Baseband Digital Transmission Multiamplitude Signal Transmission
Baseband Digital Transmission Multiamplitude Signal Transmission
Binary Vs.Multiamplitude signal Binary signal 1 bit of information Two level to represent 0 and 1 If we use multiple amplitude levels We can transmit multiple bits per signal waveform ■Question Probability of Error Vs.Bandwidth ??
Binary Vs. Multiamplitude signal ◼ Binary signal ◼ 1 bit of information ◼ Two level to represent 0 and 1 ◼ If we use multiple amplitude levels ◼ We can transmit multiple bits per signal waveform ◼ Question ◼ Probability of Error Vs. Bandwidth ???
Signal waveform with 4 amplitude levels Normalized pulse whose energy is 1 80=序0ss7 0 ,otherwise Consider 4 equally spaced Amplitude ■Am=(2m-3)d,m=0,1,2,3 ■0rAn={-3d,-d,d,3d0 4 waveform called PAM(Pulse Amplitude Modulated) signal ■Snm(t)=Ang(t),0≤t≤T See figure 4.19,page 190
Signal waveform with 4 amplitude levels ◼ Normalized pulse whose energy is 1 ◼ ◼ Consider 4 equally spaced Amplitude ◼ ◼ Or ◼ 4 waveform called PAM(Pulse Amplitude Modulated) signal ◼ ◼ See figure 4.19, page 190 1 , 0 ( ) 0 , t T g t T otherwise = A m d m m = − = (2 3) , 0,1, 2,3 { 3 , , ,3 } A d d d d m = − − s t A g t t T m m ( ) ( ), 0 =
Signal waveform with 4 amplitude levels Can transmit 2 bits of information per waveform Assign information to waveform ■00→s0) ■01→s ·10→s2() .11→S3() ■ Definition of Symbol Each pair of information bits (00,01,10,11}is called symbol Time duration T is called Symbol Duration If Bit rate R=1/Tp,then Symbol interval T=2Tp
Signal waveform with 4 amplitude levels ◼ Can transmit 2 bits of information per waveform ◼ Assign information to waveform ◼ 00 → s0 (t) ◼ 01 → s1 (t) ◼ 10 → s2 (t) ◼ 11 → s3 (t) ◼ Definition of Symbol ◼ Each pair of information bits {00, 01, 10, 11} is called symbol ◼ Time duration T is called Symbol Duration ◼ If Bit rate R =1/Tb , then Symbol interval T = 2Tb
More on Symbol and Symbol interval Bit rate R=1/Tp Information 0100110 Modulator Symbol Source M=2水 01 S1(t) 00 so(t) 1 S() 0 s(t) Tp 2Tb. T=2Tb Ex:9600bps 4800sps
More on Symbol and Symbol interval ◼ Bit rate R=1/Tb Information Source 0100110. Modulator M=2k Symbol 01 00 11 0. s1 (t) s0 (t) s3 (t) s? (t) Tb 2Tb . T=2Tb Ex: 9600bps = 4800sps