1.2.1 Origin of the Multiple Systems
Currently the 3G research work of ITU is
mainly undertaken by 3GPP and 3GPP2. The goal of ITU in terms of 3G is to
establish the ITM-2000 family and implement global roaming between different 3G
systems.
Family concept
1)
Network part
In one intermediate meeting of ITU-T SG11
in March 1997, the ITM-2000 Family Concept put forward in Europe
was passed. This concept was based on the existing networks and involved at
least two major standards: GSM MAP and IS-41.
2)
Radio interface part
In the ITU-R TG8/1 meeting in September
1997, the discussion on the radio interface family concept started. In a
special meeting of TG8/1 in January 1998, the concept of suite was put forward
and applied and this put the family concept out of use. This means that there
may be more than one radio interface standard but the concept of more than one
standard is not yet accepted, rather, these different standards are expected to
ultimately form a unified standard.
The following two factors have caused
various technical differences:
1) Relationship
with 2G
The network part must be compatible with
2G, that is, the 3G networks are gradually evolved from the 2G networks. There
are two major 2G core networks: GSM MAP and IS-41.
Radio interfaces: The American IS-95 CDMA
and IS-136 TDMA operators emphasize on the backward compatibility (evolutional)
while the European GSM and Japanese PDC operators emphasize on the backward
incompatibility of the radio interface (revolutionary).
In terms of frequency spectrum, the key
issue is that the ITM-2000 frequencies allocated by ITU have already been
applied to the PCS service in USA USA USA
1.2.2 RTT Technical Proposal
The eighth research group of ITU-R, i.e.
the TG8/1 Task Group is responsible for promoting the assessment and merge of
IMT-2000 Radio Transmission Technology (RTT). Up till September 1998, there
have been up to 16 RTT proposals including the MSS (Mobile Satellite Service).
They all come from 16 RTT assessment groups of IMT-2000 and are listed as
follows:
1)
UTRA WCDMA (Europe )
2)
DECT (Europe )
3)
cdma2000 (USA
4)
UWC-136 (USA
5)
WIMS WCDMA (USA
6)
WCDMA/NA (USA
7)
WCDMA (Japan
8)
TD-SCDMA (China
9)
Global CDMA (Synchronous, Korea
Global CDMA (Asynchronous, Korea
1 LEO satellite system SAT-CDMA
ESA wideband satellite system
SW-CDMA
CDMA/TDMA hybrid bandwidth
satellite system SW-CTDMA
ICO RTT
INMARSAT satellite system
Horizons
Iridium LLC satellite system
INX
Among these proposals, the first ten are
RTT proposals for the IMT-2000 terrestrial system and the last six reflect the
efforts of incorporating the MSS (Mobile Satellite Service) into the IMT-2000.
These proposals reflect the concern of many
countries as to the future mode of IMT-2000 and their basic wishes to exercise
effective influence. However, as viewed from the market basis, backward
compatibility and overall features, the UTRA WCDMA of ETSI and the cdma2000 of
USA are the most competitive; therefore, the key to the merge of RTT lies in
the progress of effectively merging these two proposals.
1.2.3 Technical Merge
IMT-2000 includes both the Terrestrial
Mobile Service (TMS) and the Mobile Satellite Service (MSS). The suggestion of
one globally uniform and better-merged 3G mobile communication standard is
conducive to whether operators, manufacturers, subscribers and policy planning
& management bodies, so it is warmly welcomed by all countries in the
world.
As far the sixteen RTT candidate schemes
are concerned, the ultimate result of merging terrestrial mobile communications
will bring the biggest competitiveness to the WCDMA (DS) of ETSI and the
cdma2000 of USA TIA in terms of the FDD mode; while for the TDD mode, the
TD-CDMA put forward by ETSI UTRA and the D-SCDMA put forward by China CATT will
be the major objects of further integration. At the end of March 1999, Ericsson
and Qualcomm reached a series of agreements on the IPR and this act cleared way
the obstacles from intellectual property rights for promoting a global CDMA
standard. At the end of May 1999, the Operator Harmonization Group (OHG)
composed of 31 global major operators and 11 major manufacturers put forward a
merge proposal of the IMT-2000. This proposal played a positive role in
promoting the unification of the major parameters (chip rate, pilot structure,
core network protocol based on GSM-MAP and ANSI-41). All the participants
unanimously agreed that the chip rate should be 3.84Mcps for FDD-DS-CDMA and
3.6864Mcps for FDD-MC-CDMA, which is also called FDD-cdma2000-(MC). In June
1999, the 17th meeting of TG8/1 was held in Beijing
The 18th meeting of ITU TG8/1 was held in Helsinki , Finland
1.2.4 Comparison Among the Three Major Technical Systems
1. WCDMA
Formulated by the European standardization
organization 3GPP, WCDMA is widely supported by the global standardization
organizations, equipment manufacturers, component suppliers and operators. It
will become one of the mainstream future 3G systems.
The core network evolves on the basis of
and can thus be compatible with the existing GSM/GPRS networks.
It can be based on the TDM, ATM and IP
technologies to evolve towards the all-IP network architecture.
Logically, the core network comprises two
parts: The circuit domain and the packet domain to complete the circuit-switched
services and the packet-switched services respectively.
Based on the ATM technology, the UTRAN
uniformly processes voice and packet services and evolves towards the IP
network architecture.
MAP and GPRS tunneling technologies are the
core of the mobility management mechanism in the WCDMA system.
The air interface adopts the WCDMA
technologies with the signal bandwidth of 5 MHz and the chip rate of 3.84 Mcps.
It uses the AMR voice encoding scheme and supports the synchronous/asynchronous
Node B operation mode. Besides, the following modes are applied in the WCDMA
system: Uplink/downlink closed loop power control plus outer loop power
control; open loop (STTD & TSTD) and closed loop (FBTD) transmit diversity;
pilot-assisted coherent demodulation; convolutional coding and Turbo coding;
QPSK modulation in both the uplink and the downlink.
2. cdma2000 system
The cdma2000 system is a 3G standard put
forward on the basis of the IS-95 standard. Its standardization work is
currently undertaken by 3GPP2.
Circuit Switched (CS) domain: Adapted from
the 2G IS95 CDMA network, the circuit domain has introduced a service platform
based on the WIN infrastructure.
Packet Switched (PS) domain: A packet
network based on the Mobile IP technology.
Radio Access Network (RAN): Based on the
ATM switch platform, it provides abundant adaptation layer interfaces.
The air interface adopts the cdma2000
technologies and is compatible with the IS95. The signal bandwidth is N´1.25MHz (N = 1, 3, 6, 9, 12) and the chip rate is N´1.2288Mcps. It uses the 8K/13K QCELP or 8K EVRC voice coding mode
and its BTS needs to run in the GPS/GLONESS synchronous mode. The following
modes are applied in the cdma2000 system: Uplink/downlink closed loop power
control plus outer loop power control; OTD and STS transmit diversion in the
forward direction to improve the anti-fading capacity of channels and the
signal quality of the forward channels; pilot-assisted coherent modulation in
the reverse direction to improve the demodulation performance; convolutional
coding and Turbo coding; BPSK in the uplink and QPSK in the downlink.
3. TD-SCDMA system
The TD-SCDMA standard is put forward by the
Chinese Wireless Telecommunication Standard (CWTS) Group and now it has been
merged into the specifications related to the WCDMA-TDD of 3GPP.
The core network evolves on the basis of
and can thus be compatible with the existing GSM/GPRS networks.
It can be based on the TDM, ATM and IP
technologies to evolve towards the all-IP network architecture.
Logically, the core network comprises two
parts: The circuit domain and the packet domain to complete the
circuit-switched services and the packet-switched services respectively.
Based on the ATM technology, the UTRAN
uniformly processes voice and packet services and evolves towards the IP
network architecture.
MAP and GPRS tunneling technologies are the
core of the mobility management mechanism in the WCDMA system.
The air interface adopts the TD-SCDMA mode.
The TD-SCDMA features 3S: Smart antenna,
Synchronous CDMA and Software radio.
The key technologies used in TD-SCDMA
include Intelligent Antenna + Joint Detection, Multi-slot CDMA + DS-CDMA,
Synchronous CDMA, Channel Coding/Decoding and Interleaving (the same as in
3GPP) and Baton Handover.
A comparison of the above three systems is
given in the table below.
Table 1-1 Comparison among the three major technical systems
System
|
WCDMA
|
cdma2000
|
TD-SCDMA
|
Using countries
|
|||
Inheritance from
|
GSM
|
Narrowband CDMA
|
GSM
|
Synchronous mode
|
Asynchronous/synchronous
|
Synchronous
|
Synchronous
|
Chip rate
|
3.84Mcps
|
N×1.2288Mcps
|
1.28Mcps
|
Signal bandwidth
|
5MHz
|
N×1.25MHz
|
1.6MHz
|
Air interface
|
WCDMA
|
cdma2000 compatible with IS-95
|
TD-SCDMA
|
Core network
|
GSM MAP
|
ANSI-41
|
GSM MAP
|
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