On the power of cooperation: Can a little help a lot?

In this paper, we propose a new cooperation model for discrete memoryless multiple access channels. Unlike in prior cooperation models (e.g., conferencing encoders), where the transmitters cooperate directly, in this model the transmitters cooperate through a larger network. We show that under this indirect cooperation model, there exist channels for which the increase in sum-capacity resulting from cooperation is significantly larger than the rate shared by the transmitters to establish the cooperation. This result contrasts both with results on the benefit of cooperation under prior models and results in the network coding literature, where attempts to find examples in which similar small network modifications yield large capacity benefits have to date been unsuccessful

Normalized Entropy Vectors, Network Information Theory and Convex Optimization

We introduce the notion of normalized entropic vectors -- slightly different from the standard definition in the literature in that we normalize entropy by the logarithm of the alphabet size. We argue that this definition is more natural for determining the capacity region of networks and, in particular, that it smooths out the irregularities of the space of non-normalized entropy vectors and renders the closure of the resulting space convex (and compact). Furthermore, the closure of the space remains convex even under constraints imposed by memoryless channels internal to the network. It therefore follows that, for a large class of acyclic memoryless networks, the capacity region for an arbitrary set of sources and destinations can be found by maximization of a linear function over the convex set of channel-constrained normalized entropic vectors and some linear constraints. While this may not necessarily make the problem simpler, it certainly circumvents the "infinite-letter characterization" issue, as well as the nonconvexity of earlier formulations, and exposes the core of the problem. We show that the approach allows one to obtain the classical cutset bounds via a duality argument. Furthermore, the approach readily shows that, for acyclic memoryless wired networks, one need only consider the space of unconstrained normalized entropic vectors, thus separating channel and network coding -- a result very recently recognized in the literature

Minimum-Information LQG Control - Part I: Memoryless Controllers

With the increased demand for power efficiency in feedback-control systems, communication is becoming a limiting factor, raising the need to trade off the external cost that they incur with the capacity of the controller's communication channels. With a proper design of the channels, this translates into a sequential rate-distortion problem, where we minimize the rate of information required for the controller's operation under a constraint on its external cost. Memoryless controllers are of particular interest both for the simplicity and frugality of their implementation and as a basis for studying more complex controllers. In this paper we present the optimality principle for memoryless linear controllers that utilize minimal information rates to achieve a guaranteed external-cost level. We also study the interesting and useful phenomenology of the optimal controller, such as the principled reduction of its order

Half-Duplex Relaying for the Multiuser Channel

This work focuses on studying the half-duplex (HD) relaying in the Multiple Access Relay Channel (MARC) and the Compound Multiple Access Channel with a Relay (cMACr). A generalized Quantize-and-Forward (GQF) has been proposed to establish the achievable rate regions. Such scheme is developed based on the variation of the Quantize-and-Forward (QF) scheme and single block with two slots coding structure. The results in this paper can also be considered as a significant extension of the achievable rate region of Half-Duplex Relay Channel (HDRC). Furthermore, the rate regions based on GQF scheme is extended to the Gaussian channel case. The scheme performance is shown through some numerical examples.Comment: 7 pages, 4 figures, conference pape