Vertical Handoff in Wireless Cellular Networks

Topics: Wireless LAN, IEEE 802.11, Wi-Fi Pages: 46 (14228 words) Published: August 21, 2013
1. INTRODUCTION
Communication is always necessary in building relations to mankind, when two persons meet they need some medium to interchange their views but due to distance barriers some tools are required to communicate each other. At the end of 19th century, reckoned \scientist Graham Bell laid the first stone in the field of communication using different tools regardless of distance. He invented first wired base telephony equipment. It was the solution for the voice communication for the people how far apart they are. After this radio based communication systems Era started. It was an extension of wired based networks. In the beginning it was developed for some special purposes like military and police usage. With the passage of time these systems emerged to allow common peoples to communicate with each other, rather then using wired based network. After this the age of faster communication and capabilities of voice get started and evolved into new telecommunication system.

1.1 Evolution of Cellular Communication:
During the 1980s mobile cellular network’s age started, because the wireless communication has under gone different changes during the past 10 years, So its experienced enormous growth. The Figure 1.1 shows the evolution of the cellular networks. In this figure we have categorized the Cellular networks into five different parts. The first four are existing parts and the last one is the future part.

Figure 1.1: Evolution of Cellular Network
1.2.1 First Generation (1G)
First Generation mobiles networks utilize analogue transmissions. In 1979 Nippun Telephone and Telegraph (NTT) in Japan introduces the first operational cellular networks. In North America AT&T introduces the First Generation mobile systems for the customer in 1980s. This system was named as Advanced Mobile Phone Service (AMPS). In First Generation the basic structure of Cellular communication is characterized and many problems were resolved regarding accomplishment of cellular network. In First generation mobile networks the primary ambition was the voice chat. The above stated system was operational at 40 MHz bandwidth and 800 to 900 MHz Frequency. In 1988 this range was expended up to 10 MHz called expended spectrum in AMPS.

1.2.2 Second Generation (2G)
At the end of 1980s Second Generation (2G) mobile network system was launched. In this system the traditional voice services and low rate data service was provided. The foremost change in this system regarding the First Generation was the switching from analogue to digital transmission, so due to digital transmission better data services and spectrum efficiency was provided. During Second Generation (2G) era the Global System for mobile communication (GSM) was developed in Europe. Using this system International roaming and seamless services was offered in Europe. In the beginning GSM operates at 900 MHz Frequency band with bandwidth of 50 MHz. Many more advancement was made in GSM during last two decades of previous century, due to these improvements GSM became 2.5 G cellular networks. GSM cellular network was implemented over 190 countries and have approximately 800 million subscribers. In 1996 a new digital cellular system with additional services and supporting more data rate, called TDMA was put into practice. At the end of 20th century Second Generation (2G) cellular system was dominated, whoever it was evolving into a new generation called 3G due to increasing rate of mobile traffic. The enhancement of GPRS in GSM enabled it to support relatively high data rate and sharing capacity between the different users. Theoretically General Packet Radio Services (GPRS) support 160 Kbps but practically it provides only 40 Kbps.

1.2.3 Third Generation (3G)
The unexpected success of Second Generation (2G) networks persuaded the Telecom Companies to explore more to fulfil the upcoming user requirement of larger data rate and Quality of...
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