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

I n f o r m a t i o n T r a n s m i s s i o n C h a p t e r 4 , D i g i t i a l m o d u l a t i o n OVE EDFORS Electrical and information technology

L e a r n i n g o u t c o m e s ● A f t e r t h e s e l e c t u r e s ( s l i d e s s p a n t w o l e c t u r e s ) , t h e s t u d e n t s h o u l 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 o f h o w d i g i t a l i n f o r m a t i o n i s c a r r i e d o n a n a l o g s i g n a l s ( d i g i t a l m o d u l a t i o n ) , i n c l u d i n g a m p l i t u d e , p h a s e a n d f r e q u e n c y m o d u l a t i o n / k e y i n g , – u n d e r s t a n d h o w t h e m o d u l a t i o n p u l s e s h a p e d e t e r m i n e s b a n d w i d t h o f t h e s i g n a l a n d w h a t t h e n a r r o w e s t p o s s i b l e t r a n s m i s s i o n b a n d w i d t h i s f o r a c e r t a i n d a t a r a t e , – u n d e r s t a n d h o w o n e o r m o r e b i t s a r e m a p p e d o n t o s i g n a l c o n s t e l l a t i o n p o i n t s , – b e a b l e t o p e r f o r m b a s i c c a l c u l a t i o n s u s i n g r e l a t i o n s b e t w e e n d a t a r a t e s , s i g n a l c o n s t e l l a t i o n s , p u l s e c h a p e s a n d t r a n s m i s s i o n s p e c t r u m / b a n d w i d t h s , – u n d e r s t a n d t h e f u n d a m e n t a l p r i n c i p l e s o f h o w d i g i t a l i n f o r m a t i o n i s d e t e c t e d a t t h e r e c e i v e r , i n c l u d i n g o p t i m a l r e c e i v e r s , – u n d e r s t a n d t h e r e l a t i o n s h i p s b e t w e e n r e c e i v e s s i g n a l q u a l i t y a n d r e s u l t i n g b i t - e r r o r r a t e s , – b e a b l e t o p e r f o r m b a s i c c a l c u l a t i o n s o n r e s u l t i n g r e c e i v e r p e r f o r m a n c e ( b i t - e r r o r r a t e s ) w h e n t h e m o d u l a t i o n t y p e a n d t h e r e c e i v e d s i g n a l q u a l i t y a r e g i v e n . O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 2

Wh e r e a r e w e i n t h e B I G P I C T U R E ? Digital modulation/ Lecture relates to pages transmission 127-146 in textbook. techniques O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 3

D i fg e r e n t m o d u l a t i o n f o r m a t s • Amplitude modulation, ASK (amplitude shift keying) We will focus primarily on this one! • Phase modulation, PSK (phase shift keying) • Frequency modulation, FSK (frequency shift keying) Transmitted signal, with amplitude, phase or frequency carrying the information O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 4

A m p l i t u d e , p h a s e a n d f r e q u e n c y m o d u l a t i o n   A t Comment: 00 01 11 00 10 - Amplitude carries information 4ASK - Phase constant (arbitrary) 00 01 11 00 10 - Amplitude constant (arbitrary) 4PSK - Phase carries information 00 01 11 00 10 - Amplitude constant (arbitrary) 4FSK - Phase slope (frequency) carries information O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 5

Tie p u l s e s h a p e d e t e r m i n e s t h e b a n d w i d t h o c c u p i e d O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 6

T r a i n o f p u l s e s , r e p r e s e n t i n g 1 1 0 1 • Square pulses Ones mapped to positive pulses • Raised cosine Zeros mapped to negative pulses O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 7

Tie m o d u l a t i o n p r o c e s s Complex domain Bits Radio   c s t signal m LP Mapping PAM Re{ }    exp j 2 f t Complex c numbers Symbol ∞ s LP ( t )= ∑ time c m v ( t − mT s ) PAM: m =−∞ “Standard” basis pulse criteria ∞ 2 dt = 1 or = T s (energy norm.) | v ( t ) | ∫ −∞ ∞ (orthogonality) * ( t − mT s ) dt = 0 for m ≠ 0 ∫ v ( t ) v −∞ O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 8

B a s i s p u l s e s a n d s p e c t r u m Assuming that the complex numbers c m representing the data are independent, then the power spectral density of the base band PAM signal becomes: 2             j 2 πft S f v t e dt LP     which translates into a radio signal (band pass) with 1              S f S f f S f f BP LP c LP c 2 t t T s Many possible pulses O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 9

B a s i s p u l s e s TIME DOMAIN FREQ. DOMAIN Rectangular [in time] f  Normalized freq. T Normalized time t/ T s s (Root-) Raised-cosine [in freq.] Normalized freq. f × T s Normalized time t/ T s O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 0

I n t e r p r e t a t i o n a s I Q - m o d u l a t o r For real valued basis functions v ( t ) we can view PAM as:        s t Re s t   I LP Re c In-phase signal m    cos 2 f t c Radio Pulse c f signal c m Mapping shaping filters o -90     sin 2 f t c   Im c Quadrature signal m        s t Im s t Q LP (Both the rectangular and the (root-) raised-cosine pulses are real valued.) O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 1

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R e c t a n g u l a r p u l s e s Base-band signal (low pass) Radio signal (band pass) O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 2

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R e c t a n g u l a r p u l s e s Complex representation Signal constellation diagram O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 3

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R e c t a n g u l a r p u l s e s Power spectral density for BPSK Normalized freq. f × T b O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 4

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R a i s e d - c o s i n e p u l s e s ( r o l l - o fg 0 . 5 ) Base-band signal (low pass) Radio signal (band pass) O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 5

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R a i s e d - c o s i n e p u l s e s ( r o l l - o fg 0 . 5 ) Complex representation Signal constellation diagram O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 6

B i n a r y p h a s e - s h i f t k e y i n g ( B P S K ) R a i s e d - c o s i n e p u l s e s ( r o l l - o fg 0 . 5 ) Much higher spectral efficiency than BPSK (with rectangular pulses). Power spectral density for BAM/BPSK Normalized freq. f × T b O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 7

Q u a t e r n a r y P S K ( Q P S K o r 4 - P S K ) R e c t a n g u l a r p u l s e s Radio signal (band pass) Complex representation O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 8

Q u a t e r n a r y P S K ( Q P S K o r 4 - P S K ) R e c t a n g u l a r p u l s e s Power spectral density for QPSK T wice the spectrum efficiency of BPSK (with rect. pulses). TWO bits/pulse instead of one. O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 1 9

A g o l d e n b a n d w i d t h r u l e The narrowest bandwidth of any pulses that act independently is [- 1/2T, 1/2T ] where T is the symbol interval O v e E d f o r s E I T A 3 0 - C h a p t e r 4 ( P a r t 3 ) 2 0