Ch1 gsm “ global system for mobile communication
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  • 1. HISTORY OF COMMUNICATION - CONTENT -communication systems overview - Introduction to Cellular Fundamentals - Network Architecture - GSM Air Interface - Digital Mobile Elements - GSM Network Protocols
  • 2. HISTORY OF COMMUNICATION • Communication systems
  • 3. HISTORY OF COMMUNICATION Voice Communications
  • 4. HISTORY OF COMMUNICATION Basic Communications System Elements ● Source ● Destination ● Transmission Medium Source Destination Transmission Medium
  • 5. HISTORY OF COMMUNICATION Transmission Medium Wired Wireless • Transmission Medium
  • 6. HISTORY OF COMMUNICATION Telephone Networks Early Switching Devices Switches are devices that cause a connection between two transmitting/receiving devices. Modern Switching Devices Today many different types of automated switches are used which make it possible for fast placement of calls.
  • 7. HISTORY OF COMMUNICATION Wired VS Wireless • Losses • Mobility • Security • Bandwidth • Cost
  • 8. FUNDAMENTAL OF CELLULAR SYSTEM Transition from analog to digital • Capacity Compression in digital gives more channels • compatibility with other systems As ISDN (Integrated service Digital Network) • Cost • Quality • Security
  • 9.  Some techniques used in wireless communication:  FDM  TDM  FDMA  TDMA Cellular FUNDEMENTALS
  • 10. FDM Cellular FUNDEMENTALS
  • 11. TDM Cellular FUNDEMENTALS
  • 12. FrequencyFDMA  FDMA is the division of each bandwidth (RX,TX) into many frequency bands (channels) Cellular FUNDEMENTALS
  • 13. TDMA  It allows several users to share the same radio frequency (RF) by dividing it into different timeslots Time Frequency Cellular FUNDEMENTALS
  • 14. TDMA/FDMA Cellular FUNDEMENTALS Time Frequency
  • 15. Cellular FUNDEMENTALS • Types of telephones Fixed (PSTN) telephones Cordless Telephones Mobile Telephones Handset The base
  • 16. Modes OF Transmission in wireless  Simplex communication system  Example:  Television , radio TX RXCommunication is possible in one direction only Cellular FUNDEMENTALS
  • 17.  Half – Duplex communication system  Example :  Police radio TX+RX TX +RX Two-way communication on the same channel. At any given time a user can only transmit or receive Cellular FUNDEMENTALS
  • 18.  Full – Duplex communication system  Example :  GSM mobile radio TX+RX TX +RX • simultaneous two-way communication • Two simultaneous but separate channels are provided for communication to and from the terminals Cellular FUNDEMENTALS
  • 19. Simple growth was the single transmitting/receiving station - heavy, bulky and expensive - no switching between regions - low quality - limited capacity - rapid market saturation - power hungry transceiver - power level was not safe MS High transmitted power Up link Down link Cellular FUNDEMENTALS
  • 20. Cellular FUNDEMENTALS
  • 21. First generation cellular system - Introduction of analog cellular systems in the late 1970s and 1980s - analog system - incompatible systems - limited to voice service - no encryption - FM modulation - FDMA transmission technology - suffer from capacity saturation Cellular FUNDEMENTALS
  • 22. Second Generation cellular system - Introduction of digital cellular systems (90’s) - development of unified international standard for mobile communications - pan-national roaming - digital encryption - enhanced range of services (data + voice) - low power consumption - light weight, compact and pocket size terminals - TDMA transmission technology - huge capacity Cellular FUNDEMENTALS
  • 23. Third generation cellular system - Multimedia services - W-CDMA transmission technology - Large BW - Higher Bit Rate - More Services Cellular FUNDEMENTALS
  • 24. FUNDAMENTAL OF CELLULAR SYSTEM The cellular structure - area divided into small zones (cells) - cells grouped into clusters - this gives less power usage - enable frequency reuse
  • 25. FUNDAMENTAL OF CELLULAR SYSTEM Cluster size=7
  • 26. Good Coverage requires high number of Sites and Cells Area Coverage 83% Population Coverage 99,5%
  • 27. FUNDAMENTAL OF CELLULAR SYSTEM • Cell shape
  • 28. FUNDAMENTAL OF CELLULAR SYSTEM
  • 29. FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
  • 30. FUNDAMENTAL OF CELLULAR SYSTEM
  • 31. FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
  • 32. FUNDAMENTAL OF CELLULAR SYSTEM adaptive power control - as cellular mobile moves power seen at Bs changed - so we use adaptive power control to maintain it P1 P2
  • 33. FUNDAMENTAL OF CELLULAR SYSTEM
  • 34. FUNDAMENTAL OF CELLULAR SYSTEM cell types - macrocell - microcell - picocell Very small cells
  • 35. Macrocell BS BS BS Microcell Microcell FUNDAMENTAL OF CELLULAR SYSTEM
  • 36. FUNDAMENTAL OF CELLULAR SYSTEM Pico Cell
  • 37. FUNDAMENTAL OF CELLULAR SYSTEM Satellite Global Subur ban & rural Urban Pico-Cell Micro-CellMacro-Cell In-building Pico-Cell
  • 38. FUNDAMENTAL OF CELLULAR SYSTEM cell splitting - as traffic load increases in a cell - to increase channels designer tend to split cell into smaller cells - R decrease Dc decrease so more capacity
  • 39. FUNDAMENTAL OF CELLULAR SYSTEM cell splitting
  • 40. FUNDAMENTAL OF CELLULAR SYSTEM channel allocation techniques - Fixed channel assignment technique (less Ts) - dynamic channel assignment technique (largest Ts) - hybrid channel assignment technique (Improved) 1,4,7 2,5,8 3,6,9 1-9 7,8,9 1,4 2,5 3,6 Fixed Dynamic Hybrid
  • 41. FUNDAMENTAL OF CELLULAR SYSTEM channel characteristics - Multipath fading t1 t2 t3
  • 42. FUNDAMENTAL OF CELLULAR SYSTEM -It gives a Rayleigh fading distribution - Rayleigh fading is frequency selective
  • 43. FUNDAMENTAL OF CELLULAR SYSTEM • To overcome multipath fading we use : - Microscopic diversity and combining techniques - Frequency hopping - Error correction - Interleaving technique - adaptive power control
  • 44. FUNDAMENTAL OF CELLULAR SYSTEM -Microscopic diversity techniques : 1-Time diversity technique 2-Frequency diversity technique
  • 45. FUNDAMENTAL OF CELLULAR SYSTEM 3-Space diversity technique
  • 46. FUNDAMENTAL OF CELLULAR SYSTEM -Space diversity technique
  • 47. FUNDAMENTAL OF CELLULAR SYSTEM - Combining techniques : 1-Selective technique - used in mobile due to simplicity 2-Maximal ratio technique - Best fading reduction 3-Equal gain technique Receiver comparator
  • 48. FUNDAMENTAL OF CELLULAR SYSTEM - Shadow fading -The Solution of this problem by using Macroscopic Diversity By selecting a BS which is not shadowed when others are.
  • 49. FUNDAMENTAL OF CELLULAR SYSTEM - Doppler shift - +ve if the mobile moves toward the BS - -ve if the mobile moves away from the BS - The Doppler frequency shift should be compensated so that a correct frequency synchronization is achieved .
  • 50. FUNDAMENTAL OF CELLULAR SYSTEM - Co-channel interference D c
  • 51. FUNDAMENTAL OF CELLULAR SYSTEM - Adjacent channel interference Frequency Signal level (dB) Filter Required ch. Adjacent channel interference
  • 52. FUNDAMENTAL OF CELLULAR SYSTEM - Channel management 1,8,15 2,9,16 5,12,19 6,13,20 7,14,21 4,11,18 3,10,17 Frequency (MHz) Amplitude
  • 53. FUNDAMENTAL OF CELLULAR SYSTEM - Delay Spread (Time dispersion) - Due to multipath fading - To overcome this we use delay equalizer 1 2 3 4 65 1 2 3 4 65 Path 1 Path 2 t1 t2 t3
  • 54. FUNDAMENTAL OF CELLULAR SYSTEM - Distance between MS and BS - This makes Time alignment Problem - To overcome this system should respond to this delay T1 T2 T3 A B A B
  • 55. FUNDAMENTAL OF CELLULAR SYSTEM - Path loss Pr α Pt Rβ β = 3 ~ 4 Signal level (dB) Distance
  • 56. FUNDAMENTAL OF CELLULAR SYSTEM - Combined signal loss Path loss Rayleigh fading Shadowing Signal level (dB) Log d