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A cross-layer study of the scheduling problem.

机译：调度问题的跨层研究。

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摘要

This thesis is inspired by the need to study and understand the interdependence between the transmission powers and rates in an interference network, and how these two relate to the outcome of scheduled transmissions. A commonly used criterion that relates these two parameters is the Signal to Interference plus Noise Ratio (SINR). Under this criterion a transmission is successful if the SINR exceeds a threshold. The fact that this threshold is an increasing function of the transmission rate gives rise to a fundamental trade-off regarding the amount of time-sharing that must be permitted for optimal performance in accessing the wireless channel. In particular, it is not immediate whether more concurrent activations at lower rates would yield a better performance than less concurrent activations at higher rates. Naturally, the balance depends on the performance objective under consideration. Analyzing this fundamental trade-off under a variety of performance objectives has been the main steering impetus of this thesis.;We start by considering single-hop, static networks comprising of a set of always-backlogged sources, each multicasting traffic to its corresponding destinations. We study the problem of joint scheduling and rate control under two performance objectives, namely sum throughput maximization and proportional fairness. Under total throughput maximization, we observe that the optimal policy always activates the multicast source that sustains the highest rate. Under proportional fairness, we explicitly characterize the optimal policy under the assumption that the rate control and scheduling decisions are restricted to activating a single source at any given time or all of them simultaneously.;In the sequel, we extend our results in four ways, namely we (i) turn our focus on time-varying wireless networks, (ii) assume policies that have access to only a, perhaps inaccurate, estimate of the current channel state, (iii) consider a broader class of utility functions, and finally (iv) permit all possible rate control and scheduling actions. We introduce an online, gradient-based algorithm under a fading environment that selects the transmission rates at every decision instant by having access to only an estimate of the current channel state so that the total user utility is maximized. In the event that more than one rate allocation is optimal, the introduced algorithm selects the one that minimizes the transmission power sum. We show that this algorithm is optimal among all algorithms that do not have access to a better estimate of the current channel state.;Next, we turn our attention to the minimum-length scheduling problem, i.e., instead of a system with saturated sources, we assume that each network source has a finite amount of data traffic to deliver to its corresponding destination in minimum time. We consider both networks with time-invariant as well as time-varying channels under unicast traffic. In the time-invariant (or static) network case we map the problem of finding a schedule of minimum length to finding a shortest path on a Directed Acyclic Graph (DAG). In the time-varying network case, we map the corresponding problem to a stochastic shortest path and we provide an optimal solution through stochastic control methods.;Finally, instead of considering a system where sources are always backlogged or have a finite amount of data traffic, we focus on bursty traffic. Our objective is to characterize the stable throughput region of a multi-hop network with a set of commodities of anycast traffic. We introduce a joint scheduling and routing policy, having access to only an estimate of the channel state and further characterize the stable throughput region of the network. We also show that the introduced policy is optimal with respect to maximizing the stable throughput region of the network within a broad class of stationary, non-stationary, and anticipative policies.
机译：本论文的灵感来自于需要研究和理解干扰网络中传输功率和速率之间的相互依赖性，以及这两者与调度传输的结果之间的关系。涉及这两个参数的常用标准是信号干扰加噪声比（SINR）。在此标准下，如果SINR超过阈值，则传输成功。该阈值是传输速率的增加函数的事实引起了关于必须共享的分时量的基本权衡，为了获得最佳性能，该分时量必须能够访问无线信道。特别是，与以较高速率进行的较少并行激活相比，以较低速率进行的更多并行激活是否会产生更好的性能，这不是立即的。自然，平衡取决于所考虑的性能目标。分析各种性能目标下的基本权衡取舍一直是本文的主要推动力。;我们首先考虑由一组始终积压的源组成的单跳静态网络，每个网络将流量多播到其对应的目的地。我们研究了两个性能目标下的联合调度和速率控制问题，即总吞吐量最大化和比例公平。在总吞吐量最大化的情况下，我们观察到最优策略始终会激活维持最高速率的多播源。在比例公平下，我们假设速率控制和调度决策仅限于在任何给定时间或同时激活所有资源的前提下明确描述最优策略的特征;随后，我们通过四种方式扩展结果：也就是说，我们（i）将精力放在时变的无线网络上；（ii）假定只能访问当前信道状态的估计（可能不准确）的策略；（iii）考虑更广泛的实用程序功能，最后（iv）允许所有可能的速率控制和调度动作。我们在衰落环境下引入了一种基于梯度的在线算法，该算法通过仅访问当前信道状态的估计值来选择每个决策瞬间的传输速率，从而使总用户效用最大化。如果一个以上的速率分配是最优的，引入的算法将选择一个使传输功率总和最小的算法。我们证明了该算法在所有无法更好地估计当前信道状态的算法中都是最佳算法。接下来，我们将注意力转向最小长度调度问题，即，代替具有饱和源的系统，我们假设每个网络源都有有限的数据流量，可以在最短的时间内传递到其相应的目的地。我们考虑单播流量下具有时不变信道和时变信道的两个网络。在时不变（或静态）网络的情况下，我们将在Directed Acyclic Graph（DAG）上找到找到最小长度的计划的问题映射为找到最短路径的问题。在时变网络情况下，我们将对应的问题映射到随机最短路径，并通过随机控制方法提供最佳解决方案;最后，而不是考虑源总是积压或数据流量有限的系统，我们专注于突发流量。我们的目标是通过一组任意播流量商品来表征多跳网络的稳定吞吐量区域。我们引入一种联合调度和路由策略，该策略只能访问信道状态的估计值，并进一步表征网络的稳定吞吐量区域。我们还显示出，对于在固定，非固定和预期策略的广泛类别中最大化网络的稳定吞吐量区域而言，引入的策略是最佳的。

著录项

  • 作者

    Pantelidou, Anna.;

  • 作者单位

    University of Maryland, College Park.;

  • 授予单位 University of Maryland, College Park.;
  • 学科 Engineering Electronics and Electrical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 175 p.
  • 总页数 175
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 无线电电子学、电信技术;
  • 关键词

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