Introduction & Wireless Transmission


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Introduction & Wireless Transmission

  1. 1. Simplified Reference Model Application Transport Network Data Link Physical Medium Data Link Physical Application Transport Network Data Link Physical Data Link Physical Radio Network Network
  2. 2. Reference Model <ul><li>Physical Layer : </li></ul><ul><li>Bit Stream to signal conversion </li></ul><ul><li>Frequency selection </li></ul><ul><li>Generation of carrier frequency </li></ul><ul><li>Data modulation over carrier frequency </li></ul><ul><li>Data encryption </li></ul>
  3. 3. Reference Model <ul><li>Data Link Layer : </li></ul><ul><li>Data Multiplexing </li></ul><ul><li>Error detection and correction </li></ul><ul><li>Medium Access </li></ul><ul><li>In essence : </li></ul><ul><li>Reliable point-to-point transfer of data between sender and receiver. </li></ul>
  4. 4. Reference Model <ul><li>Network Layer : </li></ul><ul><li>Connection setup </li></ul><ul><li>Packet routing </li></ul><ul><li>Handover between networks </li></ul><ul><li>Routing </li></ul><ul><li>Target device location </li></ul><ul><li>Quality of service (QoS) </li></ul>
  5. 5. Reference Model <ul><li>Transport Layer : </li></ul><ul><li>Establish End-to-End Connection </li></ul><ul><li>Flow control </li></ul><ul><li>Congestion control </li></ul><ul><li>TCP and UDP </li></ul><ul><li>Applications – Browser etc. </li></ul>
  6. 6. Reference Model <ul><li>Application Layer: </li></ul><ul><li>Multimedia applications </li></ul><ul><li>Applications that interface to various kinds of data formats and transmission characteristics </li></ul><ul><li>Applications that interface to various portable devices </li></ul>
  7. 7. Overlay Networks - the global goal regional metropolitan area campus-based in-house vertical handover horizontal handover integration of heterogeneous fixed and mobile networks with varying transmission characteristics
  8. 8. <ul><li>Frequency Ranges </li></ul>WIRELESS TRANSMISSION 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100  m 3 THz 1  m 300 THz visible light VLF LF MF HF VHF UHF SHF EHF infrared UV optical transmission coax cable twisted pair <ul><li>VLF = Very Low Frequency UHF = Ultra High Fequency </li></ul><ul><li>LF = Low Frequency SHF = Super High Frequency </li></ul><ul><li>MF = Medium Frequency EHF = Extra High Frequency </li></ul><ul><li>HF = High Frequency UV = Ultraviolet Light </li></ul><ul><li>VHF = Very High Frequency </li></ul><ul><li>wave length  , speed of light c  3x10 8 m/s, frequency f </li></ul>
  9. 9. Frequencies <ul><li>kHz Range (Low and Very Low frequencies) </li></ul><ul><li>Used for short distances using twisted copper wires </li></ul><ul><li>Several KHz to MHZ (Medium and High Frequencies) </li></ul><ul><li>For transmission of hundreds of radio stations in the AM and FM mode </li></ul><ul><li>Use co-axial cables </li></ul><ul><li>Transmission power is several kW. </li></ul>
  10. 10. Frequencies <ul><li>Several MHz to Terra Hz Range (VHF and UHF) </li></ul><ul><ul><li>Typically 100 MHz to 800 MHz and extending to terraHz) </li></ul></ul><ul><ul><li>Conventional Analog TV (174-230 MHz and 470-790 MHz) </li></ul></ul><ul><ul><li>DAB Range (220 – 1472 MHz) </li></ul></ul><ul><ul><li>DTV (470 – 872 MHz) </li></ul></ul><ul><ul><li>Digital GSM (890-960MHz) </li></ul></ul>
  11. 11. Frequencies <ul><li>3G Mobile Systems (1900-2200 MHz) </li></ul><ul><li>Super High(SH) and Extremely Super High(ESH) </li></ul><ul><ul><li>Hundreds of GHz </li></ul></ul><ul><ul><li>Fixed Satellite Services </li></ul></ul><ul><ul><li>Close to infra-red. </li></ul></ul>
  12. 12. Frequencies <ul><li>For Several TerraHz : </li></ul><ul><ul><li>Optical Transmission </li></ul></ul><ul><ul><li>Why do we need very high transmission frequencies? </li></ul></ul><ul><ul><li>The information content in video, satellite data etc is enormous. </li></ul></ul><ul><ul><li>If we need to accommodate many signals simultaneously, we need a high bit rate which in turn demands high frequency. </li></ul></ul>
  13. 13. REGULATIONS <ul><li>International Telecommunications Union (ITU), Geneva responsible for world-wide coordination of telecommunications activity. </li></ul><ul><li>ITU – R (Radio Communications sector) handles standardization in Wireless sector. </li></ul>
  14. 14. REGULATIONS ITU-R Region-1 Europe, Middle East, Former Russia, Africa Region-2 Greenland, N & S America Region-3 Australia, New Zealand
  15. 15. Frequency Allocation
  16. 16. REGULATIONS PDC : Personal Digital Cellular NMT : Nordic Mobile Telephone DECT : Digital Enhanced Cordless Telephone PACS : Personal Access Communications System
  17. 17. SIGNALS A sine wave is represented as g(t) = A t sin ( ω .t + ø) Here, A t : Maximum amplitude w : angular frequency = 2 π f ø : Phase Displacement
  18. 18. SIGNALS <ul><ul><li>Different representations of signals </li></ul></ul><ul><ul><ul><ul><li>amplitude (amplitude domain) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>frequency spectrum (frequency domain) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>phase state diagram (amplitude M and phase  in polar coordinates) </li></ul></ul></ul></ul>A [V]  I= M cos  Q = M sin   A [V] t[s]
  19. 19. Signals <ul><li>According to fourier series, it is possible to reconstruct the original signal using the sine and cosine functions. </li></ul><ul><li>G(t) = ½ C + </li></ul>In the above eqn, C represents the DC component.
  20. 20. Signals <ul><li>As n varies, increasing number of harmonics are added to the signal representation. </li></ul><ul><li>As n approaches infinity, the original signal is truly represented. </li></ul><ul><li>The given signal has to be modulated over a career frequency. </li></ul>
  21. 21. Antenas <ul><li>An Antenna aids in transforming a wired medium to a wireless medium </li></ul><ul><li>Antennas couple electromagnetic energy to the space and from the space TO and FROM a wire/coaxial cable. </li></ul>
  22. 22. ISOTROPIC RADIATOR ANTENNA <ul><li>Theoretical reference antenna is the isotropic radiator. </li></ul><ul><li>It emits equal power in all directions. </li></ul>z y x z y x
  23. 23. Antennas <ul><li>Practical Antennas Exhibit Directional properties . </li></ul><ul><li>Thin Centre-fed Dipole: </li></ul>λ /2 <ul><li>Dipole consists of two collinear conductors separated by a small feeding gap. </li></ul><ul><li>Generally, the length of the Dipole is half the wavelength of the signal to be transmitted/received.( λ = C/f where is is the speed of light {3*10 8 m/s) </li></ul>
  24. 24. Wavelength <ul><li>Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength. </li></ul>
  25. 25. Dipole Antenna <ul><li>When the signal is obstructed by mountains, buildings etc, the power of the sinal gets weak. </li></ul><ul><li>It can be boosted by additional devices. </li></ul>
  26. 26. Directional Antenna <ul><li>Several directional antennas can be combined to form a sectored antenna. </li></ul>
  27. 27. Signal Propagation Range distance sender transmission detection interference <ul><li>Transmission range </li></ul><ul><ul><li>communication possible </li></ul></ul><ul><ul><li>low error rate </li></ul></ul><ul><li>Detection range </li></ul><ul><ul><li>detection of the signal possible </li></ul></ul><ul><ul><li>no communication possible </li></ul></ul><ul><li>Interference range </li></ul><ul><ul><li>signal may not be detected </li></ul></ul><ul><ul><li>signal adds to the background noise </li></ul></ul>
  28. 28. Path Loss during Transmission <ul><li>Propagation in free space is always in a straight line like that of light. </li></ul><ul><li>Receiving power proportional to 1/d² in vacuum – much more in real environments (d = distance between sender and receiver) </li></ul><ul><li>Receiving power additionally influenced by </li></ul><ul><li>Fading (frequency dependent) </li></ul><ul><li>shadowing </li></ul><ul><li>reflection at large obstacles </li></ul><ul><li>refraction depending on the density of a medium </li></ul><ul><li>scattering at small obstacles </li></ul><ul><li>diffraction at edges </li></ul>
  29. 29. Path Loss Effects reflection scattering diffraction shadowing refraction
  30. 30. Signal Propagation effects <ul><li>Signal Penetration through objects : </li></ul><ul><li>At lower frequency, the penetration is higher. </li></ul><ul><li>At very high frequencies, the transmission behavior of the wave is close to that of light, </li></ul>
  31. 31. Propagation behavior of waves <ul><ul><ul><li>Ground Wave (<2 MHz): Can follow earth’s surface and can propagate long distances </li></ul></ul></ul><ul><ul><ul><li>[Submarine communication, AM Radio etc] </li></ul></ul></ul><ul><ul><ul><li>Sky Wave (2-30 MHz) : Waves are reflected. They can bounce back and forth between ionosphere and earth’s surface and can travel around the world. </li></ul></ul></ul><ul><ul><ul><li>Line of Sight [>30 MHz) : The waves are bent by refraction. </li></ul></ul></ul>
  32. 32. Multipath Propagation
  33. 34. Multipath Propagation <ul><li>Radio waves sent from the sender to the receiver can travel in a straight line as well as may reach the destination after being reflected by several obstacles. </li></ul><ul><li>The signal arrives at different times at the receiver. THIS EFFECT IS CALLED DELAY SPREAD </li></ul>
  34. 35. Multipath Propagation <ul><li>The original signal gets a spread signal </li></ul><ul><li>The order of delays is 2 to 12 micro secs. </li></ul>
  35. 36. Effects of delay spread <ul><li>Short-pulse signals will be spread into a broader impulse or several weaker pulses. </li></ul><ul><li>In the fig, the impulse at the sender is received as three smaller pulses at the receiver. </li></ul><ul><li>Also, the power level of the received pulses will be low. So, they will be perceived as noise. </li></ul>
  36. 37. Effects-2 of delay spread <ul><li>Inter Symbol Interference : </li></ul><ul><li>The second symbol is separated from the first in the transmitted signal. </li></ul><ul><li>At the receiver, they overlap because of delays. </li></ul><ul><li>If the pulses represent symbols, they will interfere with each other and there will be INTER SYMBOL INTERFERENCE. </li></ul>
  37. 38. One possible solution <ul><li>Receiver should know the delay characteristics of different paths. </li></ul><ul><li>Receiver can compensate for the distortion </li></ul><ul><li>Receiver can equalize the signals based on the channel characteristics. </li></ul>
  38. 39. Effects of mobility <ul><li>Channel characteristics change over time and location </li></ul><ul><ul><li>signal paths change </li></ul></ul><ul><ul><li>different delay variations of different signal parts </li></ul></ul><ul><ul><li>different phases of signal parts </li></ul></ul><ul><li> quick changes in the power received (short term fading) </li></ul>short term fading long term fading t power
  39. 40. Solution for Long Term Fading <ul><li>Senders can increase/decrease power on a regular basis so that the received power is within certain bounds. </li></ul>
  40. 41. Long Term Fading <ul><li>Additional changes in </li></ul><ul><ul><li>distance to sender </li></ul></ul><ul><ul><li>obstacles further away </li></ul></ul><ul><li> slow changes in the average power received (long term fading) </li></ul>