Reliable Communication with Feedback: Coding Schemes and Fundamental Limits

双向通信系统中，每一端都有一个发送器/接收器，这是普遍存在的。双向信息流使得使用某种反馈来帮助对抗信道噪声和不确定性成为可能。长期以来，人们已经认识到，反馈不仅可以在信道具有记忆时帮助增加容量，而且实际上可以降低复杂性和延迟，以满足性能目标。然而，就如何利用反馈的能力而言，实践与理论之间的差距仍然很大。这是一个关于反馈通信系统的理论驱动设计和实践驱动理论的研究项目。设计和分析的方法紧密结合，并在香农理论和现代编码理论的指导下，通过反馈和稀疏图码的置信传播解码的协同组合，该项目研究了可靠传输和联合信源信道编码的可实现方案，可以利用即使是少量的反馈的力量，以改善延迟率权衡。为了帮助弥合理论与实践之间的差距，该项目的一个主要目标是分析与传统模型无关的技术基本限制和性能指标，如以一小部分容量传输时的指数错误率下降。

Two-way communication systems, with a transmitter/receiver at each end, are ubiquitous.The bi-directional information flow gives rise to the possibility of using some kind of feedback in order to help combating channel noise and uncertainty.It has long been recognized that feedback not only can help increase capacity when the channel has memory, but it may actually lead to decreased complexity and delay in order to meet performance targets. However, the gulf between practice and theory remains wide as far as taking advantage of the capabilities of feedback.This is a research project on both theory-driven design and practice-driven theory of feedback communication systems. Methods of design and analysis are tightly coupled and guided by the teachings of both Shannon theory and modern coding theory.Through the synergistic combination of feedback and belief propagation decoding of sparse-graph codes, the projects studies implementable schemes for both reliable transmission and joint source-channel coding that can harness the power of even a modicum of feedback in order to improve delay-rate tradeoffs. To help bridge the gap between theory and practice, a major thrust of the project is on the analysis of technology-independent fundamental limits departing from conventional models and performance measures such as the exponential error rate decrease when transmitting at a fraction of capacity.