Advanced Mobile Phone System
Advanced Mobile Phone System or AMPS is the analog mobile phone system standard, introduced in the Americas during the early 1980s. Though analog is no longer considered advanced at all, the relatively seamless cellular switching technology AMPS introduced was what made the original mobile radiotelephone practical, and was considered quite advanced at the time.It was the first-generation technology, using FDMA, which has inherent problems with capacity and security. Each cell has 416 channels or frequencies in the 824~849MHz range for transmissions from mobile stations, paired with 416 channels in the 869~894MHz range for transmissions from base stations, and must use a different set than neighboring cells to avoid interference. This significantly reduces the number of channels available at each site in real-world systems. Each AMPS channel pair is 30kHz wide. The AMPS band was taken from the same 806~890MHz frequency band which was originally UHF TV channels 70~83. (The remainder went mostly to public safety use, after the few TV stations using those channels were required to move.)
Later, AMPS was upgraded to D-AMPS using digital TDMA, called second-generation or 2G. The D-AMPS standard is also known as IS-54. IS-54 was supplanted by IS-136, which added many of the features found in competing GSM and CdmaOne standards, such as text messaging and circuit switched data. This increased capacity by dividing each 30kHz channel pair into three time slots and digitally compressing the voice data, yielding three times the call capacity at the expense of voice quality. It also made calls more secure because analog scanners could not access digital signals, and new scanners in the U.S were prohibited by the FCC from accessing cellphone frequencies.
Total Access Communication System or TACS is the European version of AMPS. ETACS was an extended version of TACS with more channels. TACS and ETACS are now obsolete in Europe, having been replaced by the more scalable and all-digital GSM system.