Bidirectional multi-pair network with a MIMO relay: Beamforming strategies and lack of duality

Abstract

We address the problem of a multi-user relay network, where multiple single-antenna node pairs want to exchange information by using a multiple antenna relay node. Due to the half-duplex constraint of the relay, the exchange of information takes place in two steps. In the first step, the nodes transmit their data to the relay, while in the second step, the relay is broadcasting the data by using linear and non-linear precoding strategies. We focus on the second step in this paper. We first consider the problem of maximizing the overall rate achievable using linear and dirty-paper type precoding strategies at the relay. Then, we consider minimizing the total power at the relay subject to individual SINR constraints using the same strategies at the relay. We show that the downlink-uplink duality does not hold for the setup considered here, which is a somewhat surprising result. We also show that the beamforming strategy which is optimal in the single-pair case performs very well in the multi-pair case for practically relevant SNR. The results are illustrated by numerical simulations.

MIMO precoding for cooperative relay transmission

“…For users and antennas configura tion (4,4,4) and (3,3,3), we can achieve d = 1 for both of them. For users and antennas configuration (4,4,6) and (3,3,5), both of them show better perfor mance with d = 3 at the cost of the relay antennas N increasing. Moreover, it is observed that the slopes of curves are steepening as N increases.…”

“…Specifically, the pre coding matrix Q i for the i th superposition signal can be constructed as (6) where P i is a N × (K -1) submatrix of the effective channel matrix U r by removing its i th columns. Apparently Q i is an orthogonal projection matrix.…”

“…Multiple pairs of source nodes used to exchange information by relay with their part ners. For instance, the multi way relay channel (MWRC) with multi cast messages [3][4], and the multi pair TWRC [5][6].…”

Multipair Two-Way Relay Network With Harvest-Then-Transmit Users: Resolving Pairwise Uplink-Downlink Coupling

“…The simplified problem is equivalently reformulated as a DC program using rank relaxation, provided that there exists a rank guarantee of the solution. Unfortunately, the considered problem involves a single beamformer serving a group of users, and currently there is no rank guarantee of the solution, even for its special case of TWR without energy harvesting [13]. To this end, we establish a rank-one guarantee for the one pair users case, and a rank-two guarantee for the general multi-pair users case.…”

“…However, the current research on WPCNs is still at its infancy, focusing on basic point-to-point systems. This paper will take a step further to discuss the wirelessly powered multipair two-way relay (TWR) network, which is a natural generalization of many basic relay systems [12], [13]. Wirelessly powered TWR has extensive applications in sensor networks, medical electronics, smart homes and wearable computations etc., where information exchange between energy-constrained devices is often required.…”