3G UMTS networks: What is UMTS and why does it use WCDMA?

The third generation of mobile networks, also referred to as 3G, is primarily enabled by two cellular technologies: UMTS (Universal Mobile Telecommunication System) and CDMA2000 (Code Division Multiple Access Year 2000). UMTS is the 3G migration path used by the most widely deployed second-generation (2G) technology, GSM.

UMTS (Universal Mobile Telecommunication System) is a third-generation cellular technology that allows 2G GSM networks to migrate to 3G. UMTS employs Wideband CDMA (WCDMA) for its radio interface to enable peak download data rates of up to 2 Mbps and average download speeds of around 384 kbps.

What is 3G UMTS (Universal Mobile Telecommunication System)?

While many of us mostly think about 4G and 5G as the key mobile technologies in recent times, the third-generation (3G) cellular technologies arguably were game-changers in the mobile telecom industry. Before 3G, the perception of mobile phones was primarily voice, text and a limited amount of web browsing.

With 3G, video streaming on a mobile phone became a reality, which played an instrumental role in shaping the mobile broadband market as we know it today. If you have ever used a 3G USB dongle as an internet source for your laptop, you may already have benefited from UMTS.

UMTS (Universal Mobile Telecommunication System) is a third-generation (3G) mobile communications technology that allows 2G GSM networks to migrate to 3G. UMTS employs WCDMA and uses circuit and packet switching to deliver voice calls, text messages and mobile data with peak speeds of up to 2 Mbps.

UMTS and CDMA2000 were the leading technologies of the 3G era. UMTS is a 3G standard specified by 3GPP (Third Generation Partnership Project), Release 1999. CDMA2000, on the other hand, was developed as part of another project, 3GPP2.

UMTS was the 3G migration path for the well-known second-generation GSM networks (Global System for Mobile Communications). GSM later saw the GPRS and EDGE enhancements that introduced packet-switching into GSM networks. Like GPRS and EDGE, UMTS delivers voice calls and text messages through circuit-switching and mobile data through packet-switching.

UMTS and CDMA2000 are the two key paths for the 3G network deployments worldwide. CDMA2000 (Code Division Multiple Access – Year 2000) provided the 3G migration path for 2G cdmaOne networks (IS-95). We have a dedicated post on CDMA2000 and IS-95 if you want to learn more about these technologies.

The 3G UMTS networks allowed mobile phone users to enjoy bit rates of up to 384 kbps, higher than the data rates 2G GSM networks could enable. UMTS networks can enable maximum theoretical download bit rates of up to 2 Mbps and average download bit rates of up to 384 kbps.

Before the launch of UMTS, the GSM EDGE enhancement (shown on the mobile phone as the E symbol) offered maximum theoretical download speeds of up to 384 kbps, but the real-life average was between 130-200 kbps.

For GSM customers, UMTS meant buying a new phone that could work with the new WCDMA standard. UMTS is the technology that led to the introduction of High-Speed Packet Access (HSPA) which we normally see on mobile phones as the H or H+ symbol like the picture below.

Does UMTS use CDMA or WCDMA?

3G UMTS employs Wideband Code Division Multiple Access (WCDMA or W-CDMA) for the radio access network to enable wireless connectivity. Unlike CDMA2000, which uses narrowband carriers, UMTS uses wideband carriers and supports carrier bandwidths of 5 MHz, 10 MHz and 20 MHz, where 5 MHz is most common.

UMTS networks employ Code Division Multiple Access (CDMA) as the access technology, which enables peak downlink bit rates of up to 2 Mbps. The earlier GSM networks are based on a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).

WCDMA is used in FDD UMTS networks because it is spectrally more efficient than FDMA and TDMA used by GSM networks. It uses unique codes instead of unique frequency carriers to separate users within a cell, allowing all cells in an area to use the same carrier frequency without interference.

CDMA is also used by the other key 3G technology, CDMA2000, but in UMTS, the CDMA technology is called Wideband CDMA because the bandwidth of the channels is wider than what is used by CDMA2000 networks. Channel bandwidths of 5 MHz, 10 MHz and 20 MHz were possible in UMTS, but 5 MHz was the channel bandwidth that was mostly deployed.

For 3G UMTS migration, GSM radio networks were upgraded to the WCDMA technology. The core network architecture did not change because the earlier GSM enhancements, GPRS and EDGE, had already introduced new network nodes, SGSN and GGSN, for the packet-switched capability.

UMTS networks were backwards compatible, which means any 3G mobile phone could still connect to the 2G GSM networks. GSM and UMTS networks were also well-integrated to support GSM <-> UMTS Inter-technology handovers (IRAT – Inter Radio Access Technology). Please have a look at our dedicated post for more information on SGSN and GGSN.

How does the 3G UMTS network work?

When GSM networks were originally launched, they were based on the circuit-switched technology for voice, SMS and data services. The data services were offered through Circuit-Switched Data (CSD), and High-Speed Circuit Switched Data (HSCSD).

CSD and HSCSD technologies were not efficient, so changes were made to the network architecture when GPRS (General Packet Radio Service) got introduced. GPRS was launched before UMTS, and it introduced two new network nodes, GGSN and SGSN, into the mobile core network to support packet-switched data.

UMTS network inherited the same core network architecture introduced at the time of GPRS/EDGE enhancements. The core network continued using the MSC for circuit-switched functions such as voice and text and SGSN for the packet-switched data services. The other core network components, HLR, AuC and EIR, also exist in the UMTS network.

The UMTS radio access network is called UTRA or Universal Terrestrial Radio Access. UMTS can operate in both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes. Most UMTS deployments follow the FDD mode which is based on the Wideband Code Division Multiple Access (WCDMA) technology.

The TDD version of UMTS uses the Time Division Synchronous Code Division Multiple Access (TD-SCDMA) technology. Developed in China, TD-SCDMA uses the same frequency band for both uplink and downlink communication.

The table below shows the mapping between GSM and UMTS network components.

The later enhancements in the UMTS network, including High-Speed Packet Access (HSPA) and Evolved High-Speed Packet Access (HSPA+), are based on the same network architecture. Have a look at a simplified network diagram showing GSM and UMTS networks. When 4G LTE technology was introduced, new core network components were added to the architecture to allow LTE and UMTS networks to coexist and work together.

What is the frequency range for 3G UMTS?

UMTS networks can operate in FDD (Frequency Division Duplex) and TDD (Time Division Duplex). The frequency range differs slightly for FDD and TDD and is also location dependent. UMTS can operate in different frequency bands, including 850 MHz, 900 MHz, 1700 MHz and 2100 MHz.

UMTS employs various frequency ranges within the 850 MHz, 900 MHz, 1700 MHz and 2100 MHz bands for different geographical regions. Generally, with FDD, the frequency band for Europe and Africa is 2110-2170 MHz in the downlink and 1920-1980 MHz in the uplink. For America, this range changes to 1930-1990 MHz in the downlink and 1850-1910 MHz in the uplink.

UMTS supports carrier bandwidths of 5 MHz, 10 MHz, and 20 MHz, but 5 MHz is the standard bandwidth. For Evolved HSPA (HSPA+), the channel bandwidth is 10 MHz.

How is UMTS different from HSPA, HSPA+ and LTE?

UMTS networks provided the 3G technology as part of 3GPP Release 1999, which saw the introduction of HSPA and HSPA+ in later 3GPP releases.

UMTS is the underlying technology that supports voice calls, text messages and data. HSPA enhances UMTS by enabling high-speed download and upload speeds. HSPA combines HSDPA (High-Speed Downlink Packet Access) and HSUPA (High-Speed Uplink Packet Access).

HSPA can offer peak download speeds of up to 14.4 Mbps and peak uploads of up to 5.76 Mbps. With Evolved HSPA (HSPA+), the peak data rates improved to 42 Mbps for downloads and 11.5 Mbps for uploads.

LTE or Long Term Evolution of mobile networks, is a fourth-generation technology that provides a 4G migration path to third-generation UMTS and CDMA2000 networks. 4G LTE networks do not replace 3G UMTS, but they both coexist so that when a phone user is in an area where LTE coverage is not available, they can still access the mobile network through 3G UMTS.

The most noticeable difference for an average phone user is the speed; the original LTE networks can provide average download speeds of between 15-20 Mbps (in the UK). The advanced LTE networks can provide average speeds of around 50-80 Mbps (UK). LTE networks can generate higher peak data rates than the earlier CDMA-based 3G networks, which you can learn more about in our dedicated post on 4G LTE and LTE-Advanced.

Conclusion

UMTS stands for Universal Mobile Telecommunication System, and it is a third-generation mobile cellular technology that allows 2G GSM networks to migrate to 3G. UMTS is one of the leading 3G technologies alongside CDMA2000, and it is the successor of the most widely deployed 2G standard, GSM.

UMTS was specified in the 3GPP release 1999, and it employs Wideband Code Division Multiple Access (WCDMA) for its radio interface. It enables theoretical bit rates of 2 Mbps and real-life download data rates of up to 384 kbps. UMTS networks also provided the underlying technology for the HSPA and HSPA+ enhancements that improved download and upload speeds in the 3G networks.