How are AMPS and D-AMPS different from GSM and CDMA?

AMPS and D-AMPS are cellular technologies that existed during the first and second generations of mobile networks. While second-generation (2G) cellular technologies still exist today, both AMPS and D-AMPS are now obsolete and have been replaced by GSM and CDMA mobile networks.

AMPS was a first-generation (1G) cellular technology, and D-AMPS was a second-generation (2G) cellular technology. D-AMPS was the digital version of AMPS that used a combination of FDMA and TDMA to enable mobile communications. AMPS is now obsolete, and D-AMPS has been replaced by GSM or IS-95 networks.

AMPS or Advanced Mobile Phone System was a leading first-generation (1G) cellular technology that used FDMA to enable analogue cellular communications. D-AMPS (Digital Advanced Mobile Phone System) was the digital version of AMPS and a second-generation (2G) technology that applied TDMA (Time Division Multiple Access) to AMPS.

AMPS and D-AMPS have been replaced by GSM or IS-95

In the early 1990s, there were two leading second-generation (2G) technologies: GSM (Global System for Mobile Communications) and D-AMPS (Digital Advanced Mobile Phone System). By the mid-1990s, a new technology, IS-95 (Interim Standard 1995), emerged, which would later become one of the leading second-generation technologies.

IS-95 (cdmaOne) was the first-ever mobile network to use the Code Division Multiple Access (CDMA) technology for the air interface. While GSM continued to dominate the global 2G network deployments, the CDMA-based IS-95 became the other leading 2G technology.

As a result, there have been two primary tracks for the evolution of mobile networks, one following the GSM path and the other following the CDMA path. In the late 1990s, before the arrival of 3G, two dedicated collaboration groups, 3GPP and 3GPP2, were formed to manage these two tracks.

The 3GPP-led second generation (2G) technology is GSM which uses Universal Mobile Telecommunication System (UMTS) for 3G migration. On the other hand, the 3GPP2-led second-generation (2G) technology is IS-95 which used cdma2000 for migrating to 3G.

Second-generation D-AMPS networks have now been dismantled and replaced by either IS-95 or GSM networks. Digital Advanced Mobile Phone System (D-AMPS) was based on Interim Standard 136 (IS-136) and followed the CDMA route for 3G migration.

What is Advanced Mobile Phone System – AMPS?

AMPS stands for Advanced Mobile Phone System, and it was an analogue technology standard that was among the leading first-generation (1G) cellular technologies. It was introduced in the early 1980s in the US, followed by other countries. The first generation of mobile networks (1G) started in a very decentralised way.

1G employed a range of different technologies, including AMPS in the US, NMT ( Nordic Mobile Telephone) in Scandinavia, C-Netz (Radio Telephone Network C) in Germany, TACS (Total Access Communication System) in the UK and Ireland, and JTACS (Japanese Total Access Communication System) in Japan.

TACS was a variant of AMPS, and it was used not only in UK and Ireland but also in some other European countries. Even though Japan was the first country to launch a commercial cellular network in 1979, it later adopted JTACS for its 1G journey. JTACS was a slightly modified version of TACS.

AMPS, like other 1G technologies, was based on Frequency Division Multiple Access (FDMA) for the radio access to connect mobile phones to the mobile network. It employed frequency bands from 824 MHz to 894 MHz for communication over the air interface. This range includes separate frequency bands for downlink (forward link) and uplink (reverse link). The channel bandwidth in AMPS was 30 kHz.

What is Digital Advanced Mobile Phone System – D-AMPS?

D-AMPS or Digital Advanced Mobile Phone System is the digital version of AMPS that uses a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) for the air interface. It is specified by Interim Standard 136 or IS-136 and is also referred to as TDMA.

D-AMPS is the digital upgrade path for AMPS, that enabled the second generation (2G) of mobile networks in the US and various other countries. Like GSM, the most widely deployed second-generation (2G) technology standard, D-AMPS was launched in the early 1990s.

Like AMPS, D-AMPS employs the 824 MHz to 894 MHz frequency band for the radio access network. This frequency band is split into 824 MHz to 849 MHz for the reverse channel or uplink (cell phone to the base station) and 869 MHz to 894 MHz for the forward link or downlink (base station to the cell phone).

The uplink and downlink frequency bands are divided into pairs of 30 kHz frequency channels through FDMA. Each 30 kHz channel is further split into three (3) timeslots by applying TDMA. Techniques like digital voice compression are also utilised to use the available network capacity efficiently.

The communication in D-AMPS networks is encrypted to ensure network security. Since the digital networking in D-AMPS is achieved through Time Division Multiple Access (TDMA), D-AMPS is also often referred to as TDMA.

As per the IS-136 specifications, second-generation D-AMPS networks include features like text messaging and circuit-switched data (CSD) in addition to traditional voice calling.

D-AMPS was similar to 2G GSM networks

Digital Advanced Mobile Phone System (D-AMPS) as a technology standard has common grounds with the most widely deployed second-generation (2G) GSM networks. GSM, like D-AMPS, employs a combination of FDMA and TDMA for its air interface.

GSM supports multiple frequency bands, including 850 MHz, 900 MHz, 1800 MHz and 1900 MHz. The frequency band in GSM is first split into uplink and downlink sub-bands and then further into pairs of 200 kHz frequency channels.

The 200 kHz channel bandwidth of GSM networks is considerably higher than the 30 kHz bandwidth used by D-AMPS. Each GSM channel is further divided into eight (8) timeslots.

From an end-user perspective, the GSM networks initially offered voice calls, text messages and circuit-switched data (CSD), which is similar to D-AMPS. However, GSM networks later introduced a packet-switched technology General Packet Radio Service (GPRS), which changed the landscape of mobile data.

D-AMPS networks were based on circuit-switching, which was sufficient for voice calls and text messages but not efficient enough for mobile data. By replacing D-AMPS networks with GSM or IS-95, the packet-based mobile data technology became available to the customers. GPRS and IS-95B are packet-switched enhancements for GSM and IS-95 networks, respectively.

Here are some helpful downloads

Thank you for reading this post. I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need extra support, especially when preparing for a new job, studying a new topic, or buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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