4 Technology

Note: Most of the underlying technological aspects of UMTS are common among all W-CDMA variants. Please see W-CDMA for more info. The followings are some technical information specific to UMTS, not shared by FOMA or other W-CDMA implementations.

Simply put, UMTS is the combination of the W-CDMA air interface (the protocol that defines over-the-air transmissions between UMTS mobile phones and towers), GSM's MAP (Mobile Application Part) core (the protocol that provides mobile functionality like to route calls to and from mobile subscriber), and the GSM family of speech codecs like AMR and EFR (the protocols which defines how audio is digitized, compressed and encoded). Techincally speaking, W-CDMA (as per the definition of IMT2000) is merely the air interface, while UMTS is the complete stack of communcation protocols designated for 3G global mobile telecommunications and as a direct successor to GSM. However, W-CDMA is frequently used as a general, umbrella term to collectively refer to the family of 3G standards that uses WCDMA as its air interface, that includes UMTS, FOMA and J-Phone.

Like other real-world W-CDMA implementations, UMTS uses a pair of 5Mhz channels, one in the 1900 MHz range for uplink and one in the 2100 MHz range for downlink. In contrast, cdma2000 uses one or more arbituary 1.25 MHz channels of each direction of transmissions. UMTS is frequently being criticized for its heavy bandwidth requirements.

The specific frequency band s originally defined by the UMTS standard are 1885-2025 MHz and 2110-2200 MHz, for uplink and downlink respectively. See #External Links at the bottom of this page for a map of UMTS frequency allocation.

For existing GSM operators, it is a simple but costly migration path to UMTS: most of the rest of their infrastructures may remain the same, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers can still be prohibitively expensive.

A major difference of UMTS compared to GSM is the air interface forming Generic Radio Access Network (GRAN). It can be connected to various backbone networks like the Internet, ISDN, GSM or to a UMTS network. GRAN 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.

5 Interoperatibility and global roaming

At the air interface level, UMTS itself is incompatible with GSM. Though all UMTS phones sold today (as of 2004) are UMTS/GSM dual-mode phones, hence they can also make and receive calls on regular GSM networks. If a UMTS customer travels to an area without UMTS coverage, a UMTS phone will automatically switch to GSM (roaming charges may apply). If the customer travels outside of UMTS coverage during a call, the call will be transparently handed off to available GSM coverage.

Regular GSM phones cannot be used on the UMTS networks.

Japan Telecom (now Vodafone Japan) has a 3G network called J-Phone, which uses W-CDMA technology and is compatible with UMTS. This make UMTS the first truly global wireless standard. The current global wireless standard, GSM, is available everywhere in the world except Japan and Korea.

NTT DoCoMo's 3G network, FOMA, uses W-CDMA as well, but it's incomaptible with UMTS. However, NTT Docomo has a 20% interest in 3UK and 18% interest in AT&T Wireless. These foreign interests serve as test-bed for their future global roaming solutions. (as of March 2004)

All UMTS/GSM dual-mode phones should accept existing GSM SIM cards. You can possibly roam on UMTS networks using GSM SIM cards (as in the case of how an existing GSM customer may roam on J-Phone's network in Japan).

In the United States, UMTS will initially be offered (by AT&T Wireless) on the 1900 MHz spectrum only, due to exisiting limitation of spectrum allocated in the United States. UMTS phones designated for the US will be unlikely to be operable overseas and vice versa, mirrors the current situation of GSM phones and GSM networks in the US use different frequencies from those used in the rest of the world. However, the FCC has made reasonable promises to free up additional spectrum in the 2100 MHz band, and most UMTS licensees seem to consider ubiquituous, transparent global roaming an important issue. The possibility of ubiquituous, transparent UMTS global roaming remains to be seen. (as of May 2004)

6 Spectrum allocation

Over 120 licenses have already been awarded to operators worldwide, specifying W-CDMA radio access technology that builds on GSM. With the technology still emerging, politicians hurriedly set up license auctions, which funneled billions of dollars in license fees into cash starved public budgets. In Germany alone, license holders paid a total 50.8 billion euros. As the technology is still immature, revenue from these licenses will only start to trickle in 2004.

The UMTS spectrum allocated by ITU is already used in the USA. The 1900 MHz range is used for 2G ( PCS) services, and 2100 MHz range is used by the military. FCC is trying to free up the 2100 MHz range for 3G services, though it will still mean UMTS in the USA will have to share some spectrums with existing 2G services in the 1900 MHz band. 2G GSM services in most of the rest of the world uses the 900 MHz and 1800 MHz bands and hence do not share any spectrum with planned UMTS services.

Until the FCC allocates new spectrum specifically for 3G, there will be no firm answer to what frequencies UMTS will operate on in the United States. Currently, AT&T Wireless has committed to provide UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services.

7 Other competing standards

There are other competing 3G standards, such as CDMA2000 and proprietary systems including iBurst from Arraycom, Flarion and wCDMA-TDD (IPWireless). However, It is expected that 3GSM/UMTS will eventually inherit the global dominance of the GSM family to become the de-facto global standard for 3G.

Both CDMA2000 and WCDMA are accepted by ITU as part of the IMT-2000 faimly of 3G standards, in addtion to China's own 3G standard, TD-SCDMA, and EDGE.

CDMA2000, being an evolutionary upgrade to cdmaOne, does not require new spectrum allocation and will operate comfortably in existing PCS spectrums.

Most existing GSM operators take a wait-and-see approach to UMTS, due to the prohibitively high cost of obtaining new frequency spectrums and new equipments. So currently UMTS deployment is led by upstart 3, who does not have any existing GSM deployments.

Many GSM operators in the USA seem to have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, Cingular launched EDGE in limited markets, and T-Mobile USA plans to provide EDGE nationwide in the near future. The benefit of EDGE is that it leverages existing GSM spectrums and is compatible with existing GSM handsets. EDGE provides a short-term upgrade path for GSM operators and directly competes with CDMA2000.

8 Problems and issues

Some of the main problems operators still face are:

• the handover from an UMTS radio cell to a GSM radio cell
• handsets overweight, batteries not having enough capacity
• for fully fledged UMTS, with Video on Demand features, one base station needs to be set up every 100 meters, which while economically feasible in urban areas, remains impossible in less populated suburban and rural areas.
• competition for broadband access from Wi-Fi.
• whether they will be able to make money from new 'value added' services, or whether increased competition, greater supply, and the possibility of internet on mobiles will just cannibalise existing revenues.

9 See also

• W-CDMA: The technology UMTS is based on
• cdma2000: competing 3G standard, evolved out of the CDMA standard (aka IS-95 or cdmaOne)
• Wi-Fi: a local area wireless technology that is complemtary to UMTS, but undermines many of the early UMTS business models.
• Handset

10 External links

• UMTS FAQ on UMTS World
• Worldwide W-CDMA frequency allocations on UMTS World
• Worldwide UMTS Deployment on UMTS Forum
• UMTS TDD Alliance The Global UMTS TDD Alliance

mobile telephony standards

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