Digital communication fundamentals for cognitive radio

CENG 5931 GNU Radio

Instructor:Dr.Collins

Presented by

Geetha Paturi

(0933346)

1. Introduction2. Digital Modulation techniques3. Multicarrier Modulation4. Advantages and disadvantages of multicarrier modulation5. Comparison between single and multicarrier modulation

6. Multicarrier equalization techniques7. Intersymbol interference 8. Pulse Shaping9. Conclusion

Contents

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 bandwidthC: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

dttstsd jiij22 )()(

jiij ssd

Decision Rule

Nearest neighbor rule

waveform representation

ijsrsr ji ,

ijsrsr ji ,

T

j

T

i dttstrdttstr00

)()()()(

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

Energy per bit

Power efficiency

dttsPEM

ii

i

s

1

0

2 )(

M

EE s

b2log

bP E

d 2min

M-ary Phase Shift Keying

1,,1,0),2

cos()(

Mmm

ttAts ci

M-ary Quadrature Amplitude Modulation

Constellation map of 16 QAM

QAM Receiver

Multicarrier modulationSingle 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 loadingDISADVANTAGES• 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 reductionTo 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

To channel

SOURCE IMPULSE MODULATION

H(f)Pulse

shaping filter

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 1997doi: 10.1109/81.633882