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. Like first-generation systems, various types of second-generation technology have been developed. The three most successful variants of secondgeneration technology are Interim Standard 136 (IS-136) TDMA, IS-95CDMA, and the Global System for Mobile communications (GSM). Each of these came about in very different ways.
IS-136 and IS-54
IS-136 and IS-54
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 signaling 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.
Today AMPS, IS-54B, and IS-136 are all in service. AMPS and IS-54 operate only in the 800-MHz band, whereas IS-136 can be found both in the 800-MHz band and in the 1900-MHz band, at least in North America. The 1900-MHz band in North America is allocated to Personal Communications Service (PCS), which can be described as a family of second-generation mobile communications services.
occupying 30 KHz. Some of the channels, known as control channels, are dedicated to control signaling 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.
Today AMPS, IS-54B, and IS-136 are all in service. AMPS and IS-54 operate only in the 800-MHz band, whereas IS-136 can be found both in the 800-MHz band and in the 1900-MHz band, at least in North America. The 1900-MHz band in North America is allocated to Personal Communications Service (PCS), which can be described as a family of second-generation mobile communications services.
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