Optimal Broadcasting of Two Files over an Asymmetric Channel

We study the problem of scheduling les over a broadcast channel in an asymmetric environment. The goal is to minimize the mean response time for clients who access the broadcast channel. Asymmetric channels gained a lot of attention since they are used to model wireless communication, Teletext systems, and web caching in satellite systems. This paper addresses the 2-les case. We design a simple algorithm that deenes the optimal schedule given the demand probability for each le. Our solution is extended to include other important factors, such as dependencies between les, variable-length les, and diierent priorities for the clients. Adding dependencies is important in the web caching environment since clients may wish to access more than one le in the broadcast channel. For all the above extensions, we prove the surprising result that there exists a simple optimal schedule. Such a schedule is composed of a repeated pattern of AA AB where A is the more \popular" le and B is the less \popular" le.