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

First generation of mobile networks

The mobile wireless technology creation, development, revolution and evolution started in early 1970s. In past four decades mobile wireless technology has come a long way in terms of data transfer speed, spectrum efficiency and bandwidth utilization techniques. Mobile network technologies are classified according to their generations which are based on types of services and data rates they provide to the end-user.

Zero G refers to the pre-cellular mobile telephony technology era. In the beginning (In 1970s) the mobile telephone systems were huge and were usually mounted on vehicles. They were called radio telephone systems and are considered to be the predecessors of modern cellular mobile phones. That is why they are sgenerally referred as belonging to 0G. Communication technologies used in 0G were PTT( Push To Talk) , MTS (Mobile Telephone Systems), IMTS(Improved Mobile Telephone Systems) and AMTS(Advance Mobile Telephone Systems) etc.

Understanding First Generation (1G) Mobile Networks

First generation refers to the handheld mobile phones using analog communication techniques to transmit voice over radio waves. These phones were large and heavy with big antennas and were also referred as “brick phones” and “bag phones”.

1980 was the year when mobile cellular technology took first breath and since then it has experience rapid and enormous growth. In 1979 first cellular system in the world became operational by Nippon Telephone and Telegraph (NTT) in Tokyo, Japan. It uses analog transmission of speech services. Two years later Europe also joined the cellular club and thus the two most popular analog systems i.e. Nordic Mobile Telephone (NMT) and Total Access Communication Systems (TACS) were born. A few other analog systems were also developed by different European countries during that time. All these systems offered handover and roaming services but mobile networks were unable to interoperate among countries. This was one BIG disadvantage of 1G.

In USA Advance Mobile Phone Systems (AMPS) was launched in the year 1982. The system was allocated 40 MHZ Bandwidth with the frequency range of 800-900MHz. In 1988 an additional 10MHz bandwidth was added to the already available spectrum. AMPS offered 832 channels with the data rate of almost 10Kbps. Initially Omnidirectional Antennas were used but later on they switched to directional antennas because of its better cell reuse factor.

1G systems mostly used Frequency Modulation (FM) for radio transmission and the traffic on multiple channels was combined through Frequency Division Multiple Access (FDMA) System.

Disadvantages of 1G.

1. Analog Signals does not allow advance encryption methods hence there is no security of data 
2. Signal sniffing and signal jamming are very easy in analog system.
3. The user identification number could be stolen easily and which could be used to make any call and the user whose identification number was stolen had to pay the call charges.
4. Analog signals can easily be affected by noise and interference and the call quality decreases.
5. Analog systems were expensive and the call charges were very high.

Summary of Salient Features of Different Generations of Mobile Networks

The figure below gives and idea of what are different features of mobile networks from 1st generation to 4th generation. Inshaa Allah I shall explain these mobile network generations in details in my future posts. So keep visiting :)