UMTS

Mobile telephone networks of the third generation (3 G) have been operating in Germany since 2004. They are based on the digital transmission standard UMTS (Universal Mobile Telecommunications System). The frequency range allocated to the networks is between 1920 and 2170 MHz. Other mobile radio frequencies can be used as well. 3G is sometimes also referred to as WCDMA. The abbreviation is derived from the initials of the channel access method Wide Code Division Multiple Access employed by UMTS.

Radio network cells

Functional principles

As with GSM technology, the areas to be served are divided into so-called cells, each of which is supplied by stationary transmitter stations (base stations). At a base station, often three antennas are installed which provide three sectors, each covering an angle of 120°, with one radio channel each.

In UMTS-networks data are transferred differently than in GSM: no set frequency channels and time slots are allocated to individual connections, but all network subscribers use the available frequency band at the same time. UMTS systems typically operate at a channel bandwidth of 5 MHz. The single data streams are identified by an individual code and are spread to the width of the available frequency band. Using the known code, the data stream intended for the receiver is then decoded by the receiver from the received signal mixture.

Higher data transmission rate makes UMTS networks multimedia capable

A significantly higher data transmission rate can be achieved with UMTS than with GSM and the data transfer methods GPRS (General Packet Radio Service) and EDGE (Enhanced Data Rates for GSM Evolution) based on GSM. UMTS networks are multimedia capable, that is, they can transfer images, sound and data. However, the networks are also used for traditional mobile telephony.

Frequency division duplexing

So-called frequency division duplexing is preferably used to distinguish the data sent by the base station from that sent by the mobile phone according to the information provided by the producers. This means that another frequency band is used for the connection from the base station to the mobile phone than in the opposite direction. The signal has a noise-like character.

Another possibility is so-called time division duplexing. Here the same frequency band is alternately used in both directions of the connection. The signal is pulsed. This method is currently only intended for smaller networks such as company internal networks.

Transmitter power

Fine and fast adjustment of the transmitter power ensures the trouble-free operation of a UMTS network. This applies to base stations as well as to mobile terminals. To minimise mutual interference, the handsets operate at the lowest possible transmitter power levels.

During connection setup the transmitter power is increased in quick succession only until a stable connection between terminal and base station has been established. Compared to GSM networks, terminals in UMTS networks show opposite behaviour: In GSM networks a high transmitter power is used at the beginning of a connection setup. The transmitter power is reduced to the required level only after the connection has been established.

Extensions

With the mobile communications standards HSPA (High Speed Packet Access) and HSPA+ based on UMTS even a higher data transmission rate can be achieved than with the original UMTS technology. The improvements originate mainly from the introduction of superior modulation techniques and improved antenna technologies.