IT 802DMobile Communications<br />Debasis Das<br />
Recommended Books<br />J. Schiller, Mobile Communications, Addison –Wesley, 2003<br />2. T. S. Rapport, Wireless Communica...
Introduction<br />2/27/2011<br />3<br />Debasis Das   Mallabhum Institute of Technology<br />
Module Topics<br />General Overview: History, Transmission Medium, <br />Need, Advantages, Disadvantages<br />Different St...
Usage Scenarios<br />Fixed & wired<br />Desktops connected to a wired set up<br />Mobile & wired<br />Laptops get connecte...
Mobile Devices That Need to Communicate<br />Cellular handsets<br />Walkie-talkies<br />Pager<br />PDA/Pocket computer<br ...
What Do We Need!<br />A means of carrying information from  one party to another<br />A means of modifying the carrier to ...
RF Can Do the Job<br />Electromagnetic waves  in RF frequencies can travel long distances<br />The carrier  frequency can ...
RF Bands<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />9<br />
Electromagnetic Bands<br />Up to 300 GHz<br />RF band<br />Up to  300 THz<br />IR band<br />Above 300 THz <br />Visible li...
Wireless Communication Scenarios- 1<br />Lambda=c/f          wavelength<br />C=3*10^8 meters/s<br />LF – submarine communi...
Wireless Communication Scenarios- 2<br />VHF & UHF; Digital audio 232 to 230 MHz, 1452 to 1472 MHz<br />Digital TV 470 to ...
Basic RF Communication<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />13<br />Receiver<br />Tran...
Propagation Basics<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />14<br />Receivers<br />Transmi...
Various Range in Transmission<br />Transmission range : The zone around the transmitter where communication is possible. R...
Radiation Pattern<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />16<br />Transmitters<br />Direc...
Antenna Issues<br />Theoretical isotropic antenna is one that radiates equal energy in all directions.<br />Practical ante...
Multiplexing<br />Space division multiplexing (SDM)<br />Frequency division multiplexing (FDM)<br />Time division multiple...
Channel Allocation<br />Borrowing channel allocation (BCA)<br />Borrow unused channel frequencies from neighboring cells<b...
Inverse Square Law<br />Radio energy available at any point some distance away from the transmitter<br />Is inversely prop...
Modes of Propagation<br />Ground wave<br />Sky wave<br />Space wave<br />2/27/2011<br />Debasis Das   Mallabhum Institute ...
Ground Wave propagation<br />Radio waves in the low frequency ranges (< 2 MHz)<br />Radio energy travels along the ground ...
Sky Wave Propagation<br />There is a ionized belt around the earth( 2 to  30 MHz)<br />Radio wave is reflected in this ion...
Space Wave Propagation<br />Wavelengths are short enough to penetrate the ionosphere (> 30 MHz)<br />Energy needs to trave...
Other Signal Propagation Effects<br />Blocking/shadowing<br />Reflection<br />Refraction<br />Scatter<br />Diffraction<br ...
Multipath Situation<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />26<br />Skyscraper<br />Trans...
Multipath + Channel Characteristics<br />Multipath causes delay spread<br />Effect= Inter-symbol interference<br /> short ...
Mobile Communication Schemes<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />28<br />(A)<br />CDM...
North American Systems-1<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />29<br />
North American Systems-2<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />30<br />
European Systems<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />31<br />
Japanese Systems<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />32<br />
Basic Modulation Schemes(Digital)<br />In wireless network analog modulation need to be used, these include following basi...
Reasons for Going Analog<br />Antenna<br />Antenna need to comparable to wavelength of carrier<br />Frequency Division mul...
Modulation in a Transmitter<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />35<br />Analog baseba...
Demodulation in Receiver<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />36<br />Analog baseband ...
ASK<br />Simple scheme, send one level of carrier amplitude for 1 and another for 0<br />Needs low bandwidth<br />But ampl...
FSK<br />Used often in RF communication, binary FSK or BFSK<br />Different frequencies are send for the two digital  level...
Phase Shift Keying<br />Change phase of carrier by 180 degrees, every time baseband changes from 1 to 0 or 0 to 1. binary ...
MSK(Min Phase Shift Keying)<br />Avoids abrupt phase changes<br />Data bits are separated into odd and even bits, duration...
Advanced PSK<br />2 bits are considered together, smaller phase shifts for each group of 2 bits, 4 phase shifts are used<b...
QAM<br />Phase shift keying and amplitude keying is combined<br />QPSK and several levels of amplitude <br />64QAm for exa...
Multi Carrier Modulation<br />MCM, orthogonal frequency division multiplexing(OFDM), coded OFDM<br />Used in European digi...
Spread Spectrum<br />Direct sequence spread spectrum<br />Frequency hopping spectrum system<br />2/27/2011<br />Debasis Da...
Frequency Hopping Spread Spectrum<br />Available bandwidth is split into many channels plus guard spaces<br />Transmitter ...
FHSS System<br />2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />46<br />Narrowband signal<br />Spread...
Cellular Systems<br />One base station serving a cell (limited area)<br />Higher the user density, smaller the cell<br />F...
2/27/2011<br />Debasis Das   Mallabhum Institute of Technology<br />48<br />Frequency Re-use Clusters<br />f3<br />f3<br /...
Advantages of Small Cells<br />Higher capacity<br />Space division multiplexing allows frequency reuse,  more users can be...
Disadvantages of Small Cells<br />Infrastructure needed<br />Larger amount of infrastructure, in terms of base stations, t...
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It 802 d_intro&wlan

  1. 1. IT 802DMobile Communications<br />Debasis Das<br />
  2. 2. Recommended Books<br />J. Schiller, Mobile Communications, Addison –Wesley, 2003<br />2. T. S. Rapport, Wireless Communications, Principle and Practices<br />3. Forouzan, Data Communications and Networking, TMH<br />2/27/2011<br />2<br />Debasis Das Mallabhum Institute of Technology<br />
  3. 3. Introduction<br />2/27/2011<br />3<br />Debasis Das Mallabhum Institute of Technology<br />
  4. 4. Module Topics<br />General Overview: History, Transmission Medium, <br />Need, Advantages, Disadvantages<br />Different Standards. AMPS, GSM, GPRS, 3G.<br />2/27/2011<br />4<br />Debasis Das Mallabhum Institute of Technology<br />
  5. 5. Usage Scenarios<br />Fixed & wired<br />Desktops connected to a wired set up<br />Mobile & wired<br />Laptops get connected to wired networks in hotels<br />Fixed & wireless<br />Temporary arrangements, places where fixed wiring may not be possible<br />Mobile & wireless<br />Topic of this course, users are completely free to move around<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />5<br />
  6. 6. Mobile Devices That Need to Communicate<br />Cellular handsets<br />Walkie-talkies<br />Pager<br />PDA/Pocket computer<br />Cordless phones<br />Laptops on wireless LANs<br />Tablet computers<br />eReaders<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />6<br />
  7. 7. What Do We Need!<br />A means of carrying information from one party to another<br />A means of modifying the carrier to convey information<br />Standardized formats for communication<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />7<br />
  8. 8. RF Can Do the Job<br />Electromagnetic waves in RF frequencies can travel long distances<br />The carrier frequency can be modulated to carry information<br />The carrier needs to be changed in some way to be proportional to the input information<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />8<br />
  9. 9. RF Bands<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />9<br />
  10. 10. Electromagnetic Bands<br />Up to 300 GHz<br />RF band<br />Up to 300 THz<br />IR band<br />Above 300 THz <br />Visible light, UV <br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />10<br />
  11. 11. Wireless Communication Scenarios- 1<br />Lambda=c/f wavelength<br />C=3*10^8 meters/s<br />LF – submarine communications, penetrates water and other obstacles<br />MF & HF - radio broadcasts<br />AM band; 520 kHz to 1605.5 kHz<br />SW band; 5.8 MHz to 26.1 MHz<br />FM band; 87.5 MHz to 108 MHz<br />UHF & VHF – TV broadcasts 174 MHz to 230 MHz & 470 to 790 MHz<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />11<br />
  12. 12. Wireless Communication Scenarios- 2<br />VHF & UHF; Digital audio 232 to 230 MHz, 1452 to 1472 MHz<br />Digital TV 470 to 862 MHz<br />Analog mobile phone 450-465 MHz<br />Digital GSM 490-960 MHz, 1710-1880 MHz<br />DECT cordless 1880-1900 MHz<br />3G cellular, UMTS standard 1900-1980 MHz, 2020-2025 MHz, 2110-2190 MHz ….<br />Most wireless mobile communication use the VHF and UHF bands. Small antennas.<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />12<br />
  13. 13. Basic RF Communication<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />13<br />Receiver<br />Transmitter<br />
  14. 14. Propagation Basics<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />14<br />Receivers<br />Transmitter<br />Transmission range<br />Detection range<br />Interference range<br />
  15. 15. Various Range in Transmission<br />Transmission range : The zone around the transmitter where communication is possible. Receiver receives enough signal so that error rates are very low<br />Detection range : transmitted power can be detected, error rate is high however<br />Interference zone : not high enough to be detected but adds to the interference with other signals<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />15<br />
  16. 16. Radiation Pattern<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />16<br />Transmitters<br />Directional<br />Omni-directional<br />
  17. 17. Antenna Issues<br />Theoretical isotropic antenna is one that radiates equal energy in all directions.<br />Practical antenna is a dipole, length lambda/2, centre fed, two halves of lambda/4<br />Dipoles are Omni-directional<br />Sectorized antennas are multiple directional antenna on a single pole<br />Multiple element antennas help combat fading effects<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />17<br />
  18. 18. Multiplexing<br />Space division multiplexing (SDM)<br />Frequency division multiplexing (FDM)<br />Time division multiplexing (TDM)<br />Code division multiplexing (CDM)<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />18<br />
  19. 19. Channel Allocation<br />Borrowing channel allocation (BCA)<br />Borrow unused channel frequencies from neighboring cells<br />Fixed channel allocation (FCA)<br />Channel allocations per cell is fixed<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />19<br />
  20. 20. Inverse Square Law<br />Radio energy available at any point some distance away from the transmitter<br />Is inversely proportional to the square of the distance<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />20<br />Surface area= 4.pi.d^2<br />d<br />
  21. 21. Modes of Propagation<br />Ground wave<br />Sky wave<br />Space wave<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />21<br />
  22. 22. Ground Wave propagation<br />Radio waves in the low frequency ranges (< 2 MHz)<br />Radio energy travels along the ground mainly<br />Enclosed between the ground and the Ionosphere<br />Radio transmissions in medium wave are examples<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />22<br />
  23. 23. Sky Wave Propagation<br />There is a ionized belt around the earth( 2 to 30 MHz)<br />Radio wave is reflected in this ionosphere and travels long distance<br />Wavelengths are shorter than the frequency band that uses the ground wave mode<br />Radio shortwave transmissions are examples<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />23<br />
  24. 24. Space Wave Propagation<br />Wavelengths are short enough to penetrate the ionosphere (> 30 MHz)<br />Energy needs to travel in straight line to the receiver<br />TV transmissions are an example<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />24<br />
  25. 25. Other Signal Propagation Effects<br />Blocking/shadowing<br />Reflection<br />Refraction<br />Scatter<br />Diffraction<br />Multi path propagation<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />25<br />
  26. 26. Multipath Situation<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />26<br />Skyscraper<br />Transmitter<br />Car<br />Obstacle<br />
  27. 27. Multipath + Channel Characteristics<br />Multipath causes delay spread<br />Effect= Inter-symbol interference<br /> short term fading<br />(It can help if an estimate can be made of these multi path delays, at least the main path. Sender transmits a “training sequence : known to receiver, programs an equalizer to compensate<br />Long term fading, due varying distance from sender, compensate by raising/ lowering power transmitted so that received power is within specified range<br />Doppler shift<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />27<br />
  28. 28. Mobile Communication Schemes<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />28<br />(A)<br />CDMA<br />(B)<br />Cellular<br />
  29. 29. North American Systems-1<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />29<br />
  30. 30. North American Systems-2<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />30<br />
  31. 31. European Systems<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />31<br />
  32. 32. Japanese Systems<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />32<br />
  33. 33. Basic Modulation Schemes(Digital)<br />In wireless network analog modulation need to be used, these include following basic schemes<br />Amplitude Shift Keying ASK<br />Frequency Shift Keying FSK<br />Phase shift keying PSK<br />The digital input is converted to analog baseband signal before modulation<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />33<br />
  34. 34. Reasons for Going Analog<br />Antenna<br />Antenna need to comparable to wavelength of carrier<br />Frequency Division multiplexing<br />Analog modulation shifts baseband signal to different carrier signal. Higher carrier frequency gives you higher bandwidth<br />Medium Characteristics<br />Path loss, penetration of obstacles, reflection, scattering, diffraction are wavelength dependent <br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />34<br />
  35. 35. Modulation in a Transmitter<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />35<br />Analog baseband signal<br />Digital<br />modulation<br />Analog Modulation<br />Modulated<br />signal<br />Digital data<br />Radio carrier<br />
  36. 36. Demodulation in Receiver<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />36<br />Analog baseband signal<br />Analog<br />demodulation<br />Synchronization<br />decision<br />Digital<br />signal<br />Radio carrier<br />
  37. 37. ASK<br />Simple scheme, send one level of carrier amplitude for 1 and another for 0<br />Needs low bandwidth<br />But amplitude is affected by multipath , noise, path loss etc.<br />ASK is not used for RF communication<br />However, is used in optical communication<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />37<br />
  38. 38. FSK<br />Used often in RF communication, binary FSK or BFSK<br />Different frequencies are send for the two digital levels<br />Sudden phase changes can generate high frequencies<br />Frequency modulation in continuous phase modulation (CPM) is used<br />Demodulation can use two fixed frequency filters<br />Needs larger bandwidth, less susceptible to noise<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />38<br />
  39. 39. Phase Shift Keying<br />Change phase of carrier by 180 degrees, every time baseband changes from 1 to 0 or 0 to 1. binary PSK<br />BPSK can be simply multiplying the carrier by +1 when input is 1 and multiplying by -1 when input is 0<br />Reception uses phase locked loop for reference<br />Compared to FSK, PSK is more resistant to interference<br />Receiver and transmitter are more complex to design<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />39<br />
  40. 40. MSK(Min Phase Shift Keying)<br />Avoids abrupt phase changes<br />Data bits are separated into odd and even bits, duration of bits are doubled<br />Two frequencies f1 & f2, such that f2=2*f1<br />Phase is shifted based different criteria<br />Gaussian MSK is a variation, GMSK is used in most European wireless standards <br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />40<br />
  41. 41. Advanced PSK<br />2 bits are considered together, smaller phase shifts for each group of 2 bits, 4 phase shifts are used<br />This is the QPSK scheme<br />Carrier reference is a must, frequent synchronization required<br />Differential PSK, decides phase shifts with respect from the last phase, not absolute<br />DQPSK is one of the most efficient schemes<br />IS-136, PACS of US and Japanese PHS of Japan are examples<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />41<br />
  42. 42. QAM<br />Phase shift keying and amplitude keying is combined<br />QPSK and several levels of amplitude <br />64QAm for example can combine QPSK and 4 levels of amplitude<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />42<br />
  43. 43. Multi Carrier Modulation<br />MCM, orthogonal frequency division multiplexing(OFDM), coded OFDM<br />Used in European digital audio broadcast (DAB), WLAN standards such as IEEE 802.11, HIPERLAN2<br />Good ISI tolerance<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />43<br />
  44. 44. Spread Spectrum<br />Direct sequence spread spectrum<br />Frequency hopping spectrum system<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />44<br />Spread spectrum signal<br />X<br />Modulator<br />Transmission<br />signal<br />User<br />data<br />Radio<br />carrier<br />Chipping<br />sequence<br />Correlator<br />Demodulator<br />X<br />Integrator<br />Decision<br />Data<br />Carrier<br />
  45. 45. Frequency Hopping Spread Spectrum<br />Available bandwidth is split into many channels plus guard spaces<br />Transmitter and receiver stay on a channel for some time and then jump to another, the sequence of this change is the hopping sequence<br />Slow hopping: transmitter uses one frequency for several bit times.<br />Fast hopping: transmitter changes even during one bit period<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />45<br />
  46. 46. FHSS System<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />46<br />Narrowband signal<br />Spread <br />spectrum<br />signal<br />Data<br />Modulator<br />Modulator<br />Frequency<br />synthesizer<br />Hopping<br />sequence<br />Narrowband signal<br />Demodulator<br />Demodulator<br />Data<br />Frequency<br />synthesizer<br />Hopping <br />sequence<br />
  47. 47. Cellular Systems<br />One base station serving a cell (limited area)<br />Higher the user density, smaller the cell<br />Frequency re-use is possible<br />3 and 7 cell clusters are common<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />47<br />
  48. 48. 2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />48<br />Frequency Re-use Clusters<br />f3<br />f3<br />f3<br />f7<br />f3<br />f2<br />f2<br />f2<br />f2<br />f5<br />f1<br />f1<br />f1<br />f5<br />f6<br />f4<br />f3<br />f3<br />f4<br />f1<br />f2<br />f2<br />f2<br />f3<br />f1<br />f7<br />f1<br />f1<br />f2<br />f3<br />f3<br />f3<br />f3<br />f5<br />f6<br />f2<br />3 frequency cluster<br />7 frequency cluster<br />
  49. 49. Advantages of Small Cells<br />Higher capacity<br />Space division multiplexing allows frequency reuse, more users can be supported<br />Less transmission power<br />Mobile station power need to be limited, smaller cells allow better communication<br />Local interference only<br />Need to worry about local interference only<br />Robustness<br />More base stations mean that the system would not fail as a whole if some base stations fail<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />49<br />
  50. 50. Disadvantages of Small Cells<br />Infrastructure needed<br />Larger amount of infrastructure, in terms of base stations, towers and other s will be needed<br />Handover needed<br />With mobile users, users moving from one cell to another, calls will have to be maintained<br />Frequency planning<br />Careful frequency planning needed to avoid interference when you have only a handful of frequencies allocated<br />2/27/2011<br />Debasis Das Mallabhum Institute of Technology<br />50<br />
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