  In this paper, throughput and energy efficiency of secure wireless
transmission of delay sensitive data generated by random sources is studied. A
fading broadcast model in which the transmitter sends confidential and common
messages to two receivers is considered. It is assumed that the common and
confidential data, generated from Markovian sources, is stored in buffers prior
to transmission, and the transmitter operates under constraints on buffer/delay
violation probability. Under such statistical quality of service (QoS)
constraints, effective capacity of time-varying wireless transmissions and
effective bandwidth of Markovian sources are employed to determine the
throughput. In particular, secrecy capacity is used to describe the service
rate of buffers containing confidential messages. Moreover, energy per bit is
used as the energy efficiency metric and energy efficiency is studied in the
low signal-to-noise (SNR) regime. Specifically, minimum energy per bit required
for the reliable communication of common and confidential messages is
determined and wideband slope expressions are identified. The impact of
buffer/delay constraints, correlation between channels, source
characteristics/burstiness, channel knowledge at the transmitter, power
allocation, and secrecy requirements on the throughput and energy efficiency of
common and confidential message transmissions is identified.
