Cellular concept in mobile communication
- 1. BASICS OF MOBILE COMMUNICATION BY D.S.HIREMATH, LECTURER DEPARTMENT OF ELECTRONICS AND COMMUNICATION B.L.D.E.A’S SHRI S.S.M. POLYTECHNIC ,VIJAYAPUR
- 2. CONTENTS • Evolution of mobile communication • Cellular concept • Frequency reuse • Cell splitting • Cell sectoring 2
- 3. EVOLUTION OF MOBILE 3 First Generation, 1G These phones were the first mobile phones to be used, which was introduced in 1982 and completed in early 1990. It was used for voice services and was based on technology called as Advanced Mobile Phone System (AMPS). The AMPS system was frequency modulated and used frequency division multiple access (FDMA) with a channel capacity of 30 KHz and frequency band of 824- 894MHz .The features of 1G are •Speed -2.4 kbps •Allows voice calls in 1 country •Use analog signal. •Poor voice quality
- 4. • Poor battery life • Large phone size • Limited capacity • Poor handoff reliability • Poor security • Offered very low level of spectrum efficiency • Second Generation (2G) • 2G refers to the second generation based on GSM and was emerged in late 1980s. It uses digital signals for voice transmission • The main features of 2G and 2.5G are • Data speed was upto 64kbps • Use digital signals • Enables services such as text messages, picture messages and MMS(Multimedia • message) • Provides better quality and capacity 4
- 5. 2.5 G : The GSM technology was continuously improved to provide better services which led to development of advanced Technology between 2G and 3G • Provides phone calls • Send/receive e-mail message • Web browsing • Speed : 64-144 kbps • Camera phones • THIRD GENERATION- 3G 3G is based on GSM and was launched in 2000. The aim of this technology was to offer high speed data. The original technology was improved to allow data up to 14 Mbps and more using packet switching. The main features of 3G are: • Speed 2 Mbps • Increased bandwidth and data transfer rates to accommodate web -based applications and audio and video files. • Send/receive large email messages 5
- 6. • High speed web/more security/video conferencing/3D gaming • TV streaming/mobile TV/Phone calls • High bandwidth requirement • Fourth Generation (4G) • 4G offers a downloading speed of 100Mbps.4G provides same feature as 3G and additional services like Multi-Media Newspapers, to watch T.V programs with more clarity and send Data much faster than previous generations .LTE (Long Term Evolution) is considered as 4G technology. 4G is being developed to accommodate the QoS and rate requirements set by forthcoming applications like wireless broadband access, MultimediaMessaging Service (MMS), video chat , mobile TV, HDTV content, Digital Video Broadcasting (DVB).The main features of 4G are • Capable of provide 10Mbps -1Gbps speed • High quality streaming video • Combination of Wi-Fiand Wi-Max • High security 6
- 7. • Expanded multimedia services • Low cost per-bit • Need complicated hardware • Expensive equipment required to implement next generation network Fifth Generation (5G) • 5G refer to Fifth Generation which was started from late 2010s. The main focus of 5G will be on world-Wireless World Wide Web (WWWW). It is a complete wireless communication with no limitations. The main features of 5G are • It is highly supportable to WWWW (wireless World Wide Web) • High speed, high capacity • Provides large broadcasting of data in Gbps • Multi-media newspapers,watch TV programs with the clarity(HD Clarity) • Support interactive multimedia, voice , streaming video, internet and Better performance 7
- 8. In a cellular network, total area is subdivided into smaller areas called “cells”. Each cell can cover a limited number of mobile subscribers within its boundaries. Each cell can have a base station with a number of RF channels. A cellular network allows cellular subscribers to wander anywhere in the country and remain connected to the Public Switched Telephone Network(PSTN) via their mobile phones 8 CELLULAR CONCEPT
- 9. Total available frequency resources are divided into seven parts, each part consisting of a number of radio channels and allocated to a cell site. In a group of 7 cells, available frequency spectrum is consumed totally. The same seven sets of frequency can be used after certain distance. The group of cells where the available frequency spectrum is totally consumed is called a cluster of cells. Two cells having the same number in the adjacent cluster, use the same set of RF channels and hence are termed as “Co-channel cells”. The distance between the cells using the same frequency should be sufficient to keep the co-channel interference to an acceptable level. Hence, the cellular systems are limited by Co-channel interference. 9
- 10. A cellular network has a hierarchical structure and it is formed by connecting the major components mentioned below :- •Mobile phones - main piece of equipment as far as a subscriber is concerned •Base Station(BS) •Mobile Switching Centre(MSC) Each cellular base station is allocated a group of radio channels within a small geographic area called a cell Neighboring cells are assigned different channel groups. 10
- 11. Frequency reuse, or, frequency planning, is a technique of reusing frequencies and channels within a communication system to improve capacity and spectral efficiency. Frequency reuse is one of the fundamental concepts on which commercial wireless systems are based that involve the partitioning of an RF radiating area into cells. The increased capacity in a commercial wireless network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission Frequency Reuse 11
- 12. Frequency reuse in mobile cellular systems means that frequencies allocated to the service are reused in a regular pattern of cells, each covered by one base station. The repeating regular pattern of cells is called cluster. Since each cell is designed to use radio frequencies only within its boundaries, the same frequencies can be reused in other cells not far away without interference, in another cluster. Such cells are called ‘co- channel’ cells. The reuse of frequencies enables a cellular system to handle a huge number of calls with a limited number of channels. 12
- 13. Figure shows frequency planning with cluster size of 7, showing the co-channels cells in different clusters by the same letter. The closest distance between the co-channel cells (indifferent clusters) is determined by the choice of the cluster size and the layout of the cell cluster. Consider a cellular system with S duplex channels available for use and let N be the number of cells in a cluster. If each cell is allotted K duplex channels with all being allotted unique and disjoint channel groups we have S=KN under normal circumstances. Now, if the cluster are repeated M times within the total area, the total number of duplex channels, or, the total number of users in the system would be T=MS=KMN Clearly, if K and N remain constant, then T∝M and, if T and K remain constant, then N ∝ 1/M. Hence the capacity gain achieved is directly proportional to the number of times a cluster is repeated. 13
- 15. The Increased number of cells would increase the number of clusters over the coverage region, which again would increase the number of channels and thus capacity. The distance between co-channel cells also reduces to half (D=D/2) as the cell radius is reduced to half(R =R /2). Thus the co- channel reuse ratio (Q=D/R ) remains same. 15
- 16. In cell sectoring a single omni-directional antenna at base station is replaced by several directional antennas, each radiating within a specified sector. By using directional antennas power is transmitted in single desired direction decreasing number of interfering co-channel cells and co-channel interference. The technique for decreasing co-channel interference and thus increasing system performance by using directional antennas is called sectoring. The factor by which the co-channel interference is reduced depends on the amount of sectoring used. A cell is normally partitioned into three sectors. When sectoring is employed, the channels used in a particular cell are broken down into sectored groups and are used only within a particular sector. 16 Cell sectoring