[PPT] - I n f o r m a t i o n T r a n s m i s s i o n PowerPoint Presentation

SLIDE 1

I n f

r

m a t i

n

T r a n s m i s s i

n

C h a p t e r 4 , C h a n n e l s

OVE EDFORS Electrical and information technology

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 2

L e a r n i n g

u

t c

m

e s

A

f t e r t h i s l e c t u r e t h e s t u d e n t s h

u

l d

– u

n d e r s t a n d t h e b a s i c p r

p

e r t i e s

f

w i r e d c h a n n e l s , s u c h a s c a b l e s a n d

p

t i c a l fi b e r s ,

– k

n

w

t h e b a s i c p r

p

e r t i e s

f

w i r e l e s s c h a n n e l s , i n c l u d i n g p r

p

a g a t i

n

l

s

s i n f r e e s p a c e a n d a n t e n n a g a i n s ,

– u

n d e r s t a n d h

w

n

i

s e e n t e r s t h e s y s t e m a n d h

w

i t i s c h a r a c t e r i z e d ,

– u

n d e r s t a n d t h e b a s i c p r i n c i p l e s

f

h

w

m

v

e m e n t s a n d m u l t i p l e w i r e l e s s p r

p

a g a t i

n

p a t h s c r e a t e D

p

p l e r e f f e c t s a n d f a d i n g ( v a r i a t i

n

s i n s i g n a l s t r e n g t h ) , a n d

– b

e f a m i l i a r w i t h t h e p r i n c i p l e

f

t h e m a g n e t i c r e c

r

d i n g c h a n n e l ( f

r

s t

r

i n g d a t a ) .

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 3

Wh e r e a r e w e i n t h e B I G P I C T U R E ?

Models of transmission and storage media. Lecture relates to pages 105–117 in textbook.

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O v e E d f

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s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 4

Wi r e s , c a b l e s a n d fi b e r s

» Coaxial cable » Used for high frequency transmission » Shielded and controlled properties » Twisted pair » Standard telephone line

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O v e E d f

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s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 5

Mo d e l

f

a t r a n s m i s s i

n

l i n e ( w i r e )

Model of short (unit length) section of line:

resistive loss
inductance from wires
“short circuit” resistance
capacitance between wires

... Model of entire wireline unit length sections in series

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O v e E d f

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s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 6

Wi r e s , c a b l e s a n d fi b e r s

Wires and cables have quite high attenuation
Where the propagation “constant” is given by
Sinusoid in – sinusoid out, but with an attenuation and a phase shift

NOTE: Due to something called the skin effect, the resistance R is frequency dependent at high frequencies, so that

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O v e E d f

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s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 7

A t t e n u a t i

n
f

a w i r e p a i r ( p h

n

e l i n e )

For longer wire lengths

the attenuation is huge at higher frequencies.

They are already in

place, so let’s use them…

Frequency [Hz] Received power [dB]

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O v e E d f

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s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 8

P r

p

a g a t i

n

i n a fi b e r

Fibers have low attenuation (< 0.5 dB/km). Reflections inside the fiber lead to dispersion – the light pulse will Smear out in time.

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O v e E d f

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h a p t e r 4 ( P a r t 1 ) 9

R a d i

C

h a n n e l s – F r e e s p a c e

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O v e E d f

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s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 1

F r e e

s

p a c e l

s

s

If we assume RX antenna to be isotropic: Attenuation between two isotropic antennas in free space is (free-space loss):

An isotropic antenna radiates equally in all directions.

d

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O v e E d f

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s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 1 1

A n t e n n a g a i n

An antenna will collect its power from an effective area A. The larger antenna, the

more power it will collect

Similarly, it will focus its transmit power in a certain direction where the power density

then will be higher

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s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 1 2

F r e e

s

p a c e l

s

s , F r i i s ’ l a w

Received power, with antenna gains GTX and GRX:

In free space, the received power decays with distance at a rate of 20 dB/decade

If we write the expression in dB ...

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O v e E d f

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s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 1 3

N

i

s e s

u

r c e s

The total noise situation in a receiver depends on several noise sources

Analog circuits Detector Noise picked up by the antenna Thermal noise in circuits Output signal with requirement

n quality

Wanted signal

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h a p t e r 4 ( P a r t 1 ) 1 4

R e c e i v e r n

i

s e : N

i

s e s

u

r c e s ( 1 )

The noise power spectral density of a noise source is usually given in one of the following ways: 1) Directly [W/Hz] 2) Noise temperature [Kelvin]

Noise

The noise power N is also determined by the bandwidth B of the receiver Here k is Boltzmann’s constant (1.38x10-23 W/Hz) and TK is the is the temperature of the noise source in Kelvin.

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O v e E d f

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h a p t e r 4 ( P a r t 1 ) 1 5

R e c e i v e r n

i

s e : N

i

s e s

u

r c e s ( 2 )

Antenna example Noise temperature

f antenna 1600 K

Noise free antenna Na Model Multiply with bandwidth to get noise power Power spectral density of antenna noise is

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O v e E d f

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h a p t e r 4 ( P a r t 1 ) 1 6

D i s t r i b u t i

n
f

t h e n

i

s e

T

h e n

i

s e i s m

s

t

f

t e n a s s u m e d t

h

a v e a G a u s s i a n d i s t r i b u t i

n
Wi

t h t h i s d i s t r i b u t i

n

i t i s p

s

s i b l e t

c

a l c u l a t e t h e p r

b

a b i l i t y t h a t a n

i

s e s a m p l e e x c e e d s a c e r t a i n l e v e l .

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 1 7

Mu l t i

p

a t h p r

p

a g a t i

n

, T w

w

a v e s

Wave 1 + Wave 2 Wave 2 Wave 1 At least in this case, we can see that the interference pattern changes on the wavelength scale.

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O v e E d f

r

s E I T A 3

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h a p t e r 4 ( P a r t 1 ) 1 8

S m a l l

s

c a l e f a d i n g

Illustration of interference pattern from above Transmitter Reflector

Movement

Position

A B

A B Received power [log scale]

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 1 9

S m a l l

s

c a l e f a d i n g

R

a y l e i g h f a d i n g

Amplitude distribution when mean amplitude is 1, 2, 4, and 10.

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 2

D

p

p l e r s h i f t s

Frequency of received signal: where the Doppler shift is

Receiving antenna moves with speed vr at an angle θ relative to the propagation direction

f the incoming wave, which

has frequency f0.

c

r

v  f f   

 

cos

r

v f c    

The maximal Doppler shift is

max

v f c  

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 2 1

Mo r e t h a n

n

e i n c

m

i n g w a v e

Spectrum of received signal when a f0 Hz signal is transmitted. RX RX movement

Incoming waves from several directions (relative to movement or RX)

All waves of equal strength in this example, for simplicity.

1 1 2 2 3 3 4 4

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O v e E d f

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h a p t e r 4 ( P a r t 1 ) 2 2

Ma g n e t i c r e c

r

d i n g

Store magnetic field with different orientation

Figure source: http://hyperphysics.phy-astr.gsu.edu

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O v e E d f

r

s E I T A 3

C

h a p t e r 4 ( P a r t 1 ) 2 3

S U MMA R Y

Wi

r e s , c a b l e s a n d fi b e r s

– Wi

r e l s a n d c a b l e s a r e L T I s y s t e m s

– B

a n d w i d t h

f

w i r e s a n d c a b l e s d e p e n d

n

l e n g t h

– C

a

x i a l c a b l e s c a n c a r r y h i g h e r b a n d w i d t h s t h a n w i r e s

– F

i b e r s h a v e l

w

a t t e n u a t i

n
R

a d i

c

h a n n e l s

– F

r e e

s

p a c e p r

p

a g a t i

n

– A

n t e n n a g a i n s

– F

r i i s ' l a w

– N

i

s e p r

p

e r t i e s a n d c a l c u l a t i

n

– Mu

l t i

p

a t h p r

p

a g a t i

n

: F a d i n g a n d D

p

p l e r s h i f t s

Ma

g n e t i c r e c

r

d i n g

– S

t

r

i n g m e s s a g e s b y c h a n g i n g m a g n e t i z a t i

n
f

t a p e ( T r a n s m i t t i n g t

a

n

t

h e r t i m e )

SLIDE 24