UMTS: Universal Mobile Telecommunications System

Universal Mobile Telecommunications System (UMTS) is a key 3G mobile technology identified by the ITU. UMTS is the natural evolutionary choice for operators of GSM networks, a 2G mobile network. Using fresh radio spectrum to support increased numbers of customers in line with industry forecasts of demand for data services over the next decade and beyond, "UMTS" is synonymous with a choice of WCDMA radio access technology that has already been selected by approaching 120 licensees worldwide.

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 following is a list of key UMTS components:

• UMTS systems (including satellite)

• PublicLandMobile Network (PLMN)
• MSC/VLR or SGSN
• Location Area
• Routing Area (PS domain)
• UTRAN Registration Area (PS domain)
• Cell
• Sub cell

UMTS system uses the same core network as the GPRS and uses entirely new radio interface. The core network provides the switching, routing, transport, and database functions for user traffic. The core network contains circuit-switched elements such as the MSC, VLR, and gateway MSC (GMSC). It also contains the packet-switched elements SGSN and GGSN. The EIR, HLR, and AuC support both circuit- and packet-switched data. The Asynchronous Transfer Mode (ATM) is the data transmission method used within the UMTS core network.

The new radio network in UMTS is called UTRAN (UMTS Terrestrial Radio Access Network) and is connected to the core network (CN) of GPRS via Iu interface. The Iu is the UTRAN interface between the Radio network controller RNC and CN.

CDMA: Code Division Multiple Access

Code Division Multiple Access (CDMA) is a cellular technology defined by Qualcomm in IS-95 and IS-2000.Other widely used multiple access techniques for cellular are Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA).

CDMA is a form of Direct Sequence Spread Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elements: 1) The signal occupies a bandwidth much greater than that which is necessary to send the information, which results in immunity to interference and jamming and multi-user access; 2) The bandwidth is spread by means of a code which is independent of the data; 3) The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.

Due to increasing market demand for a convered network for both voice and data cpmmunications, CDMA technologies are evolving into CDMA2000 to meet the challenges. CDMA2000 is the 3rd Generation solution based on IS-95. Unlike some 3G standards, It is an evolution of an existing CDMA wireless standard. CDMA2000 supports 3G services as defined by the International Telecommunications Union (ITU) for IMT-2000. The goal is access to any service, anywhere, anytime from one terminal - true converged, mobile services.

The term Code Division Multiple Access (CDMA) is also widely used to refer to a key technology in the Universal Mobile Telecommunications System (UMTS). The two different uses of this term can be confusing. Actually, the Qualcomm standard CDMA and UMTS have been competing for adoption in many markets.

GSM/GPRS/UMTS Mobile Wireless Network Evolution

n the past decades, the mobile wireless network has migrated from the first generation (1G) to the third generation (3G), and 4G is in the time table. As one of the technology branches in the mobile wireless communication, the GSM has been upgraded to GPRS, and then UMTS. The road map of the GSM/UMTS network evolution is charged by the Third Generation Partnership Project (3GPP).

The GSM/GPRS/UMTS network evolution contains not only technical evolution but also expansion to network architecture and services.

• Technical evolution: how network elements are developed and with which technology.
• Network evolution: in result of network element evolutions the general architecture and functionality of the network is changing.
• Service evolution: demand generated by the end-users that can be supported by the technical features of the network.

	GSM	GPRS	UMTS
Network Elements	Mobile station (MS) Base transceiver station (BTS) Base station controller (BSC) Base station subsystem (BSS) Mobile switching center (MSC) Authentication center (AuC) Home location register (HLR) Visitor location register (VLR)	Terminal Equipment (TE)Base transceiver site (BTS) Base Station Controller (BSC) GPRS Support Nodes (GSNs) Serving GPRS support node (SGSN) Gateway GPRS support node (GGSN)	Radio Network Controller (RNC)Node BUMTS User EquipmentPlus GPRS components
Network Functions	Circuit Switched Voice/DataNarrow band access	Circuit Switched Voice Packet Switched data Narrow band access	Packet switch for voice and dataIP multimedia subsystem (IMS)Broadband access using UTRAN
Services	Voice	VoiceShort messagesLow speed data	VoiceMessagesHigh speed dataMultimedia

Radio Access Network (RAN) Standards for 3G UMTS and CDMA2000 Networks

A radio access network (RAN) refers to the network that sits between the mobile phones, and the core network (CN). Both UMTS and CDMA2000 networks have their own radio access network air interface definitions. RAN provides radio bearers between the core network and the mobile station for the transport of user data and non-access stream signaling, thus enabling mobile stations to access the service offered by the PSTN and Internet. The main RAN function includes establishment, maintenance, and termination of radio channels; radio resource management; and mobility management. The RAN consists of the base station (BS) and packet control function (PCF). The base station is further decomposed in one control and one or multiple radio-terminating equipment portions named base station controller (BSC) and base transceiver station (BTS), respectively.

W-CDMA (Wideband Code Division Multiple Access) is the first 3G air interface for the UMTS technologies, a third generation follow-on to the 2G GSM networks deployed worldwide. W-CDMA can be implemented by migrating via GPRS and EDGE on the 2G network infrastructure of the GSM standard that is used in Europe and worldwide. W-CDMA allows transmission of signals for various services with variable data rates on 5 MHz bandwidths. Key features of WCDMA are cited below:

• Radio channels are 5MHz wide.
• Chip rate of 3.84 Mcps
• Supports two basic modes of duplex, frequency division and time division. Current systems use frequency division, one frequency for uplink and one for downlink. For time division, FOMA uses sixteen slots per radio frame, where as UMTS uses 15 slots per radio frame.
• Employs coherent detection on uplink and downlink based on the use of pilot symbols.
• Supports inter-cell asynchronous operation.
• Variable mission on a 10 ms frame basis.
• Multicode transmission.
• Adaptive power control based on SIR (Signal-to-Interference Ratio).
• Multiuser detection and smart antennas can be used to increase capacity and coverage.
• Multiple types of handoff between different cells including soft handoff, softer handoff and hard handoff.

New air interface technologies such as HSPA and HSPA+ are defined for the UMTS systems with better performance and functionalities.

On the other hand, CDMA2000 covers a family of mobile communication technologies that further develop the 2G mode CDMAOne, whose use is restricted to the USA, South America, Korea and Japan. CDMA2000 3G network, uses its own radio access network technologies. The CDMA2000 standards CDMA2000 1xRTT, CDMA2000 EV-DO, and CDMA2000 EV-DV are approved radio interfaces for the ITU's IMT-2000 standard and a direct successor to 2G CDMA, IS-95 (cdmaOne). CDMA2000 is standardized by 3GPP2. CDMA2000 is designed to use transmission bandwidth of 1.25 MHz.

UMTS/WCDMA Logical, Transport and Physical Channels

WCDMA is the main air interface standard for the 3G UMTS mobile network. The mobile station and base station communicate by means of several physical channels that are transmitted on a given frequency assignment. The "Downlink" refers to a radio link for the transmission of signals from the base station to a UE (mobile station) while the "Uplink" refers to a radio link for the transmission of signals from a UE (mobile station) to the base station.

There are three types of channels in the WCDMA technologies: Physical Channel, Transport Channel and Logical channel. The Transport Channels are interface between MAC and Layer 1, while Logical Channels are interface between MAC and RLC. The logical and transport channels define WHAT data are transported, while the physical channels define HOW and with what physical characteristic the data are transport.

Transport channels can be further subdivided into Common Transport Channels; and dedicated transport channels. Common transport channel types are:

• Random Access Channel (RACH): A contention based uplink channel used for transmission of relatively small amounts of data, e.g. for initial access or non-real-time dedicated control or traffic data.
• Common Packet Channel (CPCH): A contention based channel used for transmission of bursty data traffic. This channel only exists in FDD mode and only in the uplink direction. The common packet channel is shared by the UEs in a cell and therefore, it is a common resource. The CPCH is fast power controlled.
• Forward Access Channel (FACH): Common downlink channel without closed-loop power control used for transmission of relatively small amount of data.
• Downlink Shared Channel (DSCH): A downlink channel shared by several UEs carrying dedicated control or traffic data.
• Uplink Shared Channel (USCH): An uplink channel shared by several UEs carrying dedicated control or traffic data, used in TDD mode only.
• Broadcast Channel (BCH): A downlink channel used for broadcast of system information into an entire cell.
• Paging Channel (PCH): A downlink channel used for broadcast of control information into an entire cell allowing efficient UE sleep mode procedures. Currently identified information types are paging and notification. Another use could be UTRAN notification of change of BCCH information.
• High Speed Downlink Shared Channel (HS-DSCH): A downlink channel shared between UEs by allocation of individual codes, from a common pool of codes assigned for the channel.

Dedicated transport channel types are:

• Dedicated Channel (DCH): A channel dedicated to one UE used in uplink or downlink.
• A general classification of logical channels is into two groups; Control Channels (for the transfer of control plane information) and Traffic Channels (for the transfer of user plane information).

Control Channels:

• Broadcast Control Channel (BCCH): A downlink channel for broadcasting system control information.
• Paging Control Channel (PCCH): A downlink channel that transfers paging information. This channel is used when the network does not know the location cell of the UE, or, the UE is in the cell connected state (utilising UE sleep mode procedures).
• Common Control Channel (CCCH): Bi-directional channel for transmitting control information between network and UEs. This channel is commonly used by the UEs having no RRC connection with the network and by the UEs using common transport channels when accessing a new cell after cell reselection.
• Dedicated Control Channel (DCCH): A point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is established through RRC connection setup procedure.
• Shared Channel Control Channel (SHCCH): Bi-directional channel that transmits control information for uplink and downlink shared channels between network and UEs. This channel is for TDD only.

Traffic Channels:

• Dedicated Traffic Channel (DTCH): A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for the transfer of user information. A DTCH can exist in both uplink and downlink.
• Common Traffic Channel (CTCH): A point-to-multipoint unidirectional channel for transfer of dedicated user information for all or a group of specified UEs.

UMTS Network Interfaces and Protocol Stack

UMTS network follows the typical communication model in telecom which defines a set of horizontal and vertical layers. The horizontal layers are physical, network, transport and application layers – as defined in the OSI model. The vertical layers are functional areas, namely control plane, user plane and data plane. Control planes are used to control a link or a connection; user planes are used to transparently transmit user data from the higher layers. The UMTS network interfaces and protocol stacks follow the same communication model. Standard transmission issues, which are independent of UTRAN requirements, are applied in the horizontal transport network layer. The UTRAN requirements are addressed in the horizontal radio network layer across different types of control and user planes. The UMTS network introduces four new key interfaces and protocol stacks: Uu, Iub, Iur, and Iu.

Iu: Radio Access Network Application Part (RANAP) [3G TS 25.413]. This interface provides UTRAN–specific signaling and control over the Iu. The following is some typical RANAP functions:

• Overall radio access bearer (RAB) management, which includes the RAB’s setup, maintenance, and release
• Management of Iu connections
• Transport of nonaccess stratum (NAS) information between the UE and the CN; for example, NAS contains the mobility management signaling and broadcast information.
• Exchanging UE location information between the RNC and CN
• Paging requests from the CN to the UE
• Overload and general error situation handling

Iur: Radio Network Sublayer Application Part (RNSAP) [3G TS 25.423]. This interface provides UTRAN–specific signaling and control for the following sample functions:

• Management of radio links, physical links, and common transport channel resources
• Paging
• SRNC relocation
• Measurements of dedicated resources

Iub: Node B Application Part (NBAP) [3G TS 25.433]. This interface provides UTRAN specific signaling and control for the following sample areas:

• Management of common channels, common resources, and radio links
• Configuration management, such as cell configuration management
• Measurement handling and control
• Synchronization (TDD)
• Reporting of error situations

Uu: Radio Resource Control (RRC) [3G TS 25.331]. This interface handles the control plane signaling over the Uu between the UE and the UTRAN. Some of the functions offered by the RRC

include the following areas:

• Broadcasting information
• Management of connections between the UE and the UTRAN, which include their establishment, maintenance, and release
• Management of the radio bearers, which include their establishment, maintenance, release, and the corresponding connection mobility
• Ciphering control
• Outer loop power control
• Message integrity protection
• Timing advance in the TDD mode
• UE measurement report evaluation
• Paging and notifying

UMTS 3G Mobile Wireless Network Architecture

Universal Mobile Telecommunications System (UMTS), standardized by the 3GPP, is the 3G mobile communication technology successor to GSM and GPRS. UMTS combines the W-CDMA, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs.

W-CDMA is the most popular cellular mobile telephone variant of UMTS in use. UMTS, using W-CDMA, supports up to 14.0 Mbit/s data transfer rates in theory with High Speed Downlink Packet Access (HSDPA), although the performance in deployed networks could be much lower for both uplink and downlink connections.

A major difference of UMTS compared to GSM is the air interface forming Generic Radio Access Network (GeRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GeRAN includes the three lowest layers of OSI model. The network layer (OSI 3) protocols form the Radio Resource Management protocol (RRM). They manage the bearer channels between the mobile terminals and the fixed network including the handovers.

The UMTS standard is an extension of existing networks based on the GSM and GPRS technologies. In UMTS release 1, a new radio access network UMTS terrestrial radio access network (UTRAN) is introduced. UTRAN, the UMTS radio access network (RAN), is connected via the Iu to the GSM Phase 2+ core network (CN). The Iu is the UTRAN interface between the radio network controller (RNC) and CN; the UTRAN interface between RNC and the packet-switched domain of the CN (Iu–PS) is used for PS data and the UTRAN interface between RNC and the circuit-switched domain of the CN (Iu–CS) is used for CS data.

UTRAN is subdivided into individual radio network systems (RNSs), where each RNS is controlled by an RNC. The RNC is connected to a set of Node B elements, each of which can serve one or several cells. Two new network elements, namely RNC and Node B, are introduced in UTRAN.

The RNC enables autonomous radio resource management (RRM) by UTRAN. It performs the same functions as the GSM BSC, providing central control for the RNS elements (RNC and Node Bs).

Node B is the physical unit for radio transmission/reception with cells. Node B connects with the UE via the W–CDMA Uu radio interface and with the RNC via the Iub asynchronous transfer mode (ATM)–based interface. Node B is the ATM termination point.