# Covert Communications via Full-Duplex User Relaying

## TL;DR

This paper introduces a new method for secure communication where a user helps send hidden messages without being detected.

## Contribution

The novel approach ensures covert data is undetectable by optimizing transmission and cancellation techniques.

## Key findings

- The system model uses a full-duplex relay to maximize covert communication rates.
- Phase steering and power allocation confuse the warden while maintaining covertness.
- Covert data cancellation at the warden is achieved to meet detection probability thresholds.

## Abstract

In this paper, we investigate a covert communication system with a full-duplex decode-and-forward (DF) relay and introduce a user-relaying scheme that maximizes the covert rate while ensuring the covertness requirement. In our system model, Alice (transmitter) sends regular data to Carol (regular user) and occasionally embeds covert data for Bob (covert user). Meanwhile, Willie (warden) monitors for covert transmissions. Carol assists Alice by acting as a full-duplex DF relay, decoding both data types via successive interference cancellation and relaying covert data using phase steering and power allocation to confuse Willie. Our proposed scheme adopts a novel approach in which the covert data received by Willie is perfectly canceled, optimizing Alice’s and Carol’s transmissions to maximize the covert rate while keeping Willie’s detection probability below a given threshold.