The Wiretapped Diamond-Relay Channel

TL;DR

This paper investigates the secure communication capabilities of a diamond-relay channel under wiretapping, proposing a scheme that combines network coding, beamforming, and interference alignment to achieve optimal secure degrees of freedom.

Contribution

It introduces a novel secure transmission scheme for the wiretapped diamond-relay channel that optimally exploits source-relay links and relay techniques to maximize secure degrees of freedom.

Findings

Achieves the optimal secure degrees of freedom for the channel.

Proposes a scheme combining network coding, beamforming, and interference alignment.

Provides a converse proof assuming known wiretapped link locations.

Abstract

In this paper, we study a diamond-relay channel where the source is connected to $M$ relays through orthogonal links and the relays transmit to the destination over a wireless multiple-access channel in the presence of an eavesdropper. The eavesdropper not only observes the relay transmissions through another multiple-access channel, but also observes a certain number of source-relay links. The legitimate terminals know neither the eavesdropper's channel state information nor the location of source-relay links revealed to the eavesdropper except the total number of such links. For this wiretapped diamond-relay channel, we establish the optimal secure degrees of freedom. In the achievability part, our proposed scheme uses the source-relay links to transmit a judiciously constructed combination of message symbols, artificial noise symbols as well as fictitious message symbols associated with secure network coding. The relays use a combination of beamforming and interference alignment in their transmission scheme. For the converse part, we take a genie-aided approach assuming that the location of wiretapped links is known.