得关注的是,相继干扰消除(Successive Interference Cancellation,SIC)技术作为一种简单而强大的多包接收技术,是研究者近年来取得的重大突破,而如何结合SIC技术来设计物联网低时延数据聚合调度算法具有非常重要的理论研究意义.因此,本文以最大程度地增加可并发传输的链路数目为目标,利用跨层并发传输的思想来进行数据聚合调度,并结合SIC技术来实现链路调度,提出了一种新颖的低时延数据聚合调度算法.实验结果表明,与现有算法相比,本文所提算法在数据聚合时延优化方面最多可达43.8％.     

Ad hoc网络中基于多波束天线的集中式低时延调度算法

UxDMA算法是一种高效的集中式算法,是用于时分多址、频分多址和码分多址信道分配的统一算法。在UxDMA的基础上,利用多波束天线的多波束形成能力,针对低时延定向ad hoc网络提出了一种集中式调度算法——CLSM(Centralized Low-delay Scheduling Algorithm Based on Multi-beam Antennas)。CLSM通过不同时延等级限制的报文来比较着色后发送链路的优先级,优先选择高优先级链路传输。通过仿真验证了CLSM的性能：与UxDMA相比,该算法在多时延限制的发送端调度中表现出了更好的吞吐量和时延性能。     

LTE系统的下行分组调度算法研究

在LTE系统中,调度功能由位于e Node B的调度器完成,包括下行调度器和上行调度器,分别负责管理下行和上行链路的资源分组调度。相对于由RNC控制资源分组调度的WCDMA系统而言,LTE系统可以及时根据信道情况自适应改变调制方式和编码速率,并减少系统的传输延迟。本文重点研究了TD-LTE系统的下行分组调度算法,在分析经典分组调度算法及其评价标准的基础上,给出了一种新的基于Qo S参数的分组调度算法——RAD算法。该方案的主要目的是按照实际网络中各用户的需求,优先完成QCI等级高的用户的数据传输,以尽量减少重传次数,同时兼顾公平原则。     

Novel algorithm for time division multiple access in broadband ISDN passive optical networks

For shared access to a broadband communication network using the asynchronous transfer mode (ATM) a passive optical network (PON) has previously been proposed. A novel algorithm to evaluate the time division multiple access (TDMA) protocol which controls the traffic from the various subscribers towards the shared access equipment (upstream direction) is proposed. It uses counters to estimate the moment of a data packet arrival at the subscriber side. By this ‘look-ahead’ technique no extra upstream channels are needed to initiate the polling by the subscriber. The algorithm guarantees fair access for all subscribers and minimizes the necessary overhead. Both the maximum access delay and overhead may be readily calculated, and the obtained results were supported by numerical simulation. Applicability in the standard broadband network environment has been proved by hardware design simulation.     

Analysis of a polling system for telephony traffic with application to wireless LANs

Recently, polling has been included as a resource sharing mechanism in the medium access control (MAC) protocol of several communication systems, such as the IEEE 802.11 wireless local area network, primarily to support real-time traffic. Furthermore, to allow these communication systems to support multimedia traffic, the polling scheme often coexists with other MAC schemes such as random access. Motivated by these systems, we develop a model for a polling system with vacations, where the vacations represent the time periods in which the resource sharing mechanism used is a non-polling mode. The real-time traffic served by the polling mode in our study is telephony. We use an on-off Markov modulated fluid (MMF) model to characterize telephony sources. Our analytical study and a counterpart validating simulation study show the following. Since voice codec rates are much smaller than link transmission rates, the queueing delay that arises from waiting for a poll dominates the total delay experienced by a voice packet. To keep delays low, the number of telephone calls that can be admitted must be chosen carefully according to delay tolerance, loss tolerance, codec rates, protocol overheads and the amount of bandwidth allocated to the polling mode. The effect of statistical multiplexing gain obtained by exploiting the on-off characteristics of telephony traffic is more noticeable when the impact of polling overhead is small.     

Performance analysis of bandwidth requests under unicast, multicast and broadcast pollings in IEEE 802.16d/e

In the polling mode in IEEE 802.16d/e, one of three modes: unicast, multicast and broadcast pollings, is used to reserve bandwidth for data transmission. In the unicast polling, the BS polls each individual MS to allow to transmit a bandwidth request packet, while in the multicast and broadcast pollings, the truncated binary exponential backoff (TBEB) mechanism is adopted as a contention resolution among mobile stations (MSs) in a multicast or broadcast group. This paper investigates the delay of bandwidth requests in the unicast, multicast and broadcast pollings, by deriving the delay distribution of the unicast polling and the TBEB by means of analytical methods. We consider an error-free channel as well as an error-prone channel with i.i.d. constant packet error rate per frame. Furthermore, we find the utilization of transmission opportunity to see efficiency of the bandwidth in the TBEB. Performance evaluations are provided to show that analytical results are well-matched with simulations. By the numerical results, we can find the optimal parameters such as the initial backoff window size of the TBEB and the number of transmission opportunities (or slots) satisfying quality of service (QoS) requirement on delay and loss, and thus we can determine which scheme is better than others depending on the probability of a request arrival during one frame. Numerical examples address that the TBEB performs better than the unicast polling for light traffic loads and vice versa for heavy traffic loads. Also, it is shown that the multicast polling has better performance than the broadcast polling in the sense of shorter delay, lower loss probability and higher utilization of transmission opportunity.     

Performance analysis of the ATM shuffleout switch under arbitrarynonuniform traffic patterns

Shuffleout is a blocking multistage asynchronous transfer mode (ATM) switch using shortest path routing with deflection, in which output queues are connected to all the stages. This paper describes a model for the performance evaluation of the shuffleout switch under arbitrary nonuniform traffic patterns. The analytical model that has been developed computes the load distribution on each interstage link by properly taking into account the switch inlet on which the packet has been received and the switch outlet the packet is addressing. Such a model allows the computation not only of the average load per stage but also its distribution over the different links belonging to the interstage pattern for each switch input/output pair. Different classes of nonuniform traffic patterns have been identified and for each of them the traffic performance of the switch is evaluated by thus emphasizing the evaluation of the network unfairness     

Analysis of an identifier splitting algorithm combined with polling(ISAP) for contention resolution in a wireless access network

A contention resolution scheme for an uplink contention channel in a wireless access network is presented. The scheme consists of a tree algorithm, namely the identifier splitting algorithm (ISA), combined with a polling scheme. Initially, ISA is used, but at a certain level of the tree, the scheme switches to polling of the stations. This scheme is further enhanced by skipping a few levels in the tree when starting the algorithm (both in a static and a dynamic way) and by allowing multiple instants simultaneously. An analytical model of the system and its variants leads to the evaluation of its performance, by means of the delay density function and the throughput characteristics. This model is used to investigate the influence of the packet arrival rate, the instant at which the ISA scheme switches to polling, the starting level of the ISA scheme, and the use of multiple instances on the mean delay, the delay quantiles, and the throughput     

Analysis of mean packet delay for upstream transmissions in passive optical networks with sleep mode

The sleep mode has been introduced to improve the energy efficiency of passive optical networks (PONs) with interleaved polling with adaptive cycle time (IPACT) as a medium access control (MAC) scheme. For energy saving, the sleep mode of each optical network unit (ONU) is activated based on the packet queue length for upstream traffic. We model such a PON as an N-user M/G/1 queue with reservations and vacations. Based on the framework of M/G/1 queueing analysis with some modification made to incorporate the nature of IPACT as well as the sleep mode, we derive a closed form expression of the mean packet delay. A unique challenge in our analysis is that certain quantities such as the residual time of an on-going sleep period for the upstream channel must be considered from the network's viewpoint while the delay due to the sleep mode experienced by a packet must be considered from the ONU's viewpoint. Simulation experiments are conducted to validate the analytical results and to show that the results are relatively insensitive to packet arrival statistics for large sleep periods. Finally, we demonstrate how a sleep period can be chosen given the quality-of-service (QoS) requirement on the mean packet delay.     

Modeling multiple IP traffic streams with rate limits

We start with the premise, and provide evidence that it is valid, that a Markov-modulated Poisson process (MMPP) is a good model for Internet traffic at the packet/byte level. We present an algorithm to estimate the parameters and size of a discrete MMPP (D-MMPP) from a data trace. This algorithm requires only two passes through the data. In tandem-network queueing models, the input to a downstream queue is the output from an upstream queue, so the arrival rate is limited by the rate of the upstream queue. We show how to modify the MMPP describing the arrivals to the upstream queue to approximate this effect. To extend this idea to networks that are not tandem, we show how to approximate the superposition of MMPPs without encountering the state-space explosion that occurs in exact computations. Numerical examples that demonstrate the accuracy of these methods are given. We also present a method to convert our estimated D-MMPP to a continuous-time MMPP, which is used as the arrival process in a matrix-analytic queueing model.     

Performance of packet voice transmission using IEEE 802.16 protocol

The IEEE 802.16 standard defines three types of scheduling services for supporting real-time traffic, unsolicited grant service (UGS), real-time polling service (rtPS), and extended real-time polling service (ertPS). In the UGS service, the base station (BS) offers a fixed amount of bandwidth to a subscriber station (SS) periodically, and the SS does not have to make any explicit bandwidth requests. The bandwidth allocation in the rtPS service is updated periodically in the way that the BS periodically polls the SS, which makes a bandwidth request at the specified uplink time slots and receives a bandwidth grant in the following downlink subframe. In the ertPS service, the BS keeps offering the same amount of bandwidth to the SS unless explicitly requested by the SS. The SS makes a bandwidth request only if its required transmission rate changes. In this article we study the performance of voice packet transmissions and BS resource utilization using the three types of scheduling services in IEEE 802.16-based backhaul networks, where each SS forwards packets for a number of voice connections. Our results demonstrate that while the UGS service achieves the best latency performance, the rtPS service can more efficiently utilize the BS resource and flexibly trade-off between packet transmission performance and BS resource allocation efficiency; and appropriately choosing the MAC frame size is important in both the rtPS and ertPS services to reduce packet transmission delay and loss rate     

On the Analysis of the Bluetooth Time Division Duplex Mechanism

Efficient communication in Bluetooth networks requires design of intra and inter-piconet scheduling algorithms, and therefore, numerous algorithms have been proposed. However, due to complexities of the Bluetooth MAC, the performance of these algorithms has been analyzed mostly via simulation. We present analytic results regarding the exhaustive, gated, and limited (pure round robin) scheduling algorithms in piconets with bidirectional and unidirectional traffic. We show that a piconet operated according to the limited scheduling algorithm is equivalent to a 1-limited polling system and present exact results regarding symmetric piconets with bidirectional traffic. Then, the difficulties in analyzing the performance of the exhaustive and gated algorithms in a piconet with bidirectional traffic are demonstrated. In addition, we present exact analytic results for piconets with unidirectional traffic. We show that, surprisingly, in symmetrical piconets with only uplink traffic, the mean waiting time is the same for the exhaustive and limited algorithms. This observation results from the differences between piconets and traditional polling systems and can be extended for time-division-duplex systems with arbitrary packet lengths. Furthermore, we show that the mean waiting time in a piconet with only uplink traffic is significantly higher than its corresponding value in a piconet with only downlink traffic. Finally, we numerically compare the exact results to approximate results, presented in the past.     

依据用户妥善安排的多址接入协议在分布式无线网络中的性能研究

本文基于有效竞争预约接入、无冲突轮询传输的思想提出了在多跳分布式无线网络中支持节点移动性和多跳网络结构的依据用户妥善安排的多址接入(UPMA)协议.该协议能够保证发送节点快速接入信道,从而大大提高信道的使用效率.用仿真方法研究了多跳分布式无线网络中采用该协议时的网络性能.结果表明,UPMA协议可以提供较高的通过量、较低的平均分组时延和较小的平均分组丢失率.