Simultaneous Signal-and-Interference Alignment for Two-Cell Over-the-Air Computation

TL;DR

This paper introduces a novel simultaneous signal-and-interference alignment scheme for two-cell multi-antenna systems to optimize over-the-air computation, maximizing interference-free streams for large-scale sensing and distributed learning.

Contribution

It proposes a new SIA scheme that divides spatial channels for signal alignment and interference management, enhancing multi-cell AirComp performance.

Findings

Maximizes interference-free streams to half of spatial degrees-of-freedom.

Number of streams is independent of device population.

Extension to multi-cell scenarios is discussed.

Abstract

The next-generation wireless networks are envisioned to support large-scale sensing and distributed machine learning, thereby enabling new intelligent mobile applications. One common network operation will be the aggregation of distributed data (such as sensor observations or AI-model updates) for functional computation (e.g., averaging) so as to support large-scale sensing and distributed machine learning. An efficient solution for data aggregation, called "over-the-air computation" (AirComp), embeds functional computation into simultaneous access by many edge devices. Such schemes exploit the waveform superposition of a multi-access channel to allow an access point to receive a desired function of simultaneous signals. In this work, we aim at realizing AirComp in a two-cell multi-antenna system. To this end, a novel scheme of simultaneous signal-and-interference alignment (SIA) is proposed that builds on classic IA to manage interference for multi-cell AirComp. The principle of SIA is to divide the spatial channel space into two subspaces with equal dimensions: one for signal alignment required by AirComp and the other for inter-cell IA. As a result, the number of interference-free spatially multiplexed functional streams received by each AP is maximized (equal to half of the available spatial degrees-of-freedom). Furthermore, the number is independent of the population of devices in each cell. In addition, the extension to SIA for more than two cells is discussed.