Overview of
The Universal Mobile Telecommunication System
(DRAFT, July 2002)
Table of Contents
1. 3G Systems
2. UMTS Services
3. UMTS Architecture
4. Core Network
5. Radio Access
6. User Equipment
1. 3G Systems
3G Systems are intended to provide a global mobility with wide range of services including telephony, paging, messaging, Internet and broadband data. International Telecommunication Union (ITU) started the process of defining the standard for third generation systems, referred to as International Mobile Telecommunications 2000 (IMT-2000). In Europe European Telecommunications Standards Institute (ETSI) was responsible of UMTS standardisation process. In 1998 Third Generation Partnership Project (3GPP) was formed to continue the technical specification work. 3GPP has five main UMTS standardisation areas: Radio Access Network, Core Network, Terminals, Services and System Aspects and GERAN.
3GPP Radio Access group is responsible of:
Radio Layer 1, 2 and 3 RR specification
Iub, Iur and Iu Interfaces
UTRAN Operation and Maintenance requirements
BTS radio performance specification
Conformance test specification for testing of radio aspects of base stations
Specifications for radio performance aspects from the system point of view
3GPP Core Network group is responsible of:
Mobility management, call connection control signalling between the user equipment and the core network.
Core network signalling between the core network nodes.
Definition of interworking functions between the core network and external networks.
Packet related issues.
Core network aspects of the lu interface and Operation and Maintenance requirements
3GPP Terminal group is responsible of:
Service capability protocols
Messaging
Services end-to-end interworking
USIM to Mobile Terminal interface
Model/framework for terminal interfaces and services (application) execution
Conformance test specifications of terminals, including radio aspects
3GPP Services and System Aspects group is responsible of:
Definition of services and feature requirements.
Development of service capabilities and service architecture for
cellular, fixed and cordless applications.
Charging and Accounting
Network Management and Security Aspects
Definition, evolution, and maintenance of overall architecture.
Third Generation Partnership Project 2 (3GPP) was formed for technical development of cdma2000 technology which is a member of IMT-2000 family.
In February 1992 World Radio Conference allocated frequencies for UMTS use. Frequencies 1885 - 2025 and 2110 - 2200 MHz were identified for IMT-2000 use. See the UMTS Frequency page for more details. All 3G standards are still under constant development. In 1999 ETSI Standardisation finished for UMTS Phase 1 (Release '99, version 3) and next release is due December 2001. UMTS History page has a list of all major 3G and UMTS milestones. Most of the European countries and some countries round the world have already issued UMTS licenses either by beauty contest or auctions.
2. UMTS Services
UMTS offers teleservices (like speech or SMS) and bearer services, which provide the capability for information transfer between access points. It is possible to negotiate and renegotiate the characteristics of a bearer service at session or connection establishment and during ongoing session or connection. Both connection oriented and connectionless services are offered for Point-to-Point and Point-to-Multipoint communication.
Bearer services have different QoS parameters for maximum transfer delay, delay variation and bit error rate. Offered data rate targets are:
144 kbits/s satellite and rural outdoor
384 kbits/s urban outdoor
2048 kbits/s indoor and low range outdoor
UMTS network services have different QoS classes for four types of traffic:
Conversational class (voice, video telephony, video gaming)
Streaming class (multimedia, video on demand, webcast)
Interactive class (web browsing, network gaming, database access)
Background class (email, SMS, downloading)
UMTS will also have a Virtual Home Environment (VHE). It is a concept for personal service environment portability across network boundaries and between terminals. Personal service environment means that users are consistently presented with the same personalised features, User Interface customisation and services in whatever network or terminal, wherever the user may be located. UMTS also has improved network security and location based services.
3. UMTS Architecture
A UMTS network consist of three interacting domains; Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE). The main function of the core network is to provide switching, routing and transit for user traffic. Core network also contains the databases and network management functions.
The basic Core Network architecture for UMTS is based on GSM network with GPRS. All equipment has to be modified for UMTS operation and services. The UTRAN provides the air interface access method for User Equipment. Base Station is referred as Node-B and control equipment for Node-B's is called Radio Network Controller (RNC). UMTS system page has an example, how UMTS network could be build.
It is necessary for a network to know the approximate location in order to be able to page user equipment. Here is the list of system areas from largest to smallest.
UMTS systems (including satellite)
Public Land Mobile Network (PLMN)
MSC/VLR or SGSN
Location Area
Routing Area (PS domain)
UTRAN Registration Area (PS domain)
Cell
Sub cell
4. Core Network
The Core Network is divided in circuit switched and packet switched domains. Some of the circuit switched elements are Mobile services Switching Centre (MSC), Visitor location register (VLR) and Gateway MSC. Packet switched elements are Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). Some network elements, like EIR, HLR, VLR and AUC are shared by both domains.
The Asynchronous Transfer Mode (ATM) is defined for UMTS core transmission. ATM Adaptation Layer type 2 (AAL2) handles circuit switched connection and packet connection protocol AAL5 is designed for data delivery.
The architecture of the Core Network may change when new services and features are introduced. Number Portability DataBase (NPDB) will be used to enable user to change the network while keeping their old phone number. Gateway Location Register (GLR) may be used to optimise the subscriber handling between network boundaries. MSC, VLR and SGSN can merge to become a UMTS MSC.
5. Radio Access
Wide band CDMA technology was selected to for UTRAN air interface. UMTS WCDMA is a Direct Sequence CDMA system where user data is multiplied with quasi-random bits derived from WCDMA Spreading codes.
In UMTS, in addition to channelisation, Codes are used for synchronisation and scrambling. WCDMA has two basic modes of operation: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). UTRAN interfaces are shown on UMTS Network page.
The functions of Node-B are:
Air interface Transmission / Reception
Modulation / Demodulation
CDMA Physical Channel coding
Micro Diversity
Error Handing
Closed loop power control
The functions of RNC are:
Radio Resource Control
Admission Control
Channel Allocation
Power Control Settings
Handover Control
Macro Diversity
Ciphering
Segmentation / Reassembly
Broadcast Signalling
Open Loop Power Control
6. User Equipment
The UMTS standard does not restrict the functionality of the User Equipment in any way. Terminals work as an air interface counter part for Node-B and have many different types of identities. Most of these UMTS identity types are taken directly from GSM specifications.
International Mobile Subscriber Identity (IMSI)
Temporary Mobile Subscriber Identity (TMSI)
Packet Temporary Mobile Subscriber Identity (P-TMSI)
Temporary Logical Link Identity (TLLI)
Mobile station ISDN (MSISDN)
International Mobile Station Equipment Identity (IMEI)
International Mobile Station Equipment Identity and Software Number (IMEISV)
UMTS mobile station can operate in one of three modes of operation:
PS/CS mode of operation: The MS is attached to both the PS domain and CS domain, and the MS is capable of simultaneously operating PS services and CS services.
PS mode of operation: The MS is attached to the PS domain only and may only operate services of the PS domain. However, this does not prevent CS-like services to be offered over the PS domain (like VoIP).
CS mode of operation: The MS is attached to the CS domain only and may only operate services of the CS domain.
UMTS IC card has same physical characteristics as GSM SIM card. It has several functions:
Support of one User Service Identity Module (USIM) application (optionally more that one)
Support of one or more user profile on the USIM
Update USIM specific information over the air
Security functions
User authentication
Optional inclusion of payment methods
Optional secure downloading of new applications
Other UMTS overviews in the web:
TU Wien UMTS Overview
IEC UMTS Overview
Radio interfaces
This page is a draft version and is still under development. Last modified July 15, 2002.
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