On the Sum Capacity of the Gaussian X Channel in the Mixed Interference Regime

TL;DR

This paper investigates the sum capacity of the Gaussian X channel under mixed interference conditions, showing that multiple access schemes are near-optimal in certain subregions and deriving bounds that quantify this near-optimality.

Contribution

It introduces three new upper bounds for the sum capacity and characterizes the regions where multiple access transmission approaches optimality in the mixed interference regime.

Findings

Multiple access transmission is near-optimal in significant subregions.

Three new upper bounds for sum capacity are derived.

The gap between sum capacity and multiple access sum rate is small in key regions.

Abstract

In this paper, we analyze the Gaussian X channel in the mixed interference regime. In this regime, multiple access transmission to one of the receivers is shown to be close to optimal in terms of sum rate. Three upper bounds are derived for the sum capacity in the mixed interference regime, and the subregions where each of these bounds dominate the others are identified. The genie-aided sum capacity upper bounds derived also show that the gap between sum capacity and the sum rate of the multiple access transmission scheme is small for a significant part of the mixed interference region. For any \delta > 0, the region where multiple access transmission to one of the receivers is within \delta from sum capacity is determined.