1.2 Types and Differences of 3G Systems

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. Because the USA requires the sharing of frequency spectrum with 2G systems, the backward compatibility of the radio interfaces is especially emphasized and technically the USA requires gradual evolution. In contrast, most of the other countries have new IMT-2000 frequency bands that feature very large flexibility. What’s more, the intellectual property rights play a very significant role, for example, Qualcomm has its own patent declaration. Competition is also a major factor to contribute to the technical differences.

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. In this meeting, a framework agreement was reached on Recommendations Rec, IMT and RSPC of the technical specifications of radio interfaces. 3GPP, 3GPP2 and the Standards Development Organizations (SDOs) were encouraged to support the above OHG proposal and TG8/1 Task Group was appointed to carry out more detailed work of the MSS proposal.
The 18th meeting of ITU TG8/1 was held in Helsinki, Finland in November 1999, and the Recommended Specification of Radio Interfaces of IMT-2000 was adopted. This meant that the TG8/1's work in formulating the technical specifications of radio interfaces in the 3G mobile communication systems had basically come to an end and the development and application of 3G mobile communication systems would enter the essential phase. TD-SCDMA, WCDMA and cdma2000 were determined as the ultimate three technical systems.

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
Europe and Japan
USA and Korea
China
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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