Pulse Amplitude Modulation dan Pulse Code Modulation oleh Risanuri Hidayat

Pulse Amplitude Modulation 04/05/62 PAM-PCM

Demodulation of PAM 04/05/62 PAM-PCM Low Pass Band Pass Low Pass Band Pass By using very narrow *make sure that Sinc function is big and flat by reduce time 04/05/62 PAM-PCM

PAM-TDM before filtering Multiplexing PAM-TDM LPF Clock Pulse generator Sampler switch PAM1 PAM2 PAM-TDM before filtering PAM-TDM to the transmission line 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 04/05/62 PAM-PCM

Nyquist Sampling 04/05/62 PAM-PCM For n channel Two signal are sampled equally Tx=the time interval between adjacent channels or samples For n channel Nyquist interval for one signal 04/05/62 PAM-PCM

Bandwidth Requirement S1 S2 S3 S4 Tx BF -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 04/05/62 PAM-PCM

Transmitting Analog signal in Digital format 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) 04/05/62 PAM-PCM

Pulse Code Modulation 04/05/62 PAM-PCM 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 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 Where N is the number of binary digit per code word M is the number of quantization level 04/05/62 PAM-PCM

Quantization 04/05/62 PAM-PCM V M Steps -V Sampling Signal Where M = no. of steps = quantization step -V V t 04/05/62 PAM-PCM

Encoding 04/05/62 PAM-PCM V -V -V V t 000 001 010 011 100 101 110 111 1 1 1 1 1 0 1 0 0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 04/05/62 PAM-PCM

Quantization Error 04/05/62 PAM-PCM Quantization Noise Quantization Noise Uniform distribution 04/05/62 PAM-PCM

Signal to Noise Ratio 04/05/62 PAM-PCM The average power Time average Continuous RV time 04/05/62 PAM-PCM

Signal to Noise Ratio[1] where 04/05/62 PAM-PCM

Signal to Noise Ratio[2] In dB Encoding : each quantization level is encoded into N binary digit No.of level No.of binary digit per code word 04/05/62 PAM-PCM

TDM-PCM (E1 standard) 04/05/62 PAM-PCM voice (2x3.4k=6.8k) 300 3.4k time 500 800 MAN WOMAN (2x3.4k=6.8k) Nyquist Each sample is quantized and encoded into 8 bits Bit rate = x 8 = 64kbps ; with 32 channels 1channel = 8 bits therefore 8 x 488.25nsec = 3.9 sec Total bit length = 8 bit x 32 channels = 256 bits 04/05/62 PAM-PCM