Degrees of freedom of the MIMO interference channel with cooperation and cognition

In this paper, we explore the benefits, in the sense of total (sum rate) degrees of freedom (DOF), of cooperation and cognitive message sharing for a two-user multiple-input-multiple-output (MIMO) Gaussian interference channel with M₁, M₂ antennas at transmitters and N₁, N₂ antennas at receivers. For the case of cooperation (including cooperation at transmitters only, at receivers only, and at transmitters as well as receivers), the DOF is min{M₁ + M₂,N₁ + N₂, max(M₁,N₂), max(M₂,N₁)}, which is the same as the DOF of the channel without cooperation. For the case of cognitive message sharing, the DOF is min{M₁+ M₂,N₁+N₂, (1-1_T2)((1-1_R2)max(M₁,N₂)+1_R2(M₁+N₂))+ 1_T2(M₁ + M₂), (1 - 1_T1)((1 - 1_R1)max(M₂,N₁) + 1_R1(M₂ + N₁)) + 1_T1(M₁ + M₂)} where 1_Ti = 1 (0) when transmitter i is (is not) a cognitive transmitter and 1_Ri is defined in the same fashion. Our results show that while both techniques may increase the sum rate capacity of the MIMO interference channel, only cognitive message sharing can increase the DOF. We also find that it may be more beneficial for a user to have a cognitive transmitter than to have a cognitive receiver.