1. EE521 Analog and Digital Communications
James K. Beard, Ph. D.
Tuesday, January 18, 2005
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2. Essentials Text: Bernard Sklar, Digital Communications, Second Edition
Prerequisites
Consent of Instructor (Dr. Silage)
SystemView (CD-ROM with text)
Office
E&A 709
Hours TBA, Tuesday afternoons planned
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3. Today’s Topics Course overview Baseband signals and modulation
Introduction to SystemView
Feedback
What is your background?
What do you expect from EE320?
Discussion (as time permits)
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4. ECE Department’s Thumbnail
EE521 Digital Communications
Prerequisite: Instructor's Permission (Dr. Silage)
Modulation
Coherent detection
Signal-to-noise ratio
Probability of bit and symbol error
Modulations – PSK, FSK, ASK, QAM, M-ary FSK, M-ary PSK
Was EE400
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5. Course Summary Fourteen weeks of classes
Two in-progress exams, one final exam
In-progress on 5th and 12th weeks, 20% of grade each
Final on fifteenth week, 20% of grade
Individually assigned project
Assigned in fifth week
Execute your project in SystemView
40% of grade
Deductions from final grade
0.5% for each unexcused absence
1% for each missed 10 minute Pop Quiz response
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6. Two Semesters in the Plan
EE521 is coordinated with a second course next semester
EE521 covers approximately half of the text
The follow-on covers the second half of the text
Course number TBA
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7. Topics (1 of 3) Formatting and baseband modulation
Encoding digital, text and analog data
Sources of corruption: noise, channel issues
Pulse code modulation
Uniform and non-uniform quantization levels
Baseband modulation
Baseband modulation and detection
Digital signals in noise
Detection of encoded data from digital signals
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8. Topics (2 of 3) Bandpass modulation and demodulation Channel coding
Rationale – advantages and disadvantages
Modulation and detection of digital signals
Coherent and non-coherent detection
Error performance for M-ary encoding
Channel coding
Waveform coding and error control
Sequences and error detection and correction
Block codes
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9. Topics (3 of 3) Modulation and coding trade space
Goals and requirements
Sampling and aliasing
Channel capacity
Designs for maximum data rate and minimum errors
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10. Next Semester Communication link analysis Channel coding
Synchronization
Multiplexing and multiple access
Encryption
Channel issues
Supplementary topics
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11. Essential Technologies
Analog and digital signal processing
Real and complex signals
Vector representation of phase
Sampling capabilities and limitations
Probability and Statistics
Behavior of noise in linear systems
Effect of noise on decoding operations
Coding, modulation, and demodulation
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12. History 1864 – Maxwell predicted radio waves
1887 – Hertz demonstrated radio waves
1897 – Lodge demonstrated wireless communications
1901 – Marconi demonstrated transatlantic communications
1903 – DeForest demonstrated first vacuum tube amplifier
1906 – Fessenden started first AM radio station
1927 – First TV broadcasts
1947 – Microwave relay from Boston to NYC
1947 – Bell Labs announced the transistor
1955 – TI announced production silicon transistors
1958 – First satellite voice channel
1981 – First cell phone system, in Scandinavia
1988 – First digital cell phone system in Europe
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13. Formatting and Baseband Modulation
Topics from Text Chapter 2
2.1, Baseband signals
2.3, Messages, characters and symbols
2.4, Formatting analog information
Baseband signals
Messages, characters, and symbols
Formatting data
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14. Sklar Chapter 2
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15. Baseband Signals
Definition: Data source, the signal to be presented to data sink at receiver end
Principal types
Digital
Text or data
Analog
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16. Message, Characters and Symbols
Definitions
Message – the data to be presented to the data sink or used to generate analog output at the receiver
Character – base message unit, such as a letter of the alphabet or an 8 or 16 bit word produced by an ADC
Symbol – a grouping of bits for encoding
Characters and symbols are often different sizes
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17. Formatting Analog Information
Operations are
Sampling – uniformly spaced captures of a waveform
Digitization – reduction of a data sample to a set of discrete levels
Limitations include
Aliasing; the digitized forms of two signal differing from one another by the sample rate are identical
Quantization; may be uniform or non-uniform, and presents a noise floor
Clipping; there is a maximum value that may be represented
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18. Sampling Can be characterized as An ADC operates on the held signal
Switch a waveform into a follower
At the sample time
Switch a holding capacitor into the holding circuit
Switch off the waveform input
The follower becomes an integrator with no input and holds the signal
An ADC operates on the held signal
Sampling is an analog operation and has a frequency response
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19. Aliasing
Definition:
A tone signal with a frequency higher than the sample rate will produce a data format identical to that of a tone with a frequency lower than sample frequency
The difference between the two frequencies is an integer multiple of the sample frequency
Usual ambiguity range is from minus half the sample frequency to plus half the sample frequency
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20. Issues With Sampling
Signal center frequency is often much larger than the bandwidth
Two techniques are used to keep data rate to twice the signal bandwidth
Quadrature demodulation, the use of two LO’s in quadrature with two mixers to produce two baseband signals in quadrature
Digital quadrature demodulation, undersampling at IF followed by digital quadrature demodulation
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21. Real vs. Complex Sampling
For real sampling at frequency fs > 2.B
The ambiguity range is 0 to fs
Negative frequencies are ambiguous with positive frequencies
For quadrature demodulation and output samples at frequency fqs > B
The ambiguity range is –fqs/2 to +fqs/2
Positive and negative frequencies are unambiguous
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22. Digital Quadrature Demodulation
Undersample
Signal at frequency f0 with bandwidth B
Sample at rate fqs
Result
Signal aliases to plus or minus half the sample rate
FIR filter and decimate to produce the final result
Signal is then ready for FFT or other processing
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23. Digitization Levels Uniform and non-uniform commonly used
Uniform sampling levels – used for high quality systems
Requires more bits, typically 10 to 16 bits
Music
Radar and sonar
Non-uniform sampling levels – used where bandwidth drives the channel utility
Cell phones
Some desk phones and VOIP
Typically 8 bits
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24. Effects Both types have a “hard” ceiling
Extra ADC circuitry offers hard limiting in place of end-around overflow
Noise floor is different
Uniform levels – usually characterized as an additive noise with an RMS value of 1/12 the LSB (see next slide for real-world considerations)
Nonuniform levels – COMDAC levels or fine at low amplitudes, coarse at high levels
Quantization noise floor higher for large signals
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25. Real-World Sampling and ADC
Sampling is
The last mixer in the receiver chain
Produces signal at baseband from signal at IF
Sample clock phase noise is part of the signal chain error sources
Dynamic range
Dynamic range is less than theoretical with nearly all ADCs
Effective number of bits (ENOB) and SNR are two synonymous ways of specifying ADC dynamic range
ENOB is typically 1.5 bits less than the word length of an ADC
Spurious spectral lines
Sample aperture time and duration jitter can cause low level tonal components in ADC output
Can come from inside the ADC chip or from the sample clock
Some resulting spurious lines are signal-dependent
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26. Trades in Quadrature Demodulation
Trades for analog quadrature demodulator
Matching of channels for in-phase and quadrature channels limits negative frequency discrimination
Negative frequency ghosting typical 40 dB to 60 dB
Traces for digital quadrature demodulator
Ghosting is determined by sampling and FIR filtering/decimation scheme
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27. Why Digital Quadrature Demodulation
Advantages
Only one ADC, no multiplexing or matching
Performance is determined by
Antialiasing filtering prior to ADC
Specifications of FIR decimation filters
Disadvantages
Sampling is done at IF
Jitter and aperture time specs are tougher
Exchanged difficulties – from analog channel matching to problems in sampling at IF
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28. SystemView Overview
Simulations of digital signal processing operations
Analog, through oversampling and emulation of analog operations
Digital, through direct emulation
Analysis
Bode plots, root locus, other
Visualization
Time domain plots
Virtual spectrum analyzer
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29. Why SystemView
Dual-gate MOSFET RF converter, 144 MHz to 10 MHz. Uses the RCA 3N140 for its overload and mixing capabilities. Circa 1968.
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30. 11/14/2018
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31. Summary
Course overview: we will learn how to implement critical technologies for digital communications
Course is integrated with a follow-on next semester
Baseband signals are where we do modulation == formatting for the channel
SystemView lets us have most of the benefits of a lab with minimum time
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32. Feedback Around the room Please let me know What your background is
Design
SystemView
Communications
What you expect from this course
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33. Text and Assignment Text Assignment: Read Text
Benard Sklar, Digital Communicatinons ISBN
SystemView User's Manual, Elanix, Inc
Assignment: Read Text
Chapter 2, 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8
Load SystemView and examine the samples and demos
Browse appendices of text for review and supplementary material
Look at TUARC
K3TU, websites
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