On Achievable Throughput Region of Prioritized Transmissions Via Network Coding

We investigate the achievable throughput regions for scenarios involving prioritized transmissions. Prioritized transmissions are useful in many multimedia networking applications where the transmitted data have an inherent hierarchy such that a piece of data at one level is only useful if all the pieces of data at all the lower levels are present. Formally, the prioritized transmission refers to the notion that, given M prioritized packets in the decreasing order of importance, a₁, a₂, ..., a_m to be delivered to a receiver, then the packet a_i is useful to a receiver only if it has received all packets a_j with j < i successfully. Thus, the prioritized throughput can be abstractly represented j - 1 where j is the position of the first lost packet. In this paper we investigate the achievable throughput regions of prioritized transmissions from a source to multiple receivers via a shared and lossy channel. We assume that the source is an oracle such that it knows precisely whether a packet is lost or received at any receiver in any future time slot, thus it can schedule the packet transmission in such a way to maximize the receiver throughputs. We show that using network coding technique, the achievable throughput region for the broadcast scenarios can be substantially enlarged. Furthermore, for some erasure patterns, the achievable throughput region using network coding technique is optimal in the sense that no scheme can do better.