176 research outputs found
Capacity of Coded Index Modulation
We consider the special case of index coding over the Gaussian broadcast
channel where each receiver has prior knowledge of a subset of messages at the
transmitter and demands all the messages from the source. We propose a
concatenated coding scheme for this problem, using an index code for the
Gaussian channel as an inner code/modulation to exploit side information at the
receivers, and an outer code to attain coding gain against the channel noise.
We derive the capacity region of this scheme by viewing the resulting channel
as a multiple-access channel with many receivers, and relate it to the 'side
information gain' -- which is a measure of the advantage of a code in utilizing
receiver side information -- of the inner index code/modulation. We demonstrate
the utility of the proposed architecture by simulating the performance of an
index code/modulation concatenated with an off-the-shelf convolutional code
through bit-interleaved coded-modulation.Comment: To appear in Proc. IEEE Int. Symp. Inf. Theory (ISIT) 2015, Hong
Kong, Jun. 2015. 5 pages, 4 figure
Iteratively Decoded Irregular Variable Length Coding and Sphere-Packing Modulation-Aided Differential Space-Time Spreading
In this paper we consider serially concatenated and iteratively decoded Irregular Variable Length Coding (IrVLC) combined with precoded Differential Space-Time Spreading (DSTS) aided multidimensional Sphere Packing (SP) modulation designed for near-capacity joint source and channel coding. The IrVLC scheme comprises a number of component Variable Length Coding (VLC) codebooks having different coding rates for the sake of encoding particular fractions of the input source symbol stream. The relative length of these source-stream fractions can be chosen with the aid of EXtrinsic Information Transfer (EXIT) charts in order to shape the EXIT curve of the IrVLC codec, so that an open EXIT chart tunnel may be created even at low Eb/N0 values that are close to the capacity bound of the channel. These schemes are shown to be capable of operating within 0.9 dB of the DSTS-SP channel’s capacity bound using an average interleaver length of 113, 100 bits and an effective bandwidth efficiency of 1 bit/s/Hz, assuming ideal Nyquist filtering. By contrast, the equivalent-rate regular VLC-based benchmarker scheme was found to be capable of operating at 1.4 dB from the capacity bound, which is about 1.56 times the corresponding discrepancy of the proposed IrVLC-aided scheme
On the Design of a Novel Joint Network-Channel Coding Scheme for the Multiple Access Relay Channel
This paper proposes a novel joint non-binary network-channel code for the
Time-Division Decode-and-Forward Multiple Access Relay Channel (TD-DF-MARC),
where the relay linearly combines -- over a non-binary finite field -- the
coded sequences from the source nodes. A method based on an EXIT chart analysis
is derived for selecting the best coefficients of the linear combination.
Moreover, it is shown that for different setups of the system, different
coefficients should be chosen in order to improve the performance. This
conclusion contrasts with previous works where a random selection was
considered. Monte Carlo simulations show that the proposed scheme outperforms,
in terms of its gap to the outage probabilities, the previously published joint
network-channel coding approaches. Besides, this gain is achieved by using very
short-length codewords, which makes the scheme particularly attractive for
low-latency applications.Comment: 28 pages, 9 figures; Submitted to IEEE Journal on Selected Areas in
Communications - Special Issue on Theories and Methods for Advanced Wireless
Relays, 201
Deterministic Rateless Codes for BSC
A rateless code encodes a finite length information word into an infinitely
long codeword such that longer prefixes of the codeword can tolerate a larger
fraction of errors. A rateless code achieves capacity for a family of channels
if, for every channel in the family, reliable communication is obtained by a
prefix of the code whose rate is arbitrarily close to the channel's capacity.
As a result, a universal encoder can communicate over all channels in the
family while simultaneously achieving optimal communication overhead. In this
paper, we construct the first \emph{deterministic} rateless code for the binary
symmetric channel. Our code can be encoded and decoded in time per
bit and in almost logarithmic parallel time of , where
is any (arbitrarily slow) super-constant function. Furthermore, the error
probability of our code is almost exponentially small .
Previous rateless codes are probabilistic (i.e., based on code ensembles),
require polynomial time per bit for decoding, and have inferior asymptotic
error probabilities. Our main technical contribution is a constructive proof
for the existence of an infinite generating matrix that each of its prefixes
induce a weight distribution that approximates the expected weight distribution
of a random linear code
DRASIC: Distributed Recurrent Autoencoder for Scalable Image Compression
We propose a new architecture for distributed image compression from a group
of distributed data sources. The work is motivated by practical needs of
data-driven codec design, low power consumption, robustness, and data privacy.
The proposed architecture, which we refer to as Distributed Recurrent
Autoencoder for Scalable Image Compression (DRASIC), is able to train
distributed encoders and one joint decoder on correlated data sources. Its
compression capability is much better than the method of training codecs
separately. Meanwhile, the performance of our distributed system with 10
distributed sources is only within 2 dB peak signal-to-noise ratio (PSNR) of
the performance of a single codec trained with all data sources. We experiment
distributed sources with different correlations and show how our data-driven
methodology well matches the Slepian-Wolf Theorem in Distributed Source Coding
(DSC). To the best of our knowledge, this is the first data-driven DSC
framework for general distributed code design with deep learning
Practical implementation of identification codes
Identification is a communication paradigm that promises some exponential
advantages over transmission for applications that do not actually require all
messages to be reliably transmitted, but where only few selected messages are
important. Notably, the identification capacity theorems prove the
identification is capable of exponentially larger rates than what can be
transmitted, which we demonstrate with little compromise with respect to
latency for certain ranges of parameters. However, there exist more trade-offs
that are not captured by these capacity theorems, like, notably, the delay
introduced by computations at the encoder and decoder. Here, we implement one
of the known identification codes using software-defined radios and show that
unless care is taken, these factors can compromise the advantage given by the
exponentially large identification rates. Still, there are further advantages
provided by identification that require future test in practical
implementations.Comment: submitted to GLOBECOM2
Quickest Sequence Phase Detection
A phase detection sequence is a length- cyclic sequence, such that the
location of any length- contiguous subsequence can be determined from a
noisy observation of that subsequence. In this paper, we derive bounds on the
minimal possible in the limit of , and describe some sequence
constructions. We further consider multiple phase detection sequences, where
the location of any length- contiguous subsequence of each sequence can be
determined simultaneously from a noisy mixture of those subsequences. We study
the optimal trade-offs between the lengths of the sequences, and describe some
sequence constructions. We compare these phase detection problems to their
natural channel coding counterparts, and show a strict separation between the
fundamental limits in the multiple sequence case. Both adversarial and
probabilistic noise models are addressed.Comment: To appear in the IEEE Transactions on Information Theor
Random Access for Machine-Type Communication based on Bloom Filtering
We present a random access method inspired on Bloom filters that is suited
for Machine-Type Communications (MTC). Each accessing device sends a
\emph{signature} during the contention process. A signature is constructed
using the Bloom filtering method and contains information on the device
identity and the connection establishment cause. We instantiate the proposed
method over the current LTE-A access protocol. However, the method is
applicable to a more general class of random access protocols that use
preambles or other reservation sequences, as expected to be the case in 5G
systems. We show that our method utilizes the system resources more efficiently
and achieves significantly lower connection establishment latency in case of
synchronous arrivals, compared to the variant of the LTE-A access protocol that
is optimized for MTC traffic. A dividend of the proposed method is that it
allows the base station (BS) to acquire the device identity and the connection
establishment cause already in the initial phase of the connection
establishment, thereby enabling their differentiated treatment by the BS.Comment: Accepted for presentation on IEEE Globecom 201
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