1. WCDMA System Overview 1.1 Development of Mobile Communications

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. It is widely applied in Britain, Japan and some Asian countries.
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 IS-95 and the European GSM system.
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 and 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 and China. The major services of mobile communications are currently still voice services and low-speed data services. With the development of networks, data and multimedia communications have also witnessed rapid development; therefore, the target of the 3G mobile communication is to implement broadband multimedia communication.
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 were incorporated into the IMT-2000 CDMA TDD part of the technical specification. This showed that the work of the TG8/1 in formulating the technical specifications of radio interfaces in 3G mobile communication systems had basically come into an end and the development and application of the 3G mobile communication systems would enter a new and essential phase.

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 to construct a new radio access network and smoothly evolves a core switching network from the existing GSM mobile switching network to provide more diversified services. The UTRA (Universal Terrestrial Radio Access) is used as the radio interface standard.
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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