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Introduction
As
is known to all, mobile communications began its development in
1980s. Now the growth rate of mobile communications has surpassed
that of fixed network, and has got a great popularity. Up until
now, the total number of mobile users has exceeded 400 million in
the world, and people's demand in this respect is pushing forward
the further development of mobile communications. Mobile communications
thus far have undergone two generations, i.e., the 1G analog system
in the 1980s and the 2G digital narrowband system in the 1990s.
In recent years, with the broadband technology popping up as a promising
solution in wireless communications, the mobile communications system
is evolving toward the so-called CDMA-based and broadband 3G. This
paper just sets out to deal with mobile-related technologies and
explores their development.
2
GSM vs. CDMA
The
1G analog system corresponds to Frequency Division Multiple Access
technology (FDMA), which provides a bandwidth of 9.6kbit/s. The
typical 1G systems include AMPS in US, NMT in Nordic countries and
TACS in the UK. The 2G digital system mainly refers to the Time
Division Multiple Access (TDMA) and the Code Division Multiple Access
(CDMA), both of which provides a transmission rate of 9.6～28.8kbit/s.
Typical 2G systems include GSM in Europe, the digitally enhanced
IS-136 in North America, CDMAOne IS-95A, IS-95B and PDC in Japan.
Compared to 1G, the 2G system is stronger in privacy protection,
spectrum efficiency, applications and standardization. Both 1G and
2G are designed to meet voice communications needs, which will remain
the cornerstone and mainstay business at present and in the near
future, and digital voice communications will keep its prevalent
position in the mobile market. This is especially true for developing
countries, where people's demand for communications is still focused
on voice. So in the next few years, 2G will remain a pillar business
in the mobile market in suchlike countries.
3
Mobile Intelligent Network (IN)
The
growth of mobile communications is intensifying the expectation
of operators and users to expand the range of services. In a development
perspective, the communications network in the future will surely
be a broadband, intelligent and personalized one. So the network
architecture of 2G GSM and CDMA systems will gradually evolve to
an intelligent one, and the IN concept is to be introduced into
the mobile network. By adding IN-related functional modules the
mobile network will be empowered to provide more new services in
an easy manner so as to meet the ever-increasing and changing user
demands. The IN functional modules corresponding to GSM and CDMA
networks are CAMEL (Customized Applications for Mobile Network Enhanced Logic)
and WIN (Wireless Intelligent Network) respectively. It is worth
noting that the CDMA system in North America is applied the ANSI-41D
protocol. In order to support intelligent services, a series of
WIN protocols are defined based on the signaling structure and service
flow of the ANSI41D protocol, including IS-771, IS-826 and IS-848.
All those protocols will be ultimately integrated into the ANSI-41E
protocol, which is to be an all-IN-based core network protocol.
While CDMA wireless IN is in progress in North America, the ETSI
is driving the application of intelligence on the GSM network by
working out mobile IN protocol series to provide CAMEL service for
GSM users. CAMEL adopts the IN service control function and provides
a mechanism to enable the GSM network to offer services independent
of the service network. Intelligence, personalization and broadband
represent an irreversible trend of future communications. This will
surely serve to speed up the perfection and development of the mobile
IN technology.
4
GPRS vs. CDMA2000 1x
With
the explosive growth of Internet in the world, the mobile data service
is on rise in usage. That is why we are convinced that in the mobile
world data traffic will at last exceed voice one. However, to build
the 3G system that is targeted at future multimedia communications,
there is still a long way to go. So how to make use of the existing
2G system to transmit data is a necessary task for us to fill in
the market gap. Analysts believe that most of the 3G features can
be neatly realized via the current 2G technology, especially given
that the demand for mobile data communications is a by-product of
the soaring growth of mobile communications and the Internet. There
are two approaches for that purpose. One is to add data transport
capability in the voice-dominant cellular mobile communications
system; the other is to combine mobile communications with the Internet.
By doing so a number of technologies were produced, e.g., the General
Packet Radio Service (GPRS), the Enhanced Data Rate for GSM Evolution
(EDGE), the IS-95B aggregation technology, the CDMA20001x technology,
the Wireless Application Protocol (WAP), Bluetooth and so on. Among
them, GPRS and CDMA2000 1x, especially GPRS (a GSM-based packet
switching technology), are attracting much attention and of special
practical significance to China.
GPRS is launched to cater to the soaring growth and increasing
integration of GSM and the global Internet market. It provides GSM
operators an important platform for them to expand service portfolio
from solely voice to integrated information services, thus laying
a foundation for the GSM transition to 3G. In that sense it is dubbed
as “the propeller of future 3G market”. GPRS is characterized by
the following: a) it provides end-to-end packet data transmission
from wireless part to wireline part. On the wireless part, voice
and packet channels can be allocated on demand in an dynamic way
to make an effective use of the frequency resource; b) it provides
higher access rate for users (115kbit/s) and less access time; c)
it provides SMS, WAP and existing data services in a more effective
manner; d) its bottom layer is based on TCP/IP, making it able to
be seamlessly connected to the Internet; e) it supports billing
according to time of usage and traffic; f) With the wide GSM coverage,
it provides anytime anywhere data access; g) by taking GPRS it is
not necessary to incur major changes to the GSM equipment. Most
of the experts believe that GPRS is a 2.5G system that stands between
GSM and 3G. In the wake of GPRS and if GSM operators have no 3G
spectrum, they can make use of EDGE to bring up the rate to above
384kbit/s that is quite close to the level of 3G system. If operators
have 3G spectrum by then, they can directly translate GPRS into
3G.
Similar
to GPRS as a stopgap means, CDMA2000 1x is a standard for the narrowband
IS-95 system to evolve to 3G. It provides data rates of up to 144kbit/s
and introduces supportive channels, thus able to carry multiple
data traffic and services for one single user. This has laid a good
foundation for supporting various multimedia packet services in
the future.
5 3G
In the past years, the 3G system has been mainly driven by three
factors. Firstly, very few 2G spectrum is left for use － actually
not more than 100MHz, and the spectrum efficiency is not satisfactory.
In addition, with the non-stop launching of new data services, the
capacity in hot areas of cities or countries is yet to be sufficient.
In comparison, the 3G system needs only a bit more than 230MHz with
a high spectrum efficiency, a wide coverage and better performance,
thus able to solve the current service deployment bottleneck. Secondly,
with the acceleration of the informatization process, people are
raising more demands for mobile data services. Although 2G can also
generate certain data services, due to the bandwidth limit, multimedia
data services like the Internet, E-commerce, high-speed data, moving
pictures and VOD can not be fully deployed. In that regard, 3G can
tailor different applications to provide access rates from 9.6kbit/s
to 2Mbit/s, thus satisfying such user demands. Thirdly, the globalization
has made it urgent to put in place a universally unified mobile
communications terminal to realize global roaming. However, the
multi-mode air interface and the network equipment of 2G make it
hard to fulfill such a requirement. So we can count on the 3G system
to bring into shape a unified mobile terminal for us to roam around
at our will.
At this point of time, the ITU mainly recognizes three kinds
of 3G standards, i.e., the US-advocated CDMA2000, the WCDMA proposed
by Europe and Japan and the TD-SCDMA from China, which are all featured
by high spectrum efficiency, wide coverage, satisfactory performance
and adaptability to broadband multimedia communications. On top
of that, the standards also have their own technical characteristics.
The core network of WCDMA is based on GSM-MAP, which makes it
able to operate on a core network that is based on ANSI-41 via network
expansion. The system can gradually evolve from 2G GSM system, and
support transmission of multiple parallel services on one link.
It also supports high-speed packet access and has adopted a more
flexible operation mode, including the support of asynchronous operation
between base stations, adaptive antenna array, multi-user detection,
the adoption of TD duplex in an unbalanced band and the adoption
of frequency multiplexing within one cell.
The
core network of CDMA2000 is based on ANSI-41. The system leverages
wireless interfaces of direct spectrum spread CDMA technology and
complies with or even over-satisfying all ITU requirements. The
system is empowered with an advanced media access control to support
high-speed data services in an effective way. Meanwhile, it is capable
of exerting an advanced multimedia OoS control and supports differentiated
QoS control. The system can also well handle the priority issue
between competing services. It can flexibly select voice, voice/data
and data modes according to environment and requirements, and support
both distributed and centralized packet data services. It can also
choose to adopt independent packet control and signaling for voice
transmission and support FDD duplex and TDD duplex. Besides that,
the system supports forward multi-carrier structure and orthogonal
direct spectrum spreading with flexibility and scalability, and
the evolution from CDMAOne is no difficult. It can also employ technologies
such as auxiliary pilot, orthogonal diversity and multi-carrier
diversity to improve the system performance.
Based on GSM, TD-SCDMA adopts the intelligent antenna and low
code rate technology to achieve a high spectrum efficiency, thus
making it good at easing the short supply of frequency resources
in densely populated areas. Also, the system exhibits an eminent
advantage in asymmetric mobile data transmission like the Internet
surfing and multimedia services such as VOD. The base station antenna
consists of an intelligent array, which can automatically decide
and track the location of the handset and ensure that the transmission
beam is pointed to the direction where the handset heads, thus bringing
down the transmission power of base stations. The uplink signal
can synchronize with the base station demodulator, thus reducing
the interference between code heads, simplifying the hardware structure
and cutting back on the cost. Also, TD-SCDMA is equipped with the
software radio technology. When operators plan to add new services,
the software on the same hardware platform can be used to process
the baseband signal. Meanwhile, different services can be realized
by loading different sorts of software. Plus, the base station in
the system leverages a highly integrated and cost-effective design.
Last but not least, the TD-SCDMA system is compatible with GSM.
After
years of research work on 3G, especially taking into account the
first two objectives, we must say that substantial progress has
been made. Whereas, generally speaking, the 3G system is still in
the stage experiments. Only a few individual systems have been commercialized
thus far.
One
of the important features of the 3G standard is an emphasis on evolution.
To ensure operator benefits, the Europe-originated GSM system started
by the narrowband 2G voice service, then evolved to data communications,
namely, the 2.5G GPRS service currently being deployed. The next
stage will be broadband data communications. In this evolution process,
the telecommunications technology is growing at a fast pace. Five
years ago, nearly all textbooks classified broadband into ATM-based
ISDN. However, nowadays the broadband network is already closely
linked to an all-IP protocol. Whereas, 3G is still A TM-based, that
is why people thought they were on the wrong path and the European
3G-WCDMA standardization organization 3GPP tried to work out further
standards for evolution to an all-IP network. The standard currently
in force is Release 99 (the 1999 version), which is not based on
IP. Then there was Release 2000 (the 2000 version). Later, Release
2000 was found to be too complex. So two further steps were made:
first Release 4 (version 4) and then Release 5 (version 5) before
going all the way up to an all-IP network. Such a standardization
process probably will take 3 to 5 years of time. Due to this, telecos
are now prudent in commercializing 3G. Even if the above technical
problems concerning 3G is resolved, there are still some unavoidable
obstacles in the way of spreading 3G applications. Firstly, users
are dealing with cellphones for the purpose of convenience in communications.
Although 3G may provide a wide array of service capabilities, it
is still yet to be known to what extent users may really need them.
Secondly, 3G system requires hefty investments, which will then
be burdened on users in the form of service charges. In addition,
it is quite possible that the functionally rich 3G handsets won't
be sold cheaply. So whether or not users is willing to accept the
handset model remains a question. Thirdly, 3G handsets may reach
a transmission rate of up to 384kb／s or even higher, but the handset
speed is subject to system capacity limitations. With a limited
system capacity, the more users the slower the rate. Experts estimate
that it would be very difficult for 3G handsets to get to the theoretical
speed. Therefore, it will take 2 to 3 years of time for 3G to become
a mature commercial system. Given all that, the 3G system nevertheless
has demonstrated the following key features: highly efficient channel
coding/decoding; smart antenna; initial synchronization and Rake
multi-path diversity reception; multi-user detection and power control.
All in all, the emergence of 3G system will fundamentally change
our way of communications, thus turning the anytime anywhere communications
into a reality.
6 4G
The
most noted trend of future generations of mobile communications
system is the requirement for high data speed, high flexibility
and seamless roaming. To that end, there will be even greater technical
challenges looming ahead. Besides, the system performance (e.g.,
cell size and transmission rate) is to a great extent dependent
on frequencies. Some people tend to think that since there is no
"revolutionary" changes taking place in technical indicators
and applications, there should not be a term of "4G" in
place. So the data rate of the 4G system should be at least one
order of magnitude above that of 3G, and 4G should include the following
four main features. Firstly, it should enable adaptive resource
allocation to handle changing traffic and channel conditions with
a strong self-organization capability and flexibility. Secondly,
it should be able to combine the rules of fixed mobile broadcast
network or other networks to exert a control over the volume distribution
of those features. Thirdly, the protocol should enable the co-existence
of both low and high code users according to network dynamics and
changing channel conditions. In those respects, 4G should demonstrate
a performance superior than 2G and 3G. Fourthly, the Digital Broadband
concept should be incorporated. In the "millimeter" process,
the propagation condition is relatively difficult. Correspondingly
the cell size will be much smaller, thus bringing about a series
of technical headaches. Compared to 4G, the 5G system will also
come into reality in the future. Table 1 shows the development of
mobile communications (the deployment time of 4G and 5G systems
are rough estimates).
|
Time
|
System
|
Technology
|
Service
|
|
1980s
|
1G
|
Analog
|
Analog cellular telephone, analog cordless
telephone
|
|
1990s
|
2G
|
Digital personal
|
Digital cellular: GSM, IS-54, PDC Digital
cordless: DECT, PHS Mobile satellite
|
|
2000s
|
3G
|
Global standard
|
IMT-2000 (3G cellular), with a maximum data
rate of 2Mbps
|
|
2010s
|
4G
|
High data rate, flexibility, IP-based
|
4G cellular broadband access, ITS, HAPS
Minimum data rate:2~20Mbps; maximum data rate:156Mbps
|
|
2020s
|
5G
|
High data rate, flexibility, IP-based
|
5G cellular, broadband access, ITS, HAPS
Minimum data rate: 2~20Mbps; maximum data rate: 600Mbp s
|
7
Conclusion
The
advent of a new century and China's entry to the WTO brought along
both opportunities and challenges to China's mobile communications
industry. Therefore, an in-depth analysis of the development of
mobile communications systems is helpful for us to sum up experiences,
head in the right direction and get hold of opportunities to accomplish
the building of a mobile communications network that is tailored
to future user needs.
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Author Biography
Mr. Zhang Guanghai graduated from Harbin
Industrial University in 1991 and got his Ph. D. at South China
Technological University in 1998. In 2000, he accompolished his
post-doctorate research in Tsinghua University. He is now working
for China Mobile Communication Corporation.
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