All the changes AMPS (Advanced Mobile Phone System) invented by Bell Labs and first installed in the United States in 1982. In all mobile phone system, a geographic region divides up into cells, which is why the devices are sometimes called cell phones.
In AMPS cells they are typically 10 to 20 km across in digital systems the cells are smaller. Each cell uses some set of frequencies not used by any neighbors. The key idea that gives cellular systems for more capacity than previous systems is the use of relatively small cells and the reuse of transmission frequencies in nearby cells. Thus, the cellular design increases the system capacity by at least an order of magnitude, more than cells get smaller. Smaller cells mean that the less power is needed, which leads to smaller and cheaper transmitters and handsets.
Working of AMPS :
- In an area where the number of users has grown to point that the system is overloaded, the power can be reduced and the overloaded, the power can be reduced and the overloaded cells split to small micro cells to permit more frequency reuse. At the center of each cell is base station to which all telephones in the cell transmit.
- The base station consists of computer and transmitter/receiver connected to antenna. In small system all the base station are connected to a single device called MSC (Mobile Switching Center) or MTSO(Mobile Telephone Switching Office).
- The MSCs are essential to ending offices as in telephonic systems and are in fact connected to at least one telephone system end office.
- At any instant mobile telephone is logically in one specified cell and under the control of that cell base station. The telephone is then informed of its new boss and if a call is in progress, it is asked to switch to new channel.
- This process called handoff takes about 300 msec. Channel assignment is done by the MSC, the nerve center of system. The base stations it is really just dumb radio relays.
- It is an analog system and based on initial electromagnetic spectrum allocation for cellular service by the federal communication commission.
- It uses frequency division multiple access for multiple simultaneous conversations.
- When the number of conversations is very high it requires high bandwidth.
- It was first to use hexagonal cells.
- Cells in AMPS are 10 km to 20 km across.
- Since, it was analog technology, it suffers from noise and eavesdropping.