Joint Institute for Signal and Image
Processing / University of Edinburgh and Heriot-Watt
University
Organiser: Norbert
Goertz, Institute for Digital Communications, The School of
Engineering and Electronics, The University of Edinburgh
Sponsors:
NEWCOM, The Royal Academy of Engineering, Vodafone Group Foundation,
The School of Engineering and Electronics
26 March 2007
Prof.
Li Ping
City
University of Hong Kong
"Interleave-Division
Multiple-Access (IDMA), Superposition Coded Modulation (SCM) and
OFDM-IDMA"
Video Conference Room, 13:00-14:00
(Slides)
Abstract:
This talk provides an
overview of interleave-division multiple-access (IDMA) that employs
interleaving as the only mechanism to distinguish users. IDMA
possesses many desired features for future wireless systems that are
difficult to fulfill simultaneously with other alternatives. These
include
low receiver cost (near single-user turbo-receiver complexity),
near optimal multi-user performance,
de-centralized asynchronous control,
simple interference cancelation for multiple access interference (MAI) and inter-symbol interference (ISI) problems,
high single-user throughput (e.g., > 10 bits/Hz).
The basic IDMA principles can be directly extended from binary modulation to multi-ary modulation. This leads to the so-called superposition coded modulation (SCM) scheme in which all the bandwidth resource is allocated one or a few users. IDMA can also be combined with OFDM. Such combinations provide a solution to both MAI and ISI problems. Interestingly, it also provides a solution to the peak-to-average-power-ratio (PAPR) problem in OFDM. The clipping distortion for peak power reduction can be effectively minimized using a sub-optimal soft compensation technique. Several distinguished features of the new scheme are explained, such as
low PAPR,
robustness against fading,
capacity achieving performance
flexibility in resource allocation
Comparisons with other coded modulation schemes (in particular, BICM) will be provided.
and
"Multi-User
Gain, Maximum Eigenmode Beamforming and IDMA"
Video
Conference Room, 14:30-15:30
(Slides)
Abstract:
We
consider multi-user MIMO systems with rate constraints. We show that
significant performance improvements, quantified by multi-user gain
(MUG), can be achieved by a low-cost maximum eigenmode beamforming
(MEB) strategy. This technique avoids complicated correlation matrix
optimization and water-filling operations at the transmitter (as
required by the optimal approach). It provides a simple yet nearly
optimal approach to exploit the advantages offered by MIMO. We show
that IDMA is an efficient method to realize MUG based on the MEB
strategy.
10 October 2007
Prof.
Daniel J. Costello, Jr.
University
of Notre Dame, Indiana, USA
"The
Genesis of Coding Theory"
AGB Seminar Room,
12:00-13:00
Abstract:
This talk gives an
historical overview of the theory of channel coding dating back to
the work of Shannon in 1948. The important advances in channel coding
in each 10 year period since 1948 are viewed from a common
perspective: the power and bandwidth efficiencies needed to achieve
certain levels of error performance. The most important contributions
of the last half century are highlighted, including Hamming codes,
Reed-Solomon codes, convolutional codes, soft decision decoding,
trellis coded modulation, concatenated codes, turbo codes,
low-density parity-check codes, and iterative decoding. Finally,
areas of potential future research in channel coding are briefly
discussed.
and
"LDPC
Convolutional Codes: What are they? How do they work? Are
they any good?"
AGB Seminar Room,
15:00-16:30
Abstract:
Low-density
parity-check (LDPC) convolutional codes have been shown to be capable
of achieving the same capacity-approaching performance as LDPC block
codes with iterative message-passing decoding. In this paper,
we define two distinct classes of LDPC convolutional codes:
time-invariant and time-varying, and connections with quasi-cyclic
LDPC block codes are discussed. Then encoding and decoding
procedures are reviewed. Two iterative message-passing decoders
are presented: a one-shot decoder that treats a terminated LDPC
convolutional code as a big block code and a high-speed pipeline
decoder that takes advantage of the unique structural properties of
convolutional codes and can be used for continuous (non-terminated)
transmission. VLSI implementation requirements for these
decoders are also discussed. We then compare several
aspects of LDPC convolutional codes with LDPC block codes, including
encoding complexity, decoding complexity, decoder storage
requirements, decoding delay, and error performance. Finally, a
pseudo-codeword analysis is used to investigate the behavior of
iterative message-passing decoding for LDPC convolutional codes. In
particular, we show that LDPC convolutional codes have better
convergence properties than LDPC block codes in the low-to-moderate
SNR region due to an improved pseudo-codeword weight spectrum.
12 June 2007
Dr.
Marcus Greferath
University
College Dublin / Claude Shannon Institute, Dublin, Ireland
Abstract:
LDPC codes have been attracting
attention over the recent decade. They were (re)discovered soon after
the famous TURBO codes, and it can be said that they belong to the
oldest codes known, since they were originally described in seminal
work by Gallager and in the sixties. This talk will describe a family
of LDPC codes that are derived from what are called 0-1-geometries
which have found in a geometric structure called inversive space. We
will briefly discuss basic properties and show some performance
diagrams. These diagrams suggest that these codes might be useful in
various applications like general communications as well as data
storage.
12 June 2007
Dr.
Mark Flanagan
University
College Dublin / Claude Shannon Institute, Dublin, Ireland
Abstract:
We demonstrate a construction technique
for low-density parity check (LDPC) codes based on m-dimensional
finite Euclidean geometries. These codes are shown to be regular
Gallager codes with Tanner graphs of girth eight. The minimum
distance of these codes is shown to be lower-bounded by 2^m. The
codes are also amenable to an efficient partly parallel decoder
implementation, which may be used in conjunction with the turbo
decoding message passing (TDMP) algorithm for LDPC decoding. It is
also shown how results on these codes and their lattices, yielding a
code class with highly flexible code length and rate. Finally,
simulation results show that both classes of codes have very good
error-correcting performance.
27 October 2006
Prof.
Sergios Theodoridis
University
of Athens, Greece
"Support
Vector Machines: A geometric point of view"
Abstract:
Support
Vector Machines have been established as one of the major
classification and regression tools for Pattern Recognition and
Signal Analysis. Over the last decade a number of theoretical
arguments have been developed in order to justify their enhanced
performance. The most widely known scenario is to look at them as
maximum margin classifiers. Another approach is via learning theory
arguments and the structural risk minimization principle, which leads
to an optimal trade off between performance and complexity. An
alternative path is to look at the cost function, associated with the
SVM´s, as a regularized minimizer that asymptotically tends to
the Bayesian classifier. A less known viewpoint is the geometric one
that leads to the notion of reduced convex hulls. For the
non-separable class case, the SVM solution is shown to be equivalent
with computing the minimum distance between two reduced versions of
the original convex hulls that “encircle” the two classes (for
the two class case).In this talk I will focus on the geometric
approach and new results will be discussed concerning a) novel,
necessary for our case, theorems concerning the structure and
properties of the reduced convex hulls (RCH) and b) novel
algorithms for computing the minimum distance between the resulting
RCH´s. This problem is far from being trivial, since existing
algorithms, which compute the minimum distance between convex hulls,
rely on their respective extreme points. However, computing the
extreme points of a reduced convex hull, as we have shown, is a
computationally hard task of a combinatorial nature. A basic
projection theorem, that we have shown, will be discussed that
bypasses the combinatorial burden of the task and opens the way to
employ geometric minimum distance algorithms to the SVM task.
Most important, this theorem “respects” inner products, thus
allowing to the well known kernel trick to be easily incorporated
into the algorithmic schemes, making them appropriate for the general
nonlinear non-separable problem. The derived geometric algorithms are
much more efficient compared to the classical and widely used SMO
algorithm and its versions. A number of tests with well known test
beds have shown that, sometimes, a gain of an order of
magnitude in the number of kernel computations, for similar error
rates, can be achieved. Furthermore, the new schemes are closer to
our intuitive understanding of an iterative algorithm in simple
geometric arguments.
11 October 2006
Prof.
Joachim Hagenauer
Munich University of
Technology, Germany
"Information
Theory and Genetics"
Abstract:
We view
the process between the DNA and the proteins as a communications
process. The information transfer between DNA-variations (SNPs) and
diseases is measured with Shannon's mutual information using
simulated and clinical data (Schizophrenia, Parkinson and Graves
autoimmune disease) . We further create distance measures between
different DNA sequences derived from mutual information for
classification and recognition methods. From classification results
we create mammalian and human phylogenetic trees. A communication
theory model allows the evaluation of the synchronization process for
the DNA to mRNA transcription for E-coli bacteria.
11 May 2006
Prof.
Joseph Boutros
Ecole Nationale
Supérieure des Télécommunications, Paris,
France
"Near
outage limit space-time coding for MIMO channels"
Abstract:
We
study simple space-time coding techniques for multiple-input
multiple-output (MIMO) quasi-static channels (2Tx and 4Tx systems)
capable of achieving near outage limit performance.
The core of
our space-time code is an h-pi-diagonal state multiplexer that
guarantees full diversity and a quasi-optimal coding gain on the MIMO
channel. The whole range of word error probability is attained at
signal-to-noise ratios extremely close to theoretical limits. In
addition, at a fixed signal-to-noise ratio, the word error
probability is insensitive to the block length.
and
"Enhanced
channel decoding via EM source-channel estimation"
Abstract:
We
investigate the joint source-channel estimation and decoding problem.
We consider a non-uniform binary source transmitted over a
binary-input output-symmetric channel, namely the BEC, BSC and AWGN
channels. The source sequence is encoded via systematic and
non-systematic low-density parity-check codes. The proposed joint
source-channel iterative estimation technique relies on the
Expectation Maximization (EM) algorithm that will be associated to
the message passing LDPC decoding for both systematic and non
systematic codes. Simulation results confirm the strong improvement
in performance over the case in which source a priori information is
not considered. Furthermore, within this proposed joint
source-channel iterative estimation via Expectation Maximization no
loss in error-rate performance is observed with respect to the
perfect knowledge case.
20 April 2006
Prof.
Mikael Skoglund
Royal
Institute of Technology (KTH), Stockholm, Sweden
"Dirty
Paper Modulation"
Abstract:
We
present a symbol-by-symbol approach to Costa's "dirty paper"
precoding problem. Our scheme is based on joint optimization of a
modulator (encoder) and detector (decoder), subject to a constraint
on the average transmit power. The modulator maps an information
symbol (taken from a finite alphabet) and an interference symbol
(from the complex field) onto a transmitted constellation point. The
detector picks the information symbol (as function of the received
symbol) which minimizes the average error probability. We illustrate
that the new "dirty paper modulation" scheme outperforms
Tomlinson-Harashima precoding, which is a classical suboptimal
solution to the known-interference precoding problem. In our
simulations, the new approach is also able to perform close to the
no-interference bound.
16 January 2006
Prof.
Lajos Hanzo
University
of Southampton
"Genetics
in wireless communications"
and
"Advances in multicarrier systems"
15 November 2005
Dr.
Cheng-Xiang Wang
Heriot-Watt
University, Edinburgh
"Analog
and Digital Mobile Radio Channel Simulators Based on Sum-of-Sinusoids
Principles"
Abstract:
A
profound understanding and accurate modeling of mobile radio channels
are of great significance for the effective design, parameter
optimization, and performance evaluation of any mobile communication
systems. The sum-of-sinusoids channel modeling approach has widely
been accepted as an efficient and flexible method for the simulation
of mobile radio channels. This presentation addresses the principles
and applications of sum-of-sinusoids channel simulators for both
analog (waveform) and digital mobile radio channels.
10 and 11 October 2005 (several talks)
Prof.
Ulrich Heute
Christian-Albrechts
University, Kiel, Germany
"Integral
and Diagnostic Speech-Quality Measurement: State of the Art,
Problems, and New Approaches"
Abstract:
The
user’s overall impression of a speech signal which has been
filtered, transmitted, coded, or processed by some system, can be
described in terms of the integral quality. There are well-defined
auditory methods to assess integral quality: Mostly, an
absolute-category rating in a listening-only situation is used
(resulting in the mean-opinion score, MOS). Numerous other methods
exist, using different scales or more refined test situations, e.g.,
conversational tests.
For this integral quality, proposals
exist for efficient instrumental, signal-based measurements, yielding
MOS estimates, like the standard P.862 (ITU-T, 2001) or the TOSQA
model (Berger, 1998). Such estimates have problems with distortions
not taken into account during the model development. Furthermore,
these estimates do not allow to characterize the quality of speech
signals: They might provide the same MOS for two signals which are
perceived to sound differently in an auditory test.
A
different approach has been well-known that overcomes these problems:
Quality attributes can be aimed at, which
- concern detailed and
distinct distortion effects,
- thus, allow for a system
diagnosis, and
- together form an integral-quality-impression
model
- which is able to cope also with future distortions.
Earlier work into that direction has been known to have
problems, too. Avoiding some weaknesses and re-defining more suitable
attributes, the diagnostic approach is re-visited, including an
integral quality measure to be finally derived. New, important types
of distortions, like time-varying, bursty data-packet loss in
internet transmission, are to be included. First results are
reported, and further work is outlined.
"Design
of Efficient Digital FIR Filters: A Case Study"
Contents:
1.
Introduction
2. Lowpass Tolerance Scheme
3. Non-Recursive Filters in 2nd Canonical (Direct) Form
4.
Non-Recursive Filters in Cascade Form
5. Partially Recursive Cascade Structures
6. Recursive Filters
7. Comparison of Expenditure
8. Conclusions
26 and 28 July 2005 (several talks)
Prof.
Wolfgang Utschick
Munich
University of Technology, Germany
"Multiuser
multiple input multiple output (MIMO) wireless systems"
Overview:
A tutorial talk about Multiple Input Multiple Output (MIMO) wireless systems which gives an overview of the most exciting topics (tutorial talk).
A tutorial course about the very
principles of linear and nonlinear Rx and Tx equalizers with a focus
on Tx processing and a strong concentration
on Tomlinson
Harashima Precoding (lecture course)
A couple of accompanying conference talks (from recent conferences) with respect to the topics in 1 and 2 (conference style).
28 June 2005
Dr.
Liam O'Carroll
School
of Mathematics, University of Edinburgh
"An
Introduction to the Mathematical Aspects of Reed-Solomon Codes"
Abstract:
Reed-Solomon codes
are arguably the most important family of codes for burst-error
correction in channel coding, especially in their use as the outer
code in a concatenated code. Even to discuss them in the binary
case (which is the case we consider) involves coming to grips with
the arithmetic of finite ('Galois') fields GF(2^m) of 2^m elements.
In this talk, we aim to give a gentle introduction to the
mathematical construction and properties of Reed-Solomon codes.
First we look at the integers modulo p, p a prime, (i.e., at GF(p))
so as to introduce basic ideas in a simple setting where examples can
be calculated easily. (Indeed, the mathematics here finds application
in the construction of Costas Arrays, used in frequency hopping codes
in e.g. radar, and in the RSA encryption system.) Then we
consider the arithmetic of GF(2^m), again looking at easily
calculated examples. Finally we show how Reed-Solomon codes arise in
this setting, again using concrete examples to illustrate the theory.
16 June 2005
Prof.
Maja Bystrom
Boston
University, USA
"Linking
Networks: Coding for Heterogeneous Systems"
Abstract:
As
networks increase in size and number of users, optimal or
near-optimal resource allocation becomes increasingly important.
Furthermore, adaptability in the face of changing channel and source
conditions is an interesting challenge. We first review some issues
in providing for reliable communications over heterogeneous networks,
that is, networks composed of wireline and wireless links. We propose
that while serial concatenated codes were designed to provide good
overall performance with reasonable system complexity, they may arise
naturally in certain cases, such as the interface between two
networks. Then, a new method of code rate allocation, based on code
performance bounds, that is flexible in the face of channel
variations, is proposed. In particular, we consider the problem of
constrained rate allocation between nonsystematic block codes in a
serial concatenated coding system. Given constraints on system
parameters, such as a limit on the overall rate, analytic guidelines
for the selection of good inner code rates are found by using an
upper bound on the average system block error rate.
19 May 2005
Prof.
Johannes Huber
University
Erlangen-Nuremberg, Germany
"Information
Combining: Models, Bounds, and Applications"
Abstract:
11 April 2005
Prof.
John B. Anderson
Lund
University, Sweden
"From
BPSK to MIMO: Thirty Years of Coding and Modulation"
Abstract:
The last 30 years
have seen the cost of signal processing drop almost to nothing. This
has revolutionized communication and brought us from simple digital
modulation to coded modulation to MIMO systems. We will review this
history and give a personal view of how one idea led to another and
where the technology may go from here.