Universal Mobile Telecommunications System Study Guide
Undergraduate Communication Engineering Course
UMTS (Universal Mobile Telecommunications System) is a third-generation (3G) mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS represents a significant evolution from 2G GSM/GPRS systems, offering substantially higher data rates and enhanced multimedia capabilities.
| Band | Uplink (MHz) | Downlink (MHz) | Region |
|---|---|---|---|
| Band I (2100) | 1920-1980 | 2110-2170 | Europe, Asia |
| Band II (1900) | 1850-1910 | 1930-1990 | Americas |
| Band III (1800) | 1710-1785 | 1805-1880 | Europe, Asia |
| Band IV (1700) | 1710-1755 | 2110-2155 | Americas |
| Band V (850) | 824-849 | 869-894 | Americas |
| Band VIII (900) | 880-915 | 925-960 | Europe, Asia |
European Telecommunications Standards Institute (ETSI) establishes GSM (Group Spécial Mobile) for 2G digital cellular systems.
First GSM networks deployed in Europe, offering circuit-switched voice and SMS.
ETSI selects WCDMA as the air interface for UMTS. 3GPP formed to develop global 3G specifications.
NTT DoCoMo launches the first commercial UMTS network in Japan (FOMA service).
UMTS services launched across Europe, with operators acquiring 3G licenses through auctions.
High-Speed Packet Access (HSPA) enhances UMTS to provide data rates up to 14.4 Mbps.
Operators begin migrating to LTE (4G), but UMTS/HSPA remains widely deployed as fallback.
The UMTS network architecture consists of three main domains: the User Equipment (UE), the UMTS Terrestrial Radio Access Network (UTRAN), and the Core Network (CN). This structure follows the same principles as GSM but with significant enhancements to support WCDMA and high-speed data services.
┌─────────────────────────────────────────────────────────────────┐
│ UMTS NETWORK │
├─────────────────────────────────────────────────────────────────┤
│ │
│ ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │
│ │ User │ │ UTRAN │ │ Core Network │ │
│ │ Equipment │◄────►│ (Radio │◄────►│ (CN) │ │
│ │ (UE) │ Uu │ Access) │ Iu │ │ │
│ └──────────────┘ └──────────────┘ └──────────────┘ │
│ │
│ Components: │
│ • UE: Mobile device with USIM │
│ • UTRAN: Node B (Base Station) + RNC (Radio Controller) │
│ • CN: MSC/VLR (Circuit) + SGSN/GGSN (Packet) + HLR/AuC │
│ │
└─────────────────────────────────────────────────────────────────┘
The mobile terminal consisting of:
The radio access network comprising:
The service delivery infrastructure:
UTRAN is a critical component of UMTS, responsible for all radio-related functionality. It represents a significant architectural change from GSM's Base Station Subsystem (BSS), introducing new concepts like soft handover and macro-diversity.
┌──────────────────────────────────────────────────────────────┐
│ UTRAN │
├──────────────────────────────────────────────────────────────┤
│ │
│ ┌─────────────┐ ┌─────────────┐ │
│ │ RNC │◄───────►│ RNC │ (Radio Network │
│ │ (SRNC) │ Iur │ (DRNC) │ Controllers) │
│ └──────┬──────┘ └──────┬──────┘ │
│ │ │ │
│ │ Iub │ Iub │
│ │ │ │
│ ┌──────┴──────┐ ┌──────┴──────┐ │
│ │ Node B │ │ Node B │ (Base Stations) │
│ │ (Serving) │ │ (Drift) │ │
│ └──────┬──────┘ └──────┬──────┘ │
│ │ │ │
│ │ Uu │ Uu │
│ │ │ │
│ ┌──────┴──────┐ ┌──────┴──────┐ │
│ │ UE │◄─────────►│ UE │ (User Equipment)│
│ │ (Mobile) │ Soft │ (Mobile) │ │
│ └─────────────┘ Handover └─────────────┘ │
│ │
└──────────────────────────────────────────────────────────────┘
The Node B is the UMTS base station, equivalent to the BTS in GSM but with enhanced capabilities to support WCDMA.
| Function | Description |
|---|---|
| Air Interface Processing | Channel coding, interleaving, spreading, modulation/demodulation |
| Power Control | Fast closed-loop power control (1500 Hz) to combat near-far problem |
| RF Processing | Transmission and reception on multiple carriers |
| Soft Handover Execution | Combining signals from multiple cells |
| Measurement | Radio link quality monitoring and reporting to RNC |
The RNC is the governing element in UTRAN, analogous to the BSC in GSM but with significantly more intelligence and functionality.
Serving RNC (SRNC): The RNC that terminates the Iu link for a specific UE. It handles the RRC connection and has full control of the radio resources for that connection within the UTRAN.
Drift RNC (DRNC): An RNC that controls cells used by a mobile but does not terminate the Iu link. The SRNC delegates radio resource control to the DRNC for cells in its jurisdiction.
Controlling RNC (CRNC): The RNC that controls a specific Node B or cell, managing its resources and configuration.
| Identifier | Full Name | Purpose |
|---|---|---|
| RNC-ID | Radio Network Controller ID | Unique identifier for each RNC in the network |
| C-ID | Cell ID | Identifies a cell within an RNC (16 bits) |
| URA-ID | UTRAN Registration Area ID | Group of cells for paging optimization |
| SAC | Service Area Code | Location area for service-based paging |
| LAC | Location Area Code | Carried from GSM, used for mobility management |
The UMTS Core Network is an evolution of the GSM/GPRS core network, designed to support both circuit-switched (CS) and packet-switched (PS) services efficiently. It is divided into domains based on the type of service provided.
┌──────────────────────────────────────────────────────────────────┐
│ UMTS CORE NETWORK │
├──────────────────────────────────────────────────────────────────┤
│ │
│ ┌─────────────────────┐ ┌─────────────────────┐ │
│ │ CIRCUIT SWITCHED │ │ PACKET SWITCHED │ │
│ │ (CS) │ │ (PS) │ │
│ │ │ │ │ │
│ │ ┌───────────────┐ │ │ ┌───────────────┐ │ │
│ │ │ MSC │ │ │ │ SGSN │ │ │
│ │ │ (Mobile │ │ │ │ (Serving │ │ │
│ │ │ Switching │ │ │ │ GPRS Support │ │ │
│ │ │ Center) │ │ │ │ Node) │ │ │
│ │ └───────┬───────┘ │ │ └───────┬───────┘ │ │
│ │ │ │ │ │ │ │
│ │ ┌───────┴───────┐ │ │ ┌───────┴───────┐ │ │
│ │ │ GMSC │ │ │ │ GGSN │ │ │
│ │ │ (Gateway MSC) │ │ │ │ (Gateway │ │ │
│ │ │ │ │ │ │ GPRS Support │ │ │
│ │ │ │ │ │ │ Node) │ │ │
│ │ └───────────────┘ │ │ └───────────────┘ │ │
│ │ │ │ │ │
│ │ VLR (Visitor │ │ PCU (Packet │ │
│ │ Location Reg) │ │ Control Unit) │ │
│ └─────────────────────┘ └─────────────────────┘ │
│ │
│ ┌──────────────────────────────────────────────────────────┐ │
│ │ COMMON ELEMENTS (CS & PS) │ │
│ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ ┌────────┐ │ │
│ │ │ HLR │ │ AuC │ │ EIR │ │ SMSC │ │ │
│ │ │ (Home │ │ (Auth. │ │ (Equip. │ │ (Short │ │ │
│ │ │ Location│ │ Center) │ │ Identity│ │ Msg │ │ │
│ │ │ Reg.) │ │ │ │ Reg.) │ │ Center)│ │ │
│ │ └──────────┘ └──────────┘ └──────────┘ └────────┘ │ │
│ └──────────────────────────────────────────────────────────┘ │
│ │
└──────────────────────────────────────────────────────────────────┘
The CS domain handles traditional voice telephony services and circuit-switched data, inherited largely from GSM with enhancements for UMTS.
The GMSC acts as the entry point for incoming calls to the UMTS network from external networks. It queries the HLR to determine the current location of the called subscriber and routes the call accordingly.
The VLR maintains temporary subscriber information for users currently in the MSC's service area. It stores:
The PS domain provides packet data services, evolved from GPRS, optimized for bursty data traffic and internet connectivity.
| Function | Description |
|---|---|
| Mobility Management | Tracking UE location, routing area updates |
| Session Management | PDP context activation, modification, deactivation |
| Packet Routing | Forwarding IP packets to/from GGSN |
| Charging | Data volume collection for billing |
| Security | Ciphering and integrity protection for PS domain |
| Inter-UTRAN Handover | Coordinating PS handover between RNCs |
The GGSN serves as the gateway between the UMTS packet network and external packet data networks (PDN) such as the Internet or corporate intranets.
A PDP context is a data structure that describes the packet data connection between the UE and the external network. It contains:
The central database containing permanent subscriber information:
Provides security parameters for authentication:
Database for mobile equipment validation:
UMTS defines standardized interfaces between network elements to ensure interoperability between equipment from different vendors. These interfaces carry both user traffic and control signaling.
┌─────────────────────────────────────────────────────────────────────┐
│ UMTS INTERFACES │
├─────────────────────────────────────────────────────────────────────┤
│ │
│ UE ═══════ Uu ═══════ Node B ═══════ Iub ═══════ RNC │
│ │ │ │ │
│ │ │ │ Iur (RNC-RNC) │
│ │ │ ▼ │
│ │ │ ┌─────────┐ │
│ │ │ │ RNC │ │
│ │ │ └────┬────┘ │
│ │ │ │ │
│ │ └────────── Iub ─────────┘ │
│ │ │
│ └────────────────────── Iu-CS ────────────────────┐ │
│ Iu-PS ────────────────────────┼──────────────┐ │
│ │ │ │
│ ┌──────────────────────────────────────────────────┼──────────┐ │ │
│ │ CORE NETWORK │ │ │ │
│ │ ┌──────────────┐ ┌──────────────┐ │ │ │ │
│ │ │ MSC │◄── Gs ──►│ SGSN │◄────┘ │ │ │
│ │ │ + │ │ │ │ │ │
│ │ │ VLR │ │ │ │ │ │
│ │ └──────┬───────┘ └──────┬───────┘ │ │ │
│ │ │ │ │ │ │
│ │ │ C/D/E │ Gn │ │ │
│ │ ▼ ▼ │ │ │
│ │ ┌──────────────┐ ┌──────────────┐ │ │ │
│ │ │ HLR │ │ GGSN │◄──── Gi ───► PDN │ │ │
│ │ │ AuC │ │ │ (Internet) │ │ │
│ │ └──────────────┘ └──────────────┘ │ │ │
│ └────────────────────────────────────────────────────────────────┘ │ │
│ │ │
│ External Networks: │ │
│ • PSTN/ISDN (via GMSC) ◄─── B ─────────────────────────────────────┘ │
│ • Other PLMNs (roaming) ◄─── E ──────────────────────────────────────┘
│ │
└─────────────────────────────────────────────────────────────────────┘
Uu Interface: The radio interface between UE and Node B (UTRAN). This is the WCDMA air interface operating at 5 MHz bandwidth.
| Interface | Between | Protocol | Function |
|---|---|---|---|
| Iub | Node B ↔ RNC | NBAP (Node B Application Part) | Radio resource management, control of Node B |
| Iur | RNC ↔ RNC | RNSAP (Radio Network Subsystem App. Part) | Soft handover support, macro-diversity |
| Iu | RNC ↔ CN | RANAP (Radio Access Network App. Part) | Connection management, mobility management |
| Iu-CS | RNC ↔ MSC | RANAP over ATM/IP | Circuit-switched services |
| Iu-PS | RNC ↔ SGSN | RANAP over ATM/IP | Packet-switched services |
| Interface | Between | Protocol | Purpose |
|---|---|---|---|
| C | MSC ↔ HLR | MAP (Mobile App. Part) | Routing info, subscriber data |
| D | VLR ↔ HLR | MAP | Location updates, subscriber data |
| E | MSC ↔ MSC | MAP/ISUP | Handover coordination |
| Gs | MSC ↔ SGSN | BSSAP+ | Combined CS/PS mobility |
| Gr | SGSN ↔ HLR | MAP | PS subscriber data |
| Gd | SGSN ↔ SMS-GMSC | MAP | SMS delivery via PS domain |
| Gn | SGSN ↔ GGSN | GTP (GPRS Tunneling Protocol) | Packet routing within PLMN |
| Gp | SGSN ↔ GGSN (diff. PLMN) | GTP with security | Inter-PLMN packet routing |
| Gi | GGSN ↔ External PDN | IP | Connection to Internet/corporate nets |
UMTS employs a layered protocol architecture based on the OSI model, with specific protocols designed to handle the unique requirements of mobile wireless communications.
The control plane handles signaling between UE and network, including connection management, mobility management, and radio resource control.
Protocols between UE and Core Network:
Protocols between UE and UTRAN:
The physical layer implements WCDMA technology:
The MAC layer manages logical channels and maps them to transport channels. Key functions include:
The RLC layer provides three modes of operation:
| Mode | Description | Use Case |
|---|---|---|
| Transparent Mode (TM) | No RLC overhead, no segmentation/reassembly | Broadcast channels (BCCH, PCCH) |
| Unacknowledged Mode (UM) | Segmentation/reassembly, no retransmission | Real-time services (voice, streaming) |
| Acknowledged Mode (AM) | Segmentation, reassembly, ARQ retransmission | Non-real-time data (downloads, web) |
PDCP exists only for packet-switched services. Its functions include:
RRC is the main control protocol in UTRAN, handling:
UMTS defines a three-layer channel architecture: Logical Channels (what is transmitted), Transport Channels (how it is transmitted), and Physical Channels (actual radio transmission).
┌─────────────────────────────────────────────────────────────────┐
│ UMTS CHANNEL HIERARCHY │
├─────────────────────────────────────────────────────────────────┤
│ │
│ LOGICAL CHANNELS TRANSPORT CHANNELS PHYSICAL │
│ (L2 - MAC) (L1 - Layer 1) CHANNELS │
│ │
│ ┌─────────────────┐ ┌─────────────────┐ ┌──────────┐ │
│ │ Control │ │ Common │ │ Primary │ │
│ │ • BCCH │──────►│ • BCH │────►│ CCPCH │ │
│ │ • PCCH │ │ (Broadcast) │ │ (S-CCPCH)│ │
│ │ • DCCH │ ├─────────────────┤ ├──────────┤ │
│ │ • CCCH │ │ Common │ │ Primary │ │
│ │ • SHCCH │──────►│ • FACH │────►│ CCPCH │ │
│ │ • CTCH │ │ • PCH │ │ (S-CCPCH)│ │
│ └─────────────────┘ │ (Forward Access │ ├──────────┤ │
│ │ / Paging) │ │ PRACH │ │
│ ┌─────────────────┐ ├─────────────────┤ │ PCPCH │ │
│ │ Traffic │ │ Dedicated │ ├──────────┤ │
│ │ • DTCH │──────►│ • DCH │────►│ DPCH │ │
│ │ • CTCH │ │ (Dedicated) │ │ (DPDCH + │ │
│ └─────────────────┘ ├─────────────────┤ │ DPCCH) │ │
│ │ Common │ ├──────────┤ │
│ │ • RACH │────►│ AICH │ │
│ │ • CPCH │────►│ CSICH │ │
│ │ • DSCH │────►│ PDSCH │ │
│ │ • HS-DSCH │────►│ HS-PDSCH │ │
│ └─────────────────┘ └──────────┘ │
│ │
└─────────────────────────────────────────────────────────────────┘
Logical channels define the type of information being transferred. They are classified into Control Channels (for signaling) and Traffic Channels (for user data).
| Channel | Name | Direction | Description |
|---|---|---|---|
| BCCH | Broadcast Control Channel | DL | Broadcasts system information to all UEs in cell |
| PCCH | Paging Control Channel | DL | Transmits paging information for UE in idle mode |
| CCCH | Common Control Channel | UL/DL | Signaling between UE and network (RRC connection) |
| DCCH | Dedicated Control Channel | UL/DL | Dedicated signaling for specific UE (active connection) |
| DTCH | Dedicated Traffic Channel | UL/DL | User data for specific UE (voice, packet data) |
| CTCH | Common Traffic Channel | DL | Point-to-multipoint user data (e.g., MBMS) |
| SHCCH | Shared Channel Control Channel | UL/DL | Control for shared transport channels |
Transport channels define how data is transmitted over the radio interface, including coding, interleaving, and mapping to physical resources.
Physical channels are the actual radio transmission channels with specific carrier frequencies, scrambling codes, and channelization codes.
| Channel | Name | Function |
|---|---|---|
| CPICH | Common Pilot Channel | Phase reference for coherent detection, signal strength measurement |
| CCPCH | Common Control Physical Channel | Carries BCH (P-CCPCH) and FACH/PCH (S-CCPCH) |
| DPCH | Dedicated Physical Channel | Carries DCH (DPDCH for data, DPCCH for control) |
| SCH | Synchronization Channel | Cell search and synchronization (P-SCH and S-SCH) |
| PICH | Paging Indicator Channel | Indicates upcoming paging message on PCH |
| AICH | Acquisition Indicator Channel | Confirms RACH preamble reception |
| HS-PDSCH | High Speed Physical Downlink Shared Channel | HSDPA data transmission |
| Channel | Name | Function |
|---|---|---|
| PRACH | Physical Random Access Channel | Carries RACH preamble and message |
| PCPCH | Physical Common Packet Channel | Carries CPCH (contention-based packet data) |
| DPDCH | Dedicated Physical Data Channel | Carries user data (I/Q multiplexing) |
| DPCCH | Dedicated Physical Control Channel | Carries pilot, TPC, TFCI, FBI |
| HS-DPCCH | HS-Dedicated Physical Control Channel | HSDPA feedback (CQI, ACK/NACK) |
UMTS represents the evolution from 2G GSM to 3G mobile communications, introducing WCDMA technology while maintaining backward compatibility with the GSM core network. The architecture is divided into three main components:
First UMTS standard with basic WCDMA, separating CS and PS domains.
Introduced TD-SCDMA (TDD mode) and all-IP core network options.
Added HSDPA (High Speed Downlink Packet Access) for enhanced data rates.
Introduced HSUPA (High Speed Uplink Packet Access) for symmetric high speeds.
HSPA+ enhancements with MIMO, higher order modulation, reaching 42+ Mbps.