Abstract:
The essay points out the difference in the development of 3G between
China and European countries and discusses how to develop 3G in China.
It then outlines the advantages and characteristics of TD-SCDMA and
finally predicts the prospects for 3G and TD-SCDMA.
Keywords: 3G, TD-SCDMA, prospects prediction
In
recent years, the third-generation mobile communications (3G) has
been a focus of considerable attention. It is only not long ago
that people's prospects about 3G were quite good; however, this
year there has been frequent news about the postponement of the
launch of 3G service. NTT DoCoMo, which had intended to roll out
3G service in May 2001, announced in Japan that it would put off
its large-scale provision of 3G service. So have a few European
operators. Consequently, people have begun talking about 3G as "loud
thunder but small raindrops." What is more, the auction of
the 3G frequency bands at high prices by West European countries
has put operators heavily in debt and lessened to a certain extent
people's somehow-shaken confidence in 3G. Some people even suspect
that 3G is a big foam.
Indeed, watching worldwide, the world economy as a whole and telecoms
in particular are experiencing a temporary downturn after one upsurge
after another. Most telecoms giants have started cutting down the
number of employees throughout the world. Industry professionals
consider that the winter of the IT industry has arrived. In such
a situation, 3G service seems to be incompatible with the present
needs. Well, what are prospects for 3G internationally? Are prospects
for 3G bright in China?
1. How to Develop 3G in China
In spite of the change in the growth speed of the world economy,
China's IT market is not turning down, but rather rising as if a
force came suddenly to the fore. Especially its mobile communications
is booming at an unexpected speed and has become the focus of people's
attention. China has become the largest market for mobile communications
in the world. As is well known, 3G will be a cake that numerous
companies vie with each other for. Affected by various factors such
as economy, environment and population, the country has different
development conditions from those of other countries. This determines
that China will take a road of developing 3G with Chinese characteristics.
1.1 China and European countries have different driving forces for
the development of 3G.
At present, mobile phone penetration in Europe has exceeded 60%,
with that of some European countries even exceeding 75%, and mobile
voice service has approached the saturation point. Therefore, the
3G driving force in Europe is not voice service but a new service
model, i.e., high-speed multimedia service model. The indication
of success for such a service model is consumers' willingness to
pay for it. This requires various multimedia data services that
are compatible with market needs. Thus the 3G driving force in Europe
is mobile multimedia services that meet market needs. They must
first and foremost have irreplacebility, which means that 2G or
2.5G systems are not able to provide them or to provide them satisfactorily.
Next, 3G must be technologically able to realize them so that they
provide good performance. The last but not the least is that the
general public must like the 3G service provided. 3G will stop developing
unless all of these requirements are addressed.
The situation in China is widely divergent from that in Europe.
As of September 2001, the number of its mobile users reached 130
million; however, this figure represents only a penetration of 10%.
The country has much room for growth in mobile communications, compared
with the over 60% penetration in Europe and countries like the U.S.
and Japan. That is why China is still enjoying an annual increase
of 5 million mobile phone users. If it starts the construction of
3G networks in 2003, in which mobile phone penetration will not
reach 15%, mobile voice service will still be the mainstream of
mobile communications service. Currently, in cities with a high
mobile phone density, there is already a strain on the frequency
resources for the existing GSM systems. The number of people on
the move in Chinese big cities is increasingly growing, leading
to a further strain on the frequency resources in these cities.
Besides, with the introduction of GPRS, a part of the precious band
of GSM will be allocated to GPRS data service. And accompanying
the restructuring of the telecoms industry, new mobile operators
will inevitably emerge, taking away the band originally allocated
to 2G. All these factors will contribute to the exhaustion of the
country's 2G frequency resources. How to overcome the contradiction
between the high speed growth of mobile voice service and the strain
on the frequency resources is the most urgent problem to be solved
in the development of our mobile communications. It is also a difficulty
that we have not overcome fundamentally by using 2G and 2.5G systems.
The reason why China wants to develop 3G is by no means that its
consumers are in bad need for high-speed multimedia service; but
rather its 3G driving force is the growing need for mobile voice.
China needs new frequency bands and a new system of standards which
allows a high frequency utilization rate. If we do not see it, 3G
in China will be a foam. The business model to develop 3G in China
should be such that can meet the ever growing needs for mobile voice
while gradually increasing mobile data service provided. Therefore
the 3G driving force in China is more strong and practical than
that in Europe. In line with the actual situation of our country,
the most important criterion on whose basis we can choose our 3G
standard is the highest frequency utilization rate.
1.2 China and European countries have different initial coverage
requirements for 3G networks
Since European countries have very wide coverage mobile network
coverage and very high mobile phone penetration rates and their
3G driving force is new high speed mobile multimedia service, they
build 3G networks in order to realize full coverage, thereby meeting
the needs for new high speed mobile multimedia service.
Unlike European countries, mobile users in China are distributed
in an extremely way. In densely-populated large and medium-sized
cities, the strain on the frequency resources is particularly acute
and there is a high proportion of users who have demand for high-speed
mobile data service, whereas such strain is not acute. Meanwhile,
considering China's vast territory and limited economic conditions,
it is neither economical nor necessary to build a nationwide 3G
network at one stroke. Therefore, initially operators owning a GSM
network need not to realize full coverage, instead, they may set
up 3G isolated islands to address the strain on voice frequencies
and mobile access to high-speed data service in big cities. Besides,
it is necessary to build a hybrid network by relying on the existing
GSM system and using 3G/GSM DFDM (Dual frequency and Dual Mode)
terminals. The use of DFDM terminals enables access to GSM service
in areas without 3G coverage and to 3G service in areas with 3G
coverage. Later, as 3G grows, the number of 3G isolated islands
increases so that they merge together and realize full coverage.
But this will take several years. As for operators without a GSM
network, they may use 3G networks to cover large and medium-sized
cities while providing access to 3G mobile service and broadband
fixed radio service. They may provide various service applications
on the 3G platform while keeping mobile voice as their major profitable
service. Additionally, in view of the characteristics of 3G service,
3G networks in China must be able to meet the needs of developing
high-speed mobile data service and have the capability to transmit
asymmetrical services efficiently.
3.
Advantages and Characteristics of TD-SCDMA
In May 2000, the International Telecommunications Union (ITU)
approved three mainstream standards based on CDMA. They are:
MC CDMA: It refers to cdma2000, proposed by the United States, using
single carrier and occupying 1.25 MHz x 2 (2.5 MHz) symmetrical
frequency range.
DS CDMA: It refers to WCDMA, proposed by Europe and Japan, using
single carrier and occupying 5 MHz x 2 (10 MHz) symmetrical frequency
range.
TD-SCDMA: It consists of two standards, whose high layer protocols
are identical, while there are two choices for their physical layers:
TD-SCDMA, proposed by Datang Telecoms Group on behalf of China,
using single carrier and occupying only 1.6 MHz asymmetrical frequency
range.
UTRA TDD (TD-CDMA), proposed by Siemens on behalf of the European
Union, using single carrier and occupying 5 MHz asymmetrical frequency
range.
Of
the three approved international 3G standards, the ones proposed
by the United States and Europe adopt FDD (Frequency Division Duplex)
while the ones proposed by China and Germany adopt TDD (Time Division
Duplex). In FDD, transmission and reception of the mobile system
are conducted on two separate channels at symmetrical frequencies
and guaranteed frequency ranges are used to separate the transmit
and receive channels while transmission and reception of the TDD
mobile system are conducted on different time slots of a channel
at the same frequency (i. e., carrier) and guaranteed time is used
to separate the transmit and receive channels.
TFD-SCDMA
is the first standard China has ever proposed and widely accepted.
It was proposed later than the European UTRA TDD standard. However,
since it has so obvious technical advantages that Siemens, which
has proposed UTRA TDD, decided in July 2001 to give up R&D of
products on the basis of its own standard and participate in the
development of TD-SCDMA. This means that TD-SCDMA will be the only
3G standard of the TDD mode and use exclusively the 3G frequencies
allocated to TDD by ITU.
To
sum up, TD-SCDMA has the following unique good points:
It does not need symmetrical frequencies and has a high frequency
utilization rate and system capacity.
TD-SCDMA
adopts TDD, using different time slots within the same frequency
range for transmission and reception and occupying only a single
bandwidth of 1.6 MHz for 2 Mbit/s data service. So, compared with
the other technologies, TD-SCDMA uses the least frequency. As we
know, frequency is a resource that cannot be regenerated and frequency
ranges available are very limited. With more flexibility in frequency
selection and the ability to utilize fragmental frequencies, TD-SCDMA
technology has the highest frequency utilization rate. In addition,
with the introduction of smart antennas, it effectively reduces
multi-access interference, thus increasing the capacity of the system
significantly. Of all the three 3G standards, under the condition
of the same bandwidth occupancy, TD-SCDMA has a system capacity
obviously higher than the other standards and far higher than the
GSM network.
It can support asymmetrical transmission systems more effectively.
In
the TDD mode, the transmission of upstream and downstream data is
determined by controlling the length of time for upstream and downstream
transmission. Thus the ability to control and change flexibly the
proportion of the time for transmission and reception is especially
useful to the efficient transmission of asymmetrical services in
the Internet in the future. Since there is a high proportion of
retrieval traffic in the Internet. In retrieval traffic the volume
of upstream data from terminals to the base station is little whereas
that of downstream data is enormous, resulting in serious asymmetry
between the amounts of the transmitted and received information.
Only by adopting the TDD mode can the time for upstream transmission
be reduced self-adaptively and the time for downstream transmission
lengthened so as to realize efficient transmission of asymmetrical
services. This is an advantage that the FDD mode does not have.
It has good backward compatibility with the GSM network.
Since
the TD-SCDMA system can access both the 2G GSM/MAP core network
and the 3G core network, it may set up 3G isolated islands first
on the basis of the 900 MHz GSM network. It uses GSM/TD-SCDMA DFDM
terminals to enable the user to use 3G high-speed data and voice
services in 3G coverage areas and to use GSM voice service, low
speed data service, roaming and hand-over in GSM coverage areas.
TD-SCDMA enables operators to offer 3G service at a low cost while
utilizing fully the existing investment. As demand for 3G service
and the number of 3G isolated islands continuously increase, 3G
will ultimately cover the whole country.
It entails low cost.
From
the perspective of operators, the TD-SCDMA system uses narrow band
and entails low operating cost. The use of smart antennas significantly
reduces the cost of base stations by eliminating the need of using
high power RF devices. Besides, the introduction of software-defined
radio (SDR) technology enables the functionality of a specialized
chip on a generic chip through software and the enhancement of system
functionality and performance through the upgrade of software so
that it is not necessary to replace old equipment. All this further
reduces the cost. From the perspective of manufacturers, TD-SCDMA
is an autonomous intelligent property that is still developing and
improving. Domestic manufacturers may own the TD-SCDMA patent by
transplanting their own expertise in developing TD-SCDMA-based products.
This can significantly cheapen their patent royalties. Finally,
from the perspective of end users, the technical advantages of TD-SCDMA
allow more users to be supported by a single base station, thus
lowering the cost shared by users.
From
the above, we can easily see that since the various advantages of
TD-SCDMA are compliant with our actual conditions, it is the best
solution for China's 3G system.
4.
Prediction on the Prospects for 3G and TD-SCDMA
It
is widely accepted in the industry that the postponement of the
launch of 3G is the result of the synergic effect made by various
factors. Notably, the postponement of the standardization affected
the progress of R&D of equipment. The market was not mature
so that the business model of high-speed mobile multimedia service
was still under examination. The technology itself was not mature;
especially, terminal technology remained to be further development.
The last but not the least, the effect of the capital market on
3G was also important.
Nevertheless,
as analysts consider, the postponement of 3G development signifies
that this technology has returned to its normal development orbit.
We need not maintain a pessimistic view. In view of current development
of mobile communications, we are sure the 3G age will come sooner
or later, fuelled by a competitive market.
On
the other hand, the postponement of 3G development furnishes an
opportunity for TD-SCDMA to catch up. Contrary to 3G, good news
about TD-SCDMA has been arriving frequently. After its being approved
by ITU and 3GPP, progress has made in the development of TD-SCDMA-based
equipment. Graphic transmission and telephone conversation have
been realized between base stations and analog terminals; communications
between prototypes has been cut over on a pilot basis; and recently
an internal trial network has successfully transmitted signals.
TD-SCDMA is moving systematically to complete success in China.
The
value of 3G is unquestionable. It will come into our daily life
and have an impact on it sooner or later. As the first international
standard proposed by China, TD-SCDMA will make its contributions
to the development of mobile communications both in China and in
the world.
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Yang Yigang: Mr. Yang graduated from the
Wuhan Posts and Telecommunications Institute in 1979 and obtained
an MA degree from BUPT in digital signal processing in 1986. He
has been in charge of product development and optical communications
at the Wuhan Academy of P&T Sciences. He organized the work
of development on the IS-95CDMA system as head of the IS-95CDMA
group of the State 863 Program, and was awarded twice the third
place Prize for Scientific and Technological Progress by the former
Ministry of Posts and Telecoms, and the State Excellence Prize for
Inventions and Patents. Mr. Yang is currently vice-president of
the Academy of Telecoms Technologies and vice president of Datang
Telecom Technology Co., Ltd. |
