Relay-Assisted Interference Network: Degrees of Freedom
Ramy Abdallah Tannious, Aria Nosratinia · IEEE Transactions on Information Theory · 2012
This paper investigates the degrees of freedom of the interference channel in the presence of a dedicated multiple-input multiple-output (MIMO) relay. The relay is used to manage the interference at the receivers. It is assumed that all nodes including the relay have channel state information only for their own links and that the relay hasM≥Kantennas in aK-user network. We pose the question: what is the benefit of exploiting the direct links from the source to destinations compared to a simpler two-hop strategy. To answer this question, we first establish the degrees of freedom of the interference channel with an MIMO relay, showing that aK-pair network with an MIMO relay has [(K)/2] degrees of freedom. Thus, appropriate signaling in a two-hop scenario captures the degrees of freedom without the need for the direct links. We then consider more sophisticated encoding strategies in search of other ways to exploit the direct links. Using a number of hybrid encoding strategies, we obtain nonasymptotic achievable sum rates. We investigate the case where the relay (unlike other nodes) has access to abundant power, showing that when sources have powerPand the relay is allowed power proportional toO(P2) , the full degrees of freedomKare available to the network.