On the Capacity Regions of Two-Way Diamond Channels

TL;DR

This paper investigates the capacity regions of two-way diamond channels, proposing strategies for deterministic models and approximations for Gaussian channels, achieving near-optimal capacity bounds.

Contribution

It introduces new relay strategies for deterministic models and extends these to approximate the capacity regions of Gaussian two-way diamond channels.

Findings

Capacity in deterministic models can be achieved simultaneously in both directions.

Proposed schemes achieve capacity within constant gaps for Gaussian channels.

The smallest gap for the general Gaussian two-way relay channel is improved.

Abstract

In this paper, we study the capacity regions of two-way diamond channels. We show that for a linear deterministic model the capacity of the diamond channel in each direction can be simultaneously achieved for all values of channel parameters, where the forward and backward channel parameters are not necessarily the same. We divide the achievability scheme into three cases, depending on the forward and backward channel parameters. For the first case, we use a reverse amplify-and-forward strategy in the relays. For the second case, we use four relay strategies based on the reverse amplify-and-forward with some modifications in terms of replacement and repetition of some stream levels. For the third case, we use two relay strategies based on performing two rounds of repetitions in a relay. The proposed schemes for deterministic channels are used to find the capacity regions within constant gaps for two special cases of the Gaussian two-way diamond channel. First, for the general Gaussian two-way relay channel with a simple coding scheme the smallest gap is achieved compared to the prior works. Then, a special symmetric Gaussian two-way diamond model is considered and the capacity region is achieved within four bits.