UMTS: carrying the world on its shoulders

The Holy Grail of mobile phone companies is to offer customers one phone that works anywhere in the world

For effective, efficient communications, standardisation is critical, and nowhere is this more evident than in the areas of mobile computing and cellular telephony.

If you need data access or email through your cellphone you’re likely to be using one of two different technologies. The first is called Code Division Multiple Access (CDMA), and it is the basis for the major network services offered by Telecom in New Zealand. While it is popular in the US and parts of South East Asia, it plays second fiddle to the competing standard, GSM (Global System for Mobile communications).

GSM uses a Time Division Multiple Access approach to frame structure. GSM service is the network technology of choice at Vodafone worldwide as well as for numerous other carriers.

Both CDMA and GSM are second-generation (2G) technologies, and they have co-existed for several years. Each technology has its supporters. CDMA phones are engineered specifically for an individual carrier, whereas GSM phones make use of a removable memory card called the Subscriber Identity Module (SIM). Physically smaller than a secure digital flash memory card, a SIM card contains all the key information required to activate a phone, including the user’s telephone number, personal identification number, address book and encoded network identification details. A user can easily move a SIM from one phone to another.

Although GSM phones are interoperable with one another, different countries use different parts of the frequency spectrum, so “world phones” typically must be capable of using several frequencies.

Today, the fastest growing use of cellular networks is for the transmission of all kinds of data and rich media, including websites, video, music, images and maps, and driving directions. The older 2G networks simply couldn’t handle that volume of traffic, and they couldn’t offer the speed needed for transmitting large files. The answer was to make the services faster and build out the networks to deal with more traffic.

Here, too, the CDMA and GSM paths continued their separate but parallel development. CDMA brought us CDMA2000 and the 1xRTT networks. The most recent developments are 1x Evolution Data Optimised, or EVDO, as operated by Telecom in New Zealand, and 1x Evolution Data/Voice, or EVDV.

Similarly, GSM begat General Packet Radio Service, or GPRS, which begat Enhanced Data Rates for GSM Evolution, or EDGE.

EDGE was developed to enable the transmission of large amounts of data at a high speed, 384kbit/sec. The latest generation is called Wideband Code Division Multiple Access (WCDMA).

And this finally brings us to the Universal Mobile Telecommunications System.

The International Telecommun-ication Union (ITU), a specialised agency of the United Nations, has attempted to coordinate these competing technologies to improve throughput and increase interoperability. The International Mobile Telecommunications 2000 standard is a third-generation digital communications specification from the ITU. And the European (that is, GSM-based) implementation of IMT-2000 is UMTS, which is based on WCDMA. Previous cellular telephone data systems were mostly circuit-switched, requiring a dedicated connection. WCDMA is packet-switched, using the Internet Protocol. The first commercial WCDMA network was launched in Japan in 2001.

UMTS has been specified as an integrated application for mobile voice and data systems with wide-area coverage. Using globally harmonised spectrum in paired and unpaired bands, early implementations of UMTS offer theoretical bit rates of up to 384kbit/s in situations where the mobile device is actually moving. The current goal is to achieve 2Mbit/s when both ends of the connection are (at least temporarily) stationary.

UMTS operates on radio frequencies identified by the ITU IMT-2000 specification document and licensed to operators, using a 5MHz-wide channel that simplifies deployment for network providers that have been granted large, contiguous blocks of spectrum. Most UMTS systems use frequencies between 1,885 and 2,025 MHz.

UMTS assigns separate carrier frequencies to incoming and outbound signals, a process called frequency division duplexing (FDD). For symmetric traffic, such as two-way videophones, FDD is highly efficient, allowing uplink and download data rates to be equal, in contrast to technologies such as Asymmetric Digital Subscriber Line service, which typically offers upload rates that are much slower than its download rates. FDD reduces interference and wastes no bandwidth in switching from transmitting to receiving.

Ongoing work within the Third Generation Partnership Project promises increased throughput speeds over the WCDMA Radio Access Network. High-Speed Downlink Packet Access and High-Speed Uplink Packet Access technologies are already standardised, and commercial operators in Asia and North America are putting them through network trials.

Vodafone New Zealand has just launched its own HSDPA upgrade and will roll it out nationwide in the coming months. With theoretical download speeds as high as 14.4Mbit/s and uplink speeds of up to 5.8Mbit/s, these technologies will make it possible for UMTS to offer data transmission speeds comparable to those of wired networks.

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