Relays can provide alignment for the K-user interference channel without channel state information at the transmitters

Abstract

Abstract-Channel state information at the transmitters (CSIT) is of importance for interference alignment schemes to achieve the optimal degrees of freedom (DoF) for wireless networks. This paper focuses on the K-user interference channel and shows that, employing relays between the sources and the destinations, interference alignment is possible without CSIT. Furthermore, the optimal DoF can be achieved with the help of relays. Specifically, a transmission strategy is designed and it is shown that the DoF K 2 can be achieved with a two-slot transmission strategy using either (i) one relay with K − 1 antennas, or (ii) K(K − 2) single antenna relays. It is also shown that when each relay is equipped with L antennas, we needrelays to achieve the optimal DoF.

Finite-SNR Precoder Designs for the Interference Relay Channel Without CSI at the transmitters

“…The power constraint on the relay is given as E{ x R 2 } ≤ P t . Unlike [15], a more general approach is considered where the transmitters and the relay broadcast together in the 2 nd time slot. This approach is called the joint beamforming approach.…”

“…IA Precoder [15] Since IA aims to achieve the maximum network DoF (which is a high-SNR metric), the "noise terms" in (7) can be removed. To decode the intended message at the k th receiver, all the K -1 interfering terms must be aligned in one dimensional subspace at that receiver.…”

“…These drawbacks still obligate the practicality of IA based schemes. Recently, it was demonstrated in [15], [16] that some drawbacks of BIA can be eliminated by the help of the relays.…”

“…The assumption of CSIT in [17]- [20] is the major difference between these works and [2], [15], [16]. The relay-aided IA schemes in [2], [15], [16] have more practical relevance because the relays are located in between the transmitters and the receivers and therefore, can have more accurate CSI feedback from the receivers as compared to the CSI feedback to the transmitters which are located farther from the receivers. Secondly, for conventional singleinput-single-output interference channels (SISO-ICs) without relays, time-varying channels with long symbol extensions are required to obtain the optimal DoF [3].…”

“…In Section III, we mention the IA feasibility conditions for a relay-aided SISO-IC which also motivates us to use the system model in Section II-B. Section IV briefly reviews the IA [15] and the MSMSE precoders [1] with more details on the derivations. In Section V, we elaborate on the conventional IA and the MSMSE schemes with power control at the relay, and propose scaled-IA based precoder initialization to improve power savings.…”