SGER: Distributed Optimization of Spatial Resources in Wireless Local Area Networks

动机：无线局域网具有非常有前景的商业潜力，可以在各种应用场景中广泛部署和使用，但也面临许多重大的工程困难。例如，小的小区尺寸和未经许可的频谱导致复杂的空间交互，缺乏通用的空中接口来支持移动和时间敏感的应用，相互竞争的用户（接入点和移动站）之间的交互可能形成令人惊讶和不可预测的模式。此外，无线局域网中的端到端传输通常穿越一个混合网络，在主干中有无线跳点和有线链路。这在跨层TCP-IP-MAC-PHY交互中提出了独特的挑战，并为优化介质访问控制（MAC）和物理层（PHY）算法以增强最终用户体验提供了新的机会。工业界和学术界都不乏关于如何改进无线互联网服务交付的近期想法。缺少的是一个优化框架，它可以捕获网络应用程序级别的效用，并且可以弄清楚MAC或PHY层的任何特定增量变化是积极的还是消极的。这个差距是SGER提案的重点。Kelly和Low在有线世界中创建了这种效用最大化框架的对应物，它导致了对TCP拥塞控制的更深层次的理解，以及高能物理社区对新的“FAST TCP”协议的开发和现场测试。这种方法的关键观点是从一个给定的网络协议开始，然后问：“如果这个分布式协议是一个潜在全局优化问题的解决方案，那么这个优化问题是什么？”无线世界提出了非常重大的挑战，新框架需要捕捉小区内的空间交互，在未经许可的频谱中运行，MAC层的竞争和调度混合，以及通过编码技术实现不同速率可靠性权衡的灵活性。例如，我们知道TCP吞吐量可以通过空间资源的协调来提高，特别是通过时空编码。嵌入式分集将空间分集转换为一种细粒度资源，当信道良好时，它可以提供机会性通信；当信道不太好时，它可以提供可靠的通信，并保证延迟。我们期望在基于完整的无线效用最大化框架的特定跨层设计中看到显著的好处，但该提案的价值是可以应用于任意无线协议或编码技术的一般原理证明。项目重点和智力价值：这个SGER项目是一个概念证明-特别关注媒体访问机制的建模和利用嵌入式多样性的新编码范式。未来12个月SGER调查的具体目标是确定编码（具有嵌入式多样性）和调度（用于介质访问）是解决方案的全局优化问题。在解决效用最大化问题中的干扰和设计嵌入分集的新空时码方面取得了初步成果。我们相信，通过填补媒介接入建模和利用编码技术这两个剩余的漏洞，将在theSGER项目结束时完成一个完整的、广泛适用的无线网络效用最大化框架。更广泛的影响：该SGER提案中的研究活动将与pi目前从事的各种教育活动完全整合。其中包括普林斯顿大学四门新的跨学科课程的课程开发，两门本科课程和两门研究生入门课程，积极监督无线局域网的本科生研究项目，以及与我们的工业合作伙伴安排学生暑期实习。该提案的一个独特而重要的方面是与无线局域网领域的五家主要电信和网络公司密切合作的详细安排：at&t实验室、思科、FlarionTechnologies、英特尔和SBC。这些与工业界的互动将进一步加强项目的研究和教育组成部分，并确保智力贡献的可见影响。在SGER项目结束时，pi将在普林斯顿举办一个关于无线局域网研究、开发和部署的研讨会。我们将编制一份与无线局域网相关的主要研究问题的清单，以及对这些主题感兴趣的工业研究人员或管理人员的清单，这可能有助于未来NSF关于无线网络数学模型相关主题的计划。

Motivation: Wireless local area networks have very promising commercial potential to be widely de-ployed and used in a variety of application scenarios, but also suffer from a number of significant engineeringdifficulties. For example, small cell sizes and unlicensed spectrum lead to sophisticated spatial interaction,there is a lack of common air-interface to support mobile and time-sensitive applications, and interactionsamong competing users, both access points and mobile stations, could form surprising and unpredictablepatterns. In addition, end-to-end transmissions in a wireless LAN often traverse a hybrid network, withwireless hops as well as wired links in the backbone. This presents unique challenges in cross layer TCP-IP-MAC-PHY interactions and offers new opportunities to optimize medium access control (MAC) and physicallayer (PHY) algorithms to enhance the end user experience.There is no shortage of near term ideas from both industry and academia about how to improve thedelivery of wireless Internet services. What is missing is an optimization framework that captures utility atthe level of networked applications, and makes it possible to figure out whether any particular incrementalchange at the MAC or PHY layer is positive or negative. The gap is the focus of this SGER proposal.Kelly and Low have created the counterpart of this utility maximization framework in the wired world,and it has led to a deeper understanding of TCP congestion control and to the development and fieldtesting of the new 'FAST TCP' protocol by the high energy physics community. The key insight in thisapproach is to start with a given network protocol and ask: 'If this distributed protocol is the solution to anunderlying global optimization problem, what is that optimization problem?' The wireless world presents avery significant challenge and the new framework needs to capture spatial interaction within a cell, operationin unlicensed spectrum, a mix of contention and scheduling at the MAC layer, and the flexibility of achievingdifferent rate-reliability tradeoffs by coding techniques.For example, we know that TCP throughput can be improved through coordination of spatial resources,specifically through space-time coding. Embedded diversity transforms spatial diversity into a fine grainedresource that can provide opportunistic communication when the channel is good and reliable communicationwith latency guarantees when it is less benign. We expect to see significant benefits in specific cross layerdesigns based on a completed framework of wireless utility maximization, but the value of the proposal is ageneral proof of principle that can apply to an arbitrary wireless protocol or coding technique.Project Focus and Intellectual Merit: This SGER project is a proof of concept - the particularfocus is on modelling the medium access mechanisms and leveraging the new coding paradigm of embeddeddiversity. The particular objective in the next 12 months of SGER investigation is to identify the globaloptimization problem to which coding (with embedded diversity) and scheduling (for medium access) is thesolution.Preliminary results have recently been obtained by the PIs on tackling interference in utility maximizationproblems and on designing new space-time codes with embedded diversity. We believe that by filling intwo remaining holes: modelling medium access and leveraging coding techniques, a complete and widelyapplicable framework of wireless network utility maximization will be completed at the conclusion of theSGER project.Broader Impacts: The research activities in this SGER proposal will be fully integrated with a varietyof educational activities currently pursued by the PIs. These include curriculum developments of four new,inter-disciplinary courses at Princeton, two at undergraduate level and two at introductory graduate level,active supervision of undergraduate research projects on wireless LAN, and student summer internshipsbeing arranged with our industrial partners.A unique and important aspect of this proposal is a detailed arrangement of close collaboration withfive major telecom and networking companies in the wireless LAN space: AT&T Labs, Cisco, FlarionTechnologies, Intel, and SBC. These interactions with the industry will further strengthen the research andeducation components of the project and ensure visible impacts of the intellectual contributions.A workshop on wireless LAN research, development, and deployment will be hosted at Princeton by thePIs at the conclusion of this SGER project. We will compile a list of major research issues associated withwireless LAN and a list of industrial researchers or managers interested in these topics, which may be helpfulto future NSF programs on topics related to mathematical models for wireless networks.