R&D Spirits
Creating Next-generation Wireless Networks
Masahiro Umehira
Senior Manager
Wireless System Innovation Laboratory
NTT Network Innovation Laboratories

The Wireless System Innovation Laboratory at NTT Network Innovation Laboratories isdevoted to creating new wireless services based on the latest wireless technology and implementing next-generation wireless network services. But what role do wireless networks play inNTT’s vision of a ubiquitous-communications-based future and what issues need to beaddressed concerning this technology? We put these questions to Masahiro Umehira, the director in charge of research at the Wireless System Innovation Laboratory.

Researching Next-generation Wireless
Systems to Support Ubiquitous Networks—Dr. Umehira, could you summarize the R&D topics
you are involved in at the moment?
At the Wireless System Innovation Laboratory, we
are researching and developing next-generation wireless systems that will play a vital role in ubiquitous
networks. There are three groups here, working on
wireless systems, adaptive signal processing, andantennas. Overall, our work covers a wide range offields from communication schemes to individual
technologies such as antennas and circuits and applications to actual service using wireless technologies.
—What specific themes are you working on?
We are conducting a number of studies into broadband wireless systems from the viewpoint of improving their frequency utilization efficiency. Current
broadband wireless systems can send up to only
about 3 bit/s/Hz. This can be substantially increased
by employing a technique called MIMO (multiple
input, multiple output), and we are now working onan even more advanced technology called multi-user
MIMO, which looks ready to make a significant
breakthrough in wireless broadband technology.
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Multi-user MIMO technology is expected to achieve
more than 20 bit/s/Hz, resulting in 1 Gbit/s wirelessaccess with frequency bandwidth of 40 MHz (Fig. 1).
We are also studying a 60-GHz-band wireless accesssystem that achieves more than 1 Gbit/s, taking
advantage of its significantly wide frequency spectrum availability.
In addition to the subject of broadband wireless systems, we are also researching technology for ubiquitous applications. This includes the concept proposal
and system construction of a ubiquitous network thatuses RFID (radio frequency identification) wirelesstags to achieve new M2M (machine-to-machine,
mobile-to-machine, and man-to-machine) services
and the study of ad-hoc network technology that canfreely configure networks wherever it is situated for
purposes such as expanding public wireless local area
network (WLAN) sites like hotspots and providing
temporary network facilities in disaster areas.
As a separate technical study, attention is being
focused on Software Defined Radio. This aims toenable wireless equipment to be used under software
control in various wireless networks such as PDC(personal digital cellular) and wireless LAN networks in the same way that personal computers perform various tasks under software control. In a similar vein, we are also developing MMIC (monolithic
microwave integrated circuit) chipsets for the subNTT Technical Review

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Breakthrough for future high-capacity broadband wireless systems: Multi-user MIMO
Recognize the carrier-to-noise ratio, fading, interference etc. of radio channels and maximize transmission rate and system
capacity.... Maximize frequency utilization efficiency (bit/s/Hz/cell)Prototype
MIMO-OFDMTransmitter

CrosstalkPrototype LSI

Receiver

Receiver(1)

Conventional MIMO/Space division multiplexing (SDM)
SDM/E-SDM)
H(1Transmitter beamforming to maximize
transmission rate

Transmitter

Transmitter

ReceiverEigenbeam SDM (E-SDM)/
Singular value decomposition (SVD)-MIMO

H(2)
SDM/E-SDM

Receiver(2)

Multi-user
MIMO
Advanced transmitter beam-forming to separate
multiple users Increases channel capacity without
increasing antenna branches of mobile terminal.

Fig. 1. Multi-user MIMO for future high-capacity wireless system.

millimeter band and are now on the verge of developing practical applications for this technology.
—What sort of impact will this R&D have on theworld?
Wireless systems give people greater freedom. People often say that mobility is the greatest killer application of wireless systems, and I have to agree withthat. Right now we’re sketching out plans for ubiquitous networks where wireless technology is used toconnect not only people but also a huge number ofobjects via tiny long-lasting terminals (Fig. 2). By
using this new ubiquitous wireless network for a wide
variety of applications such as logistical support,
environment monitoring, healthcare, multiplexedcommunications, and remote meter reading, we hope
to give people greater freedom and convenience inmany different ways.
—What are the main technical issues involved in creating the next generation of wireless systems?
For wide-area ubiquitous networks, it’s importantto get signals to travel as far as possible with the minimum of electrical power. For this purpose, novel
wireless network design including modulation, coding, and improved diversity is an important technicalVol. 3 No. 12 Dec. 2005

point to make it possible to receive weak signals reliably. Regarding broadband wireless systems, we aim
to maximize the transmission capacity and system
capacity by enhancing the base station systems,
where multi-user MIMO is based on the same concept as this. As we enhance the antenna functions ofbase stations to improve their frequency utilization
efficiency, we will make the mobile terminals operate
faster to accommodate the needs of users. In addition
to the above-mentioned future wireless technologies,
we are conducting R&D of MMIC technologies toreduce the size and cost of current wireless terminals.
Using MMIC technology, we have managed to integrate the circuitry into a 3-mm ultraminiaturizedblock where the circuits are stacked three-dimensionally like high-rise buildings. The reduced chip size
allows us to achieve higher production yields, so it
should also lead to lower costs. These developments
should help to promote the introduction of wireless
B-FLET’S services in places where optical fibers are
difficult to install, such as sparsely populated areas
and remote islands.
—And what will need to be developed and tackled in
the future?
For wireless technology as a whole, I believe thatwould be how to make more effective use of frequen7

R&D Spirits

cy. This will always be a key issue for as long as we
continue to use limited frequency resources. You
always have to bear this in mind when conducting
research and development in the field of wirelesstechnology. Power supplies are another issue thatmust be confronted. For example, when wireless tags
are commonplace, it would be a real nuisance to haveto change each one’s battery every time it runs out. So
it is essential for tags to have batteries that carry on
working until the tag has reached the end of its usefullife. To provide batteries that last for 5 to 10 years, I
expect we will have to work with power supply
researchers while at the same time taking measures toachieve further power savings in our systems.

Efforts to Standardize Wireless LAN
Technology in Japan, Europe, and the USA—What is the current state of international activities
related to wireless systems research?
On the international stage, we are mainly contributing to the standardization of wireless LAN technology. I was involved in the 5-GHz-band wireless LAN
standardization in Japan and Europe. We proposed
the OFDM (orthogonal frequency division multiplexing) technique to IEEE for IEEE802.11a and to ETSIBRAN (European Telecommunications Standards
Institute Broadband Radio Access Network) for

Broadband
Internet protocol network

HiperLAN/2. Meanwhile, Japan has set up the Multimedia Mobile Access Communication Systems Promotion Council (MMAC)—of which I am the chairman—and is moving ahead with the standardizationof wireless LAN technology while establishing links
with IEEE and ETSI. We are currently issuing proposals related to MIMO technology. Furthermore,
looking further into the future, we are preparing to
make active proposals for the 60-GHz band.
—Do you have any particular thoughts about theefforts being made at standardization?
In the period when I was involved in the standardization of a 5-GHz-band wireless LAN, we wereactive in MMAC of Japan, ETSI-BRAN of Europe,and IEEE802.11a of the USA. At that time it wasstrongly felt that wireless technology should above
all be categorized according to frequency. That’s
because using the same frequencies in different countries makes it possible to keep costs down by using
the same device components. It also means that thesame terminal can be used anywhere in the world,which is a very important point.
Like real estate, frequency is a limited resource, so
there is always fierce competition among carriers. For
example, a big row broke out over a proposal to overlap wireless LAN frequencies with the 5.15–5.25GHz frequency band used for communication

Internet
Authentication,
database, etc.

Expansion of networking

Public mobile network

Public broadband IP network

Broadband
mobileSet-top box
TV
GamePersonalcomputer

Humancommunications

Home network

Hot spot- fixed wireless accessCellular

Ubiquitous
wireless

Home

Gateway

WLAN
OfficeGateway

Gateway

Objectcommunications
RFID

RFID

RFID

Fig. 2. Trend: Broadband + Mobile + Ubiquitous.

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between satellite phone base stations and satellites.
Therefore, to start a new service, the first thing you
have to do is fight for a frequency allocation. Even at
100 MHz, there is plenty of international disagreement. This sort of problem probably never occurs inother fields of research. To use limited frequency
spectrum resources as efficiently as possible, frequency alignment is also essential.
—Are you collaborating with any other researchorganizations or businesses?
Our dealings with other research organizations aremainly for the purpose of standardization. We arealso collaborating with businesses on a case-by-casebasis. Our research is ultimately aimed at NTT services, so it is sometimes difficult to release theachievements of individual technical studies. Since
NTT is not a manufacturer, the circuits and devices
we develop can’t be turned directly into business
opportunities. But on the other hand, this is no reason
for us not to conduct individual technical studies. It’sa matter of striking the right balance, really. So NTT
develops individual technologies like MMIC that
manufacturers are unable to work on. Then, we transfer this technology to manufacturers. That’s our basic
stance.
—In your experience, how is NTT Laboratories
regarded abroad?
The members of NTT Laboratories work in manydifferent academic committees, so I think they are
acquiring good reputations to some extent on theirown. In particular, we are proud to be regarded as oneof the leaders in the field of wireless communication
system technologies and antennas and microwave circuits. Although NTT is just a communications carrier, I think our reputation in the rest of the world
depends on the sort of impact created by our new
vision. That’s because the uniqueness that NTT Laboratories shows to others derives not from individual
technologies but from the way we propose new systems and concepts.

Battling the Forces of Nature—The Attraction of Wireless Research—Incidentally, what would you say is your technicalforte?
I’ve been working on wireless technology everVol. 3 No. 12 Dec. 2005

since I was a student. In fact I first got interested in
how radios work when I was in the fifth grade of elementary school. I got drawn towards radio engineering after I built my own transistor radio. So even at
graduate school I spent my time in the radio communication laboratory. That was the time when carphones had just appeared, so my studies concentrated
on radio wave propagation and communication
schemes for mobile communications. But I wanted towork on complete systems rather than their constituent technologies, so I joined NTT because I figured I’d have more opportunities to do that working
for a communications carrier.
—What have you studied so far?
I joined NTT in 1980 (then Nippon Telegraph andTelephone Public Corporation) and started out working in the satellite communication equipment laboratory. In my first year I studied synchronization control schemes for SS-TDMA satellite communication,
but the year after that I became part of a major
research project launched to study large-scale satellite communications with the aim of building networks based on satellite communications and opticalfibers. For several years I was mainly conducting
R&D into modulation and demodulation methods forsatellite communication. During that period I spent a
year from 1987-88 as a visiting researcher in Canada
at the Communications Research Center of the
Department of Communications. Then, from 1993, I
turned to research on wireless access technology,
which is what I always wanted to study. Since then, I
have been working on research into subjects such as
wireless ATM (asynchronous transfer mode),
OFDM, broadband wireless access systems like
MIMO-OFDM, ubiquitous wireless systems formachine-to-machine communications, and software
wireless technology. At the moment, I’m managing
research on all aspects of wireless systems. It’s now
25 years since I joined NTT, and although I’ve spenta bit of time involved in the research planning department I’ve spent the rest of the time working exclusively on wireless research. I am completely satisfied
with my life as a reseacher.
—What draws you to wireless technology research?
From a purely technical viewpoint, I would say it’s
the modulation and demodulation technology used insignal transmission. When I was younger I studied allsorts of modulation schemes, and I even wrote my9

R&D Spirits

Ph.D. thesis on the subject. I have also made various
proposals in the field of standardization. And if
you’re asking what interests me about this field, thenI guess it would be the ongoing struggle against theforces of nature. For example, in satellite communication, you have to figure out how to recover a stablesignal by eliminating noise from the feeble unstableradio waves coming from a satellite 36,000 km away.
In mobile communication, you have to deal not onlywith noise but also with fading caused by variationsin the signal phase as the terminal moves. It feels
good when you figure out how to overcome natural
phenomena like these. The higher the hurdle is, thegreater the feeling of satisfaction you get when you
clear it.
—What sort of direction do you think research anddevelopment will take in the future?
From a management viewpoint, I think that
although some individual technologies may disappear, it’s important for us to set our course by keeping
a close watch on the overall state of wireless technology. For example, several different modulation
schemes have been used in wireless access technology, such as time division multiple access (TDMA)
and code division multiple access (CDMA), but ultimately CDMA was chosen for 3G mobile phones. It
is very hard to decide which out of several available
technologies will be selected and kept in use. However, as a private-sector research establishment, wemust continuously judge what will come next, taking
into consideration factors such as originality andcompetitive ability. Younger researchers have a tendency to concentrate only on their own technology, so
from my perspective it’s important to make sure they
see the bigger picture.
For example, single-carrier transmission has notbeen highly regarded for use in broadband mobile
systems, but it can overcome the power limitation
problem that is one of the weak points of current
OFDM systems. In other words, since OFDM
schemes use multiple carriers, a 100-W amplifier can
output signals with a power of only 10 W or so each,but this sort of problem would never arise in a singlecarrier system. So instead of sticking with OFDM
systems, it might be worth using single-carrier systems instead. I think that this idea has actually been
put forward. In fact, I’d quite like to try it out formyself. But these days, I can’t do that sort of thing
myself, so I’ll mention the idea to some younger
researchers.
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Taking Wireless Transmission to theExtreme—A Researcher’s Unfinished Dream—What are your ultimate goals as a researcher?
Realistically, and considering all the organizations
I’m involved in, I suppose my dream as a radio engineer would be to take wireless communication to theextreme and get rid of wires altogether. Recently, I’ve
also become interested in cognitive radio*1, which isa technology related to how frequency is used. Put
simply, it is a technique for automatically detecting
frequency bands that are not being used at a certain
time and place and allocating them to carriers thatwant to use them. At present, applications are allocated to frequency bands on a regional basis, so for
example a given band might be used for TV broadcasts in one region and for mobile phones in another.
This might seem perfectly reasonable, but there arealso many frequency bands that have been allocated
but remain unused. Although these problems can be
resolved by mutual agreement or by allowing market
forces to prevail as they do in Europe, some carriers
have run into trouble after investing vast sums ofmoney to acquire bandwidth, so it isn’t safe to simply
rely on market forces alone. Cognitive radio mightprovide a solution to this problem. Of course, that
doesn’t mean that technology can solve everything:other measures such as legislation are also required.
However, I think wireless research in the future must
consider mechanisms that relate to the overall situation and not just individual technologies. In particular, from the viewpoint of making sure that frequency
is used fairly and effectively, I think cognitive radio isa very desirable concept.
—What are your thoughts about NTT Laboratories?
As a place for doing research, it’s almost ideal.
There are always plenty of other experienced
researchers around to help out, and from the outset
you are given considerable freedom to study whatever you like. I’d be lying if I said everything here wasexactly as I wanted it, but I really think this is justabout the best environment to work in. In particular, I
think it’s great to be surrounded by people who you
can bounce ideas off. Normally, researchers only get
to discuss their work at conferences, but at NTT there
are literally loads of top-notch researchers all around*1 Cognitive radio: a term coined in 1991 by Joseph Mitola (see forexample: http://en.wikipedia.org/wiki/Cognitive_radio).

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you. And since their knowledge covers a wide rangeof fields, you can always find a specialist in any field
you need to learn about. And another thing which I
think is really important is that the researchers at NTT
Laboratories are always prepared to discuss otherpeople’s ideas with them. This open-minded attitude
makes for a very comfortable atmosphere at NTT
Laboratories.
—And finally, what would you like to say to ouryounger researchers?
I’d like to ask them not to treat research as a 9-to-5
kind of job, but to experience what it’s like to become
so absorbed in research and development that you
forget to sleep or eat. I often did that when I wasyounger. Maybe I wasn’t the world’s most efficientresearcher, and perhaps the speed at which the telecom industry was growing back then was reflected in
the research and development field. But aside from allthat I felt a definite sense of mission, and I’m reallyglad that I did. I made a lot of good friends during that
period. These days, telecommunications is becoming
mature, so there is less virgin territory than there used
to be. But it’s the researcher’s job to make breakthroughs. If you look hard enough, there ought to beplenty of new paths to go down, so I’d like to ask
younger researchers to find one that they can devote
themselves to—even if it means missing the occasional mealtime! That’s why I think that managers
such as myself should try to propose research themesthat are very interesting.

Vol. 3 No. 12 Dec. 2005

Interviewee profile■ Career highlights
Masahiro Umehira received the B.E., M.E., andPh.D. degrees in electronic engineering from Kyoto
University, Kyoto in 1978, 1980, and 2000, respectively. Since joining Nippon Telegraph and Telephone
Public Corporation (now NTT) in 1980, he has been
engaged in the R&D of modem and TDMA equipment
for satellite communications, TDMA satellite communication systems, wireless ATM, and broadband wireless access systems for mobile multimedia services.
From 1987 to 1988, he was with the Communications
Research Center, Department of Communications,
Canada, as a visiting scientist. He was involved in theEuropean ACTS AWACS project from 1997 to 1998.
He has been active in the standardization related towireless ATM and wireless LANs using the 5-GHzband in Japan, Europe, and USA. He is now the Senior
Manager of the Wireless Systems Innovation Laboratory in the NTT Network Innovation Laboratories,
where he is responsible for the R&D of wireless technologies for next-generation fixed/nomadic/mobile
wireless systems, future satellite communication systems, and ubiquitous services using RFID. He has
been a guest professor at Niigata University, Niigata
since 2004. He received the Young Engineer Awardand the Achievement Award from the Institute ofElectronics, Information and Communication Engineers of Japan (IEICE) in 1987 and 1999, respectively. He also received the Education, Culture, Sports,
Science and Technology Minister Award in 2001 andthe TELECOM System Technology Award from the
Telecommunications Advancement Foundation in
2003. He is a member of IEEE and IEICE.

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