Communication over Wireless Fading Channels: A Modern View

高效无线通信系统的设计依赖于对底层信道基本特性的深刻理解。无线信道最基本和最独特的特性是信道强度随时间的随机变化，这种现象被称为衰落。自60年代以来，衰落信道通信一直是一个研究课题。然而，从最近的研究中出现了一个非常不同的观点。对衰落的传统看法是，它是不可靠性的一个来源，必须通过各种分集技术来弥补。现代的观点更加有力，认为衰退是自然随机化的一个来源，可以利用它来获得非常显著的能力提升。该研究项目解决了这一现代范式中的几个关键问题。它们将集中在两个方面：1)机会通信：在时间、频率、天线和用户的维度上进行动态速率和功率分配，以便在信道强大的时间和地点进行传输；2)多天线通信：使用多个发射和接收天线，以增加在高度分散的衰落环境中可用的通信自由度。研究的问题集中在如何在面对信道不确定性的情况下利用随机衰落，以及现代和传统信道衰落观点之间的相互作用。

The design of efficient wireless communication systems relies on adeep understanding of the basic characteristics of the underlyingchannel. The most fundamental and unique characteristic of wirelesschannels is the random time-variation of the channel strengths, aphenomenon known as fading. Communication over fading channels hasbeen a topic of study since the 60's. A very different view of theproblem, however, emerges from recent research. The traditional viewof fading is that it is a source of unreliability that has to becompensated for by various diversity techniques. The modern view ismuch morepowerful and considers fading as a source of randomization from naturethat can be exploited to get very significant capacity boost.The research project addresses several key problems within thismodern paradigm. They will be centered around two areas: 1)opportunistic communication : the dynamic rate and power allocationover the dimensions of time, frequency, antennas and usersso that transmission is done when and where the channel is strong;2) multi-antenna communication: the use of multiple transmit andreceive antennas to increase the number of degrees of freedom availablefor communication in richly scattered fading environments. The issuesstudied are focused on how the random fading can be exploited even inthe face ofchannel uncertainty, and the interplay between the modern andtraditional views of channel fading.