  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.
