962 research outputs found
On the Shannon Cipher System With a Wiretapper Guessing Subject to Distortion and Reliability Requirements
In this paper we discuss the processes in the Shannon cipher system with
discrete memoryless source and a guessing wiretapper. The wiretapper observes a
cryptogram of -vector of ciphered messages in the public channel and tries
to guess successively the vector of messages within given distortion level
and small probability of error less than with positive
reliability index . The security of the system is measured by the expected
number of guesses which wiretapper needs for the approximate reconstruction of
the vector of source messages. The distortion, the reliability criteria and the
possibility of upper limiting the number of guesses extend the approach studied
by Merhav and Arikan. A single-letter characterization is given for the region
of pairs (of the rate of the maximum number of guesses
and the rate of the average number of guesses) in dependence on key rate
, distortion level and reliability .Comment: 14 pages, 3 figures, Submitted to IEEE Transactions on Information
Theor
Centralized and Cooperative Transmission of Secure Multiple Unicasts using Network Coding
We introduce a method for securely delivering a set of messages to a group of
clients over a broadcast erasure channel where each client is interested in a
distinct message. Each client is able to obtain its own message but not the
others'. In the proposed method the messages are combined together using a
special variant of random linear network coding. Each client is provided with a
private set of decoding coefficients to decode its own message. Our method
provides security for the transmission sessions against computational
brute-force attacks and also weakly security in information theoretic sense. As
the broadcast channel is assumed to be erroneous, the missing coded packets
should be recovered in some way. We consider two different scenarios. In the
first scenario the missing packets are retransmitted by the base station
(centralized). In the second scenario the clients cooperate with each other by
exchanging packets (decentralized). In both scenarios, network coding
techniques are exploited to increase the total throughput. For the case of
centralized retransmissions we provide an analytical approximation for the
throughput performance of instantly decodable network coded (IDNC)
retransmissions as well as numerical experiments. For the decentralized
scenario, we propose a new IDNC based retransmission method where its
performance is evaluated via simulations and analytical approximation.
Application of this method is not limited to our special problem and can be
generalized to a new class of problems introduced in this paper as the
cooperative index coding problem
Bounds on the Capacity of the Relay Channel with Noncausal State at Source
We consider a three-terminal state-dependent relay channel with the channel
state available non-causally at only the source. Such a model may be of
interest for node cooperation in the framework of cognition, i.e.,
collaborative signal transmission involving cognitive and non-cognitive radios.
We study the capacity of this communication model. One principal problem is
caused by the relay's not knowing the channel state. For the discrete
memoryless (DM) model, we establish two lower bounds and an upper bound on
channel capacity. The first lower bound is obtained by a coding scheme in which
the source describes the state of the channel to the relay and destination,
which then exploit the gained description for a better communication of the
source's information message. The coding scheme for the second lower bound
remedies the relay's not knowing the states of the channel by first computing,
at the source, the appropriate input that the relay would send had the relay
known the states of the channel, and then transmitting this appropriate input
to the relay. The relay simply guesses the sent input and sends it in the next
block. The upper bound is non trivial and it accounts for not knowing the state
at the relay and destination. For the general Gaussian model, we derive lower
bounds on the channel capacity by exploiting ideas in the spirit of those we
use for the DM model; and we show that these bounds are optimal for small and
large noise at the relay irrespective to the strength of the interference.
Furthermore, we also consider a special case model in which the source input
has two components one of which is independent of the state. We establish a
better upper bound for both DM and Gaussian cases and we also characterize the
capacity in a number of special cases.Comment: Submitted to the IEEE Transactions on Information Theory, 54 pages, 6
figure
Achievable Regions for Interference Channels with Generalized and Intermittent Feedback
In this paper, we first study a two-user interference channel with
generalized feedback. We establish an inner bound on its capacity region. The
coding scheme that we employ for the inner bound is based on an appropriate
combination of Han-Kobayash rate splitting and compress-and-forward at the
senders. Each sender compresses the channel output that is observes using a
compression scheme that is \`a-la Lim et al. noisy network coding and
Avestimeher et al. quantize-map-and-forward. Next, we study an injective
deterministic model in which the senders obtain output feedback only
intermittently. Specializing the coding scheme of the model with generalized
feedback to this scenario, we obtain useful insights onto effective ways of
combining noisy network coding with interference alignment techniques. We also
apply our results to linear deterministic interference channels with
intermittent feedback.Comment: To appear in Proc. of the 2014 IEEE International Symposium on
Information Theory, 6 pages, 2 figure
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