Advanced Mobile Phone Service
– AMPS Frequency Bands
– AMPS Control Channel
– Handover with AMPS
– Roll Out of AMPS
Total Access Communication System
Nordic Mobile Telephone

Analog Cellular Phone Standards

Advanced Mobile Phone Service

In the United States, Bell Laboratories had been working on a standard for a cellular telephone system since the 1960s. They worked together with Motorola, which focused primarily on the development of telephones. AMPS was intended to replace the outdated IMTS (Improved Mobile Telephone System), which was equivalent to the B-Netz telephone in Germany and was not a true cellular system. At the beginning of the 1980s, the AMPS standard was ready, tested and could be introduced.

AMPS Frequency Bands

From the start, AMPS had a lot of capacity available. A lower and upper band, each 20 MHz wide and 45 MHz apart, allowed 666 channels with a channel bandwidth of 30 kHz. The system was designed in a way, that several mobile operators could operated in parallel. An operator could apply for a corresponding license. The frequencies were very high compared to C-Netz: 825 MHz to 845 MHz in the lower band and 870 MHz to 890 MHz in the upper band. This means smaller cells or ranges.

AMPS Control Channel

As with the German C-Netz, there were dedicated channels for managing the mobile stations when they were not in a call. These special channels were called FOCC, Forward Control Channel and RECC Reverse Control Channel. These were purely digital channels. Here too, FSK was used with a speed of 10 kbit/s. The data is also protected by BCH codes in addition to repetitions (5 – 11 times).

Handover with AMPS

In addition to speech, a 6 kHz tone is also transmitted in a voice channel (traffic channel), the so-called Supervisor Audio Tone (SAT). The audio processing in AMPS is designed in a way, that this tone cannot be heard by the user. Both the mobile station and the base station measure the strength and the quality of the SAT. To do this, the strength of the noise in the channel (which is naturally always present) and the strength of the tone is measured. The signal/noise ratio is the measure of reception quality. If this drops below a specified limit, the system causes all neighboring base stations/cells to take measurements in the given channel. If a neighboring cell has significantly better values, a handover is initiated.

During the actual handover, the voice channel is briefly muted in order to use the channel for transmitting commands to manage the handover. This is so short that it practically goes unnoticed by the user. Anyhow, changing cells is rare in the majority of calls anyway.

Roll Out of AMPS

AMPS was introduced in Chicago in 1983. This was two years earlier than the German C-Netz. Many of the first devices were initially car phones, but also handsets came to the market soon. In September 1983 Motorola introduced the DynaTAC 8000X. It was published 8 years before the first C-Netz handheld devices came onto the market and was the first commercially available real cell hand phone in the world. It weighed 794 g and was 33 × 4.5 × 8.9 cm in size. That’s more than 1.3 liters. Nonetheless. An engineering sensation for the time. This phone became famous through the movie „Wall Street“ in which Michael Douglas often uses this device for his business. In the USA it was also called “The Brick”.

Total Access Communication System

Britain did not develop its own cellular telephone system. Instead, they decided to adapt AMPS. She called this customized system Total Access Communication System (TACS). The system was later expanded and then called ETACS. The frequency bands were higher than AMPS and the channels were narrower allowing up to 1000 channels. TACS was introduced in the UK in 1985, at the same time as the German C-Netz. Later also in Ireland and Italy as well as in most common wealth countries. Many AMPS phones were relatively easy to adapt for the TACS market. Alongside Motorola, Nokia has now established itself as a dominant manufacturer of mobile phones.

In 2001 the TACS Network was switched off.

Nordic Mobile Telephone

The Scandinavian countries, especially Sweden and Finland, developed their own mobile phone system which they called Nordic Mobile Telephone (NMT). NMT was also developed in the late 1970s and rolled out in the early 1980s.

Initially, bands in the 450 MHz range were available. This allowed for large radio cells. The system was structured similarly to AMPS. As in AMPS, the connection to the mobile stations was monitored with a constant tone, which was transmitted at 4 kHz and thus much closer to the voice signal. Like for AMPS, the quality of this tone, which was transmitted in both directions, led to the decision which cell took over the radio connection.

Many European countries, especially in the north east, adopted the NMT standard. Later there was an NMT system also for 900 MHz bands which was marketed as NMT900.

Two Scandinavian companies developed NMT and gained a lot of experience in mobile telephony. Nokia and Ericsson. In the 1980s, Nokia was still a company with various business areas. For example, it manufactured electronic devices such as televisions but also car tires and rubber boots. In 1981 they bought a car phone manufacturer: Mobira. Nokia thus had the first car phone for the NMT market. In 1985 they had their first handheld device, which was somewhat similar to Motorola’s DynaTEK. However, in those early years, the Nokia boss considered the mobile phone market to be a niche business. Nobody knew what the next 20 years would bring.