Dynamic Index Coding for Wireless Broadcast Networks

We consider a wireless broadcast station that transmits packets to multiple users. The packet requests for each user may overlap, and some users may already have certain packets. This presents a problem of broadcasting in the presence of side information, and is a generalization of the well-known (and unsolved) index coding problem of information theory. We represent the problem by a bipartite demand graph. Uncoded transmission is optimal if and only if this graph is acyclic. Next, we define a code-constrained capacity region that restricts attention to any prespecified set of coding actions. A dynamic max-weight algorithm that acts over variable length frames is developed. The algorithm allows for random packet arrivals and supports any traffic inside the code-constrained capacity region. A simple set of codes that exploit cycles in the demand graph are shown to be optimal for a class of broadcast relay problems.