Combining superposition coding and binning achieves capacity for the Gaussian cognitive interference channel

The cognitive interference channel models cognitive overlay radio systems, in which cognitive radios overhear the transmission of neighboring nodes. For the Gaussian case capacity is known in three subsets of the parameter space: the “weak interference”, “very strong interference” and “primary decodes cognitive” regime. Capacity in the “very strong interference” regime is achieved by superposing the cognitive message over the primary message while in the “primary decodes cognitive” regime the cognitive message is binned against the primary message. This paper provides a new capacity result obtained by combining the capacity achieving schemes in these two regimes thus generalizing and extending these results. Interestingly, the capacity achieving strategy for a given channel also depends on the level of cooperation among the users: that is, either superposition coding or binning is employed depending on the amount of power allotted by the cognitive transmitter to aid the primary user.