On the Capacity of an Elemental Two-Way Two-Tier Network

TL;DR

This paper analyzes the capacity of a two-tier relay network with two mobile users, proposing a novel beamforming scheme based on physical-layer network coding that nearly achieves the theoretical capacity.

Contribution

It introduces a new beamforming and power allocation scheme for a two-tier relay network, demonstrating near-capacity performance through theoretical and numerical analysis.

Findings

The proposed scheme nearly achieves the network's capacity.

Optimal beamformers are convex combinations of channel vectors.

The scheme outperforms traditional methods in simulations.

Abstract

A basic setup of a two-tier network, where two mobile users exchange messages with a multi-antenna macrocell basestation, is studied from a rate perspective subject to beamforming and power constraints. The communication is facilitated by two femtocell basestations which act as relays as there is no direct link between the macrocell basestation and the mobile users. We propose a scheme based on physical-layer network coding and compute-and-forward combined with a novel approach that solves the problem of beamformer design and power allocation. We also show that the optimal beamformers are always a convex combination of the channels between the macro- and femtocell basestations. We then establish the cut-set bound of the setup to show that the presented scheme almost achieves the capacity of the setup numerically.