On the Delay Limited Secrecy Capacity of Fading Channels

In this paper, the delay limited secrecy capacity of the flat fading channel is investigated under two different assumptions on the available transmitter channel state information (CSI). The first scenario assumes perfect prior knowledge of both the main and eavesdropper channel gains. Here, upper and lower bounds on the secure delay limited capacity are derived and shown to be tight in the high signal-to-noise ratio (SNR) regime (for a wide class of channel distributions). In the second scenario, only the main channel CSI is assumed to be available at the transmitter. Remarkably, under this assumption, we establish the achievability of non-zero secure rate (for a wide class of channel distributions) under a strict delay constraint. In the two cases, our achievability arguments are based on a novel two-stage approach that overcomes the secrecy outage phenomenon observed in earlier works.

💡 Research Summary

This paper investigates the delay‑limited secrecy capacity of a flat fading wireless channel under two distinct assumptions about the transmitter’s channel state information (CSI). The first scenario assumes that the transmitter has perfect, instantaneous knowledge of both the legitimate (main) channel gain and the eavesdropper’s channel gain. In this case the authors derive both an upper bound and a lower bound on the achievable secrecy rate when a strict per‑block delay constraint must be satisfied. The upper bound follows from the fact that any coding scheme cannot exceed the average instantaneous secrecy capacity, defined as (