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SPREAD SPECTRUM SYSTEMS

SPREAD SPECTRUM SYSTEMS. INTRODUCTION, TECHNIQUES, APPLICATIONS. MEMBERS OF THE GROUP. 2002-E-202 ALI HUSNAIN SARWAR 2002-E-203 NAVEED KHAN SHERWANI 2002-E-204 JUNAID SOHAIL 2002-E-206 MIAN MUHAMMAD BADAR FAROOQ 2002-E-207 RANA MUHAMMAND RIZWAN RIAZ 2002-E-209 SYED YASIR ALI GILANI

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SPREAD SPECTRUM SYSTEMS

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  1. SPREAD SPECTRUM SYSTEMS INTRODUCTION, TECHNIQUES, APPLICATIONS

  2. MEMBERS OF THE GROUP • 2002-E-202 • ALI HUSNAIN SARWAR • 2002-E-203 • NAVEED KHAN SHERWANI • 2002-E-204 • JUNAID SOHAIL • 2002-E-206 • MIAN MUHAMMAD BADAR FAROOQ • 2002-E-207 • RANA MUHAMMAND RIZWAN RIAZ • 2002-E-209 • SYED YASIR ALI GILANI • 2002-E-210 • RIZWAN BIN RAFIQUE CHAUDHRY

  3. BRIEF HISTORY OF SPREAD SPECTRUM THE FUTURE LIES WITHIN

  4. DISCOVERY • No known scientist is credited for the discovery of SS Systems • American movie star Hedy Lamarr and her pianist George Antheil. • They discovered the technique using a player piano to control the frequency hops. • The Germans also experimented with SS during the second World War. • The concept was again introduced in 1951 and was coined the term “Spread Spectrum”

  5. MILITARY BACKGROUND • Early research and development efforts tried to provide countermeasures for radar. • Initially used for military purposes only. • The U. S. Military alone has used SS signals over satellites for at least 25 years.

  6. INTRODUCTION SPREAD SPECTRUM SYSTEMS

  7. DEFINITION • The basic definition of spread spectrum systems is the spreading of the data plus carrier by a pseudo-noise code. • Wireless communications frequency of the transmitted signal is deliberately varied.

  8. EXPLANATION • Pseudo-noise code independent of the information data, is employed as a modulation wave form to “spread” the signal energy • The purpose of coding is to transform an information signal so that it looks more like noise.

  9. The new "spread" signals thesame total power. • Spread Spectrum signals do not interfere with co-existing signals. • Offer a potential for shared spectrum

  10. To qualify as a SS signal • The transmitted signal bandwidth is much greater than the information bandwidth. • Some function other than information being transmitted is employed to determine the resultant transmitted bandwidth.

  11. How Does SS Work? WORKING

  12. WORKING • Injection of corresponding SS code somewhere in the transmitting chain before the antenna. • Despreading at a point in the receive chain before data retrieval. • The key to that the same code must be known at both end in advance

  13. Due to special codes signals appear wide band and noise-like. • Spread spectrum signals are hard to detect on narrow band equipment.

  14. Low power spectral density (watts/hz). • The low PSD helps the SS signals with it non interfering properties. • The correlation receivers: • Interference spreads over large bandwidth

  15. SSS vs other Systems COMPARISON

  16. PROBLEMS OF COMMON WIRELESS SYSTEMS • In conventional wireless signal frequency does not change with time . • Constant frequency communication poses two basic problems. • In conventional wireless signal frequency does not change with time • Easy to intercept

  17. ADVANTAGES • Low power spectral density • Privacy due to unknown random codes. • Good anti-jam performance

  18. No wastage of bandwidth

  19. Resistance to interception

  20. Reduction of multi-path

  21. PSEUDO NOISE A pseudo-noise (PN) code sequence acts as a noise-like (but deterministic) carrier used for bandwidth spreading of the signal energy.

  22. PROPERTIES OF PN CODE • Random, but appearances can be deceptive. • Long time period. • Deterministic, periodical signal that is known to both the transmitter and receiver. • Statistical properties • These should have a good autocorrelation • The different codes must be orthogonal (having correlation index least).

  23. Important PN sequences • Walsh-Hadamard codes, M-sequences, Gold-codes and Kasami-codes. • Walsh sequences fall in the first category of orthagonal sequences. • M-sequences, Gold-codes and Kasami-codes are non orthagonal codes.

  24. Processing Gain • The processing gain is equal to the ratio of the chipping frequency to the data frequency. • G = transmitted BW/data BW. • There are two major benefits from high processing gain • Interference rejection: the ability of the system to reject interference is directly proportional to Gp. • System capacity: the capacity of the system is directly proportional to Gp.

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