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CHAPTER 2 : WIRELESS DATA TRANSMISSION (WIRELESS SIGNAL (INFRARED LIGHT…
CHAPTER 2 : WIRELESS DATA TRANSMISSION
WIRELESS SIGNAL
INFRARED LIGHT
Components
emittor, transmit
detector, receive
Types of transmission
directed
emitter and detector be directly aimed at one another
line-of-sight principle
diffused
relies on reflected light
emitters have a wide-focused beam
Advantages
not affected by other signals, except light
lights cannot penetrate walls -impossible for someone elsewhere to listen
Disadvantages
lack of mobility
range of coverage
speed of transmission
wide angle of the beam loses energy as it reflects
RADIO WAVES
most common and effective means of wireless communications today
free from some of the limitations that affect light and heat
penetrate most solid objects (with the exception of metallic ones)
radio waves are invisible
HOW RADIO DATA IS TRANSMITTED
ANALOG MODULATION
AMPLITUDE MODULATION (AM)
FREQUENCY MODULATION (FM)
PHASE MODULATION (PM)
DIGITAL MODULATION
BINARY SIGNAL
RETURN-TO-ZERO (RZ)
Should return to 0 back
NON-RETURN-TO-ZERO (NRZ)
No return to 0
POLAR NRZ / NRZ-L
Both sides involve
INVERT-ONE-ONES (NRZ-I)
Changes if next bit is 1, stay on 0
AMPLITUDE SHIFT KEYING (ASK)
Signal on 1, dead on zero
FREQUENCY SHIFT KEYING (FSK)
Double freq on 1
PHASE SHIFT KEYING (PSK)
Invert direction of 1 and 0 from each other. Default 0.
less susceptible to interference from other sources of visible light
