Coding Strategies for Noise-Free Relay Cascades with Half-Duplex Constraint

TL;DR

This paper investigates noise-free relay cascades with half-duplex constraints, deriving capacity results and proposing coding strategies that outperform simple time-sharing, for networks with relay cascades and multiple transmitting nodes.

Contribution

It introduces new relay channel models with half-duplex constraints and determines their capacity, providing optimal coding strategies and bounds for different network configurations.

Findings

Capacity is higher than time-sharing approaches.

A capacity-achieving coding strategy based on time slot allocation.

Upper bounds on rate regions derived from cut-set bounds.

Abstract

Two types of noise-free relay cascades are investigated. Networks where a source communicates with a distant receiver via a cascade of half-duplex constrained relays, and networks where not only the source but also a single relay node intends to transmit information to the same destination. We introduce two relay channel models, capturing the half-duplex constraint, and within the framework of these models capacity is determined for the first network type. It turns out that capacity is significantly higher than the rates which are achievable with a straightforward time-sharing approach. A capacity achieving coding strategy is presented based on allocating the transmit and receive time slots of a node in dependence of the node's previously received data. For the networks of the second type, an upper bound to the rate region is derived from the cut-set bound. Further, achievability of the cut-set bound in the single relay case is shown given that the source rate exceeds a certain minimum value.