Title: Platform Interferences
in Wireless Systems
Authors: K. Slattery, H. Skinner
Publisher: Elsevier, January 2008
ISBN: 978-0-7506-8757-7
With the advent of mobile computing, wireless communication has
become an integral part of the computer platform. Who would now
consider buying a laptop without wireless? At the same time, the
once simple communications device such as a cell phone now has
functions that require subsystems associated with computer devices.
The problem is that these devices were never intended to coexist.
Communications devices were not designed with high-speed digital
logic in mind and high-speed digital logic never included communications
as a design vector.
This book has two main intentions, and in my opinion, perfectly
achieved: to provide education about the principles of radio frequency
interferences (RFI) and to provide a reference source for identifying
noise-related issues and mitigating them in actual design scenarios.
One of the key points of this book is that it has been written
with the practicing EMI engineer in mind. To that end are provided
only the aspects of theory that are necessary and that help the
readers to develop their own intuitions and perspectives. Where
necessary, the provided equations are converted into code and
proposed to the readers for modeling and building their own analysis.
Another characteristic of this book that I really liked is the
large quantity of measurement results. They are used as conceptual
tools to guide the reader towards the technical conclusions or
show how the solutions proposed have an impact on the overall
system. This is one of the points of force of this book. At the
same time, the black and white edition does not help the full
readability of the graphs.
The book is composed of nine chapters and a few appendices (referring
to specific chapters) totalling about 333 pages. In the Appendices
are illustrated and well commented scripts for Mathematica (Wolfram
Research) used to work out the calculations shown in the book.
All chapters contain several examples to illustrate the concepts,
some of which can be reproduced using the above-mentioned software.
These examples can also be used to evaluate the accuracy and speed
of several commercial tools that are available today.
Chapter 1, “Introduction,” sets the scene for engineers
and students who are entering the field of wireless versus EMI.
Here is introduced the concept of wireless interference potentials
that nonintentional radiators, in the form of high-speed digital
components and signals, have on impacting wireless systems. Also
presented is the concept of a platform RF budget and a methodology
to assess the RFI risk, taking into account, in a quantitative
way, all the pertinent system factors (from radio sensitivity,
to noise figures). A well-documented number of measured results
show the importance of the study and analysis of platform-generated
RF noise for the correct functioning of wireless systems.
Signals are the focus of Chapter 2, “The Structure of Signals,”
which covers the many different aspects of the structure of signals
and how each element of this complex structure can be addressed
to develop a strategy toward minimizing the interference impact
of the signals used in the wireless platform. This chapter offers
an anatomy of the signal in which every part (edge rate, symmetry,
duty cycle, repetition rate, etc.) is physically and mathematically
related to its impact on the variation of amplitude and harmonic
components. Here also is examined the properties of repetitive
and non-repetitive signals, scrambled clocks and clocks spread
out in time. The various symbols that are used to construct a
video digital display are also investigated.
Chapter 3, “Analysis of Symbol,” is an expansion,
in depth, of Chapter 2. After a clear and sophisticated comparison
between the platform signals or symbols, there is a discussion
of those aspects of the signal structure that may be ignored or
that should not exist for RFI improvement. Section 3.3. “Wireless
Performance in the Presence of Radiated Emissions from Digital
Display-Symbols” deals with the many possible approaches
to interference mitigation that may be pursued through application
of signal structure modification techniques.
Chapter 4, “Measurement Methods,” as the authors say
“a measurement is worth a thousand opinions”, this
is the guiding line of this chapter in which are described some
of the measurement methods that can be employed in developing
an understanding of the EMI problem and in developing the proper
mitigation methods. The use of broadband measurements in conjunction
with a method to localize and identify emission sources gives
the practicing engineer a nearly complete means for identifying
and characterizing the interference potential of a given platform.
Neither of the proposed methods requires the existence of expensive
dedicated chambers. A nice cost budget is offered at the very
end of the chapter.
A brief summary of the relevant electromagnetic laws and principles
is offered in Chapter 5, “Electromagnetics.” It is
the logical premise of the following chapters.
Chapter 6, “Analytical Models,” offers the basis to
start building analytical models of the main platform interference
sources. The proposed approach assumes that one could take complex
structures, such as the interconnect channel, and model them as
sets of discrete point radiators. The same strategy is used to
model the circuit sources inside the silicon. The chapter focuses
on offering a means to compare different source configurations
as the engineer develops the functional floor plans in the design
stage. At the end of this chapter the reader has a method to quantify
potential emission problems and investigate the mitigation solutions.
The aim of Chapter 7, “Connectors, Cables and Power Planes,”
is not an academic discussion toward power delivery network design.
The goal is a systematic approach for the identification (substantiated
by theory, numerical simulations and measurements) of the design
features to tune in order to impact the interferences. This strategy
is offered in a top-down approach, from connectors, to PCB, to
package up to silicon. In this way, all the design features are
presented to the designer, each one with its degree of impact
on the noise to be mitigated.
In Chapter 8, “Passive Mitigation Techniques,” a selection
of the shielding approaches is proposed suitable for the kind
of structures dealt with in this book. Each approach can be used
in combination with the others to improve isolation between noisy
platform components and victim radios. The relative merits as
well as the potential pitfalls of near- and far-field applications
are discussed in detail. Passive mitigation is a strategy that
assumes that we have a noise source and a sensitive victim receiver
and attempts to maximize the isolation between them. This consideration
opens the way to the next and last chapter in which active mitigation
is introduced.
Chapter 9, “Active Mitigation,” deals with the source
of the noise itself. In this Chapter, three fundamental topics
are illustrated: the frequency planning, the frequency content
and the radio improvement. In the frequency planning content,
it is discussed how to move the noise out of the radio bands and
into frequencies where no radio operates. In the frequency content,
the fundamental aspects of digital circuitry are addressed that
impact the harmonic content of the noise and, from that, how to
derive possible mitigations. The radio improvement gives some
direction for possible radio improvements in dealing with noise.
This book’s system-level focus and practical examples make
it very useful for all students and professionals concerned with
EMI in wireless systems, including electrical engineers, system
designers and EMC scientists. In my opinion, if you are looking
for a book on EMI in wireless system, this is the book to start
with.
Antonio Orlandi (M’90-SM’97-F’07) was born
in Milan, Italy in 1963. He received the Laurea degree in Electrical
Engineering from the University of Rome “La Sapienza”,
Italy, in 1988. He was with the Department of Electrical Engineering,
University of Rome “La Sapienza” from 1988 to 1990.
Since 1990 he has been with the Department of Electrical Engineering
of the University of L’Aquila where he is currently Full
Professor and Chair of the UAq EMC Laboratory. He is the author
of more than 170 technical papers published in the field of electromagnetic
compatibility in lightning protection systems and power drive
systems. Current research interests are in the field of numerical
methods and modeling techniques to address signal/power integrity
and EMC/EMI issues in high speed digital systems. Dr. Orlandi
received the IEEE Transactions on EMC Best Paper Award in 1997,
the IEEE EMC Society Technical Achievement Award in 2003, the
IBM Shared University Research Award in 2004, 2005 and 2006 and
the CST University Award in 2004. He is a member of the Education,
TC-9 Computational Electromagnetics and Chairman of the TC-10
“Signal Integrity” Committees of the IEEE EMC Society.
He is Chairman of the TC-5 “Signal Integrity” Technical
Committee of the International Zurich Symposium and Technical
Exhibition on EMC. From 1996 to 2000, he has been Associate Editor
of the IEEE Transactions on EMC and from 2001 to 2006 he served
as Associate Editor of the IEEE Transactions on Mobile Computing.
EMC
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Review