All tutorials will take place on Sunday 25th September 2005
All-IP Mobile Networks
David Wisely
Cellular mobile systems, including recently
introduced 3G networks, are tightly integrated solutions
specifically tailored for the delivery of specific services
onto handheld terminals. The Internet, by contrast, is
an open network of networks held together by a few architectural
principles and function-specific protocols.
As new IP-based networks, such as Wireless LAN and WiMAX,
are introduced and convergence with cellular and broadband
is developed native IP routing and functionality will
increasingly be employed.
This course sets out to understand exactly what an all-IP
network really is, shows how existing networks fail to
qualify for this term and discusses the potential advantages
and disadvantages of such networks. The course then looks
at the key IP technologies that will form the building
blocks of all-IP mobile networks: Mobility (including Mobile
IP), Quality of Service, call control (using Session
Initiation Protocol SIP) and security.
In addition the commercial aspects of all-IP mobile networks
is tackled looking at the British Telecom 21st Century
and other business models.
The ½ day course will cover the following topics:
1. Introduction summary of key mobile developments
(2nd and 3rd generation systems) and review of relevant
IP
principles and developments
2. What exactly is an all-IP mobile network? Discussion
of key IP architectural principles and application
to mobile networks. Evaluation of current systems (WLAN,
3GPP and
3GPP2 cellular and WiMAX).Advantages and disadvantages
of all-IP mobile networks.
3. Solutions for mobility support in IP networks
starting with an analysis of Mobile IP and looking
at layer 2
and application layer solutions. Current WLAN mobility
solutions
and proposals for WiMAX mobility.
4. Quality of service (QoS) in all-IP mobile networks
introduction to IP QoS mechanisms (eg Integrated
and Differentiated
services) and extension to mobile networks. Discussion
of QoS at layer 2 and the specific problems of
providing guarantees to mobile systems.
5. Session Initiation Protocol (SIP) an introduction
to the IP call control profile that will be
used to initiate, negotiate and terminate mobile multimedia
session.
Examples
of service creation and call flows within All-IP
mobile networks will be given.
6. Relevant standards developments including
the 3GPP/3GPP2 Internet and Multimedia Subsystem
(IMS),
ETSI TISPAN
and 802 initiatives. The concepts of: open,
loose, tight and
very-tight coupling will be explained and developed.
The BT 21st Century fixed-mobile all-IP network
will be used
as an example.
7. Commercial and business model aspects of
all-IP networks. Comparison of the traditional
cellular
and Internet business
models and examination of the i-mode model.
QoS and Scheduling in Wireless Networks
Vijay G. Subramanian
Network Business, Motorola Inc.
Vijay.Subramanian@motorola.com
With the introduction of packet-data
services in wireless networks about 5 years ago, the
scheduling of multiple flows to multiple users over a shared
wireless medium through the
access points became a needed area of work. Given the fast
time-varying nature of wireless
channels as well as being a shared medium, new techniques
for scheduling were developed.
This tutorial is intended to provide an overview of the
state of the art for the theory
of wireless scheduling. Along the course specific examples
from real technologies will be
provided to showcase the applicability of the developed
theory.
As a starting
point a simple wireless network is analyzed to introduce
the key notions.
Following this a fairly general abstract model of a wireless
network is presented. Using this mathematical model we
introduce the analysis for best effort traffic, starting
with
the description of a fairly general scheduling policy
and ending with an analysis of the
optimality of this scheduling policy. For the case of
real-time traffic we introduce the
notion of stabilizing policies and their applicability
to the scheduling of real-time policies.
Thereafter, we demonstrate the applicability of these
policies to present-day technologies
with a detailed consideration of HSDPA. Finally we conclude
considering other technologies
with a focus on scheduling policy design.
Outline
1. Development of basic concepts and models
Basic setting for scheduling in Wireless Networks
Simple Case for best effort traffic
Abstract Mathematical Model for a Wireless Network
2. General Analysis for best effort traffic
Motivation for traffic model and cost function
Stochastic approximation motivation
Simple examples
Convergence to ODE
Analysis of ODE
Results for simple models
3. General Analysis for real-time traffic
Review of stability
Generalized framework for stablizing policies
Maximum weighted Rate
Minimum draining time policy
Exponential Rule
Generalization to Other Rate Regions
4. Detailed example - HSDPA scheduling
Optimization Problem to be solved
Solution - Optimal algorithm
Results best effort and real-time traffic
5. Other examples
GPRS and EDGE
UMTS - DSCH
HRPD
Spatial Channel Models for MIMO Applications
in Modern Wireless Communications
Aris Moustakas
The introduction and use of wide bandwidths
and multiple antennas in modern wireless communications
systems has necessitated the increasingly more detailed
description of the wave propagation characteristics of
the environment. Thus, the resulting channel models are
more complex, modeling various aspects of the spatial and
temporal domains of wave propagation. A vast literature
of measurement campaigns provides insight in the behavior
of the various parameters of the channel at various time-scales
and length-scales, as well as their interrelations. In
this tutorial, after introducing the basic concepts and
requirements of channel modeling, we describe a number
of channel models introduced in standards bodies (3GPP/3GPP2,
IEEE 802.xx) for various (e.g. macrocellular, microcellular)
environments. We compare these models with measurement
results. We also discuss the complexity aspects of the
various approaches of channel modeling.
Outline
1. Introduction:
a. Why do
we need to model the wireless channel?
b. Basic Aspects
of Channel-modeling
i. Approach (Deterministic vs. Stochastic)
ii. Interpretation (Descriptive or Parametric)
c.
Variability and Structure of channel at various length-scales
i. Shadow-fading and Path-loss
ii. Time-resolvable Multiple Paths
iii. Un-resolvable plane waves: Rayleigh (Fast)
Fading
2. Measured properties of Channel:
a. Parameters of the channel
i. Path-loss
ii. Shadow-fading
iii. Angle-spread
iv. Delay-spread
v. Polarization-mixing
vi. K-factors: temporal vs. spatial
b. Measured Distributions of parameters
c. Interrelations of various channel parameters
3. Description of various adopted Channel Models:
a. ITU models
b. COST-259 models
c. 3GPP/3GPP2 spatial channel model for MIMO
systems and variants
i. macrocellular
ii. microcellular
d. OFDM-based (802.xx etc) channels
for outdoors/indoors
4. Computational complexity of various channel-modeling
approaches
a. Scatterer-based method
b. Correlation-based method
Low-Density Parity-Check
(LDPC) Codes
Gerhard Kramer and Alexei Ashikhmin
ABSTRACT
The aim of this half-day tutorial is to give the participants
a basic understanding of low-density parity-check (LDPC)
codes, and of how to analyze and design them. Some knowledge
of linear error-control codes is useful but not required.
OUTLINE
The tutorial will be 2 x 1.5 hours long, and is divided
into 2 main parts.
1) Binary Erasure Channels (BECs)
- structure of LDPC codes
- iterative decoding on BECs
- irregular LDPC codes
- LDPC codes that approach capacity
2) General Channels
- iterative a-posteriori probability (APP) processing
- density evolution analysis
- extrinsic information transfer (EXIT) chart analysis
- code design
Principles of Space-Time Coding and
Signal Processing
Hesham El Gamal
Wireless communications are characterized by random propagation
conditions commonly referred to as {\em fading channels}.
Roughly, a fading channel is a linear time-varying channel
whose impulse response is a random process. Reliable communication
over a fading channel is made possible only through the
use of diversity techniques. Since the mid-90's, driven
by the ever-growing demand for higher wireless link throughput
and better reliability, the research on multiple-antenna
techniques has been focused on multiple-antenna transmission,
rather than the conventional multiple-antenna reception.
Information theoretic studies of multiple-antenna systems
promised a large increase in the throughput over single
antenna systems. Motivated by the theoretical promises,
coding over multiple antennas (space) and over time has
emerged as a powerful tool to improve the quality of service
over wireless communications. An impressive amount of work
has been done on this field in the last decade. This body
of work involves, often with cross-fertilization and synergies,
the fields of coding theory, information theory, signal
processing and communications . The impact of Space-Time
coding/decoding techniques over today's and future wireless
telecommunications standards is central.
In this tutorial, we give a comprehensive treatment of
space-time coding/decoding under different channel state
information (CSI) and feedback assumptions. We provide
a unified treatment of the different design approaches
proposed in the literature. After reviewing the information
theoretic foundations, multiple-input multiple-output (MIMO)
channels modelling, and the signal design criteria, we
discuss the different space-time coding schemes in the
literature (e.g., orthogonal designs, trellis space-time
codes, LAST codes, ...) highlighting the dvantages/disadvantages
of each approach. Similarly, we review the different approaches
of space-time signal processing and discuss the joint optimization
of coding and signal processing. Our presentation will
strive for the optimal balance between theoretical rigor
and practical utility. We will conclude the presentation
with a discussion of the open problems and challenges in
space-time coding and signal processing research.
Biography: Hesham El Gamal received the B.S. and M.S.
degrees in ECE from Cairo University, Cairo, Egypt, in
1993 and 1996, respectively, and the Ph.D. degree in ECE
from the University of Maryland at College Park, MD, in
1999. From 1993 to 1996, he served as a Project Manager
in the Middle East Regional Office of Alcatel Telecom.
From 1996 to 1999, he was a Research Assistant in the Department
of Electrical and Computer Engineering, the University
of Maryland at College Park, MD. From February 1999 to
December 2000, he was with the Advanced Development Group,
Hughes Network Systems (HNS), Germantown, MD, as a Senior
Member of the Technical Staff. In the Fall of 1999, he
served as a lecturer at the University of Maryland at College
Park. In January 2001 he joined the ECE Department at the
Ohio State University where he is now an Associate Professor.
He held visiting appointments at UCLA (Fall 2002, Winter
2003) and Institut Eurecom (Summer 2003). He is a recipient
of the HNS Annual Achievement Award (2000), the OSU College
of Engineering Lumley Research Award (2003), the OSU ECE
Department FARMER Young Faculty Development Fund (2003-2008),
and the National Science Foundation CAREER Award (2004).
He holds 5 U.S. patents and has eight more patent applications
pending. He is a Senior Member of the IEEE and currently
serves as an Associate Editor for ``Space-Time Coding and
Spread Spectrum'' for the IEEE Transactions on Communications.
Cooperative Wireless Communications
Elza Erkip
Polytechnic University, Brooklyn
elza@poly.edu
The broadcast nature of wireless communications suggests
that a source signal transmitted towards the destination
can be overheard at neighboring nodes. Cooperative communications
refers to processing of this overheard information at the
surrounding nodes and retransmission towards the destination
to create spatial diversity, thereby to obtain higher throughput
and reliability. The virtual antenna array created by cooperation
has benefits similar to those of an actual multi-antenna
system, but the design constraints are substantially different
due to the distributed nature of cooperative resources.
Cooperative systems have close ties to the relay channel
of Cover and El Gamal and to multihop communications. However,
they also have some unique features that make them suitable
for the fading wireless channel: First, relays are used
not only to mitigate path loss but also to create diversity.
Second, each wireless relay is a node in the network with
its own information to send. This leads to partnerships
among nodes with each partner sending its own information
as well as helping the others.
This tutorial provides a comprehensive overview of the
theory of cooperative communications and its practical
aspects. The outline is as follows:
1. Introduction
a. Cooperative channel model
b. Relation to the relay channel and multihop communications
c. The concept of partnerships
2. Two-user cooperation
a. Capacity and outage analysis
b. Cooperative protocols under practical constraints:
Half-duplex versus full duplex
c. Diversity-multiplexing gain trade-off for cooperation
d. Effect of channel state information at the transmitters
and receivers
3. Coding for cooperative systems
a. Cooperative channel coding: Design and analysis
b. Source and channel coding for cooperation: Layered
cooperation
4. Cooperation in a network
a. Multi-user cooperation protocols
b. Selection of partners in a network
c. Node clustering and cooperation
d.Cooperative MAC and networking
ADAPTIVE OFDM VERSUS
MC-CDMA FOR NEXT-GENERATION
WIRELESS SYSTEMS
A ONE-DAY OVERVIEW
Lajos Hanzo
School of ECS, Univ. of Southampton,
S017 1BJ, UK
Tel: +44-703-593 125, Fax: +44-703-594
508
Email:lh@ecs.soton.ac.uk; http://www-mobile.ecs.soton.ac.uk
1. MORNING SESSION: INTRODUCTION TO
OFDM/MC-CDMA
This course is
based on an amalgam of [1]-[4]. The introductory part of
this two-part overview commences with a
rudimentary coverage of the subject, assuming only a
modest background in signal processing and wireless
communications
[1, 3]. Following the fundamental OFDM/MC-CDMA principles
we continue by demonstrating that OFDM
modems can be efficiently implemented by invoking the
Fourier transform or the fast Fourier Transform (FFT).
A
number of basic OFDM design issues are discussed in an
accessible style, including the effects of dispersive
fading channels and pilot-based channel estimation, crest-factor
aspects and the impact of signal-clipping introduced
by
finite dynamic-range amplifiers. The effects of finite
A/D
conversion accuracy are also considered and a range of
synchronisation techniques are highlighted. The first
part of
the course concludes by considering the performance benefits
of adaptive modulation.
2. AFTERNOON SESSION: ADVANCED OFDM/MC-CDMA RESEARCH
2.1. A future-proof
MC-CDMA standard framework[4].
Multi-standard
operation is an important requirement for
the future generations of wireless systems. This
overview
commences with the portrayal of a versatile broadband
multiple access scheme, combining frequency-hopping
(FH)
with multicarrier DS-CDMA (FH/MC DS-CDMA). The
proposed FH/MC DS-CDMA scheme is capable of meeting
the requirements of future generations of wireless
systems,
by supporting backwards compatibility with the existing
2nd- and 3rd- generation systems, while also introducing
more advanced techniques facilitated by the employment
of Software Defined Radios (SDR) and efficient adaptive
baseband algorithms [1]-[4].
2.2. Adaptive
versus Space-time Coded OFDM/MC-CDMA [3]
The presentation
continues by demonstrating that Symbol-by-symbol adaptive
Orthogonal Frequency Division Multi-plex (OFDM) modems
have the potential of counteracting
the near instantaneous channel quality variations
of wire-less channels and hence attain an increased
throughput in
comparison to their fixed-mode counterparts. By
contrast,
various diversity techniques, such as Rake receivers
and
space-time coding, mitigate the channel quality
variations in their effort to obtain a reduced
BER. This overview
investigates a combined system constituted by a constant-power
adaptive modem employing space-time coded diver-sity techniques
in the context of both OFDM and MC-CDMA. The combined system
can be configured to pro-duce a constant uncoded BER and
exhibits virtually error
free performance, when a turbo convolutional code is con-catenated
with a space-time block code. It was found that the advantage
of the adaptive modem erodes, as the overall
diversity-order increases [3].
2.3. PIC-assisted
channel estimation for SDMA-aided multiuser OFDM [3]
OFDM systems
employing multiple transmit antennas have recently drawn
wide interest in the context of both space-time coded-
and multi-user space-division multiple access
(SDMA) arrangements. A prerequisite for using coherent
detection at the receiver is the availability of reliable
channel transfer factor estimates. Robust parallel
interference
cancellation (PIC) assisted decision-directed channel
estimation (DDCE) has been shown in the literature
to be also applicable to scenarios, where the number of
users is
in excess of the number of OFDM subcarriers - normalized
to the number of Channel Impulse Response (CIR) related
taps to be estimated - which imposed a limitation in
the
context of least-squares assisted DDCE techniques invoked
in conjunction with multiple transmit antennas. In
this paper we will demonstrate that the Recursive Least-Squares
(RLS) algorithm is applicable to optimizing the predictors'
coefficients on a CIR-related tap-by-tap basis. Compared
to 'robust', non-adaptive approaches the proposed solution
has the advantage of a potentially lower estimation
MSE
and a higher resilience to erroneous subcarrier symbol
decisions [3]
2.4. Multiuser
detection for MC-CDMA [4]
In this part of the presentation
a Genetic Algorithm
(GA)
assisted Multiuser Detector (MUD) designed for
MC-CDMA
is investigated in the context of frequency selective
Rayleigh
fading channels. The achievable BER performance
of the
GA assisted MUD as well as its near-far resistance
are investigated for a range of parameter values.
It is shown that the proposed GA assisted MUD is capable
of significantly reducing the complexity in comparison
to that of Verdu's
optimum MUD. For example, when supporting K = 20
users, the number of likelihood function evaluations
is reduced by a factor of 1300 [4]
This overview
of next-generation wireless enabling techniques will be
concluded with a future-proof new design
paradigm, highlighting a range of open problems for the
radical researcher.
3. REFERENCES
[1] L. Hanzo, S-X. Ng, W.T. Webb, T. Keller: Quadrature
Amplitude Modulation: From Basics to Adaptive Trellis-Coded,
Turbo-Equalised and Space-Time Coded OFDM, CDMA and
MC-CDMA Systems, IEEE Press-John Wiley, 2nd edition,
Sept. 2004 1105 pages.
[2] L. Hanzo, T.H. Liew, B.L. Yeap: Turbo Coding, Turbo
Equalisation and Space-Time Coding, John Wiley, August
2002,
ISBN 0-470-84726-3, p 766
[3] L. Hanzo, M. Munster, B.J. Choi and T. Keller: OFDM
and MC-CDMA for Broadband Multi-user Communications,
WLANs and Broadcasting, John Wiley - IEEE Press, May
2003, 1010 pages
[4] L. Hanzo, L-L. Yang, E-L. Kuan and K. Yen: Single-
and Multi-Carrier CDMA: Multi-User Detection, Space-Time
Spreading, Synchronisation, Standards and Networking, IEEE
Press - John Wiley, June 2003, 1060 pages
During his 28-year carreer Lajos Hanzo,
FRAEng, DSc, FIEEE, FIEE has
held various academic and research
positions in Hungary, Germany and
the UK. Since 1986 he has been with
the University of Southampton, where
he holds the Chair of Telecommunications. Over the years
he has co-authored 11 books on mobile radio
communications, published in excess of
500 research papers. Lajos has also been awarded a number
of distinctions and he is an IEEE Distinguished Lecturer
of both the Communications and the Vehicular Technology
Society. For further information on research in progress
and for associated papers and book chapters please refer
to http://www-mobile.ecs.soton.ac.uk
