# Linear Network Coding for Two-Unicast-$Z$ Networks: A Commutative Algebraic Perspective and Fundamental Limits

## TL;DR

This paper investigates the limits of network coding in two-unicast-Z networks, revealing that linear and non-linear codes can outperform traditional bounds, and introduces a commutative algebraic approach for analyzing coding feasibility.

## Contribution

It demonstrates that the generalized network sharing bound is not tight, shows the superiority of vector and non-linear codes, and develops a novel algebraic method for network coding analysis.

## Key findings

- Vector linear codes outperform scalar linear codes.
- Non-linear codes outperform linear codes in general.
- The commutative algebraic approach provides alternative proofs for coding feasibility.

## Abstract

We consider a two-unicast-$Z$ network over a directed acyclic graph of unit capacitated edges; the two-unicast-$Z$ network is a special case of two-unicast networks where one of the destinations has apriori side information of the unwanted (interfering) message. In this paper, we settle open questions on the limits of network coding for two-unicast-$Z$ networks by showing that the generalized network sharing bound is not tight, vector linear codes outperform scalar linear codes, and non-linear codes outperform linear codes in general. We also develop a commutative algebraic approach to deriving linear network coding achievability results, and demonstrate our approach by providing an alternate proof to the previous results of C. Wang et. al., I. Wang et. al. and Shenvi et. al. regarding feasibility of rate $(1,1)$ in the network.