Achievable degrees of freedom for two-way interference channel with relay

Abstract

Managing interference in a multi-user interference network is important to achieve a better performance for the network. Hence, studies to find out the performance of interference network in various conditions have been done actively. With interference alignment, a core technique to improve DoF in a multi-user interference networks, studies have shown the optimal performance of K-user MIMO interference channels (ICs), which is $K/2$ DoF. However, although there exist some remarkable results on the performance of one-way ICs, few studies on two-way ICs have been done.\In this thesis, we study the achievable DoF of two-way ICs with a relay. We propose a new interference management scheme to achieve better performance on such channels. If we use the conventional scheme for the TWIC, the performance shows that the channel can have 1/4 DoF per antenna, under the assumption of half-duplex communication. In this paper we show that the performance can be improved up to 1/3 DoF per antenna by using a conventional relay for the channel. This result gives us two novel outcome. One is showing that the TWIC can have better performance compared to the conventional one, and the other one is showing that the relay can help increase the DoF of ICs.\Throughout the paper we propose a suitable interference management scheme for 2-by-2 and 3-by-3 TWIC with relay. First, in 2-by-2 TWIC, we use three time slots, two for the user transmission and the other one for the relay broadcasting, to achieve $1/3$ DoF per antenna, where each user has $M$ antennas and the relay has $N=2M$ antennas. Similarily we show that 3-by-3 TWIC can achieve DoF up to $5/18$ DoF per antenna, with $N=3M$ antennas at the relay, by adopting techniques of interference alignment since the there are more than two users. We also show that the 3-by-3 TWIC can achieve 1/3 DoF per antenna with $N>3M$ antennas at the relay.