Degrees of Freedom on MIMO Multi-Link Two-Way Relay Channels

In this paper, the authors introduce multi-link two-way relay channels where multiple two-way relay systems are interfering with each other. They study the capacity of this system by investigating the Degree Of Freedom (DOF) with various message settings. Specifically, they consider two cases of two-way relay interference channels and two-way relay X channels. They show that the two-way relay interference channel where all nodes have M antennas obtains the DOF of 2M and compare with multi-pair two-way relay channels. Next, they introduce general message settings for two-way relay X channels. For the case where each user is equipped with 3 antennas and relays have 4 antennas, they prove that the DOF of 8 is achieved by employing network coding.