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 the same 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

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

16. 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

18. SSS vs other Systems COMPARISON

19. 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

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

21. No wastage of bandwidth

22. Resistance to interception

23. Reduction of multi-path

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

25. 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).

26. 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.

27. 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 1.Interference rejection: the ability of the system to reject interference is directly proportional to Gp. 2.System capacity: the capacity of the system is directly proportional to Gp.