CAREER: Opportunistic Communication: A Design Paradigm for Wireless Systems

对无线通信服务的需求增长速度远远快于分配额外资源(如带宽)的速度。除了有限的可用带宽外，无线系统设计者还必须应对有线网络中不常见的几个独特的挑战，例如传输和用户特定的时间和频率变化信道造成的干扰。通过物理层和网络层的和谐设计来管理有限的资源是无线系统设计中的一个核心问题，也是一个非常相关的问题。过去十年来针对这一问题的密集研究活动可以大致分为两个部分：物理层工作主要集中在点对点通信上，而网络层工作则使用物理层的抽象进行资源分配。此外，无线系统的工程设计在很大程度上围绕着使各个点对点链路可靠，并使用适当的物理层模型开发网络层。该项目对无线网络通信问题采取了基本的物理层观点，并深入了解了物理层和网络层的新设计技术，从而显著提高了整体系统容量。一种新的观点是多用户分集，这是无线网络固有的一种分集形式。在具有许多其频道独立变化的用户的系统中，可能存在其频道在任何时刻接近其峰值的用户。通过仅调度到具有最佳信道的用户的传输，利用了多用户分集增益。这种形式的“机会主义通信”大幅提升了系统的吞吐量。通过多用户分集的镜头，信道波动是可取的，这与点对点通信的观点形成了鲜明对比。该项目对多用户多样性的作用进行了系统的研究：人工诱导和利用它的方案。研究的其他具体问题包括多天线下行链路(广播)信道的基本观点和自组织网络模型。教学是这一项目不可分割的一部分，部分通过开发四门课程来进行。

Demand for wireless communication services has been growing much faster than additional resources (such as bandwidth) are allocated. Besides scarce available bandwidth, wireless system designers have to deal with several unique challenges, not commonly found in wireline networks, such as interference caused by transmissions and user specific time and frequency varying channels. Managing the limited resources through a harmonious design of the physical and networking layers is a central problem in the design of wireless systems and a very relevant one. The intense research activity over the past decade addressing this issue can be roughly dichotomized into two parts: the physical layer work focusing mostly on point to point communication and the networking layer work of resource allocation using an abstraction of the physical layer. Further, engineering design of wireless systems, for the most part, has centered around making individual point to point links reliable and developing a networking layer using an appropriate model of the physical layer. This project takes a fundamental physical layer view of the wireless network communication problems and sheds insight into novel design techniques at both the physical and the networking layer, yielding a significant boost to the overall system capacity. One novel viewpoint is multiuser diversity, a form of diversity inherent in a wireless network. In a system with many users whose channels vary independently, there is likely to be a user whose channel is near its peak at any one time. By scheduling transmissions only to users with the best channel, multiuser diversity gain is harnessed. This form of "opportunistic communication" provides a sharp boost to the system throughput. Through the lens of multiuser diversity, channel fluctuations are preferable, in sharp contrast to the point to point communication view. This project conducts a systematic study of the role of multiuser diversity: schemes to artificially induce and harness it. Other specific problems studied include a fundamental view of the multiple antenna downlink (broadcast) channel and an ad hoc networking model. Teaching is an integral part of this project and is partly carried out through the development of four courses.