Secong Generation (2G) Mobile Networks

Introduction

In the late 1980s the interest of researchers and engineers started shifting from analog signaling techniques to digital signaling. Advances in the integrated circuit (IC) technology had made digital communication not only practical but also more economic than analog communication technology.

The dawn of digital communication brought many improvements in the mobile communication. Digital communication allowed source coding and data encryption which in turn provides information security to the data being transmitted. Digital communication techniques enhanced the bandwidth efficiency and spectrum utilization of systems. In addition to that digital communication techniques enable error coding which provides more reliable and almost error free transmission. Digital signaling techniques are better equipped to counter the effects of channel fading, channel noise and interference. Thus overcoming the drawbacks of analog system. Early second generation digital communication systems are classified by their multiple access techniques e.g

• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)

In FDMA, the radio spectrum is divided into a set of frequency slots and each user is assigned a separate frequency to transmit. In TDMA, several users transmit at the same frequency but in different time slots. CDMA uses the principle of direct sequence spread-spectrum: the signals are modulated with high bandwidth spreading waveforms called signature waveforms or codes. Although the users transmit at both the same frequency and time, separation of signals is achieved because the signature waveforms have very low cross correlation.

In practice, the TDMA and CDMA schemes are combined with FDMA. Thus the term “TDMA” is used to describe systems that first divide the channel into frequency slots and then divide each frequency slot into multiple time slots. Similarly, CDMA is actually a hybrid of CDMA and FDMA where the channel is first divided into frequency slots. Each slot is shared by multiple users who each use a different code.

Motivation for 2G Digital Cellular:

• Increase System Capacity
• Add additional services/features (SMS, caller ID, etc..)
• Reduce Cost
• Improve Security
• Interoperability among components/systems (GSM only)

2G Mobile Networks

Second generation 2G cellular telecom networks were commercially launched on the Global System for Mobile (GSM) standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with Short Messaging Service (SMS) text messages. 2G technologies enabled the various mobile phone networks to provide the services such as text messages, picture messages and MMS (multimedia messages). All text messages sent over 2G are digitally encrypted, allowing for the transfer of data in such a way that only the intended receiver can receive and read it. 

There are several 2G technologies that have been deployed across the world. The most widespread deployment is, of course, the TDMA-based GSM system and the CDMA-based IS-95 system. Other 2G technologies that have been deployed include DECT (Digital European Cordless Telephone), IS-136, and the PDC-based Personal Handyphone System (PHS) in Japan.

To be continued in next blog post. The next post will deal in more detail with 2G mobile technologies and its evoloutin