Interference Assisted Secret Communication

Wireless communication is susceptible to eavesdropping attacks because of its broadcast nature. This paper illustrates how interference can be used to counter eavesdropping and assist secrecy. In particular, a wire-tap channel with a helping interferer (WT-HI) is considered. Here, a transmitter sends a confidential message to its intended receiver in the presence of a passive eavesdropper and with the help of an independent interferer. The interferer, which does not know the confidential message, helps in ensuring the secrecy of the message by sending an independent signal. An achievable secrecy rate and several computable outer bounds on the secrecy capacity of the WT-HI are given for both discrete memoryless and Gaussian channels.

💡 Research Summary

The paper tackles the inherent vulnerability of wireless communications to eavesdropping by turning interference—a traditionally harmful phenomenon—into a security asset. It introduces the “wire‑tap channel with a helping interferer” (WT‑HI) model, which consists of a legitimate transmitter (Alice), a legitimate receiver (Bob), a passive eavesdropper (Eve), and an independent interferer (Charlie). Charlie does not know the confidential message; instead, he transmits an independent, randomly generated signal that is known only to himself. The key idea is that this random signal can be treated as cooperative jamming: it degrades Eve’s ability to extract information while allowing Bob, who knows the statistical structure of both Alice’s and Charlie’s signals, to decode the intended message reliably.

For the discrete‑memoryless version of the channel, the authors develop a layered coding scheme. Alice splits her codebook into a “secret” layer and an auxiliary layer indexed by a random variable U. Charlie independently generates a random codebook according to a fixed distribution p(x_c). Bob performs joint typicality decoding over (U, X_c) to recover the secret message, whereas Eve, lacking any knowledge of X_c, sees a mixture that reduces the mutual information I(W;Z). By optimizing over the joint distribution p(u, x_s) and the interferer’s distribution p(x_c), the achievable secrecy rate is expressed as

 R_s = max_{p(u,x_s),p(x_c)}