Degrees of Freedom of the Interference Channel with a Cognitive Helper

Abstract

Abstract-In this letter, we characterize the degrees of freedom (DoF) of the K ≥ 3 user Gaussian interference network with a cognitive helper where each node is equipped with only one antenna. Specifically, each user sends one independent message to its corresponding receiver through its own antenna and via the help of the cognitive helper. For this network, we show that the sum DoF value is outer bounded by (K + 1)/2 when K is odd and K 2 /(2(K + 1)) when K is even, respectively. The new DoF outer bounds are derived based on the fact that collaboration among users does not decrease the capacity region and increasing the number of users does not increase the capacity per user. In addition, we provide a new achievable scheme to achieve a total of (K + 1)/2 DoF for any K ≥ 3. Thus, the exact DoF value of the network is characterized with the total DoF given as (K + 1)/2, whenever K is odd. The new achievable scheme is based on interference neutralization and asymptotic interference alignment.