There have been lots of technologies in the evolution of mobile communications which can a bit confusing especially when you hear two terminologies that sound quite similar. One such confusion can be AMPS vs. D-AMPS which is what we will answer in this article.
AMPS and D-AMPS are two separate technologies, the first one is analogue and the other is digital. AMPS was the analogue technology used for the first generation (1G) of mobile networks while D-AMPS is the digital version of AMPS used for the second generation (2G) of mobile networks.
What is AMPS?
AMPS stands for Advanced Mobile Phone System, and it was the analogue technology standard used for the first generation (1G) of mobile networks in the US which was followed by other countries. It was introduced in the early 1980s. AMPS employed frequency bands from 824 to 894 MHz for communication over the air interface including uplink and downlink frequencies. It used Frequency Division Multiple Access (FDMA) for connecting mobile phones to the mobile networks. AMPS used frequency channels of 30 kHz bandwidth.
The other 1G technologies that existed in other parts of the world at the same time as AMPS were NMT (Nordic Mobile Telephone), C-NETZ (Radio Telephone Network C) and TACS (Total Access Communications System). NMT was used in nordic countries, C-NETZ mainly in Germany and TACS mainly in the UK.
What is D-AMPS?
D-AMPS stands for Digital Advanced Mobile Phone System and is the digital upgrade path for AMPS. It was used for the second generation (2G) of mobile networks in the US and various other countries. D-AMPS was launched in the early 1990s in the same era when GSM (Global System for Mobile Communications) was launched. D-AMPS uses the same frequency band for communication as AMPS which is 824 MHz to 894MHz.
The frequency band is divided into two with 824-849 MHz for the uplink (Mobile phone to Base Station) and 869-894MHz for the downlink (Base Station to Mobile phone). The allocated uplink and downlink frequency bands are first divided into frequency channels of 30 kHz each using FDMA, and then TDMA is applied which further breaks each of these 30 kHz channels down into three (3) time slots. Digital voice compression is also used to make efficient use of the existing capacity.
The communication in D-AMPS networks is also encrypted to ensure security. Seemingly due to the fact that TDMA was applied to this digital version of AMPS, it is often referred to as TDMA, which can be a bit confusing considering it uses both FDMA and TDMA. Interestingly, GSM, which is the most widely deployed 2G standard, also uses a combination of FDMA and TDMA for its air interface. The other prominent technology for 2G that existed at the same time as D-AMPS and GSM was cdmaOne or IS-95.