ELEC3505 Communications
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Edmund Tse 2008
Practically:
for large , the bandwidth is slightly greater than 2f
for small , the spectrum is limited to fC plus one pair at fC fm
o The envelope of FM is constant, and the average power is P = AC2
Carsons rule
o
ELEC3505 Communications
Edmund Tse 2008
2
N0
G f df
o
o
*
j 2fT
The optimal filters frequency response is H opt f kG f e
o
Taking the inverse Fourier transform,
hopt t k G * f e j 2fT e j 2ft df
o
Since for real signals, G*(f) = G(-f):
hopt t k G f e j 2
ELEC3505 Communications
Edmund Tse 2008
General
Lecturer
o Prof. Abbas Jamalipour
o EE 732
o abbas@ee.usyd.edu.au
o Consultation time: Wednesdays 1300h-1400h
Assessment
o 10%
Group lab reports and individual lab assessments
o 5%
Individual tutorial attend
ELEC3505 Communications
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o
o
Edmund Tse 2008
Generation of binary sequence:
If + then 1, if - then 0
Main advantage is simplicity
2 types of quantisation error in DM
Slope overload distortion (quantised m(t) falls behind m(t) requires larger
Granular
ELEC3505 Communications
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Edmund Tse 2008
Requires bandwidth of 2W
Coherent detection (synchronous demodulator)
o Uses a product modulator and a LPF cut-off frequency > W but < 2fc - W
o
After filtering: proportional signal of m(t): vo t
1
AC AC cos mt
ELEC3505 Communications
o
Edmund Tse 2008
Available channel bandwidth
Affordable cost of system
Expression of reliability bit error rate (BER) or probability measured at Rx output
In ideal case, it is possible to operate with BER = 0 in noisy channel
o
ELEC3505 Communications
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Edmund Tse 2008
Convolving m(t) with h(t):
m t m t ht d
mnT nT ht d
S
S
mnT ht nT
S
n
o
S
mnT nT ht d
n
S
n
S
PAM signal s(t) = m(t)*h(t), but M f f S
Then, s f f S
M f kf
S
k
M f kf H f
k
S
So H f T sinc fT e jnfT
R
ELEC3505 Communications
Edmund Tse 2008
Bandwidth of BPF is 2W
So average power of filtered noise n(t) is 2WN0
The average power of nI(t) is average power of noise n(t)
Noise component in y(t) = nI(t)
So average power of noise = ()22WN0 = WN0
2
C 2 AC
ELEC3505 Communications
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Edmund Tse 2008
Mid-rise
Quantisation noise
o Definition:
o
o
o
o
o
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difference between the input samples m and output signal v
Artificially created by the process, rather than due to external factors
Quantiser g() maps the cont
ELEC3505 Communications
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Edmund Tse 2008
Example: A VSB signal plus ACcos(2fCt) is passed through an envelope detector. Finding the distortion
by quadrature component:
After adding carrier:
s(t) = AC[1 + Amcos(2fmt)]cos(2fCt) + ACAm(1 2a)sin(2fmt)sin(2fC