Ch1 gsm “ global system for mobile communication

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Ch1 gsm “ global system for mobile communication

  1. 1. HISTORY OF COMMUNICATION - CONTENT -communication systems overview - Introduction to Cellular Fundamentals - Network Architecture - GSM Air Interface - Digital Mobile Elements - GSM Network Protocols
  2. 2. HISTORY OF COMMUNICATION • Communication systems
  3. 3. HISTORY OF COMMUNICATION Voice Communications
  4. 4. HISTORY OF COMMUNICATION Basic Communications System Elements ● Source ● Destination ● Transmission Medium Source Destination Transmission Medium
  5. 5. HISTORY OF COMMUNICATION Transmission Medium Wired Wireless • Transmission Medium
  6. 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. 7. HISTORY OF COMMUNICATION Wired VS Wireless • Losses • Mobility • Security • Bandwidth • Cost
  8. 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. 9.  Some techniques used in wireless communication:  FDM  TDM  FDMA  TDMA Cellular FUNDEMENTALS
  10. 10. FDM Cellular FUNDEMENTALS
  11. 11. TDM Cellular FUNDEMENTALS
  12. 12. FrequencyFDMA  FDMA is the division of each bandwidth (RX,TX) into many frequency bands (channels) Cellular FUNDEMENTALS
  13. 13. TDMA  It allows several users to share the same radio frequency (RF) by dividing it into different timeslots Time Frequency Cellular FUNDEMENTALS
  14. 14. TDMA/FDMA Cellular FUNDEMENTALS Time Frequency
  15. 15. Cellular FUNDEMENTALS • Types of telephones Fixed (PSTN) telephones Cordless Telephones Mobile Telephones Handset The base
  16. 16. Modes OF Transmission in wireless  Simplex communication system  Example:  Television , radio TX RXCommunication is possible in one direction only Cellular FUNDEMENTALS
  17. 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. 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. 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. 20. Cellular FUNDEMENTALS
  21. 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. 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. 23. Third generation cellular system - Multimedia services - W-CDMA transmission technology - Large BW - Higher Bit Rate - More Services Cellular FUNDEMENTALS
  24. 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. 25. FUNDAMENTAL OF CELLULAR SYSTEM Cluster size=7
  26. 26. Good Coverage requires high number of Sites and Cells Area Coverage 83% Population Coverage 99,5%
  27. 27. FUNDAMENTAL OF CELLULAR SYSTEM • Cell shape
  28. 28. FUNDAMENTAL OF CELLULAR SYSTEM
  29. 29. FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
  30. 30. FUNDAMENTAL OF CELLULAR SYSTEM
  31. 31. FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
  32. 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. 33. FUNDAMENTAL OF CELLULAR SYSTEM
  34. 34. FUNDAMENTAL OF CELLULAR SYSTEM cell types - macrocell - microcell - picocell Very small cells
  35. 35. Macrocell BS BS BS Microcell Microcell FUNDAMENTAL OF CELLULAR SYSTEM
  36. 36. FUNDAMENTAL OF CELLULAR SYSTEM Pico Cell
  37. 37. FUNDAMENTAL OF CELLULAR SYSTEM Satellite Global Subur ban & rural Urban Pico-Cell Micro-CellMacro-Cell In-building Pico-Cell
  38. 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. 39. FUNDAMENTAL OF CELLULAR SYSTEM cell splitting
  40. 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. 41. FUNDAMENTAL OF CELLULAR SYSTEM channel characteristics - Multipath fading t1 t2 t3
  42. 42. FUNDAMENTAL OF CELLULAR SYSTEM -It gives a Rayleigh fading distribution - Rayleigh fading is frequency selective
  43. 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. 44. FUNDAMENTAL OF CELLULAR SYSTEM -Microscopic diversity techniques : 1-Time diversity technique 2-Frequency diversity technique
  45. 45. FUNDAMENTAL OF CELLULAR SYSTEM 3-Space diversity technique
  46. 46. FUNDAMENTAL OF CELLULAR SYSTEM -Space diversity technique
  47. 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. 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. 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. 50. FUNDAMENTAL OF CELLULAR SYSTEM - Co-channel interference D c
  51. 51. FUNDAMENTAL OF CELLULAR SYSTEM - Adjacent channel interference Frequency Signal level (dB) Filter Required ch. Adjacent channel interference
  52. 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. 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. 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. 55. FUNDAMENTAL OF CELLULAR SYSTEM - Path loss Pr α Pt Rβ β = 3 ~ 4 Signal level (dB) Distance
  56. 56. FUNDAMENTAL OF CELLULAR SYSTEM - Combined signal loss Path loss Rayleigh fading Shadowing Signal level (dB) Log d

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