Mtech seminar1


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Mtech seminar1

  1. 1. Barnali Dey Sikkim Manipal Institute of Technology Rangpo, Sikkim-737132,INDIA Equalization methods used in various wireless communication systems
  2. 2. Wireless Channel Impairments Major wireless channel impairments . P ath loss . M ultipath fading . S hadow fading . I nterference
  3. 3. Path Loss <ul><li>In free space, the radio waves travel outward from the transmitter in an expanding sphere. </li></ul><ul><li>The received power decreases with the inverse distance squared: </li></ul><ul><li>In the outdoor multi path environment, the exponent on d (distance) is approximately 4. </li></ul>
  4. 4. Multipath Fading <ul><li>The fields associated with the different paths add as vectors </li></ul><ul><li>The magnitude of the resultant can vary as much as 40 dB as the terminals move only a few wavelengths resultant vary unpredictably. </li></ul>
  5. 5. Shadowing <ul><li>Shadowing occurs when large objects block paths of propagation </li></ul><ul><li>Can be observed if multipath fading is short-term averaged </li></ul>
  6. 6. Interference <ul><li>In mobile receivers, interference is from other base station that transmit the same frequencies as the serving base station. </li></ul><ul><li>In wireless LANs in the 2.4 GHz unlicensed band, interference can from other LAN and microwave oven </li></ul>
  7. 7. Channel Equalization <ul><li>Equalization ( EQ) is the process of using passive or active electronic elements or digital algorithms for the purpose of altering (originally flattening) the frequency response characteristics of a system. </li></ul>
  8. 8. Various wireless systems <ul><li>WCDMA </li></ul><ul><li>Wi-Fi </li></ul><ul><li>Wi-Max </li></ul>
  9. 9. WCDMA <ul><li>Channel Impairment </li></ul><ul><li>Equalization </li></ul>
  10. 10. Channel Impairments <ul><li>Matlab channel visualization tools are utilized for observing channel impulse response for WCDMA. </li></ul><ul><li>It is observed that impulse response is broadened due to multipath effect. </li></ul>Fig : Impulse Response of Ideal channel Fig : Impulse Response of channel after placing a single scatterer at a distant position.
  11. 11. Equalization <ul><li>Rake is used for equalization in WCDMA . </li></ul><ul><li>To improve the signal to noise ratio (SNR) at the receiver RAKE receiver can combine multi-path components. </li></ul><ul><li>Rake provides a separate correlation receiver for each of the multi-path signals and Multi-path components are practically uncorrelated when their relative propagation delays exceeds one chip period. </li></ul><ul><li>It uses a multi-path diversity principle that means it rakes the energy from the multi-path propagated signal components. </li></ul>
  12. 12. Rake receiver for multipath rejection.
  13. 13. Wi-Fi <ul><li>Channel Impairments </li></ul><ul><li>Equalization in Wi-Fi </li></ul>
  14. 14. Channel Impairments <ul><li>WiFi channel impairments are simulated by keeping a scatterer (e.g. building) between the transmitter and receiver. </li></ul><ul><li>The channel is visualized using channel visualization tool of MATLAB. </li></ul>
  15. 15. Channel impulse response and frequency response with single scatterer
  16. 16. Equalization in Wi-Fi <ul><li>Wi-Fi uses adaptive equalizer to mitigate channel impairments. </li></ul>
  17. 17. Rx signal Constellation
  18. 18. WiMAX <ul><li>Channel Impairments </li></ul><ul><li>Equalization in Wi-Max </li></ul>
  19. 19. Channel IR and FR with and without Doppler effect in WiMax
  20. 20. <ul><li>Least mean-square (LMS) equalizer is basically used for channel estimation in WiMax </li></ul>Equalization
  21. 21. conclusion <ul><li>The three systems considered here are useful for different channel conditions. </li></ul><ul><li>Different kind of equalizations are used to encounter the channel impairments and this leads to a proper corrective method </li></ul>
  22. 22. Thank You