Digital communication
fundamentals for
cognitive radio
CENG 5931 GNU Radio
Instructor:Dr.Collins
Presented by
Geetha Paturi
(0933346)
Contents
1. Introduction
2. Digital Modulation techniques
3. Multicarrier Modulation
4. Advantages and disadvantages of multicarrier
modulation
5. Comparison between single and multicarrier
modulation
6. Multicarrier equalization techniques
7. Intersymbol interference
8. Pulse Shaping
9. Conclusion
Introduction
 Data communication system (requirements)
 Robust to error
 Sufficient data rates
 Network capacity constraints
 Achieve balance between these requirements to
overcome conflicting system operating parameters.
Data Transmission
(Anatomy of wireless digital
communication system)
Bit error rate(BER)
Band width efficiency
Fundamental limits:
Shannon–Hartley theorem
B:Transmission bandwidth
C:Channel capacity(b/s)
Sources of Transmission error:
Noise into data transmission & effects of a band-limited transmitted
medium.
Digital Modulation Techniques






Representation of Signals
Euclidean Distance between Signals
Decision Rule
Power Efficiency
M-ary Phase Shift Keying
M-ary Quadrature Amplitude Modulation
Representation of Signals
Euclidean Distance between Signals

From a signal constellation plot we can see how an error
may occur in the transmission whenever the actually
received signal vector is incorrectly shifted to another signal
constellation point by noise contribution.
Euclidean Distance and vector representation between two
signals is defined as

d ij 
2
 s ( t )  s
i

 
d ij  s i  s j
( t )  dt
j
2
Decision Rule
Nearest neighbor rule
 
 
r  si  r  s j ,  j  i
 
 
r  si  r  s j ,  j  i
waveform representation
T
 r (t ) s
0
T
i
( t ) dt 
 r (t ) s
0
j
( t ) dt
Power Efficiency
Power efficiency of modulation scheme measures the
largest minimum signal distance achievable by modulation
technique given the lowest transmit power available.
Energy per symbol

M 1
Es 

 s i ( t )dt
2
P
i0
i 
Energy per bit
Eb 
Es
log
Power efficiency
2
M
2

P

d min
Eb
M-ary Phase Shift Keying
s i ( t )  A  cos(  c t 
2  t
m
), m  0 ,1,  , M  1
M-ary Quadrature Amplitude Modulation
Constellation map of 16 QAM
QAM Receiver
Multicarrier modulation
Single input/Single output MCM transmitter
Single input/Single output MCM receiver
Advantages and disadvantages of
Multicarrier modulation
ADVANTAGES
• Transmission agility
• High data rate
• Immunity to non-flat fading response.
• “divide-and-conquer” channel distortion
• Adaptive bit loading
DISADVANTAGES
• Sensitive to narrowband noise
• Sensitive to amplitude clipping
• Sensitive to timing jitter, delay
Comparison between single carrier and
multicarrier
Multicarrier equalization techniques
To improve quality of received signal equalizers are
employed.
Design decisions of equalizer depend on a number of factors
such as type of distortion and implementation complexity.
Distortion reduction
To mitigate effects of distortion introduced by the channel
there are two techniques.
Channel coding-Adding redundancy
Channel equalization-effects of channel are inverted at
receiver
Intersymbol Interference
When transmissions are sent across a dispersive
channel it is possible for the output of that channel
intercepted by the receiver to be distorted via temporal
spreading resulting in overlapping of individual symbol
pulses.
Pulse Shaping
SOURCE
IMPULSE
MODULATION
H(f)Pulse
shaping
filter
To
channel
Conclusion
Mathematical tools necessary for enabling
advanced features
Various modulation schemes can be used for
transmission under different constraints and
expectations
Bit Error Rate is primarily used to define
performance
Digital communication theory at the core of
cognitive radio operations
References
1.“Cognitive radio communications and networks principles and
practice” By A.M.Wyglinski,M.nekovee,Y.T.Hou(Elevier,December
2009)
2. Sklar, B.; , "Defining, designing, and evaluating digital
communication systems ," Communications Magazine, IEEE , vol.31,
no.11, pp.91-101, Nov 1993 doi: 10.1109/35.256888
3. Kolumban, G.; Kennedy, M.P.; Chua, L.O.; , "The role of
synchronization in digital communications using chaos. I .
Fundamentals of digital communications," Circuits and Systems I:
Fundamental Theory and Applications, IEEE Transactions on , vol.44,
no.10, pp.927-936, Oct 1997
doi: 10.1109/81.633882