512 research outputs found
On the Queueing Behavior of Random Codes over a Gilbert-Elliot Erasure Channel
This paper considers the queueing performance of a system that transmits
coded data over a time-varying erasure channel. In our model, the queue length
and channel state together form a Markov chain that depends on the system
parameters. This gives a framework that allows a rigorous analysis of the queue
as a function of the code rate. Most prior work in this area either ignores
block-length (e.g., fluid models) or assumes error-free communication using
finite codes. This work enables one to determine when such assumptions provide
good, or bad, approximations of true behavior. Moreover, it offers a new
approach to optimize parameters and evaluate performance. This can be valuable
for delay-sensitive systems that employ short block lengths.Comment: 5 pages, 4 figures, conferenc
Secret Communication over Broadcast Erasure Channels with State-feedback
We consider a 1-to- communication scenario, where a source transmits
private messages to receivers through a broadcast erasure channel, and the
receivers feed back strictly causally and publicly their channel states after
each transmission. We explore the achievable rate region when we require that
the message to each receiver remains secret - in the information theoretical
sense - from all the other receivers. We characterize the capacity of secure
communication in all the cases where the capacity of the 1-to- communication
scenario without the requirement of security is known. As a special case, we
characterize the secret-message capacity of a single receiver point-to-point
erasure channel with public state-feedback in the presence of a passive
eavesdropper.
We find that in all cases where we have an exact characterization, we can
achieve the capacity by using linear complexity two-phase schemes: in the first
phase we create appropriate secret keys, and in the second phase we use them to
encrypt each message. We find that the amount of key we need is smaller than
the size of the message, and equal to the amount of encrypted message the
potential eavesdroppers jointly collect. Moreover, we prove that a dishonest
receiver that provides deceptive feedback cannot diminish the rate experienced
by the honest receivers.
We also develop a converse proof which reflects the two-phase structure of
our achievability scheme. As a side result, our technique leads to a new outer
bound proof for the non-secure communication problem
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