Impact of Relay Cooperation on the Performance of Large-scale Multipair Two-way Relay Networks

TL;DR

This paper analyzes how relay cooperation affects the sumrate in large-scale multipair two-way relay networks, showing that multiple smaller groups can achieve similar performance to a single large group, thus optimizing resource use.

Contribution

It derives a lower bound for the ergodic sumrate considering relay group size and demonstrates that smaller groups can replace large ones without significant performance loss.

Findings

Sumrate is independent of group size when groups are large.

Multiple smaller relay groups can match the performance of a single large group.

Relay cooperation is more resource-efficient with several smaller groups.

Abstract

We consider a multipair two-way relay communication network, where pairs of user devices exchange information via a relay system. The communication between users employs time division duplex, with all users transmitting simultaneously to relays in one time slot and relays sending the processed information to all users in the next time slot. The relay system consists of a large number of single antenna units that can form groups. Within each group, relays exchange channel state information (CSI), signals received in the uplink and signals intended for downlink transmission. On the other hand, per-group CSI and uplink/downlink signals (data) are not exchanged between groups, which perform the data processing completely independently. Assuming that the groups perform zero-forcing in both uplink and downlink, we derive a lower bound for the ergodic sumrate of the described system as a function of the relay group size. By close observation of this lower bound, it is concluded that the sumrate is essentially independent of group size when the group size is much larger than the number of user pairs. This indicates that a very large group of cooperating relays can be substituted by a number of smaller groups, without incurring any significant performance reduction. Moreover, this result implies that relay cooperation is more efficient (in terms of resources spent on cooperation) when several smaller relay groups are used in contrast to a single, large group.