806 research outputs found
Optimal block cosine transform image coding for noisy channels
The two dimensional block transform coding scheme based on the discrete cosine transform was studied extensively for image coding applications. While this scheme has proven to be efficient in the absence of channel errors, its performance degrades rapidly over noisy channels. A method is presented for the joint source channel coding optimization of a scheme based on the 2-D block cosine transform when the output of the encoder is to be transmitted via a memoryless design of the quantizers used for encoding the transform coefficients. This algorithm produces a set of locally optimum quantizers and the corresponding binary code assignment for the assumed transform coefficient statistics. To determine the optimum bit assignment among the transform coefficients, an algorithm was used based on the steepest descent method, which under certain convexity conditions on the performance of the channel optimized quantizers, yields the optimal bit allocation. Comprehensive simulation results for the performance of this locally optimum system over noisy channels were obtained and appropriate comparisons against a reference system designed for no channel error were rendered
An Achievable Rate Region for the Broadcast Channel with Feedback
A single-letter achievable rate region is proposed for the two-receiver
discrete memoryless broadcast channel with generalized feedback. The coding
strategy involves block-Markov superposition coding, using Marton's coding
scheme for the broadcast channel without feedback as the starting point. If the
message rates in the Marton scheme are too high to be decoded at the end of a
block, each receiver is left with a list of messages compatible with its
output. Resolution information is sent in the following block to enable each
receiver to resolve its list. The key observation is that the resolution
information of the first receiver is correlated with that of the second. This
correlated information is efficiently transmitted via joint source-channel
coding, using ideas similar to the Han-Costa coding scheme. Using the result,
we obtain an achievable rate region for the stochastically degraded AWGN
broadcast channel with noisy feedback from only one receiver. It is shown that
this region is strictly larger than the no-feedback capacity region.Comment: To appear in IEEE Transactions on Information Theory. Contains
example of AWGN Broadcast Channel with noisy feedbac
Polar Coding for Fading Channels
A polar coding scheme for fading channels is proposed in this paper. More
specifically, the focus is Gaussian fading channel with a BPSK modulation
technique, where the equivalent channel could be modeled as a binary symmetric
channel with varying cross-over probabilities. To deal with variable channel
states, a coding scheme of hierarchically utilizing polar codes is proposed. In
particular, by observing the polarization of different binary symmetric
channels over different fading blocks, each channel use corresponding to a
different polarization is modeled as a binary erasure channel such that polar
codes could be adopted to encode over blocks. It is shown that the proposed
coding scheme, without instantaneous channel state information at the
transmitter, achieves the capacity of the corresponding fading binary symmetric
channel, which is constructed from the underlying fading AWGN channel through
the modulation scheme.Comment: 6 pages, 4 figures, conferenc
Delay Optimal Secrecy in Two-Relay Network
We consider a two-relay network in which a source aims to communicate a
confidential message to a destination while keeping the message secret from the
relay nodes. In the first hop, the channels from the source to the relays are
assumed to be block-fading and the channel states change arbitrarily -possibly
non-stationary and non-ergodic- across blocks. When the relay feedback on the
states of the source-to-relay channels is available on the source with no
delay, we provide an encoding strategy to achieve the optimal delay. We next
consider the case in which there is one-block delayed relay feedback on the
states of the source-to-relay channels. We show that for a set of channel state
sequences, the optimal delay with one-block delayed feedback differs from the
optimal delay with no-delayed feedback at most one block
Asymptotic Error Free Partitioning over Noisy Boolean Multiaccess Channels
In this paper, we consider the problem of partitioning active users in a
manner that facilitates multi-access without collision. The setting is of a
noisy, synchronous, Boolean, multi-access channel where active users (out
of a total of users) seek to access. A solution to the partition problem
places each of the users in one of groups (or blocks) such that no two
active nodes are in the same block. We consider a simple, but non-trivial and
illustrative case of active users and study the number of steps used
to solve the partition problem. By random coding and a suboptimal decoding
scheme, we show that for any , where and
are positive constants (independent of ), and can be
arbitrary small, the partition problem can be solved with error probability
, for large . Under the same scheme, we also bound from
the other direction, establishing that, for any ,
the error probability for large ; again and
are constants and can be arbitrarily small. These bounds on the number
of steps are lower than the tight achievable lower-bound in terms of for group testing (in which all active users are identified,
rather than just partitioned). Thus, partitioning may prove to be a more
efficient approach for multi-access than group testing.Comment: This paper was submitted in June 2014 to IEEE Transactions on
Information Theory, and is under review no
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
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