On the Role of Feedback in LT Codes

TL;DR

This paper investigates how feedback via acknowledgments affects LT codes, revealing that while it can hinder standard LT code performance, it significantly benefits multi-layer LT codes with unequal error protection.

Contribution

The paper analyzes the impact of feedback on LT codes, showing its detrimental effects on standard codes and benefits for multi-layer LT codes with unequal error protection.

Findings

Feedback can degrade standard LT code performance.

Single feedback message improves multi-layer LT codes.

Feedback has limited potential in standard LT codes.

Abstract

This paper concerns application of feedback in LT codes. The considered type of feedback is acknowledgments, where information on which symbols have been decoded is given to the transmitter. We identify an important adaptive mechanism in standard LT codes, which is crucial to their ability to perform well under any channel conditions. We show how precipitate application of acknowledgments can interfere with this adaptive mechanism and lead to significant performance degradation. Moreover, our analysis reveals that even sensible use of acknowledgments has very low potential in standard LT codes. Motivated by this, we analyze the impact of acknowledgments on multi layer LT codes, i.e. LT codes with unequal error protection. In this case, feedback proves advantageous. We show that by using only a single feedback message, it is possible to achieve a noticeable performance improvement compared to standard LT codes.