European Analog Systems: NMT and TACS
Europe developed several national analog cellular systems before GSM. NMT and TACS became the most visible examples. Both used frequency-division access and analog speech, yet they followed different regional specifications. NMT emphasized a common Nordic system with inter-network roaming. TACS adapted the AMPS approach to the United Kingdom's 900 MHz allocation and channel plan. A handset designed for one radio plan therefore did not automatically work with the other system.
Nordic Mobile Telephone (NMT)
NMT was developed through cooperation between Denmark, Finland, Norway, and Sweden in the late 1970s, with Iceland joining the common area later. The first European NMT-450 services entered operation in Sweden and Norway in 1981, followed later by Denmark and Finland. It was one of the first systems designed from the beginning to operate across national borders. NMT-900 followed in 1986 as the 450 MHz systems approached their capacity limits. The system used analog frequency modulation for speech and for access.
Radio variants
- NMT-450: The lower band provided a large coverage area and better penetration for a given site layout. Large cells suited the sparsely populated Nordic regions, while the smaller channel pool limited capacity. The representative European specifications use 25 kHz channel spacing, 5 kHz peak FM deviation, and 1.2 kbit/s signaling.
- NMT-900: The higher band enabled a denser channel plan and smaller cells in areas with heavier traffic. Its shorter individual coverage required a denser site layout, but it served more subscribers in cities. The system used the same 25 kHz channel spacing in the representative system table. Some NMT-900 plans used an interleaved 12.5 kHz raster.
A lower frequency can improve coverage and penetration for a comparable antenna site, while capacity still depends on the number of assigned channels and the reuse plan. Moving from 450 MHz to 900 MHz therefore addressed capacity through a denser deployment and a larger channel resource rather than through a change from analog to digital transmission.
Both variants used paired frequencies for the direction to the site and the direction to the handset. The channel remained reserved for the call, while signaling controlled assignment, release, and handover. Changing the band improved radio planning options, but it did not introduce digital speech coding.
Roaming and signaling
was included in the NMT design from the beginning. A subscriber travelling from Sweden to Norway could register with a compatible visited network, while the operators exchanged the information needed for routing and billing. Participating operators exchanged the subscriber and routing information needed to let a handset use a visited NMT network while retaining its home subscription. NMT also provided automatic handover between cells and access to the public switched telephone network. Its speech path remained analog, and the original system did not provide a GSM-like standardized cryptographic protection layer.
NMT in Poland
Poland introduced its first public cellular network in 1992 under the PTK Centertel name. It used the NMT-450i variant, an improved form of NMT-450. The 450 MHz allocation supported broad rural and intercity coverage with relatively few cells, while the available channel count limited capacity in dense areas. Service was expensive, and large handsets such as the Mobira Talkman became recognizable equipment for early business subscribers. The network continued after GSM deployment and was closed near the end of the first decade of the 2000s.
NMT-450i remained a voice service with automatic transfer between cells. Broad coverage from one site reduced the number of locations needed, while the same channel could serve only one conversation at a time in a cell. The design therefore traded territorial coverage for capacity in busy areas.
Total Access Communication System (TACS)
TACS was an AMPS-derived analog cellular system selected for the United Kingdom instead of creating a completely new specification. Public cellular services began in 1985, with networks operated by Vodafone and Telecom Securicor Radio, known as Cellnet. TACS used the 900 MHz band, FDD, analog FM speech, and FDMA.
Channel plan and signaling
The representative TACS specifications use 25 kHz channel spacing, compared with 30 kHz for AMPS. The narrower raster fit more channels into the allocation and required different modulation parameters. The same comparison lists 9.5 kHz peak FM deviation and 8 kbit/s control-channel signaling for TACS, compared with 12 kHz and 10 kbit/s for AMPS. These values describe the radio plan and control signaling; they do not make TACS a digital speech system.
- AMPS channel spacing:
- TACS channel spacing:
- TACS peak deviation:
- TACS control signaling:
The control channel carried access requests, handset identity information, and call handling messages, while the voice channel used analog FM. The narrower TACS channel increased the number of assignments in the band, yet it retained the interception and cloning problems of analog 1G systems.
ETACS extension
ETACS, or Extended TACS, expanded the available channel set within the TACS family. Operators used it to increase subscriber capacity and reduce congestion as the British cellular market grew, especially in large cities. The extension retained the analog FDMA model, so it improved the channel resource without adding the digital authentication, ciphering, and SMS framework later associated with GSM. The TACS family was also used in parts of Europe, Asia, and Africa.
Why the 1G Systems Were Replaced
NMT and TACS delivered practical mobile voice service, but their analog radio paths and regional specifications imposed clear limits. Capacity grew by adding channels and sites rather than by digitally sharing a radio resource.
- Privacy: Original deployments did not have a common cryptographic air-interface protection comparable with GSM. Analog speech could be received by equipment tuned to the channel.
- Capacity: FDMA kept a full radio channel assigned to one call for its duration. Capacity therefore depended directly on the fixed channel pool and reuse plan.
- Service scope: Signaling was available, and some operators added specialized services, but the family had no common SMS and packet-data service.
- Interworking: NMT roaming worked among participating NMT networks. A single-system TACS handset still could not use the NMT air interface because the channel plan and signaling specification differed.
GSM answered these constraints with a harmonized digital radio interface, TDMA time slots, subscriber authentication, radio-link ciphering, and standardized core-network signaling. NMT and TACS therefore form an important technical bridge between early analog cellular service and the interoperable digital systems that followed. The common GSM specification replaced several regional plans with one model for terminals, subscriber identity, and roaming.
Migration to GSM involved more than replacing transmitters. Operators introduced a digital interface, new subscriber identity procedures, and a new core-network model, while users received SMS, greater capacity, and radio-link protection. That combination closed the NMT and TACS period. In practice, both generations coexisted during a transition because analog terminals and base stations were withdrawn in stages. NMT service remained available locally until GSM coverage expanded.