Introduction to the Special Issue on Models, Theory, and Codes for Relaying and Cooperation in Communication Networks [Guest Editorial]

THE demand for ever larger, more efficient, reliable, and cost effective communication networks is motivating new network architectures, such as ad hoc networks, cognitive radio, relay extensions for cellular networks, sensor networks, and wireless mesh networks. The study of such networks requires a fundamental shift from thinking of a network as a collection of independent communication pipes each with separate source and channel coding, to a multiterminal channel where users cooperate via conferencing, relaying, and joint source–channel coding. As such, there has been significant activity in the past decade toward developing information theory and coding for networks. The goal of this Special Issue is to highlight this activity with a focus on information theory for network models involving relaying and cooperation. The greatest triumph of Shannon information theory over the past 50 years has been the development of a complete understanding of many important point-to-point channels and practical codes that operate reliably near capacity (see, e.g., the IEEE TRANSACTIONS ON INFORMATION THEORY Special Issue on Codes and Graphs and Iterative Algorithms from February 2001). Multiterminal information theory, which aims to extend information theory to networks with several users, began with Shannon’s paper on the two-way channel in the early 1960s. Finding capacity for networks has proved much more difficult than for point-to-point channels, however. Even today our understanding of the two-way channel has hardly progressed beyond Shannon’s work, and the capacity of other basic multiterminal channels, such as relay and interference channels, remains unknown. Fortunately, some multiterminal channel capacity problems admit solution, including multiple-access channels and important classes of broadcast and interference channels that model, for example, cellular wireless and digital subscriber line communications. Perhaps more interestingly, the solutions to these problems have yielded new promising communication techniques, such as binning, superposition coding, successive cancellation, dirty-paper coding, and network coding. There has also been significant recent progress in understanding the scaling behavior of large networks. In spite of this progress, network information theory has had little impact on practice, perhaps because of the difficulty of addressing coding in settings involving bursty sources, sources and devices constrained by delay requirements, and limited network knowledge. As the Special Issue title suggests, solicited papers were meant to address network modeling, information theory, and