Welcome to page 2 of our Indoor Propagation information. On this page, we feature an interview
with Dr. Ted Rappaport, one of the movers and shakers in advancing the state of the art for indoor
propagation. To return to page 1, press here or click on the first link
in the table of contents. Be sure to check out Page 3 for more resources!
by Jim Pearce, Director, Pegasus
Technologies Reprinted from the Fall 2001 Edition of SSS Online, with introduction edited in 2002 and 2005.
Dr. Rappaport is recognized internationally as one of the world's leading
experts in indoor propagation. He received BSEE, MSEE, and Ph.D. degrees
from Purdue University in 1982, 1984, and 1987, respectively. In 1988 he
joined Virginia Tech's electrical and
computer engineering faculty, where he founded the Mobile &
Portable Radio Research Group (MPRG), a university research and teaching center dedicated to the wireless
communications field. In 1989, he founded TSR Technologies, Inc., a
cellular radio/PCS manufacturing firm that he sold in 1993. Several years later, Dr. Rappaport
cofounded and became chairman of Wireless Valley Communications, Inc., a microcell and in-building
design and management product company that was
purchased by Motorola in late December 2005.
In the fall of 2002, Dr. Rappaport moved to a faculty position at the University
of Texas in Austin, in the Electrical and Computer Engineering department's new
Wireless Networking and Communications
Group (WNCG). Wireless Valley Communications also moved to Austin at the same time.
Dr. Rappaport has 22 patents issued or pending and has authored,
co-authored or co-edited 17 books and more than 150 technical
journal and conference papers in the wireless field. He is series
editor for the Prentice Hall Communications Engineering and Emerging
Technologies book series, and serves on the editorial board of
International Journal of Wireless Information Networks (Plenum Press, NY)
and the advisory board of Wireless Communications and Mobile Computing
for Wiley InterScience.
His list of awards is impressive, and includes the Marconi Young Science Award in 1990,
the NSF Presidential Faculty Fellowship in 1992, the 1999 IEEE Communications Society
Stephen O. Rice Prize Paper Award, and the Sarnoff Citation from the Radio Club of
America in 2000. He is a Fellow of the IEEE, and is active in the IEEE Communications
and Vehicular Technology societies.
He is a registered professional engineer in the state of Virginia and is a Fellow and
past member of the board of directors of the Radio Club of America. He has consulted
for over 25 multinational corporations and has served the International Telecommunication
Union as a consultant for emerging nations.
Dr. Ted Rappaport
Q. Dr. Rappaport, thank you for talking with us today.
Before we get into some of the more technical questions, would you tell us how you
got interested in Electronic Engineering? And was RF your initial interest,
or did you start with some other aspect of electronics and "fall into" RF?
A. My grandfather had this really old Philco shortwave radio, a 1926 model that was
mounted on the wall in his home in Brooklyn, New York. We went there when I was 5 years old,
and he spent hours with me tuning around listening to Morse Code and Ship to Shore. Ever
since then I've been fascinated by wireless and with radio. My grandfather has long since
passed away, and my grandmother gave me that radio. My wife, for an anniversary present,
had it all restored to its original condition, and I have it in my living room. It still
works, and I listen to it every now and then.
So, that's how I got my start in radio. I got my amateur radio license when I was 14,
and my extra class license when I was 16 (call sign N9NB). I was really into it! I always knew from the
time I was 5 that I wanted to be in wireless.
I went to Purdue University, because I grew up in Indiana, and Purdue was the
in-state engineering school. I got to Purdue at a really neat time —
I started college in 1978 — and in the late 70s, you remember, 2-meter radios
were the big craze and it was before the cellular industry. At Purdue there were
several professors — and one in particular, George Cooper — who were early
pioneers of cellular. In fact, George Cooper wrote the first paper in the
world suggesting frequency hopping spread spectrum for mobile radio. It was
co-authored by a student named Ray Nettleton, and when it was published in 1972,
it was very controversial. At that time, the FCC was moving towards making a
cellular radio service, and a lot of people in the industry were scared that
this paper might undermine the standards activities that were going on at that
time. Actually, the paper suggested the Hadamard codes and the Walsh functions
and ideas that were eventually used in Qualcomm's IS95.
So, Purdue had a rich history in mobile radio and radar, and when I started
grad school I was lucky to take courses from George Cooper and learn about the
cellular industry before it was on its feet in the US.
My PhD thesis in 1985-1987 was the first broadband wireless thesis looking
at 100 megabit per second data rates inside factory buildings — this was before the internet.
Indoor propagation just hadn't been looked at much up until then. In my research, I used a very
broad 200 MHz bandwidth sounder to study multipath and propagation
around the buildings. My thesis was published and generated some interest in
the wireless community — it was the time when companies like Lucent, AT&T,
Bell Labs and British Telecom were just starting to look at broadband wireless.
GSM was just a twinkle in people's eyes back then. I wanted to be a professor
because I knew there would be a huge demand for students and for basic knowledge
that would make this wireless revolution happen. I believe that someday we will
have wireless everywhere for mobile communications, and have always believed this.
Virginia Tech gobbled me up and gave me the ball to run with here.
Q. Tell us about how you started the Mobile Portable
Radio Research Group at Virginia Tech.
A. I landed at Virginia Tech as an Assistant Professor in 1988. At that time,
it was very hard to get government funding for wireless communications. In fact,
wireless as a term wasn't even used — it died in the 40's and came back again
in the early 90s — they called it mobile radio instead of wireless.
I had this vision of a research program that would teach students and
develop new technologies for the wireless industry, so I took my vision to the
companies of the U.S. I spent a year and a half talking to industry putting
this vision together, and our early sponsors, who first came on in 1990, included
AT&T, Motorola, Bellsouth, Southwestern Bell, and FBI, and it's grown rapidly
since then.
And that's how MPRG started. It was one of the first wireless research programs
in the country. David Goodman at Rutgers started WINLAB a bit before I
started MPRG, and over the years our research and our students have spun out all
over the wireless industry. From MPRG, we've graduated over 250 graduate
students and 50 undergrads who have known a lot about wireless and have gone
on to become some of the ground floor people at Qualcomm, Metawave, WFI, and many
other companies as well.
Q. What sort of research projects do you currently
have underway at MPRG?
A. Today we're doing a lot of varied work. First of all, we're looking
at propagation issues for very high frequency, high bandwidth communications,
such as for fixed wireless access systems at 38 and 60 GHz. We're one of the
few universities in the world that actually has 60 GHz propagation measurement
communications equipment.
We're also developing new types of antennas — smart antennas with adaptive
array algorithms and multi-user detection techniques for CDMA.
We're developing new error control coding techniques that can be
applied to wideband CDMA communications.
And we're also doing wireless system design research on how to deploy a
multi-user ad hoc network like a wireless LAN — how to predict throughput
and coverage, and packet latency through some basic physical parameters
in the channel.
Q. Interesting stuff! Now, could you tell us some
about the companies you've started that resulted from MPRG research?
In 1989, I started a company with a couple of great students, and we called
it TSR Technologies, Inc. It was a cellular radio/PCS manufacturing firm, and
in 1993 we sold it to Allen Telecom and it became Grayson Wireless, which is now a
big test equipment maker.
Wireless Valley was a spinoff I did a couple of years ago with a PhD student,
Roger Skidmore, who's now running it. It's pretty exciting because it's leading
the way for in-building wireless measurement, deployment, and network management.
We'd invented some new technology and had some new concepts that we
thought could really be of value to the industry. So it's kind of a push
technology, whereas our earlier company, TSR Technologies, was kind of a
"me-too" product with a little bit easier-to-use interface.
Q. Where did you get the name Wireless Valley?
A. Well, Blacksburg sits in a beautiful part of the world, sort of a valley between the
Appalachians and the Blue Ridge Mountains, and it's absolutely gorgeous here.
When we started building the wireless program, I started calling the area
Wireless Valley. Students really liked the nickname — in fact, we had
sweatshirts we printed up in the early nineties that say, "Building the
Wireless Valley." This reflected my hopes for the region, that academic
core technologies from MPRG would lead to the start up of a
number of wireless companies. So when we started Wireless Valley, the company,
we trademarked the name.
Q. I see Wireless Valley offers a lot of hardware in
addition to the software products that work with each other for doing measurement
and channel sounding.
A. Exactly. What we've brought to the industry, and have protected by patents,
is the novel idea of multi-faceted software that can integrate with many different hardware
products for many applications. Wireless Valley's core competence is development of powerful and
easy to use software along with great knowledge of the issues that people
have to design and manage wireless networks. If we wanted to, we could do
consulting morning, noon, and night, but we've chosen not to — instead,
we've chosen to serve the industry by making products that can allow other
people to be the experts. Our products, such as SitePlanner®, InFielder PDA®
LanFielder®, and SiteSpy®,
build in a ton of knowledge into expert programs that are easy to use.
By the way, we've just issued new releases of these products this month. We have over 150
customers worldwide, and universitites are starting to use these products to build
networks and teach new wireless courses.EDITOR'S NOTE 6/13/07:Wireless Valley was
purchased by Motorola in late December 2005. Current information on the successors to these
software packages can be found at
Motorola's RF Design and Management page.
We don't manufacture hardware ourselves, but we work with a lot of different
hardware providers, we partner with them, such as
Anritsu or ZK Celltest,Praxsym,
Dynamic Telecommunications, Inc. (DTI), or
Berkeley Varitronics,
so their hardware will plug and play instantly with our
software products. We also have a good agreement with
Ciscoand the other Wireless LAN card vendors, and our products work
instantly with every 802.11b WLAN modem, bluetooth, and even wired IP-based nodes, too.
The idea here is you don't have to buy new hardware — our SitePlanner® program,
for example, will help you design and measure, as well as manage and archive all of the
information related to your network. Just plug it in to what you have already.
That's what's always been missing in the wireless industry, how to maintain
and manage knowledge of many different people. And that's the key behind
SitePlanner®. The way we learned to do this was from trying to maintain research
knowledge gained by students who learn a core knowledge and then graduate
and leave us. We'd have a great project going on a new frequency band, or
an NII study at 5.8 GHz for residential wireless, for example — the students would make
their measurements, generate their models, do their designs, learn all this great
stuff and then graduate. Well, a new student coming in doesn't want to pick
up the custom code or the custom knowledge that's been spread around in
different spreadsheets, theses, papers, and a whole bunch of notebooks. The past knowledge
base is lost, as it the measured datA. To rectify this loss, we designed a system that
will help us share, archive, manage, and grow knowledge and information.
And then we realized, that's exactly the same problem in the wireless
industry! People change jobs, people move, people forget what they've done —
and this is the same as the problem I was having as a Professor! But no
one's ever solved this problem in the wireless networking industry — the
cradle-to-grave information management problem. When you do a measurement,
a bid, a deployment, a cost analysis, something breaks — you need all this
information if you are a carrier or a manufacturer. And that is what SitePlanner®
does — it handles all that. It does it in an easy-to-use, well-organized
way so that we have the equivalent of a visual spreadsheet, where you can visualize
the entire network in a campus or building or group of buildings. You can see it in 3D,
see where the components were placed, right in the blueprint, see what it cost, see where it's been repaired,
instantly see the measurements you made when you were on-site with that system,
and it can update and archive all that information. So, you can pass this
information from the consultant or installer to the person who owns the network,
to the person who has to troubleshoot the network, and it doesn't matter if one
of those people leave or forget what they've done. That's revolutionary!
It's never existed! We have put this knowledge on palm pilots, on Ipaq computers, and on PCs,
so that an enterprise or worldwide staff can now use the internet to manage this type
of information.
Interestingly, we're getting interest in our products not only from
wireless companies, but also from wired companies wanting to know where
the wire was put in and where it was placed. And this all came from trying
to grow a research program, and trying to keep and maintain the knowledge
to try to grow the program.
Q. What do you see as the trends in wireless today?
A. We're in the convergence of wireless LAN, in-building wireless, broadband
indoor, and the cellular systems trying to get indoor, and I think that's going
to be the huge battleground over the next few years, who controls the wireless
access in buildings.
Q. Do you think the 802.11 type stuff will be
dominant there?
A. I think it's going to have a definite role. Whether it dominates or not
remains to be seen, but I think it's definitely a contender. What I'm hearing
in the industry is a convergence between 3G mobile and 802.11 wireless type products.
Q. I've heard that 3G is sort of getting pushed to
the back burner because of the explosion in 802.11. Have you seen that?
A. I've heard that, but I think 3G is getting pushed back even more because of
the 2.5G alternatives that have been coming out. The installed base for cellular
is so big now, over 630 million phones, and
they're a captive base of monthly subscribers, so anything that gives a data
offering in cellular is in immediate demand and immediately keeps customers on the network.
So I think the carriers are pushing 3G off a little because they can keep
customers paying the monthly bill by giving them things like GPRS or a high
data rate on Qualcomm's CDMA. So this forces the WLAN makers to figure out
how to unify, and that's starting to happen. The problem with 802.11b is there's
no worldwide structure trying to unify and standardize them all — it's starting
to happen with BRAN in Europe and 802.11g and 15, but it's in the early stages.
I think if the Wireless LAN folks get their act together they could dominate indoor. After
all, indoor environments are the only ones where a user can actually digest huge data rates.
You don't need them driving a car.
Q. What kind of advice would you give to people
setting up large Wireless LAN systems? What would you tell people they
need to do first?
A. Good question. First bit of advice: use a computer aided design software
program to plan out coverage and to handle cost analysis and frequency planning for your network.
This is something the cellular people learned they had to do, but the
wireless LAN people haven't figured this out yet. Now granted, cellular
base stations are more expensive than wireless LAN access points, so
people will resist this argument, but there is tremendous value in
doing some quick engineering analysis using a computer aided design tool
before you set forth into the campus or buildings. It's like using a
spreadsheet to estimate a large project — you can't really eyeball
a complex system. What is happening
today is that people will go out with rough rules of thumb, without
really considering the buildings they're going into, and they will
sort of randomly place access points where they think they belong,
based on their intuition or some simple number. And that's OK if you have just a few access
points, just like it's OK to use a hand calculator if you have just a
few calculations, but the IT community really needs to move to a computer
aided design environment like SitePlanner® because the networks are
going to get a lot larger, and there will be more users, and more interference,
and more management will eventually be needed — all the access points radiate
energy, cause interference, and rely on power, and they will all break eventually.
You need to know where they are, what they cost, how they work, and who put them in.
The value in doing strawman designs in a computer aided design platform
is that your blueprint can give you so much information, and can get you
to a better design before you just start plunking access points into the network.
The cost savings for larger networks will be tremendously great.
My second bit of advice, and this is even more valuable than the first:
use a computer aided design environment to archive your design, component
placement, and network performance data. The advantage of this is that you
build knowledge and informed intuition very quickly with the software
bringing you up on the learning curve on network design, while at the
same time the software can be used to archive where you've put the
hardware. Knowing where you put the antennas above what raised ceiling
is invaluable -- as indoor wireless networks proliferate, this is going
to become the biggest problem of all. Imagine access points that are
above raised ceilings that may start emitting spurious radiation. If
you've got to go find that with a power meter, you're going to waste
so much time walking around in a building. We can put that information
on a palm pilot so you can go right to the spot. Also, suppose your
user community builds, and you want to
get more people on the network. Interference managing is going to
become such a problem in high density WLANS that you're going to have
to have a computer aided design environment to know where you put the
components and to manage spectrum! But most indoor wireless networking companies don't
understand that yet because there just haven't been enough large
installations. Microsoft, by the way, has one of the largest WLAN
installations to date, and they are getting SitePlanner® to manage
their network.
Q. Do you think the move to 5.8 GHz and 802.11a will
push even harder on that?
A. Yes. With 802.11a, you're going to decrease the range of access
points because of the wider bandwidth. So you're going to have
more access points per building, and initially the 802.11a equipment
is going to be more expensive, so a product like SitePlanner® can
instantly save you money on the deployment. As people start
deploying 802.11a, I think you'll see the popularity of wireless
LANs increase tremendously, so there will be more access points,
more mobile users, more interference, and more issues to manage.
So going out with a best guess and just throwing 'em up in a building
isn't going to work anymore.
Q. How about UWB? Is any work going on at either
MPRG or Wireless Valley on this subject?
A. We're in close contact with the UWB community, we're excited about it,
and think it will be viable. The thing that holds it back commercially
is the FCC and FAA regulatory issues. We think eventually UWB will be allowed.
We're not directly doing UWB research, but since our work at the
University is fundamental — i.e,. when we're doing channel modeling
it's generally of a fundamental nature with as much bandwidth as possible —
a lot of our research is directly applicable to UWB. For example, at
MPRG we have a 1 GHz bandwidth channel sounder that does full I and Q
modulation and demodulation. This is 1 GHz on an RF carrier that we
can vary from 2 GHz up to 60 GHz, so when we make channel measurements
and channel models on path loss or for time delay or angle of arrival,
all of that information is useful to UWB because we're able to resolve
things to a 1 nanosecond resolution. So therefore, our work directly
benefits UWB proponents.
At Wireless Valley, since SitePlanner® uses fundamental propagation
models that are frequency independent, the good news is that it works for
UWB already and we have some customers who are doing UWB and who are
designing their systems and their coverage using SitePlanner®.
Q. Have you made any comments to the FCC in
response to the Notices of Proposed Rulemaking or studies on UWB?
A. Not directly, no. But several companies have asked me to provide
information on propagation and RF bands as part of their commenting
process, and I have done that. I don't know if those companies have
used my name in their comments or not.
Q. From looking at your website and seeing
all the things you're involved in at MPRG and Wireless Valley, it's
obvious that you have boundless energy. Are you involved in other
things as well that we haven't talked about?
A. Well, my wife and I have 3 children, the oldest is in college and I have two
girls at home that keep me on my feet. But I'm also involved in a
barbershop quartet. It's called the Uncalled Four (as opposed to
Uncalled For), and I sing lead tenor and sure love that. Also, I
really enjoy the students, and try to help them out and find them
opportunities to learn both in and outside of the classroom. And I really like
interacting with engineers in the "real world," through Wireless Valley
or through email conversations. That keeps me pretty busy!
Q. Well, you're certainly in the forefront
of what's happening in the wireless field!
It's a lot of fun, it's a great career, and I've been tremendously blessed!
Q. Dr. Rappaport, thank you very much for talking with us!
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