Pulse Amplitude Modulation and Pulse Code Modulation oleh

Pulse Amplitude Modulation and Pulse Code Modulation oleh Warsun Najib PAM-PCM

Pulse Amplitude Modulation t 0 t 0 T T 0 t 3/10/2021 t PAM-PCM 0 2

Demodulation of PAM Low Pass Band Pass 0 0 *make sure that Sinc function is big and flat by reduce time 3/10/2021 By using very narrow PAM-PCM 3

Multiplexing PAM-TDM LPF Sampler PAM 1 Pulse generator Clock PAM-TDM before filtering LPF switch PAM-TDM to the transmission line Pulse generator LPF Sampler PAM 2 Switch : determining the synchronization and sequence of the channels Clock : determine the timing of the overall system Pulse generator : produces narrow rectangular pulses to drive the sampler 3/10/2021 PAM-PCM 4

Nyquist Sampling T Two signal are sampled equally Tx=the time interval between adjacent channels or samples Nyquist interval for one signal For n channel 3/10/2021 PAM-PCM 5

Bandwidth Requirement Tx Tx S 1 S 2 S 3 S 4 -BF 0 BF With condition of equal BW and sampling equally therefore the Total BW Requirement is n x BW If BW of each channel is not equal Therefore the Total BW Requirement is n x largest BW 3/10/2021 PAM-PCM 6

Transmitting Analog signal in Digital format l Advantages · Immunity to noise : with some amount of noise digital can withstand while analog failed to provide virtually error free transmission. · Reduce signal to noise ratio · Error control coding ; parity check, Hamming code make more reliable · Signal can be completely regenerated at intermediate regenerator for long haul system. · More compatible with computer system for signal processing and digital memories for data storage. · More elaborate code can be used. · Ideal for integrated services digital network (ISDN) 3/10/2021 PAM-PCM 7

Pulse Code Modulation m(t) is sampled, each sample value is rounded off to the nearest allowable value. This value is digitally encoded as a sequence of binary digits l There are three process of Digitization 1. Sampling 2. Quantization (devide into level of voltage) The approximation of amplitude value of sinal m(t) into one of M discrete quantized values 3. Encoding Each quantization level is encoded into N binary digits l Where 3/10/2021 N is the number of binary digit per code word M is the number of quantization level PAM-PCM 8

Quantization Where M = no. of steps = quantization step V M Steps 0 -V Sampling Signal t 3/10/2021 PAM-PCM 9

Encoding V 111 110 101 100 0 011 010 001 000 -V t 11111010001101010010111 3/10/2021 PAM-PCM 10

Quantization Error Quantization Noise Uniform distribution 0 3/10/2021 PAM-PCM 11

Signal to Noise Ratio The average power Time average Continuous RV time 3/10/2021 PAM-PCM 12

Signal to Noise Ratio[1] where 3/10/2021 PAM-PCM 13

Signal to Noise Ratio[2] In d. B Encoding : each quantization level is encoded into N binary digit No. of level No. of binary digit per code word 3/10/2021 PAM-PCM 14

TDM-PCM (E 1 standard) MAN voice time 3. 1 k 300 WOMAN 0 300 3. 4 k 500 800 3. 4 k Nyquist (2 x 3. 4 k=6. 8 k) Each sample is quantized and encoded into 8 bits Bit rate = x 8 = 64 kbps ; with 32 channels 1 channel = 8 bits therefore 8 x 488. 25 nsec = 3. 9 sec Total bit length = 8 bit x 32 channels = 256 bits 3/10/2021 PAM-PCM 15