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1. INTRODUCTION
Wireless communication is used for transmission of information from one place to another without using cables. This may be one-way communication as in broadcasting systems (such as radio and TV), or two-way communication (e.g. mobile phones). The research area covers an increasing number of existing and new technologies. The term "Wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy early on. Now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet. It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control" or "wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) that is used to accomplish the operation.
The early wireless systems consisted of a base station with a high-power transmitter and served a large geographic area. Each base station could serve only a small number of users and was costly as well. The systems were isolated from each other and only a few of them communicated with the public switched telephone networks. Today, the cellular systems consist of a cluster of base stations with low-power radio transmitters. Each base station serves a small cell within a large geographic area. The total number of users served is increased because of channel reuse and also larger frequency bandwidth. The cellular systems connect with each other via mobile switching and directly access the public switched telephone networks. The most advertised advantage of wireless communication systems is that a mobile user can make a phone call anywhere and anytime. The number of mobile communication devices users is growing very fast. The number of mobiles (cellular phones) is now exceeding the number of fixed lines in many countries (Finland, Japan etc.).Cellular/mobile phones are everywhere and their utility is growing. A cell phone is a radio telephone that may be used wherever "cell" coverage is provided.
The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones. Mobile Internet access is a global phenomenon with even great implications. Leading phone manufacturers such as Ericsson, Matsushita (Panasonic), Motorola, and Nokia have put a great deal of marketing effort behind the mobile Internet phenomenon, recognizing that adoption is a complex business proposition. In Europe, WAP is has generated widespread interest because of lots of marketing and expectations put to it. In Japan NTTDoCoMo's mobile Internet service is based on a service called iMode that uses Compact HTML (CHTML) micro browsers in the phone. There are also products on the market which combine a PDA, a real web-browser and some communication interface (cellular phone, WLAN etc.) into one smart communication device. A generic phone may soon acquire a browser. And mobile phones will morph into PDAs or organizers. The handsets sold over the next few years are likely to operate much differently than those of today.
Mobile terminals are complex embedded systems, with stringent real-time requirements for signaling and voice processing. Now Web browsing, multimedia, and connectivity requirements are added to the list. There are many technical challenges to be solved to make all this to work. Ubiquity is a pinnacle that the cellular communication sector has hoped to reach for the past five years. To reach this goal, a series of networks must be built that allow consumers to use their phone anytime anywhere. The truth is ubiquity is far from becoming a reality. Across the world cellular carriers can't seem to agree on a single air interface for wireless operation. But, despite battles on the standards front, the wireless community has pushed forward in its efforts to build mobile networks and phones that deliver worldwide coverage. To make this happen, they have focused their attention on developing multimode systems that can support CDMA, TDMA, GSM, GPRS, wideband CDMA (W-CDMA), and a host of other air interfaces in the same box.
2. EVOLUTION OF MOBILE COMMUNICATIONS
The origins of radio communications are in the 19th century.
• 1864 James Clerk Maxwell presented the Maxwell Equations for electromagnetic radiation
• 1876 Alexander Graham Bell invented the telephone.
• 1887 Heinrich Hertz discovered "hertzian waves" which are now called as radio waves.
• 1896 Guglielmo Marconi carried out the world’s first radio transmission.
At the beginning of our century, e.g. the police forces in Europe and in the US were using radio telephony equipment. During the 50’s and 60’s, first radio telephone networks were introduced for public customers in the US. As the radio telephony services became more popular, the insufficient availability of radio frequencies became obvious. At the 60’s and 70’s, new technologies like dynamic channel allocation and cell-based networks were developed in order to decrease the congestion in the radio frequencies. The increasing lack of frequencies in the radio telephone services led to the development of cellular networks in the 70’s. The Bell Telephone company (US) introduced the first cellular public network AMPS (Advanced Mobile Phone Service) in 1978. It became a single standard for North America in 1982. The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb. A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area. A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell. In the 80’s, several analogue cellular radio networks entered to service around the world. Each country has proceeded in its own way in adopting standards for these networks. These standards are not mutually incompatible. Later international standards were introduced. The mobile communication technology has evolved through different generations. A short description of these generations is as follows:
1G (First Generation): First generation wide area wireless communication systems are characterized as analog radio systems and designed for voice transfer. 1G Technology uses frequency division multiple access (FDMA) to communicate, meaning simply that every call in one uses their own channels for voice communication. This kind of systems were designed and used in 1970s and 1980s. The technologies which come under 1st generation are:
♦ Advanced Mobile Phone Service (AMPS)
♦ Total Access Communication System (TACS)
♦ Nordic Mobile Telephone (NMT)
♦ Narrowband AMPS (NAMPS)
♦ Japanese Mobile Cellular System (MCS)
♦ CNET
♦ MATS-E
Analog systems created the critical mass of mobile users. Analogue technology has small subscriber and traffic capacities, and the use of radio spectrum is profuse. The limitations of analogue radio network technology became, however, clear as the number of subscribers increased. The need for more advanced solutions was urgent especially in Europe, where numerous standards in a relatively small region caused cumulative problems due to increased mobility of radio telephone users.
2G (Second Generation): Second generation (2G) cellular phone system use digital communication methods. They are capable of providing voice, data and other services. Digital technology combined with harmonized standardization has made it possible to make calls at any time, anywhere, and both speech and data can be transmitted and received. The second generation (2G) wireless systems are characterized by the use of digital radio transmission. The increase in system capacity was due to the use of hierarchical cell structures and the ability to use a single frequency channel for multiple users (code and/or time division). The technologies under 2nd generation are:
• Global System for Mobile Communication (GSM)
• North American TDMA (IS-136 TDMA)
• Extended TDMA (E-TDMA) TM
• Integrated Dispatch Enhanced Network (iDEN)
• Code Division Multiple Access (IS-95 CDMA)
• Japanese Personal Digital Cellular (PDC)
The 2G systems have been increased in the features over years. Enhancements upon this second generation of wireless systems (termed .2.5G.) have increased system capacities even further. These enhancements give for example better voice quality, faster data transfer and packet mode data communications. Present 2.5G systems satisfy our current needs at year 2003.
2.5G (Two and Half Generation): This is an enhanced version of 2G technologies. This gives higher data rate and packet data services. They are called as Packet Digital Cellular Systems. The technologies provided are:
• General Packet Radio Service (GPRS)
• Enhanced Data Rates for Global Evolution (EDGE)
• CDMA2000™ 1xRTT
• Evolution Data Only (1xEVDO)
• Evolution Data and Voice (1xEVDV)
3G (Third Generation): Third generation mobile communication systems often called with names3G, UMTS and W-CDMA promise to boost the mobile communications toned speed limits. The promises of third generation mobile phones are fast Internet surfing, advanced value-added services and video telephony. Mobile communication is promised to move from simple voice to rich media, where we use more of our senses to intensify our experiences.3G technology improves upon 2G systems in two main ways. First, is a move towards packet switching from circuit switching. Packet switching uses the communication system more effectively, therefore boosting the capacity of the system. Packet switching also enables users to always be online. This will eliminate the need for users to "dial up". Via judicious use of the frequency spectrum and inventive coding methods, 3G technology is poised to achieve bit rates up to 2 Mbps. The technologies involved are:
• Wideband Code Division Multiple Access (WCDMA)
• Code Division Multiple Access 2000 (CDMA2000)
• Time Division Synchronous CDMA (TD-SCDMA)
4G (Fourth Generation): It has not been widely defined what this is. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps. Most probable the 4G network would be a network which is a combination of different technologies (current cellular networks, 3G cellular network, wireless LAN, etc.) working together using suitable interoperability protocols (for example Mobile IP). There are also views that 4G could be some entirely new radio access technology.
5G (Fifth Generation): There is no clear definition what this is. This will be something more advanced than 4G.