Communication with Crystal-Free Radios

TL;DR

This paper investigates communication without shared clocks, focusing on zero-error capacity under timing jitter and drift, and proposes coding strategies that perform well without clock synchronization.

Contribution

It introduces the first analysis of zero-error capacity for clockless communication channels considering both jitter and drift, and designs optimal codes for certain cases.

Findings

Optimal zero-error codes are identified for some clock uncertainty scenarios.

Designs show that avoiding clock synchronization can still achieve near-perfect communication.

Clock drift makes learning the clock frequency suboptimal, favoring specialized coding strategies.

Abstract

We consider a communication channel where there is no common clock between the transmitter and the receiver. This is motivated by the recent interest in building system-on-chip radios for Internet of Things applications, which cannot rely on crystal oscillators for accurate timing. We identify two types of clock uncertainty in such systems: timing jitter, which occurs at a time scale faster than the communication duration (or equivalently blocklength); and clock drift, which occurs at a slower time scale. We study the zero-error capacity under both types of timing imperfections, and obtain optimal zero-error codes for some cases. Our results show that, as opposed to common practice, in the presence of clock drift it is highly suboptimal to try to learn and track the clock frequency at the receiver; rather, one can design codes that come close to the performance of perfectly synchronous communication systems without any clock synchronization at the receiver.