Global System for Mobile Communications (short: GSM) – behind this boring term hides the democratization of mobile telephony. The then Finnish Prime Minister Harri Holkeri spoke to the Deputy Mayor of Tampere, Kaarina Suonio, about the commercial start in Finland on July 1, 1991. Telenokia and Siemens had set up the network used for telephone calls. At the same time, network expansion began in reunified Germany. It took another year, however, before you could actually buy cell phones and make digital calls while on the move.
The Telekom predecessor Deutsche Bundespost set up the A network in what was then the Federal Republic of Germany from 1958 – so the former FRG became one of the first countries in the world with mobile communications. In principle, since then one can “call” or be called while on the go. But the devices for the A-Netz were so heavy, bulky and hungry for electricity that they could only be accommodated in larger cars. The calls were made by hand, the self-dial service that is taken for granted today did not even exist in all parts of the Federal Republic of Germany’s landline network. The technology for the “public mobile radio service” (öbL) initially cost around 15,000 D-Marks, that is as much as three VW Beetles. With a maximum of 11,000 participants, the network was hopelessly overloaded at the beginning of the 1970s. It was followed by the B and then the C network. But that too was bursting at the seams at the beginning of the 1990s with around 700,000 users, and in the metropolitan areas there was often no way through.
It doesn’t work without new technology
It was clear: If telephoning while on the move should not only be reserved for business people and fiddlers, new technology and new networks would have to be found. The GSM developed from 1982 onwards was supposed to do this. Digital instead of analog voice transmission uses radio channels more efficiently, making space for more conversations and participants. The change to higher frequencies (German C network: 400 to 470 megahertz – MHz, millions of oscillations per second) from initially 900, later 1800 MHz (internationally also 800 and 1900 MHz) for GSM seems absurd in view of the range, because lower frequencies spread better. In fact, this only helps in a network with few radio towers and participants. The network of base stations designed for GSM should be closely meshed – it is sufficient if a mast covers a radius of a few kilometers. Too much range would even be counterproductive, because then the signals from the individual cells would interfere with each other. In the open field, a 900 MHz tower covers a maximum radius of 35 kilometers, an 1800 MHz mast around eight. For the record: The GSM specifications also contain the frequency bands from 400 to below 800 MHz – but they were never used.
Since the users should be able to move freely between the individual base stations and speak without interruption, they had to and must be able to pass calls from one mast to the next. This handover was introduced with the C network. In the previously operated A and B networks, however, the connection was broken when leaving the radio cell. Also known from the C network: the SIM card, with which you can be reached on various devices under your number.
Efficiency through time slot
However, the significant increase in efficiency at the time resulted – in addition to the use of data reduction for voice transmission – the combination of frequency and time multiplex. In the original D network, 124 channels were available for transmission in the range from 890 to 915 MHz and the same number of channels for reception between 935 and 960 MHz (frequency division multiple access – FDMA). Each of these channels could be used by several subscribers at the same time because one of eight timeslots, each 577 microseconds short, is assigned to each mobile phone using time division multiple access (TDMA).
At the start of 1991, the Deutsche Bundespost demonstrated its GSM-based D network on the former Stuttgart exhibition center on Killesberg – only there were no telephones yet. The technology reached consumers exactly one year later, when Telekom started with D 1. Rival Mannesmann started one day earlier, on June 30, 1992. The prices 29 years ago were solid: Telekom wanted 3190 D-Marks for their cheapest – initially hardly available – mobile phone, the call minute on D 2 hit 1.44 D -Mark to beech. There were also basic fees of almost 80 D-Marks per month. No wonder that the technology got off to a cautious start – the end devices were a little cheaper than those for the C network, but still a long way from today’s bargain tariffs.