1. IT 802DMobile Communications Debasis Das

2. Recommended Books J. Schiller, Mobile Communications, Addison –Wesley, 2003 2. T. S. Rapport, Wireless Communications, Principle and Practices 3. Forouzan, Data Communications and Networking, TMH 2/20/2011 2 Debasis Das Mallabhum Institute of Technology

3. Introduction 2/20/2011 3 Debasis Das Mallabhum Institute of Technology

4. Module Topics General Overview: History, Transmission Medium, Need, Advantages, Disadvantages Different Standards. AMPS, GSM, GPRS, 3G. 2/20/2011 4 Debasis Das Mallabhum Institute of Technology

5. Usage Scenarios Fixed & wired Desktops connected to a wired set up Mobile & wired Laptops get connected to wired networks in hotels Fixed & wireless Temporary arrangements, places where fixed wiring may not be possible Mobile & wireless Topic of this course, users are completely free to move around 2/20/2011 Debasis Das Mallabhum Institute of Technology 5

6. Mobile Devices That Need to Communicate Cellular handsets Walkie-talkies Pager PDA/Pocket computer Cordless phones Laptops on wireless LANs Tablet computers eReaders 2/20/2011 Debasis Das Mallabhum Institute of Technology 6

7. What Do We Need! A means of carrying information from one party to another A means of modifying the carrier to convey information Standardized formats for communication 2/20/2011 Debasis Das Mallabhum Institute of Technology 7

8. RF Can Do the Job Electromagnetic waves in RF frequencies can travel long distances The carrier frequency can be modulated to carry information The carrier needs to be changed in some way to be proportional to the input information 2/20/2011 Debasis Das Mallabhum Institute of Technology 8

9. RF Bands 2/20/2011 Debasis Das Mallabhum Institute of Technology 9

10. Electromagnetic Bands Up to 300 GHz RF band Up to 300 THz IR band Above 300 THz Visible light, UV 2/20/2011 Debasis Das Mallabhum Institute of Technology 10

11. Wireless Communication Scenarios- 1 Lambda=c/f wavelength C=3*10^8 meters/s LF – submarine communications, penetrates water and other obstacles MF & HF - radio broadcasts AM band; 520 kHz to 1605.5 kHz SW band; 5.8 MHz to 26.1 MHz FM band; 87.5 MHz to 108 MHz UHF & VHF – TV broadcasts 174 MHz to 230 MHz & 470 to 790 MHz 2/20/2011 Debasis Das Mallabhum Institute of Technology 11

12. Wireless Communication Scenarios- 2 VHF & UHF; Digital audio 232 to 230 MHz, 1452 to 1472 MHz Digital TV 470 to 862 MHz Analog mobile phone 450-465 MHz Digital GSM 490-960 MHz, 1710-1880 MHz DECT cordless 1880-1900 MHz 3G cellular, UMTS standard 1900-1980 MHz, 2020-2025 MHz, 2110-2190 MHz …. Most wireless mobile communication use the VHF and UHF bands. Small antennas. 2/20/2011 Debasis Das Mallabhum Institute of Technology 12

13. Basic RF Communication 2/20/2011 Debasis Das Mallabhum Institute of Technology 13 Receiver Transmitter

14. Propagation Basics 2/20/2011 Debasis Das Mallabhum Institute of Technology 14 Receivers Transmitter Transmission range Detection range Interference range

15. Various Range in Transmission Transmission range : The zone around the transmitter where communication is possible. Receiver receives enough signal so that error rates are very low Detection range : transmitted power can be detected, error rate is high however Interference zone : not high enough to be detected but adds to the interference with other signals 2/20/2011 Debasis Das Mallabhum Institute of Technology 15

16. Radiation Pattern 2/20/2011 Debasis Das Mallabhum Institute of Technology 16 Transmitters Directional Omni-directional

17. Antenna Issues Theoretical isotropic antenna is one that radiates equal energy in all directions. Practical antenna is a dipole, length lambda/2, centre fed, two halves of lambda/4 Dipoles are Omni-directional Sectorized antennas are multiple directional antenna on a single pole Multiple element antennas help combat fading effects 2/20/2011 Debasis Das Mallabhum Institute of Technology 17

18. Multiplexing Space division multiplexing (SDM) Frequency division multiplexing (FDM) Time division multiplexing (TDM) Code division multiplexing (CDM) 2/20/2011 Debasis Das Mallabhum Institute of Technology 18

19. Channel Allocation Borrowing channel allocation (BCA) Borrow unused channel frequencies from neighboring cells Fixed channel allocation (FCA) Channel allocations per cell is fixed 2/20/2011 Debasis Das Mallabhum Institute of Technology 19

20. Inverse Square Law Radio energy available at any point some distance away from the transmitter Is inversely proportional to the square of the distance 2/20/2011 Debasis Das Mallabhum Institute of Technology 20 Surface area= 4.pi.d^2 d

21. Modes of Propagation Ground wave Sky wave Space wave 2/20/2011 Debasis Das Mallabhum Institute of Technology 21

22. Ground Wave propagation Radio waves in the low frequency ranges (< 2 MHz) Radio energy travels along the ground mainly Enclosed between the ground and the Ionosphere Radio transmissions in medium wave are examples 2/20/2011 Debasis Das Mallabhum Institute of Technology 22

23. Sky Wave Propagation There is a ionized belt around the earth( 2 to 30 MHz) Radio wave is reflected in this ionosphere and travels long distance Wavelengths are shorter than the frequency band that uses the ground wave mode Radio shortwave transmissions are examples 2/20/2011 Debasis Das Mallabhum Institute of Technology 23

24. Space Wave Propagation Wavelengths are short enough to penetrate the ionosphere (> 30 MHz) Energy needs to travel in straight line to the receiver TV transmissions are an example 2/20/2011 Debasis Das Mallabhum Institute of Technology 24

25. Other Signal Propagation Effects Blocking/shadowing Reflection Refraction Scatter Diffraction Multi path propagation 2/20/2011 Debasis Das Mallabhum Institute of Technology 25

26. Multipath Situation 2/20/2011 Debasis Das Mallabhum Institute of Technology 26 Skyscraper Transmitter Car Obstacle

27. Multipath + Channel Characteristics Multipath causes delay spread Effect= Inter-symbol interference short term fading (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 Long term fading, due varying distance from sender, compensate by raising/ lowering power transmitted so that received power is within specified range Doppler shift 2/20/2011 Debasis Das Mallabhum Institute of Technology 27

28. Mobile Communication Schemes 2/20/2011 Debasis Das Mallabhum Institute of Technology 28 (A) CDMA (B) Cellular

29. North American Systems-1 2/20/2011 Debasis Das Mallabhum Institute of Technology 29

30. North American Systems-2 2/20/2011 Debasis Das Mallabhum Institute of Technology 30

31. European Systems 2/20/2011 Debasis Das Mallabhum Institute of Technology 31

32. Japanese Systems 2/20/2011 Debasis Das Mallabhum Institute of Technology 32

33. Basic Modulation Schemes(Digital) In wireless network analog modulation need to be used, these include following basic schemes Amplitude Shift Keying ASK Frequency Shift Keying FSK Phase shift keying PSK The digital input is converted to analog baseband signal before modulation 2/20/2011 Debasis Das Mallabhum Institute of Technology 33

34. Reasons for Going Analog Antenna Antenna need to comparable to wavelength of carrier Frequency Division multiplexing Analog modulation shifts baseband signal to different carrier signal. Higher carrier frequency gives you higher bandwidth Medium Characteristics Path loss, penetration of obstacles, reflection, scattering, diffraction are wavelength dependent 2/20/2011 Debasis Das Mallabhum Institute of Technology 34

35. Modulation in a Transmitter 2/20/2011 Debasis Das Mallabhum Institute of Technology 35 Analog baseband signal Digital modulation Analog Modulation Modulated signal Digital data Radio carrier

36. Demodulation in Receiver 2/20/2011 Debasis Das Mallabhum Institute of Technology 36 Analog baseband signal Analog demodulation Synchronization decision Digital signal Radio carrier

37. ASK Simple scheme, send one level of carrier amplitude for 1 and another for 0 Needs low bandwidth But amplitude is affected by multipath , noise, path loss etc. ASK is not used for RF communication However, is used in optical communication 2/20/2011 Debasis Das Mallabhum Institute of Technology 37

38. FSK Used often in RF communication, binary FSK or BFSK Different frequencies are send for the two digital levels Sudden phase changes can generate high frequencies Frequency modulation in continuous phase modulation (CPM) is used Demodulation can use two fixed frequency filters Needs larger bandwidth, less susceptible to noise 2/20/2011 Debasis Das Mallabhum Institute of Technology 38

39. Phase Shift Keying Change phase of carrier by 180 degrees, every time baseband changes from 1 to 0 or 0 to 1. binary PSK BPSK can be simply multiplying the carrier by +1 when input is 1 and multiplying by -1 when input is 0 Reception uses phase locked loop for reference Compared to FSK, PSK is more resistant to interference Receiver and transmitter are more complex to design 2/20/2011 Debasis Das Mallabhum Institute of Technology 39

40. MSK(Min Phase Shift Keying) Avoids abrupt phase changes Data bits are separated into odd and even bits, duration of bits are doubled Two frequencies f1 & f2, such that f2=2*f1 Phase is shifted based different criteria Gaussian MSK is a variation, GMSK is used in most European wireless standards 2/20/2011 Debasis Das Mallabhum Institute of Technology 40

41. Advanced PSK 2 bits are considered together, smaller phase shifts for each group of 2 bits, 4 phase shifts are used This is the QPSK scheme Carrier reference is a must, frequent synchronization required Differential PSK, decides phase shifts with respect from the last phase, not absolute DQPSK is one of the most efficient schemes IS-136, PACS of US and Japanese PHS of Japan are examples 2/20/2011 Debasis Das Mallabhum Institute of Technology 41

42. QAM Phase shift keying and amplitude keying is combined QPSK and several levels of amplitude 64QAm for example can combine QPSK and 4 levels of amplitude 2/20/2011 Debasis Das Mallabhum Institute of Technology 42

43. Multi Carrier Modulation MCM, orthogonal frequency division multiplexing(OFDM), coded OFDM Used in European digital audio broadcast (DAB), WLAN standards such as IEEE 802.11, HIPERLAN2 Good ISI tolerance 2/20/2011 Debasis Das Mallabhum Institute of Technology 43

44. Spread Spectrum Direct sequence spread spectrum Frequency hopping spectrum system 2/20/2011 Debasis Das Mallabhum Institute of Technology 44 Spread spectrum signal X Modulator Transmission signal User data Radio carrier Chipping sequence Correlator Demodulator X Integrator Decision Data Carrier

45. Frequency Hopping Spread Spectrum Available bandwidth is split into many channels plus guard spaces Transmitter and receiver stay on a channel for some time and then jump to another, the sequence of this change is the hopping sequence Slow hopping: transmitter uses one frequency for several bit times. Fast hopping: transmitter changes even during one bit period 2/20/2011 Debasis Das Mallabhum Institute of Technology 45

46. FHSS System 2/20/2011 Debasis Das Mallabhum Institute of Technology 46 Narrowband signal Spread spectrum signal Data Modulator Modulator Frequency synthesizer Hopping sequence Narrowband signal Demodulator Demodulator Data Frequency synthesizer Hopping sequence

47. Cellular Systems One base station serving a cell (limited area) Higher the user density, smaller the cell Frequency re-use is possible 3 and 7 cell clusters are common 2/20/2011 Debasis Das Mallabhum Institute of Technology 47

48. Advantages of Small Cells Higher capacity Space division multiplexing allows frequency reuse, more users can be supported Less transmission power Mobile station power need to be limited, smaller cells allow better communication Local interference only Need to worry about local interference only Robustness More base stations mean that the system would not fail as a whole if some base stations fail 2/20/2011 Debasis Das Mallabhum Institute of Technology 48

49. Disadvantages of Small Cells Infrastructure needed Larger amount of infrastructure, in terms of base stations, towers and other s will be needed Handover needed With mobile users, users moving from one cell to another, calls will have to be maintained Frequency planning Careful frequency planning needed to avoid interference when you have only a handful of frequencies allocated 2/20/2011 Debasis Das Mallabhum Institute of Technology 49