ITR: Cross-Layer Optimization For 4G Wireless Networks: Heavy-Tailed Traffic, Multiuser Channels, and Pseudocells

本项目涉及无线网络理论和实践的一些基本方面。采用物理层创新与媒体访问控制和调度的新协议相结合的综合方法，同时考虑应用需求和传输协议动态，以解决所发现的研究问题。我们考虑了两个主要的研究方向。在第一个研究方向中，结合了蜂窝网络和自组织网络的最佳特征的“伪单元”无线网络的概念被认为是即插即用的第四代(4G)无线网络的典范。这种灵活的架构显然对在紧急情况下快速建立无线网络至关重要，在紧急情况下，固定的、甚至可能是移动的基站部署在方便的(但不是优化的)站点，以服务于移动缓慢的用户和快速移动的用户。然而，它也是我们实现无线链路速度量子跃升的愿景的关键因素，通过超越当前1-2 GHz的蜂窝频段，达到10s GHz频段的大带宽。这些频段中的路径损耗很高，一方面迫使使用密集的基站网络，另一方面允许更积极的频率重用。研究的重点是在分组化的伪单元基础设施上支持混合的用户移动性，以及实时和非实时应用的混合。这种设置与传统蜂窝网络的不同之处在于，小区大小很小，并且小区可能有很大的重叠。它与无线局域网(WLAN)的不同之处在于，尽管小区大小较小，但它允许快速移动的用户。不同于传统的分层结构(即，用于快速移动用户的大小区，覆盖在用于慢移动用户的小小区上)来处理移动性范围，将切换和基于预留的媒体接入控制相结合的以移动为中心的方法被认为允许灵活部署。要研究的新想法是支持预留信道上的优先级，以便允许例如具有进行中的实时呼叫的高移动性用户在进入新的伪小区时快速预留资源，从而隐含地实现切换。另一个重要的问题是预约信道的收发机优化，这需要解决多用户通信中的新问题。第二个研究推动力来自于众所周知的观察，即互联网流量具有重尾分布，这通常需要比传统的马尔可夫流量模型更保守的资源分配。由于过度配置在资源受限的无线环境中不具吸引力，因此考虑的方法是采用新的服务质量(Qos)框架，该框架允许积极的资源利用，通过快速服务于大部分事务(短的)，并惩罚导致重尾的长事务的一小部分。实现这一目标的调度规则与流行的轮询或公平排队调度器非常不同，并且在三十多年前的排队理论文献中被考虑。在这个项目中，我们首次(据我们所知)探索了这些结果对重尾互联网流量的影响。调度策略被扩展到共享无线信道，其中公平性与系统效率之间进行了权衡，后者规定看到最佳信道的用户应该获得链路接入。预计权衡将偏向于效率，以便有效地支持无尾交通。本文探讨了调度和TCP连接动态之间的相互作用(TCP是大多数事务在其上运行的Internet数据传输协议)，记住，网络资源匮乏的TCP连接可能会由于反复的超时和速率降低而被锁定在网络之外。最后，探讨了调度对移动性的依赖性，给高移动性用户(在给定的伪蜂窝中逗留期间访问链路的机会较小的用户)分配优先级的概念，同时考虑到整体的服务质量和公平性。我们开发的调度方法高度重视整体系统效率，因此非常适合统一费率定价，这可以说是促进无线数据网络使用增长的有效机制。

This project addresses some fundamental aspects of the theory and practice of wireless networking. An integrated approach, combiningphysical layer innovations with new protocols for medium access control and scheduling, while accounting for application requirements and transport protocol dynamics, is employed for solving the research problems that are identified. Two major research thrusts are considered. In the first research thrust, the concept of ``pseudocellular'' wireless networks, which combine the best features of cellular and ad hoc networks, is considered as a paradigm for plug-and-play fourth generation (4G) wireless networks. Such a flexible architecture is clearly critical for quick set-up of wireless networks in emergency situations, in which stationary, or perhaps even mobile, base stations are deployed at convenient (but not optimized)sites to serve both slow-moving and fast-moving users. However, it is also a key ingredient of our vision of achieving a quantum jump in wireless link speeds, by going beyond the current cellular frequency bands of 1-2 GHz to the large bandwidths available in frequency bands in the 10s of GHz. The path loss in such bands is high, forcing the use of a dense network of base stations on the one hand, and enabling more aggressive frequency reuse on the other. The focus of the research is to support a mix of user mobilities, and a mix of real-time and non real-time applications, over a packetized pseudocellular infrastructure. This setting differs from conventional cellular networks, in that the cell sizes are small, and cells may have substantial overlap. It differs from wireless Local Area Networks (WLANs), in that it allows for rapidly mobile users despite the small cell sizes. Instead of a conventional hierarchical structure (i.e., large cells for fast-moving users, overlaid on small cells for slow-moving users) to deal with a range of mobility, a mobile-centric approach, which combines handoffs and reservation-based medium access control, is considered to allow for flexible deployment. A novel idea to be investigated is the support of priorities on the reservation channel, so as to allow, for example, highly mobile users with real-time calls in progress to rapidly reserve resources when entering a new pseudocell, thus implicitly achieving a handoff. Another important issue is transceiver optimization of the reservation channel, which requires solution of new problems in multiuser communications.The second research thrust is motivated by the well-known observation that Internet traffic has a heavy-tailed distribution, which typically calls for more conservative resource provisioning than for traditional Markovian traffic models. Since overprovisioning is unattractive in resource-constrained wireless environment, the approach considered is toemploy a new Quality of Service (QoS) framework that allows foraggressive resource utilization, by serving the bulk of thetransactions (which are short) rapidly, and penalizing the small fraction of long transactions that contribute to the heavy tails. Scheduling disciplines that achieve this goal are very different frompopular round robin or fair queueing schedulers, and were considered in the queueing theory literature more than three decades ago. The implication of these results for heavy-tailed Internettraffic is explored for the first time (to the best of our knowledge) in this project. The scheduling strategy is extended to a shared wireless channel, where fairness is traded off against systemefficiency, with the latter dictating that users seeing the best channels are the ones that should get link access. The tradeoff is expected to be biased towards efficiency in order to supportheavy-tailed traffic effectively. The interaction between scheduling and the dynamics of TCP connections (TCP is the Internet data transport protocol on top of which most transactions run) is explored, keeping in mind that a TCP connection that is starved of network resources can get locked out of the network due to repeated timeouts and rate cutbacks. Finally, the dependence of scheduling on mobility is explored, with the concept of assigning priority to highly mobileusers (who have a smaller chance of getting access to the link during their sojourn in a given pseudocell), while keeping overall QoS and fairness in mind. The scheduling methods we develop place a high importance on overall system efficiency, and are therefore well-suited to flat rate pricing, which is arguably an effective mechanism of promoting usage growth in wireless data networks.