1. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr Spread spectrum modulation Chapter 9

2. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr 9.1 Introduction  Digital communication  Bandwidth(secure communication), power efficiency  Spread spectrum modulation jamming, multipath-rejection, multiple-access communications  Bandwidth in excess of the minimum bandwidth necessary  A code that is independent of the data sequence(operating in synchronism with the transmitter)  Direct-sequence spread spectrum  Modulate a wide-band code  Second modulation using a phase-shift keying  Frequency happing  pseudo-random or pseudo-noise sequence

3. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr 9.2 pseudo-noise sequences  Pseudo-noise  Periodic binary sequence with a noiselike waveform that is generated by means of a feedback shift register .  2 m -1 period  Said to be linear when the feedback logic consists entirely of modulo-2 adder (not permitted zero state)

4. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr 9.2 pseudo-noise sequences  Properties of maximum-length sequence have many of the properties possessed by a truly random binary sequence  Balance property : the number of 1s is always one more than the number of 0s  Run property : 1 run(1/2), 2 run(1/4), 3 run(1/8) total number of run = (N+1)/2 (when N=2 m -1)  Correlation property :autocorrelation function of maximum-length sequence is periodic and binary valued.  Because of the maximum-length sequence, R c(  ) is similar to tat of a random binary wave  Same envelope sinc 2 (fT) for their power spectral density  Random binary sequence: continuous spectral density  Maximum-length sequence:delta function spaced 1/NT c Hz

5. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr 9.2 pseudo-noise sequences  Choosing a Maximum-Length Sequence  How find the feedback logic : error control code  Table 9.1: shift-register length & feedback taps, image 9.3 A notion of spread spectrum  Attribute of spread- spectrum modulation  Jamming(fairly powerful broadband noise, multi-tone waveform)  Noise-like appearance so as to blend into the background)  Spread spectrum modulation

6. http://Vada.skuu.ac.kr Kdream@nature.skku.ac.kr 9.4 direct-sequence spread spectrum with coherent binary phase-shift keying  Passband transmission over a satellite channel  Mode for analysis  Synchronization  Acquisition and tracking