On the Secrecy Capacity of the Broadcast Wiretap Channel with Limited CSI Feedback

TL;DR

This paper analyzes the secrecy capacity of a broadcast wiretap channel with limited CSI feedback, providing bounds and asymptotic capacity characterization for common and independent message scenarios.

Contribution

It offers the first partial characterization of ergodic secrecy capacity with limited feedback and derives bounds that become tight with increasing feedback capacity.

Findings

Bounds on ergodic secrecy sum-capacity are established.

Asymptotic capacity is fully characterized as feedback capacity increases.

The impact of limited CSI feedback on secure broadcast throughput is quantified.

Abstract

In this paper, we investigate the problem of secure broadcasting over block-fading channels with limited channel knowledge at the transmitter. More particularly, we analyze the effect of having imperfect channel state information (CSI) via a finite rate feedback on the throughput of a broadcast channel where the transmission is intended for multiple legitimate receivers in the presence of an eavesdropper. First, we partially characterize the ergodic secrecy capacity of the system when the source broadcasts the same information to all the receivers, i.e., common message transmission. Then, we look at the independent messages case, where the transmitter broadcasts multiple independent messages to the legitimate receivers. For this case, we present lower and upper bounds on the ergodic secrecy sum-capacity. In both scenarios, we show that the proposed lower and upper bounds coincide asymptotically as the capacity of the feedback links becomes large, hence, fully characterizing the secrecy capacity in this case.