The testing went on for eight weeks, one week for each candidate. Elab was to have been first but all the others accepted its request to wait until last: it was the smallest contestant and could use the seven extra weeks. Elab, which consisted of Maseng and his colleague Odd Trandem, attracted a few smiles: “Since Elab is attached to a technical institute and has no manufacturing capability, it would appear to have little chance of success,” was the comment from Communications Systems Worldwide magazine in its autumn issue.

Maseng recalls how he and Trandem viewed with some bewilderment “the candidates from the large companies who came with whole caravans of trucks”. They had been able to pack their equipment in two small wooden crates.

The selection criteria for GSM had been decided earlier in the program. The system selected had to be substantially better than existing analog systems in at least one respect and at least as good in the others. The criteria were:
• Most efficient use of the spectrum 
• Best sound quality
• Greatest potential for the development of handheld telephones (viability)
• Greatest potential for the development of data-transfer solutions 
• Lowest cost for mobile telephones 
• Lowest infrastructure costs.

COMPARABLE RESULTS

One thing that had to be decided in advance was how to make measurements that would give comparable results. Because the frequencies had to be used sparingly, it was agreed to select the system that could transmit the most traffic in a restricted frequency band (the spectral efficiency of the system). The capacity to cope with interference from a base station on the same frequency was also to be taken into account. Indeed, the more robust the system, the closer together base stations on the same frequency could be located.

The values to be measured in a number of defined scenarios were therefore: How much bandwidth did the system need (Hz/bit) and how much interference could it withstand (C/I, dB)? On the basis of these values it would be possible to calculate the system’s spectral efficiency.

It turned out that two of the Franco-German candidates had based their proposals on wideband TDMA (channel width 2 MHz), and the other two on narrowband TDMA (channel width 300 KHz). All the Nordic systems were based on narrowband TDMA.

The Paris tests revealed that the digital solution was superior to analog systems and that sound quality at a rate of 13.4 kbps maintained the level required as standard in fixed public networks. This, says Haug, meant that an unresolved question that had been on the GSM agenda for more than four years had finally been answered.

Author: Svenolof Karlsson & Anders Lugn

RADIO TESTING IN PARIS

The media may not have understood radio testing in Paris, but this illustration proved popular among participants.

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