UMTS Tutorial : Features, Network Architecture, Advantages, Disadvantages and Comparisons

The Universal Mobile Telecommunications System (UMTS) is a third-generation (3G) mobile communication technology that provides high-speed data transfer and enhanced voice services over mobile networks. It was introduced as a successor to the 2G GSM network, bridging the gap between the narrowband GSM and the more advanced fourth-generation (4G) LTE technology. This tutorial on UMTS (3G-WCDMA) covers its network architecture, channels, frame structure, applications, advantages, disadvantages and comparison of 3G UMTS with 2G GSM and 4G LTE.

UMTS technology Overview

UMTS stands for Universal Mobile Telecommunications System. It came into existence from GSM technology developed by 3GPP. UMTS network composed of three main parts UE (User Equipment), Radio Access Network (RAN) and Core Network. UMTS is released in several phases by 3GPP standard body as shown below. UMTS is also referred by 3G. The main features of 3G standardization by ITU includes support for circuit and packet switching, support for both voice and data applications, support for seamless mobility for both voice and data, improvement in spectral efficiency, legacy support for GSM/GPRS systems, increase in voice quality, low round trip packet delay and more. Following table mentions UMTS releases with features.

Release Feature introduced
R99 WCDMA air interface introduced in UMTS
R4 IPMS (IP Multimedia Service) introduced on network side
R5 HSDPA
R6 HSUPA + Fractional DPCH
R7 HSPA, MIMO, higher modulation scheme 64QAM, continuous packet connectivity and Flexible RLC
R8 LTE, Dual cell HSDPA
R9 DC HSUPA
R10 LTE Advanced, Multi cell HSDPA
R11 8 carrier HSDPA

UMTS (3G) Features

UMTS offers range of features as follows that make it significant improvements over its predecessors.
• Data rates up to 2 Mbps
• Employs W-CDMA technology which allows multiple users to share the same frequency band simultaneously.
• Uses OVSF (Orthogonal Variable Spreading Factor) which maintains orthogonality between different channels, minimizing interference.
• Uses fast power control techniques to adjust the transmission power of UEs and Node B to maintain signal quality
• Employs soft handovers, where the UE can simultaneously connect to multiple base stations, improving connection reliability
• Modulation : QPSK for downlink, BPSK for uplink , Spreading followed by Scrambling techniques are used.
• Harmonized spectrum allocation worldwide
• Provides differentiated QoS classes
• Offers Advanced services such as real time video streaming, video conferencing etc.

UMTS network architecture and working

The UMTS network architecture is more complex than its 2G counterpart, incorporating various functional entities for voice and data service management. The key components of the UMTS network are as follows.
1. User Equipment (UE): The mobile device used by the subscriber, including handsets and data cards, is referred to as the UE. It interfaces with the UMTS network to access voice, video, and data services.
2. Radio Access Network (RAN): The UMTS RAN, also known as UMTS Terrestrial Radio Access Network (UTRAN), consists of Node B (base stations) and Radio Network Controllers (RNC). The RNC manages the radio resources and handover functions.
3. Core Network (CN): The CN is responsible for managing user sessions, mobility, and call control. It consists of Circuit-Switched Core (CS Core) and Packet-Switched Core (PS Core). CS core handles voice and video call services. PS core manages data services such as internet browsing and multimedia messaging.
4. HLR and VLR : These databases store subscriber information and enable location tracking and authentication.
5. GPRS Support Nodes (GSN): GSNs, such as the Gateway GPRS Support Node (GGSN) and Serving GPRS Support Node (SGSN), facilitate packet data transfer and routing.

UMTS network Architecture

How UMTS works : When a user initiates a service, the UE sends a request to the UMTS network through the UTRAN. The RNC allocates radio resources and ensures proper communication with the core network. Depending on whether the service is voice or data, it will be routed through the CS Core or PS Core, respectively.

UMTS Frame structure

UMTS Frame structure

The UMTS frame structure defines how data is organized and transmitted over the air. The frame format is essential for maintaining synchronization and efficient data transfer in the network. A UMTS radio frame is divided into 15 time slots, each lasting 0.667 milliseconds. The entire frame duration is 10 milliseconds. Each time slot is further divided into chips, and the standard chip rate for UMTS is 3.84 Mcps (Mega chips per second).
➨Refer UMTS Frame Structure>>.

UMTS Channels

WCDMA logical channels transport channels physical channels mapping

UMTS defines three main categories of channels: Logical Channels, Transport Channels, and Physical Channels. Each category serves a specific function in the network, facilitating the smooth transfer of voice, data, and signaling information.
• Logical channels : They define what type of information is transmitted over the network. Includes control channels (BCCH, PCCH, DCCH) and traffic channel (DTCH).
• Transport channels : They define how data is transmitted over the air interface. Includes BCH, DCH, RACH and FACH.
• Physical channels : They are responsible for transmitting the actual data over the air using specific modulation, coding, and scrambling techniques. Includes PDSCH, PUSCH and DPCH.
➨Refer UMTS channel types>>.

3G UMTS Applications

Following are the applications of UMTS technology.
• Video Calling: High-quality video calls are enabled by the higher data rates provided by UMTS.
• Mobile Internet Browsing: Faster data speeds make UMTS suitable for web browsing, streaming, and social media access.
• Multimedia Messaging Service (MMS): UMTS facilitates the sending of multimedia messages containing images, audio, and video clips.
• Telemedicine: Real-time data transfer and video communication enable telemedicine applications.
• Mobile Gaming and Entertainment: With reduced latency and higher speeds, UMTS supports multiplayer gaming and streaming services.

Advantages of UMTS (3G-WCDMA)

Following are the benefits of UMTS 3G WCDMA system.
1. Provides significantly higher data speeds compared to GSM networks, supporting multimedia applications and high-speed internet.
2. Utilizes W-CDMA, which improves spectrum efficiency and enhances network capacity.
3. Differentiated QoS classes ensure optimal performance for voice, video, and data services.
4. Harmonized frequency bands support global roaming for UMTS subscribers.

Disadvantages of UMTS

Following are the drawbacks of 3G UMTS WCDMA system.
1. The deployment of UMTS infrastructure is costlier compared to GSM due to the need for new hardware and software upgrades.
2. Network management and operation are more complex than GSM, requiring additional expertise and maintenance.
3.Due to higher data rates and continuous connection requirements, UMTS devices may consume more battery power.
4. Early UMTS devices were not backward-compatible with GSM networks, leading to interoperability issues.

Comparison of UMTS with GSM and 4G LTE

Following table compares 3G UMTS with 2G GSM and 4G LTE.

Feature GSM (2G) UMTS (3G) LTE (4G)
Data Rate Up to 14.4 kbps Up to 2 Mbps Up to 1 Gbps
Technology TDMA/FDMA W-CDMA OFDMA
Voice Quality Basic Enhanced HD Voice
Mobility Basic handover Soft handover Seamless mobility
Spectrum Efficiency Low Moderate High
Latency High Moderate Low
QoS Support Limited Differentiated QoS classes Advanced QoS
Applications Voice, SMS Voice, Video Call, Internet Voice, High-Speed Data, IoT, AR/VR

Conclusion

UMTS played a critical role in the evolution of mobile communication technologies by offering enhanced voice and data services, paving the way for the 4G LTE technology that succeeded it. Despite being gradually replaced by LTE, UMTS remains widely used in many regions, providing essential communication services. This UMTS tutorial on 3G WCDMA technology is very useful for beginners in wireless mobile cellular technology domain to understand the key concepts and features.

References

3GPP TS 25.201, Physical layer general description
3GPP TS 25.101, UARFCN

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