Transcript SCADA (Supervisory Control And Data Acquisition)

Digital Modulation
Sukiswo
[email protected]
Sistem Telekomunikasi, Sukiswo, ST, MT
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Outline



ASK
FSK
PSK
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Digital Modulation
Three basic forms of digital modulation
Analog
Digital
AM
Amplitude
ASK
FM
Frequency
FSK
PM
Phase
PSK
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Amplitude Shift Key
t 
1 1 1 1 1 0 1 0 0 0 1 1 0 1 0 1 0 0 1 0 1 1f 1
f t 
t
 ASK t 

 ASK t 
Ac sin ct
t
 t  nT 
f t    an rect 

T


n
1
where an  
0
 ASK t   f t  Ac sin ct
 Ac sin ct
  ASK t   
0

(logic 1)
(logic 0)
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Amplitude Shift Keying[1]
The ASK waveform for one pulse (logic 1)
 Ac sin ct 0  t  T
  ASK t   
elsewhere
0

In order to find an Energy Spectrum of ASK
t 
Energy Spectrum
The Autocorrelation technique is used
f t 
f t 
Delay


Rt   R f 
f t  T 
Therefore Energy Spectrum of ASK
sinc2 function
 2
T
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0
2
T

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Power Spectral Density
 Ac 

  0  c 
 2 
2
2
 Ac 

 Gb  0   c 
 2 
2
 c 
T
 c
 Ac 

  0  c 
 2 
2
2
2
 c 
T
0
 Ac 

 Gb  0   c 
 2 
2
c 
T
c
2
c 
T

 A 
GASK     c  Gb 0  c  Gb 0  c    0  c    0  c 
 2 
2
 
Detection of ASK : detect




present (logic 1) or
absent (logic 0)
Sistem Telekomunikasi, Sukiswo, ST, MT
of the carrier
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Frequency Shift Keying
11111010001101010010111
f t 
t
t
 FSK t 
 ASK t 
1
t
t
Output for 1

Output for 0

2
 ASK t 
1
Ac cosc   t
f t 
 ASK t 

 FSK t 
 ASK t 
2
Ac cosc   t
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Power Spectral Density
K   c   
K  c   
K   c   
K  c   
GASK2  
GASK1  
 c  
 c  c  
c
c  
0
c  

2 
Frequency separation
Note: To prevent significant overlapping of the bandpass of two
filters in detection process
frequency separation

Data rate
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Power Spectral Density[1]
The Actual shape of Power Spectral Density of FSK
Detection of FSK Bandpass Filter
is used to detect f1 (1) and f2 (0)
c  
c c  
2 
In general for frequency separation;
2  DataRate
2
T
m
1

or
T
T
2
  2f ;
2 f

where m is an integer
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Phase Shift Keying
1 1 1 1 1 0 1 0 0 0 1 1 0 1 0 1 0 0 1 0 1 1 f1t 
f t 
t
 PSK t 

 PSK t 
Ac cosct
t
cos 2f 0t
~
cos2f 0t   
~
 t  nT 
f t    an rect 

T

n
1
where an  
0
PSK t   f t  Ac cosct
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Power Spectral Density
 Ac 
 Ac 
2

 Gb  0   c 
 2 
2
 c 
T
 c

 Gb  0   c 
 2 
0
2
 c 
T
2
2
c 
T
c 
2

c
T

 Ac 
GPSK    
 Gb 0  c  Gb 0  c 
 2 
2
 

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
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Detection of PSK
Phase Reversal Key (PRK)
Since information is in the phase, only synchronous detection is possible
Receiver:
 PSK t 
carrier
Synchronize
(coherent)
To data detection


cos 2f 0t

cos2f 0t   

Matched filter detection


carrier
Local oscillator e.g. Crystal oscillator
known as Voltage Control Oscillator VCO
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