1. Sistem Telekomunikasi, Sukiswo, ST, MT Sukiswo sukiswok@yahoo.com
PAM dan PCM
Sukiswo
Sistem Telekomunikasi, Sukiswo, ST, MT

2. Pulse Amplitude Modulation
Sistem Telekomunikasi, Sukiswo, ST, MT

3. Sistem Telekomunikasi, Sukiswo, ST, MT
Demodulation of PAM
Low Pass
Band Pass
By using very narrow
*make sure that Sinc function
is big and flat by reduce time
Sistem Telekomunikasi, Sukiswo, ST, MT

4. Multiplexing PAM-TDM LPF PAM1 PAM2
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
Sistem Telekomunikasi, Sukiswo, ST, MT

5. Sistem Telekomunikasi, Sukiswo, ST, MT
Nyquist Sampling T
Two signal are sampled equally
Tx=the time interval between adjacent channels or samples
For n channel
Nyquist interval
for one signal
Sistem Telekomunikasi, Sukiswo, ST, MT

6. Bandwidth RequirementS1 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
Sistem Telekomunikasi, Sukiswo, ST, MT

7. Transmitting Analog signal in Digital format
Sistem Telekomunikasi, Sukiswo, ST, MT
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)
Sistem Telekomunikasi, Sukiswo, ST, MT

8. Sistem Telekomunikasi, Sukiswo, ST, MT
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
Sistem Telekomunikasi, Sukiswo, ST, MT

9. Sistem Telekomunikasi, Sukiswo, ST, MT
Quantization
M Steps
Sampling Signal
Where M = no. of steps
= quantization step -V V t
Sistem Telekomunikasi, Sukiswo, ST, MT

10. Sistem Telekomunikasi, Sukiswo, ST, MT
Encoding -V V t
000
001
010
011
100
101
110
111
Sistem Telekomunikasi, Sukiswo, ST, MT

11. Sistem Telekomunikasi, Sukiswo, ST, MT
Quantization Error
Quantization Noise
Uniform distribution
Sistem Telekomunikasi, Sukiswo, ST, MT

12. Sistem Telekomunikasi, Sukiswo, ST, MT
Signal to Noise Ratio
The average power
Time average
Continuous RV
time
Sistem Telekomunikasi, Sukiswo, ST, MT

13. Signal to Noise Ratio[1]
where
Sistem Telekomunikasi, Sukiswo, ST, MT

14. 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
Sistem Telekomunikasi, Sukiswo, ST, MT

15. Sistem Telekomunikasi, Sukiswo, ST, MT
TDM-PCM (E1 standard)
300
3.4k
3.1k
voice
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 nsec = sec
Total bit length = 8 bit x 32 channels = 256 bits
Sistem Telekomunikasi, Sukiswo, ST, MT