1G - First Generation networksSkip content
1G - First Generation mobile phone networks were the earliest cellular systems to develop, and they relied on a network of distributed transceivers to communicate with the mobile phones. First Generation phones were also analogue, used for voice calls only, and their signals were transmitted by the method of frequency modulation. These systems typically allocated one 25 MHz frequency band for the signals to be sent from the cell base station to the handset, and a second different 25 MHz band for signals being returned from the handset to the base station. These bands were then split into a number of communications channels, each of which would be used by a particular caller.
In the case of AMPS, the first 1G system to start operating in the USA (in July 1978), each channel was separated from the adjacent channels by a spacing of 30 kHz, which was not particularly efficient in terms of the available radio spectrum, and this placed a limitation on the number of calls that could be made at any one time. However, the system was a multiple access one, because a second caller could use the same channel, once the first caller had hung up. Such a system is called "frequency division multiple access" (FDMA).
In addition, because the cell transmitter's power output is restricted and designed to cover a specific area, it is possible to use the same frequencies in other cells that are far enough away for there to be no interference - this system is called frequency re-use, and enables the network capacity to be increased. The cellular structure of the network is also responsible for another feature of cell phone communications, i.e. that it is necessary for some sort of handover to take place when the mobile phone passes from one cell area to another, and this requires that the pair of frequencies used by the phone are changed at the time of handover.
NMT 450, the Nordic Mobile Telephone System using the 450 MHz band, was the first cell phone network to start operating in Europe (i.e. Scandinavia) in 1981. Later, in 1985, the United Kingdom began operations with its TACS (Total Access Communications System). With the introduction of 2G networks, the 1G phones were destined to become obsolete, as they were not adaptable to the new 2G standards and also had other drawbacks, such as their poor security due to the lack of encryption, and the fact that anyone with a receiver tuned to the right frequency could overhear the conversation.