Wireless Future - Evolution -> 2G (2nd generation of mobile networks)

Again, Daniel Collins and Clint Smith (2002) state that unlike first-generation systems, which are analog, second-generation systems are digital. The use of digital technology has a number of advantages, including increased capacity, greater security against fraud, and more advanced services. They point out three major technologies that were introduced in second generation namely, IS-54B and IS-136, GSM and CDMA.

Like first-generation systems, various types of second-generation technology have been developed. The three most successful variants of second-generation technology are Interim Standard 136 (IS-136) TDMA, IS-95 CDMA, and the Global System for Mobile communications (GSM). Each of these came about in very different ways.

1. IS-54B and IS-136

IS-136 came about through a two-stage evolution from analog AMPS. As described in more detail later, AMPS is a frequency division multiple access (FDMA) system, with each channel occupying 30 KHz. Some of the channels, known as control channels, are dedicated to control signalling and some, known as voice channels, are dedicated to carrying the actual voice conversation.

The first step in digitizing this system was the introduction of digital voice channels. This step involved the application of time division multiplexing (TDM) to the voice channels such that each voice channel was divided into time slots, enabling up to three simultaneous conversations on the same RF channel. This stage in the evolution was known as IS-54 B (also known as Digital AMPS or D-AMPS) and it obviously gives a significant capacity boost compared to analog AMPS. IS-54 B was introduced in 1990.

2. GSM

Daniel Collins and Clint Smith (2002) discuss, why there was a need for a global system for mobile communications and CDMA technology. Although NMT had been introduced in Europe as recently as 1981, the Europeans soon recognized the need for a pan-European digital system. There were many reasons for this, but a major reason was the fact that multiple incompatible analog systems were being deployed across Europe. It was understood that a single Europe-wide digital system could enable seamless roaming between countries as well as features and capabilities not possible with analog systems. Consequently, in 1982, the Conference on European Posts and Telecommunications (CEPT) embarked on developing such a system. The organization established a group called (in French) Group Speciale Mobile (GSM). This group was assigned the necessary technical work involved in developing this new digital standard. Much work was done over several years before the newly created European Telecommunications Standards Institute (ETSI) took over the effort in 1989. Under ETSI, the first set of technical specifications was finalized, and the technology was given the same name as the group that had originally begun the work on its development—GSM.

The first GSM network was launched in 1991, with several more launched in 1992. International roaming between the various networks quickly followed. GSM was hugely successful and soon, most countries in Europe had launched GSM service. Furthermore, GSM began to spread outside Europe to countries as far away as Australia. It was clear that GSM was going to be more than just a European system; it was going to be global. Consequently, the letters GSM have taken on a new meaning—Global System for Mobile communications.

3. CDMA

Although they have significant differences, both IS-136 and GSM use Time Division Multiple Access (TDMA). This means that individual radio channels are divided into timeslots, enabling a number of users to share a single RF channel on a time-sharing basis. For several reasons, this technique offers an increase in capacity compared to an analog system where each radio channel is dedicated to a single conversation. TDMA is not the only system that enables multiple users to share a given radio frequency, however. A number of other options exist—most notably Code Division Multiple Access (CDMA).