Timely Updates over an Erasure Channel

TL;DR

This paper analyzes the age of information for coded updates over erasure channels, comparing incremental redundancy and fixed redundancy schemes, and finds that fixed redundancy can outperform incremental redundancy with multiple monitors.

Contribution

It derives the average age for both IIR and FR systems over erasure channels and compares their performance, highlighting conditions where FR outperforms IIR.

Findings

Tuning redundancy to erasure rate makes FR as effective as IIR for a single monitor.

FR outperforms IIR as the number of monitors increases.

No feedback needed for FR system, simplifying implementation.

Abstract

Using an age of information (AoI) metric, we examine the transmission of coded updates through a binary erasure channel to a monitor/receiver. We start by deriving the average status update age of an infinite incremental redundancy (IIR) system in which the transmission of a k-symbol update continuesuntil k symbols are received. This system is then compared to a fixed redundancy (FR) system in which each update is transmitted as an n symbol packet and the packet is successfully received if and only if at least k symbols are received. If fewer than k symbols are received, the update is discarded. Unlike the IIR system, the FR system requires no feedback from the receiver. For a single monitor system, we show that tuning the redundancy to the symbol erasure rate enables the FR system to perform as well as the IIR system. As the number of monitors is increased, the FR system outperforms the IIR system that guarantees delivery of all updates to all monitors.