On the Feasibility of Distributed Phase Synchronization for Coherent Signal Superposition

TL;DR

This paper investigates the practicality of distributed phase synchronization for coherent signal superposition, focusing on phase-coded pilots to mitigate phase deviations caused by CFO, mobility, and hardware impairments, supported by theoretical analysis and practical demonstration.

Contribution

It introduces phase-coded pilots for distributed synchronization and analyzes phase deviation statistics under CFO, mobility, and network size, demonstrating practical feasibility with off-the-shelf radios.

Findings

Residual CFO significantly limits phase coherence duration.

Mobility and network size also impact phase synchronization stability.

Practical proof-of-concept confirms feasibility of PCPs for coherent superposition.

Abstract

In this study, we analyze the feasibility of distributed phase synchronization for coherent signal superposition, a fundamental enabler for paradigms such as coherent over-the-air computation (OAC), distributed beamforming, and interference alignment, under mobility and hardware impairments. With the focus on coherent OAC, we introduce phase-coded pilots (PCPs), a strategy where the radios communicate with each other to eliminate the round-trip phase change in the uplink (UL) and downlink (DL) to align the phase of the received symbol at a desired angle. In this study, considering a carrier frequency offset (CFO)-resilient multi-user procedure, we derive the statistics of the phase deviations to assess how fast the phase coherency degrades. Our results show that residual CFO is a major factor determining the duration of phase coherency, in addition to the non-negligible effects of mobility and the number of nodes in the network. We also provide a proof-of-concept demonstration for coherent signal superposition by using off-the-shelf radios to demonstrate the feasibility of PCPs in practice.