Pulse Amplitude Modulation and Pulse Code Modulation oleh Warsun Najib

Pulse Amplitude Modulation 29/12/61 PAM-PCM

Demodulation of PAM Low Pass Band Pass *make sure that Sinc function Low Pass Band Pass By using very narrow *make sure that Sinc function is big and flat by reduce time 29/12/61 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 29/12/61 PAM-PCM

Nyquist Sampling 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 29/12/61 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 29/12/61 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) 29/12/61 PAM-PCM

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 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 29/12/61 PAM-PCM

Quantization V M Steps -V Sampling Signal Where M = no. of steps = quantization step -V V t 29/12/61 PAM-PCM

Encoding -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 29/12/61 PAM-PCM

Quantization Error Quantization Noise Uniform distribution 29/12/61 Quantization Noise Uniform distribution 29/12/61 PAM-PCM

Signal to Noise Ratio The average power Time average Continuous RV 29/12/61 PAM-PCM

Signal to Noise Ratio[1] where 29/12/61 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 29/12/61 PAM-PCM

TDM-PCM (E1 standard) voice (2x3.4k=6.8k) 300 3.4k 3.1k time 500 800 500 800 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 29/12/61 PAM-PCM