The Degrees of Freedom of the $K$-pair-user Full-Duplex Two-way Interference Channel with and without a MIMO Relay

Abstract

In a $K$-pair-user two-way interference channel (TWIC), $2K$ messages and $2K$ transmitters/receivers form a $K$-user IC in the forward direction ($K$ messages) and another $K$-user IC in the backward direction which operate in full-duplex mode. All nodes may interact, or adapt inputs to past received signals. We derive a new outer bound to demonstrate that the optimal degrees of freedom (DoF, also known as the multiplexing gain) is $K$: full-duplex operation doubles the DoF, but interaction does not further increase the DoF. We next characterize the DoF of the $K$-pair-user TWIC with a MIMO, full-duplex relay. If the relay is non-causal/instantaneous (at time $k$ forwards a function of its received signals up to time $k$) and has $2K$ antennas, we demonstrate a one-shot scheme where the relay mitigates all interference to achieve the interference-free $2K$ DoF. In contrast, if the relay is causal (at time $k$ forwards a function of its received signals up to time $k-1$), we show that a full-duplex MIMO relay cannot increase the DoF of the $K$-pair-user TWIC beyond $K$, as if no relay or interaction is present. We comment on reducing the number of antennas at the instantaneous relay.

Submitted to the IEEE Journal on Selected Areas in Communications (JSAC) in October 2013

References in corpus (3)

• Interference Alignment and the Degrees of Freedom for the K User Interference Channel
• Two-way Interference Channels
• Multi-Way Information Exchange Over Completely-Connected Interference Networks with a Multi-Antenna Relay

Cited by in corpus (1)

• On the DoF region of the two-user Interference Channel with an Instantaneous Relay