SFWRENG 4J03 Lecture Notes - Lecture 8: Passband, Spread Spectrum, Pseudorandom Binary Sequence
12 Oct 2016
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Spreading the spectrum through pseudo noise sequence (pn) code. Despreading is achieved through the same code in r 1. Making the transmitted data appear like noise. Passband: phase shifting (psk), frequency shifting (fsk): Transmission: binary data [b(t)] pn sequence [c(t)] o/p m(t) Page 1 of 6 r(t) (x) c(t) bt. Decision device, i. e. = 0 1, 0, v 0 because you want your signal to appear as noise. {ck} polar nrz encoding c(t) digital signal discrete in amplitude & time. Pn seq generated using 3 stage feedback shift register 0011101 time to send an individual binary bit [tb]: number of flip-flops [m]: N = 2m 1 = 23 1 = 7. Interference signal [i(t)]: m(t) + i(t) r(t) Receiving r(t) c(t) z(t) bt. Product modulator z(t) = r(t) c(t) r(t) z(t) Page 2 of 6 c(t) = 1. Z(t) = b(t) + c(t) i(t) second part removed with lpf because it is high. {bk} polar nrz level encoder b(t)
