UMTS

The Third Generation mobile cellular technology developed by 3GPP^TM - known variously as Universal Mobile Telecommunications System (UMTS^TM), Freedom of Mobile Multimedia Access (FOMA), 3GSM, ..., is based on wideband code division multiple access (W-CDMA) radio technology offering greater spectral efficiency and higher bandwidth than GSM^TM.

UTRAN

The UMTS^TM Radio Access Network (UTRAN) technology is specified in the 3GPP^TM TS 25.-series specifications. The specifications cater for Frequency Division Duplex (FDD) and Time Division Duplex (TDD) forms, with high (3.84 Mc/s) and low (1.28 Mc/s) chip rate flavours. (Low chip rate TDD was developed in China, but may well be deployed elsewhere.) Other chip rates (e.g. 7.68 Mc/s) were subsequently added. Maximum commonality between FDD and TDD variants is assured by a single set of higher layer protocols and shared physical layer parameters, as far as possible.

UTRAN was originally specified for operation in several bands in the 2 GHz range (3GPP^TM TS 25.101). Subsequently, UTRAN has been extended to operate in a number of other bands, including those originally reserved for Second Generation (2G) services. Nominal carrier spacing is 5 MHz (1.6 MHz for the low-rate TDD option, 10 MHz for the 7.68 Mc/s option). Contrast this with GSM's 200 kHz channel spacing.

The UTRAN radio technology is direct-sequence CDMA. Each 10 ms radio frame is divided into 15 slots, with 2560 chips/slot at 3.84 Mc/s. Modulation is 16QAM and turbo coding gives high speed packet access. A flexible radio protocol allows multiplexing of several services (speech, video, data...) on a single carrier. Real-time and non-real-time services are catered for by configurable quality of service parameters (delay, bit error probability, frame error ratio). The architecture allows for point-to-point and also point-to-multipoint services (broadcast, multicast).

As a development of the original radio scheme, a high-speed download packet access (HSDPA, offering download speeds potentially in excess of 10 Mbit/s), and an uplink equivalent (HSUPA, also sometimes referred to as EDCH) were developed. Collectively the pair are tagged HSPA, and permit the reception of multimedia broadcast/multicast, interactive gaming and business applications, and large file download rivalling traditional terrestrial or satellite digital broadcast services and fixed-line broadband internet access. The radio frames are divided into 2 ms subframes of 3 slots, and gross channel transmission rates are around 14 Mbit/s.

3GPP's radio access undergoes continuous development, and the 'long-term evolution' exercise aims to extend the radio technology to keep UMTS^TM highly competitive to potential rival technologies, with data rates approaching 100 Mbit/s by the end of the decade.