Up till now the modern mobile communication
has experienced two generations and evolved into the third generation that is
ongoing with pre-commercialization. Many manufacturers have already carried out
their commercial trials in Europe and Asia .
The first generation is the analog cellular
mobile communication network in the time period from the middle of 1970s to the
middle of 1980s. The most important breakthrough in this period is the concept
of cellular networks put forward by the Bell Labs in the 1970s, as compared to
the former mobile communication systems. The cellular network system is based
on cells to implement frequency reuse and thus greatly enhances the system
capacity.
The typical examples of the first
generation mobile communication systems are the AMPS system and the later
enhanced TACS of USA, the NMT and the NTT. The AMPS (Advanced Mobile Phone
System) uses the 800 MHz band of the analog cellular transmission system and it
is widely applied in North America , South America and some Circum-Pacific countries. The TACS
(Total Access Communication System) uses the 900 MHz band and includes two
versions: ETACS (Enhanced TACS) in Europe and
NTACS (Narrowband TACS) in Japan Britain Japan
The main feature of the first generation mobile
communication systems is that they use the frequency reuse technology, adopt
analog modulation for voice signals and provide an analog subscriber channel
every other 30 kHz/25 kHz. However, their defects are also obvious:
1)
Low utilization of the
frequency spectrum
2)
Limited types of services
3)
No high-speed data services
4)
Poor confidentiality and high
vulnerability to interception and number embezzlement
5)
High equipment cost
6)
Large volume and big weight
To solve these fundamental technical
defects of the analog systems, the digital mobile communication technologies
emerged and the second generation mobile communication systems represented by
GSM and IS-95 came into being in the middle of 1980s. The typical examples of
the second generation cellular mobile communication systems are the DAMPS of USA
The GSM (Global System for Mobile
Communications) is originated from Europe .
Designed as the TDMA standard for mobile digital cellular communications, it
supports the 64 kbps data rate and can interconnect with the ISDN. It uses the
900 MHz band while the DCS1800 system uses the 1800 MHz band. The GSM system
uses the FDD and TDMA modes and each carrier supports eight channels with the
signal bandwidth of 200 kHz.
The DAMPS (Digital Advanced Mobile Phone
System) is also called the IS-54 (North America Digital Cellular System). Using
the 800 MHz bandwidth, it is the earlier of the two North
America digital cellular standards and specifies the use of the
TDMA mode.
The IS-95 standard is another digital
cellular standard of North America . Using the
800 MHz or 1900 MHz band, it specifies the use of the CDMA mode and has already
become the first choice among the technologies of American PCS (Personal
Communication System) networks.
Since the 2G mobile communication systems
focus on the transmission of voice and low-speed data services, the 2.5G mobile
communication systems emerged in 1996 to address the medium-rate data
transmission needs. These systems include GPRS and IS-95B.
The CDMA system has a very large capacity
that is equivalent to ten or even twenty times that of the analog systems. It
also has good compatibility with the analog systems. Currently some countries
and regions such as USA Korea Hong Kong have put the CDMA system into
operation to provide services for subscribers. As the narrowband CDMA
technologies come into maturity at a time later than the GSM technologies,
their application far lags behind the GSM ones and currently they have only
found large-scale commercial applications in North America ,
Korea China
The 3G mobile communication systems are a kind
of communication system that can provide multiple kinds of high quality
multimedia services and implement global seamless coverage and global roaming.
They are compatible with the fixed networks and can implement any kind of
communication at any time and any place with portable terminals.
Put forward in 1985 by the ITU
(International Telecommunication Union), the 3G mobile communication system was
called the FPLMTS (Future Public Land Mobile Telecommunication System) and was
later renamed as IMT-2000 (International Mobile Telecommunication-2000). The
major systems include WCDMA, cdma2000 and UWC-136. On November 5, 1999 , the 18th
conference of ITU-R TG8/1 passed the Recommended Specification of Radio
Interfaces of IMT-2000 and the TD-SCDMA technologies put forward by China
1.1.1 Standardization
Organizations
The standardization of 3G mobile
communication systems are in fact pushed forward and implemented by two
standardization organizations: 3GPP (3rd Generation Partner Project) and 3GPP2.
Established in December 1998, the 3GPP is
composed of the European ETSI, the Japanese ARIB, the Korean TTA and the
American T1. It adopts the WCDMA technologies of Europe
and Japan
In January 1999, the 3GPP2 composed of the
American TIA, the Japanese ARIB and the Korean TTA also formally came into
being. The cdma2000 and UWC-136 technologies are applied for radio access and
the cdma2000 technologies adopt the Qualcomm patents to a large extent.
ANSI/IS-41 is used for the core network.
One formal member of the above two
standardization organizations is the China Wireless Telecommunications Standard
Group (CWTS) and two Chinese companies (Huawei and Datang) are two independent
members of the 3GPP organization.
1.1.2 3G Evolution Policies
In general, the evolution policies
formulated by 3GPP and 3GPP2 are progressive. This has the following benefits:
l
Guaranteeing the existing
investment and operators’ benefits
l
Facilitating the smooth
transition of the existing technologies
From the perspective of development, the
process of evolution from the existing 2G mobile communication systems to the
IMT-2000 is a vital issue. It relates to the reuse of the existing networks
(the construction of new networks should not be the optimal solution) and the
development of multiple 2G digital network systems towards the same standard.
1. Policies of evolution from
GSM to WCDMA
The policies of evolution from GSM to WCDMA
should be as follows: The present GSM → HSCSD (High Speed Circuit Switched Data
at the rates from 14.4 kbps to 64 kbps) → GPRS (General Packet Radio Service at
the rate of 144 kbps) → Smooth seamless evolution from the network service
coverage ultimately to IMT-2000 WCDMA (DS).
1)
HSCSD: High Speed Circuit
Switched Data
HSCSD is a feature to allocate multiple
full-rate voice channels to the HSCSD structure. Its purpose is to provide the
mixture of multiple services at different air interface subscriber rates with
the single physical layer structure. Its benefits lie in the higher data rates
(up to 64 kbps; the maximum data rate depends on the manufacturers) and the use
of the existing GSM data technologies by slightly modifying the GSM system.
2)
GPRS: General Packet Radio Service
The major benefits of GPRS are as follows:
l
Standard radio packet switching
Internet/Intranet access applicable to all the places of GSM coverage
l
Variable peak data rate that
ranges from several bits per second to 171.2 kbps (the maximum data rate
depends on the manufacturers)
l
Charging by the actual data
volume: This charging method enables the subscribers to pay the cost of the
actual data volume transmitted while remaining online all the days
l
Support for the existing
services and new application services
l
Packetization over the radio
interfaces to optimize the sharing of radio resources
l
Packet switching technology to
optimize the sharing of network resources
l
Capability of extension to the
future radio protocols
Based on the existing GSM part, the packet
switching GPRS network architecture has the new network function part:
3)
WCDMA: Wideband Code Division
Multi Access
The WCDMA has become a new mature
technology aiming at the UMTS/IMT-2000. It can satisfy all the requirements
listed by the ITU to provide very effective high-speed data services and high
quality voice and image services. In the process of evolution from GSM to
WCDMA, only the core network part is smoothly evolved. As the change of the air
interface is revolutionary, so is the evolution of the radio access network part.
2. Policies of evolution from IS-95 to cdma2000
After the IS-95A (at the rates of 9.6/14.4
kbps) is evolved to the IS-95B (at the rate of 115.2 kbps) and ultimately to
cdma2000 1X, the system can provide higher capacity and a higher data rate
(144kbps) and can support the burst mode as well as adding new supplemental
channels. The cdma2000 1X EV with enhanced technologies can provide higher
performances.
The IS-95B is different from the IS-95A in
that multiple channels can be bound in the IS-95B system. These two are
basically the same in essence can they can coexist in the same carrier. In
contrast, the cdma2000 1X has greater improvements and its system equipment can
support 1X terminals and IS-95A/B terminals simultaneously. Therefore, these
three systems (IS-95A/IS-95B/1X) can coexist in the same carrier. For the
cdma2000 system, the gradual replacement method can be applied in the
transition from 2G systems to 3G systems. In other words, one carrier of the 2G
systems can be compressed to become a 3G carrier to provide the services of
medium and higher rates to the subscribers. As the 3G systems have more and
more subscribers, the number of carriers used in the 2G systems can be
gradually reduced while more carriers can be added to the 3G systems. Through
this kind of smooth upgrading, the network operators can not only provide
various latest serves to the subscribers but also well protect the investment
of the existing equipment.
In the process of evolution to the 3G
systems, the evolution of such wireless equipment as BTS and BSC deserves
special attention. The protection of operators’ investment has been fully taken
into account in the formulation of the cdma2000 standard and many radio indices
of the 3G systems are the same as in the 2G systems. From the point of view of
the BTS, the radio parts such as antenna, RF filters and power amplifiers are
all reusable while the baseband signal processing part needs to be replaced.
There are currently two branches in the
evolution to the cdma2000 1X EV: 1) The cdma2000 1X EV-DO that only supports
data services; and 2) the cdma2000 1X EV-DV that supports both data services
and voice services. For the cdma2000 1X EV-DO that only supports data services,
the HDR put forward by Qualcomm has been determined; while for the cdma2000 1X
EV-DV that supports both data services and voice services, there are several
proposals at present (one of them is the LAS-CDMA technology submitted by
China) and these are presently in the process of review.
3. Policies of evolution from DAMPS to UWC-136
The first step of evolution from IS-136
(DAMPS) to UWC-136 is to implement the GPRS-136 and the second step is to
implement UWC-136 (Universal Wireless Communications). The EDGE-based
technologies have been decided for UWCC and TIA TR-45.3, this means that the
GPRS network architecture will be used to support the 136+ high-speed data
transmission. The GPRS-136 is the official name of the 136+ packet switched
data service and its high-layer protocols (L3 protocols and above) are fully
the same as those of the GPRS system, considering the economical aspect of the
implementation. It provides the same capacity as the GPRS of GSM and its
subscribers can have access to two forms of data networks: IP and X.25. Its
major purpose is to reduce the technical difference between TIA/EIA-136 and GSM
GPRS so that the subscribers can roam between GPRS-136 and GSM GPRS networks.
One of the policies for the American TIA to develop the 3G systems is to
implement convergence of the 3G systems with the GSM system that also uses the
TDMA access mode. This is quite beneficial for the economics of global roaming
and products and it also implements the coordination protocol between UWCC and
ETSI. What’s more important, it enables the TDMA to player a more important role
in the 3G systems.
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