The Gaussian Wiretap Channel with a Helping Interferer

Due to the broadcast nature of the wireless medium, wireless communication is susceptible to adversarial eavesdropping. This paper describes how eavesdropping can potentially be defeated by exploiting the superposition nature of the wireless medium. A Gaussian wire-tap channel with a helping interferer (WTC-HI) is considered in which a transmitter sends confidential messages to its intended receiver in the presence of a passive eavesdropper and with the help of an interferer. The interferer, which does not know the confidential message assists the confidential message transmission by sending a signal that is independent of the transmitted message. An achievable secrecy rate and a Sato-type upper bound on the secrecy capacity are given for the Gaussian WTC-HI. Through numerical analysis, it is found that the upper bound is close to the achievable secrecy rate when the interference is weak for symmetric interference channels, and under more general conditions for asymmetric Gaussian interference channels.

💡 Research Summary

The paper investigates a Gaussian wire‑tap channel augmented with a helping interferer (WTC‑HI). In this model a legitimate transmitter wishes to send a confidential message to an intended receiver while a passive eavesdropper listens to the transmission. A third node, the interferer, does not know the secret message but can transmit an independent Gaussian signal that interferes with both the legitimate receiver and the eavesdropper. By exploiting the superposition property of the wireless medium, the interferer’s signal can act as artificial noise that degrades the eavesdropper more than the legitimate receiver, thereby increasing the achievable secrecy rate.

The system equations are:
Y₁ₖ = X₁ₖ + √b X₂ₖ + Z₁ₖ (receiver)
Y₂ₖ = √a X₁ₖ + X₂ₖ + Z₂ₖ (eavesdropper)
where a and b are the cross‑channel gains, Z₁ₖ and Z₂ₖ are unit‑variance Gaussian noises, and the average power constraints are 𝔼