The ρ-capacity of a graph

Motivated by the problem of zero-error broadcasting, we introduce a new notion of graph capacity, termed ρ-capacity, that generalizes the Shannon capacity of a graph. We derive upper and lower bounds on the ρ-capacity of arbitrary graphs, and provide a tighter upper bound for regular graphs. The ρ-capacity is employed to characterize the zero-error capacity region of the degraded broadcast channel.