W-CDMA researcher points out some limits.
JohnG
telecomasia.net
October 1998
Planning next century?s wireless
network: 3G, 4G and beyond
NTT DoCoMo is not only the world?s largest
wireless operator ? it also owns the second
largest wireless research lab in the world. And
that lab is currently spearheading the push for
W-CDMA: a technology which should open up
capacity and dramatically increase the
functionality of mobile networks in the 21st
Century
In this interview with Telecom Asia journalist
Swee-han Yap, Dr. Kohei Satoh, who heads the
W-CDMA research team at NTT DoCoMo,
discusses NTT?s plans for its 3G system and a
fourth-generation system down the line.
Why is NTT favoring W-CDMA over its existing
PDC standard?
We have limited spectrum in the 800-MHz and
1.5-GHz frequency band. And with the number of
subscribers already past the 40 million mark, there
is a need to increase capacity quickly. The Ministry
of Post and Telecommunication?s forecast is that in
2000, there will be more than 50 million
subscribers. However, since bandwidth is limited,
Japan tried to introduce new system which utilizes
a new frequency band which provides more
capacity and the target is to provide capacity which
is twice that of the PDC system.
Why choose to upgrade via W-CDMA and not
another technology?
In our discussion with ARIB [Association of Radio
Industries and Business], we discussed the merits
of adopting a TDMA or CDMA system. We finally
decided on a W-CDMA system. What we hope to
achieve with our third-generation mobile
communication network is to adopt W-CDMA as
our radio interface and an evolved GSM system as
our core network. Because GSM is used
world-wide, this is an important step for Japan
since this will facilitate global roaming.
What kind of applications will run on the new
W-CDMA system?
This is an important but difficult question to answer.
Now on PDC, our major services include voice and
data, but only low bit-rate data. So our hope is to
increase the bit rate speed for data transmission
substantially which is especially important for
mobile email and Internet access. Typically, a
subscriber gets 9.6-kbps data but last year we
introduced packet switching for data transfer which
offers up to 24.4-kbps. However our packet-based
data coverage area is limited.
We?re not quite decided on what new services are
going to be introduced but our top priority is to
provide high-speed mobile Internet. Full-motion
video is also in our target list. But we?re still in the
discussion stage about the kind of applications
we?re going to introduce on the W-CDMA system.
Why is high-speed Internet access such a
priority?
Now, we can only provide 9.6-kbps transmission
rates but user demand is much higher than that. In
Japanese offices, customers get 1-Mbps or
2-Mbps transfer rates but with a handset they can
only get 9.6 kbps, which is quite limited.
What are the advantages of using W-CDMA?
It?s a very promising technology for multimedia
services. It uses variable rate processing
techniques, which means it could easily achieve
multi-rate transmission. The technology?s use of a
wider bandwidth means it can transmit full-motion
video in addition to voice, data and still images.
Because the transmitted data is spread over a
wide band, W-CDMA reduces the effects of
interference, noise and changes in received power
compared to current mobile technologies. The
high-quality data transmission and high frequency
efficiency is similar with what?s available on ISDN
networks. It also eliminates the complexity of
system configurations. This means that even when
transmitting large volumes of data, it can avoid
complex system configurations which cuts down
the cost of transmission.
How far does NTT hope to take W-CDMA?
Our target, as discussed with the ITU, is to take
indoor transmission rates up to 2 Mbps and
outdoor transmission up to 384 kbps. 384 kbps is
the optimum transmission speed for pedestrian
users while 144 kbps is for users traveling in
fast-moving vehicles.
Do you plan to abandon your PDC network
and go straight to W-CDMA in 2000?
No, we?re planning to continue running both the
W-CDMA network and the PDC network for awhile.
At first, the W-CDMA system will only offer limited
coverage, so we?ll still be operating a big PDC
network and we will work towards integrating these
two systems for better efficiency. We know it?s
going to take a while to actually migrate our
subscribers from the old network to the new. We?re
going to take at least five years to do it but
hopefully we?ll be able to accomplish it in not more
than five years, but the actual time required is really
not known.
Do you think migrating from the PDC to
W-CDMA technology is going to be a difficult
process?
Yes, I think so. First of all, there is the problem of
migrating from TDMA-based PDC which operates
on 800 MHz and 1.5 GHz to CDMA-based
W-CDMA which runs on 2.2 GHz. There is also the
different bit rate, which is going to complicate
matters. The two technologies utilize different
transmission and switching schemes. We?re going
to move into ATM-based switching for our
W-CDMA system which is quite different from
what?s used on the PDC network.
What kind of handsets are going to be used
on the W-CDMA network?
We?re going to introduce voice handsets similar to
those used on PDC. For high bit-rate data
transmission, there will be the new videophones.
We?re also planning to introduce dual-mode
phones which will operate on both PDC and
W-CDMA systems. I personally believe dual-mode
terminals will be an important step towards
migrating the PDC subscribers to the new
W-CDMA network.
Do you feel Japan is disadvantaged in the
telecom research arena because GSM or
D-AMPS technologies are used in other parts
of the world?
No, I don?t see that as being a problem. For
instance, on the IMT-2000 issue, we have good
working relationships with R&D labs of different
telcos and manufacturers locally as well as abroad,
especially in Europe where there are multiple
operators in each market and different
manufacturing companies. Domestically, we
discuss with manufacturers ways to improve the
PDC technology and work together to develop new
services for PDC.
Do you think worldwide deployment of 3G networks
is going to be difficult since some of the 3G
spectrum is already used for 1.9-GHz PCS
networks?
I think this is only true for the U.S. Half of its
allocated IMT-2000 band is used up for PCS
systems. But the US used the wider portion of its
IMT-2000 band for PCS, leaving its less wide
portion free for 3G systems. And global roaming
requires the less wide band anyway. So that does
not present a problem.
What are NTT?s fourth-generation plans?
We plan to introduce a fourth generation system by
2010. It used to be one generation spanned a
decade but now each generation only takes five
years. There are plans to introduce broadband
ISDN in our fourth-generation system and
introducing data transmission speeds up to 10
Mbps. We would like to use a higher frequency
band in our fourth-generation system which could
be microwave or millimeter wave band. So we?re
currently doing research on frequency band
technology and the feasibility of running a higher
frequency band system.
What do you see as important wireless trends
in Japan?
I think there are three key words: multimedia,
personal and global. Multimedia or mobile data will
be an important trend. Subscribers will send more
emails, images, and video. The cellular handset will
increasingly become a consumer-market product
and not one just for corporate people. The PDC
service is only for Japan which is quite a limited
area. We see the next generation of mobile
communication networks to be ones that adopt a
global standard which will enable roaming on a
world-wide scale and we hope that will be
W-CDMA. This is going to be quite important in
Japan especially for people who travel widely for
business. Now when we go to South Korea, we
need CDMA phones, and when we go to India or
Singapore we need GSM terminals. With the
adoption of a global standard, we will be able to
use one terminal world-wide.
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