6.5.2 Public mobile radio communication systems

During the period under review, the following public mobile radio communication networks were in operation in Austria, in addition to public trunked radio communication networks (TETRA is the European ETSI standard for the digital area), which are used by companies or authorities:

• four GSM networks (the networks of Mobilkom, max.mobil., Connect and tele.ring) with digital voice transmission at the air interface),
• one mobile radio communications network (the D network of Mobilkom) with analog speech transfer at the radio interface.

Each of these networks had its own infrastructure, which covers the entire Austrian federal territory. Call connections within one network can therefore be implemented without having to resort to the services of other networks. In order to facilitate call connections to other networks, several switching exchanges to other fixed and/or mobile radio communications networks are interconnected directly or indirectly.

The infrastructure of a mobile radio communications system consist essentially of the following components:

Access network:

• base stations (BTS - Base Transceiver Station)
• base station controllers (control units for groups of base stations)
• connections between these network components

Transport network (core network):

• mobile switching centers (switching exchanges)
• connections between these network components

The connections between the aforementioned network components in the access or the core network are implemented with the operator's own lines, leased lines or by means of radio relay.

The base stations consist of antennae that are mounted on masts or building roofs, and switching cabinets that contain the necessary technical transmission equipment). The connection to the mobile units (mobile phones) is set up by means of radio transmission via the base stations. A base station has a range between about one kilometer and 30 kilometers. In order to secure full coverage in Austria, one operator needs 2,000 to 3,000 base stations. In areas where an operator must handle a very big volume of traffic, i.e. in regions where there are many telephone calls, further base stations must be built, in addition to those basically required for coverage. These are often so-called micro cells, using very small antennae, which are mounted on buildings, only a few meters above the street level. Micro cells cover an area with a diameter of several hundred meters and are used in densely populated urban areas.

Several dozens of base stations each are linked to a base station controller, which is responsible for the logical control of these base stations. These connections are mostly implemented by leased lines (Mobilkom), or by leased lines and via radio relay (max.mobil. and Connect).

Several base station controllers, in turn, are connected and linked to the exchanges. Every GSM operator has about ten to 20 mobile switching centres (MSC). Data bases provided at the exchanges know the whereabouts of every subscriber and can forward incoming calls to subscribers. A distinction is made between the Home Location Register (HLR), where the data on the whereabouts of the subscriber assigned to the MSC in question are stored, and the Visitor Location Register (VLR), where data for subscribers from other MSCs are stored. Whenever the "visitors" are subscribers of another network, they are called roaming subscribers (Roaming). In the world of GSM, roaming is provided, as a rule, between networks in different countries.

For public mobile radio communication systems - such as digital GSM - separate frequency ranges are laid down in the frequency usage plans. Parts of this frequency range will be allocated to mobile radio communication operators, who therefore have different frequency ranges at their exclusive disposal. The frequency range used for GSM are 900 MHz (GSM 900) or 1800 MHz (GSM 1800 - previously called DCS 1800). In addition to voice telephony, the larger part by far of the generated traffic comes from data services at transmission rates of up to 9.6 kbit/s, which providers offer. WAP (Wireless Application Protocol) is a protocol that facilitates Internet access to WAP pages, already with these low data rates, and their presentation on the small display of mobile terminals. Since 2000, with the use of HSCSD (High Speed Circuit Switched Data) and GPRS (General Packet Radio Service) GSM offers (for the respective terminal equipment) higher data rates (with GPRS the future target value in the final expansion stage is more than 100 kbit/s). As of 2002, the mobile communications system UMTS/IMT-2000 will be launched, which will facilitate multi-media services, in particular, with data rates of up to 2 Mbit/s.

In addition to GSM, which is widely distributed worldwide, several countries also operate mobile radio communication networks with analog voice telephony at the air interface, such as the D network in Austria (900 MHz frequency range). These networks can be regarded as forerunners to GSM. They offered limited functionalities. For example, data transmission and short-message services (SMS) are available only within certain limits.

Satellite systems, such as INMARSAT, are also used for mobile communications. INMARSAT uses geo-stationary satellites at an altitude of about 36,000 km and facilitates communication to almost every place on earth. The radio connection is between the mobile unit, which is much bigger than a conventional GSM unit, and a satellite. The capacity, i. e. the number of subscribers per square kilometer that can be serviced, is much lower with satellite systems than with GSM. Low-orbit systems (LEO, MEO systems) are under development or have not been able to gain market acceptance (e.g. IRIDIUM).

Paging systems only make it possible to send a message to a subscriber. They are increasingly being replaced by GSM.

In addition to the aforementioned systems, which all may also be used by private customers, there are systems that are specifically adapted to the communications need of companies and undertakings. These so-called trunked radio systems work similarly to GSM, but permit more comprehensive group communication and a very fast call set-up. The users of such systems will be, for example, the police, the fire brigade, ambulance services, construction businesses or taxi companies. So far, the individual organisations have built up, operated and used their own trunked radio networks. The standard defined by ETSI for digital trunked radio systems is in the 400 MHz range.

Fig. 69 gives an overview of the frequency bands for GSM 900, GSM 1800, DECT and the future UMTS/IMT-2000.