During the 1980s, the introduction of cellular phone networks had revolutionized mobile telephony in ways that could not have been achieved in the four decades before their introduction. However a common characteristic of the 1-G cellular systems of the 1980s was that they used analog signals to carry the information between the cell phones and the cell phone towers.

 

Second generation (2G) cellular networks were introduced in the early 1990s. These 2G networks digitized the communication between the cell phone and the tower. This single change from analog to digital yielded enormous benefits. To begin with, digital transmission could be heavily compressed by the phone before transmission. This dramatically reduced the bandwidth requirement for each phone call. Thus each cell of the cellular network could support many more simultaneous conversations than before. Secondly, the digital signal could be very easily encrypted thereby making eavesdropping much harder to do than with the 1G analog signal. Digital transmission also consumed less power, thereby further reducing the size and weight of the batteries that were used by the phones. And with digital, there was also no line noise or ‘hum’ during pauses in the conversation.

 

Finally, and arguably most significantly, digital transmission made it possible to transmit data over a wireless channel along with voice.

 

Radio telegraphy began in the 1890s as a way to transmit data symbols over a wireless communication link. Once hundred years later, the introduction 2G networks in the early 1990s, with their ability to transmit data wirelessly, curiously brought the field of radio communications full circle!

 

In yet another sense, digital telephony technology and the 2G, 3G and 4G networks that it has given rise to have also given birth to a whole new kind of internet – a wireless internet!

 

 

The evolution of digital telephony

 

Several interesting events have shaped the evolution of digital telephony.

 

Up through the 1990s, there were three primary crucibles of mobile technology evolution: The United States, Europe and Japan. Each one took an extraordinarily different route for migrating from 1G to 2G.

 

The United States made some early successful attempts in the late 1980s to create a digital version of the 1G AMPS cellular system which was already in widespread use in North America around that time. From this resulted two offshoots - the Motorola designed Narrow Band AMPS or N-AMPS and the more widely deployed Digital AMPS or D-AMPS.

 

D-AMPS which was first launched in the US in 1990, was specifically designed to be backward compatible with the analog AMPS so that you could use a dual mode (analog/digital) cell phone on both versions of the system.

 

On the other side of the world, Japan migrated its vast analog cellular network operated by Nippon Telephone and Telegraph (NTT) which was deployed through the 1980s, to a digital variant called PDC (Personal Digital Cellular). The 2G PDC cellular network began operation in Japan in 1993.

 

Meanwhile, Europe took an altogether different route for 2G adoption.