DSSS direct sequence spread spectrum signal

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    06-May-2015
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its conceptwhy it is usedits family..description of DSSSits application

Transcript of DSSS direct sequence spread spectrum signal

  • 1.Spread spectrum signal for digitalcommunication Direct Sequence Spread spectrum signal Sarbjeet Singh

2. OBJECTIVE 5.1 Concept of Spread SpectrumWhy Spread specturm used for..!spread spectrum- Family..!Direct Sequence spread spectrumApplications DS spread Spectrum 3. Spread-spectrum (SS) communicationstechnology was first described onpaper by an actress and a musician! In1941, Hollywood actress Hedy Lamarrand pianist George Antheil described asecure radio link to control torpedosand received U.S. patent #2.292.387.It was not taken seriously at that timeby the U.S. Army and was forgottenuntil the 1980s, when the came alive,and has become increasingly popularfor applications that involve radio linksin hostile environments. 4. This is based on Shannon and Hartley channel-capacitytheorem. C = B Log2 (1+ S/N)...(1)C is the channel capacity in bits per second (bps)B is the required channel bandwidth in HzS/N is the signal-to-noise power ratio C here is which represents the amount of informationallowed by the communication channel, also represents thedesired performance. Bandwidth (B) is the price to be paid,because frequency is a limited resource. S/N ratio expressesthe environmental conditions or the physical characteristics(obstacles, prsence of jam mers, interfrences, etc.). 5. Modify the above equation (1) by changing the log base from 2 to e (the Napierian number). C/B = (1/Ln2) Ln(1+S/N) = 1.443 Ln(1+S/N)...(2)Applying the MacLaurin series development forLn(1+x) = x x2/2 + x3/3 x4/4 + ...+ (-1)k+1xk/k +...:ThereforeC/B = 1.443 (S/N 1/2 (S/N)2 + 1/3 (S/N)3 - ...)S/N is usually low for spread-spectrum applications. (As just mentioned, the signal power density can be even below the noise level.) Assuming a noise level such that S/N