1 / 25

Data and Computer Communications

Data and Computer Communications. Chapter 9 – Spread Spectrum. Ninth Edition by William Stallings. Spread Spectrum. All creative people want to do the unexpected . —Ecstasy and Me: My Life as a Woman , Hedy Lamarr. Spread Spectrum.

cortez
Download Presentation

Data and Computer Communications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Data and Computer Communications Chapter 9 – Spread Spectrum Ninth Edition by William Stallings Data and Computer Communications, Ninth Edition by William Stallings, (c) Pearson Education - Prentice Hall, 2011

  2. Spread Spectrum All creative people want to do the unexpected. —Ecstasy and Me: My Life as a Woman, Hedy Lamarr

  3. Spread Spectrum

  4. Pseudorandom Numbershttp://www.math.utah.edu/~pa/Random/Random.htmlseealsorand() and srand() functions

  5. General Model of Spread Spectrum System

  6. Spread Spectrum Advantages • immunity from noise and multipath distortion • can hide / encrypt signals • several users can share same higher bandwidth with little interference • CDM/CDMA Mobile telephones

  7. Frequency Hopping Spread Spectrum (FHSS)

  8. Frequency Hopping Example

  9. FHSS (Transmitter)

  10. Frequency Hopping Spread Spectrum System (Receiver)

  11. Slow and Fast FHSS • commonly use multiple FSK (MFSK) • have frequency shifted every Tc seconds • duration of signal element is Ts seconds • Slow FHSS has Tc Ts • Fast FHSS has Tc < Ts • FHSS quite resistant to noise or jamming • with fast FHSS giving better performance

  12. Slow MFSK FHSS(PN: pseudo noise)

  13. Fast MFSK FHSS(PN: pseudo noise)

  14. Direct Sequence Spread Spectrum (DSSS) • each bit is represented by multiple bits using a spreading code • this spreads signal across a wider frequency band • has performance similar to FHSS

  15. Direct Sequence Spread Spectrum Example

  16. Direct Sequence Spread Spectrum System

  17. DSSS Example Using BPSK

  18. ApproximateSpectrum of DSSS Signal

  19. Code Division Multiple Access (CDMA) Allocatingfrequencychannelson-demand in a multi-users environnement is inefficient (needcomplexcircuitry and protocol). More efficient to giveeach user all the bandwith and givehim a « key » to encode his transmission.

  20. Code Division Multiple Access (CDMA)

  21. CDMA Example

  22. CDMA “chip” Orthogonality : http://en.wikipedia.org/wiki/Chip_(CDMA) Or not…

  23. CDMA Example

  24. CDMA for DSSS

  25. Summary • concept of spread spectrum • FHSS • FHSS using MFSK • DSSS • DSSS using BPSK • Code Division Multiple Access • CDMA for Direct Sequence Spread Spectrum

More Related