The sum-capacity of the linear deterministic three-user cognitive interference channel

Inspired by cognitive networks, we consider the linear deterministic three-user cognitive interference channel with one primary and two secondary/cognitive transmitters which approximates the Gaussian channel at high SNR. Outer bounds on the sum-rate are derived and matching transmission schemes are provided in all interference regimes, thereby completely characterizing the sum-capacity. Significant increase in the sum-capacity is demonstrated when comparing the three-user cognitive channel to the classical (non-cognitive) three-user interference channel and to the two-user cognitive channel. The paper discusses extensions to an arbitrary number of users, the relationship between the cognitive channel and the (fully cooperative) broadcast channel, and observations on the behavior of the cognitive transmitters in the different interference scenarios.