2.1 Mobile Telephony
2.1.1 Cellular Systems
The concept of cellular coverage was initially developed by AT&T/Bell Laboratories. Prior to that, the mobile telephony systems were manual systems used only for mobile voice telephony. Typically implemented with high masts that covered large areas, and with limited capacity per mast, they were only able to service few users at the same time – in some cases even only one call per mast! These systems also lacked the ability to hand over calls between masts, so mobility was limited to the specific coverage area from the servicing antenna, although in reality the coverage area was so large that only rarely would you move between coverage areas. Remember that, at that point, there were no portable mobile telephones, only vehicle-installed terminals with roof-top antennas. Over time the use of mobile telephony became increasingly popular and the idea was born that the network needed to be divided into more and smaller cells, accommodating more capacity for more users, implementing full mobility for the traffic and enabling the system to hand over traffic between these small cells.
From this initial concept several cellular systems were developed over time and in different regions of the world. The first of these cellular systems was analog voice transmission, and some ‘data transmission’ modulated into the voice channel for signaling the occasionally handover or power control command.
Some of the most used standards were/are AMPS, D-AMPS, ...