Work on NMT
The Nordic mobile telephone group was officially called NT-R 69-5 (Nordic Teleconference-Radio, 1969-working group 5). Bokstam was appointed chairman – he was also head of the MTD project – and Haug was secretary, both of them representing Televerket.
The first meeting of the group was held January 14–15, 1970, at Televerket’s offices in Farsta in southern Stockholm. Åsdal welcomed the participants but did not take part in the detailed discussions. The participants at this first meeting – which was to be followed by more than 100 others – were P.K. Olesen from Denmark, E. Jalli from Finland, J.R. Veastad, N.A. Grimsmo and R.A. Torvik from Norway, and P. Wilsson, T. Haug and H. Bokstam from Sweden.
The group’s mission was defined as “exploring the possibilities of future extension of compatible Nordic public mobile-telephone systems, preferably in the form of a joint system. This system would probably be automatic although a manual system cannot be totally ruled out.”
Its first task was to develop a frequency plan for a joint Nordic system. One criterion was that subscribers should be able to travel over a large area, even across national borders, with a limited number of channels in the mobile equipment. “The group therefore devoted nearly all its time during the first year to matching the mobile systems in the three [largely contiguous] countries,” Haug recalls.
The NMT (Nordic Mobile Telephony) group referred to subscribers who moved from one base station area to another as “roamers”; in the systems that existed in the early 1970s, they accounted for 10 percent of subscribers in Denmark and 20 percent in the Oslo region. To make telephone calls independent of a vehicle’s location, two fundamental problems had to be overcome: the system had to be able to locate the subscriber’s position; and an ongoing call had to be transferred automatically from one base station to the next.
The group coined the concept of roaming to cover the first of these functions and handover (or handoff in America) for the second.
At two meetings in 1970 and 1971, the NMT group heard about some experiences in Australia. A representative of L.M. Ericsson’s Australian subsidiary attended to describe the automatic telephone system being planned there. The group took great interest in the technique for locating subscribers. As the mobile terminals continually monitored and measured the signal strength of the closest base stations, the system was always able to determine which base station was best to call. However, this system would not be able to cope with the transfer of ongoing calls between stations.
The NMT group completed its frequency plan in the autumn of 1970. The border areas between Denmark-Sweden and Sweden-Norway, which required coordinated planning, had by then been studied in detail. The Danes contacted the German telecommunications agency to inform it of what was going on in the Nordic countries and discuss any possible impact around the Danish-German border. The guideline adopted was that the position of base stations had to be agreed with neighboring countries if a national border was less than 110 kilometers away.
Where other regulations for the use of radio transmitters were concerned, including restrictions on their movement, Sweden, Denmark and Norway decided that these could be set “using administrative procedures,” while Finland required legislative amendments.
Norway also said it wanted coordination between mobile telephony and communication with aircraft (alongside aviation channels).
Author: Svenolof Karlsson & Anders Lugn
This is the proposal that the NMN groups first chairman Håkan Bokstam put together.