Transcript EE521 Analog and Digital Communications

EE521 Analog and
Digital
Communications
James K. Beard, Ph. D.
Tuesday, January 18, 2005
[email protected]
7/16/2015
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Essentials
Text: Bernard Sklar, Digital
Communications, Second Edition
 Prerequisites
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 Consent
of Instructor (Dr. Silage)
 SystemView (CD-ROM with text)
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Office
 E&A 709
 Hours
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TBA, Tuesday afternoons planned
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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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ECE Department’s Thumbnail
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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, Mary PSK
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Was EE400
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Course Summary
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Fourteen weeks of classes
Two in-progress exams, one final exam
 In-progress on 5th and 12th weeks, 20%
 Final on fifteenth week, 20% of grade

of grade each
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
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Quiz response
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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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Topics (1 of 3)
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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
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Baseband modulation and detection
 Digital
signals in noise
 Detection of encoded data from digital signals
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Topics (2 of 3)
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Bandpass modulation and demodulation
– advantages and disadvantages
 Modulation and detection of digital signals
 Coherent and non-coherent detection
 Error performance for M-ary encoding
 Rationale
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Channel coding
 Waveform
coding and error control
 Sequences and error detection and correction
 Block codes
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Topics (3 of 3)
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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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Next Semester
Communication link analysis
 Channel coding
 Synchronization
 Multiplexing and multiple access
 Encryption
 Channel issues
 Supplementary topics
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Essential Technologies
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Analog and digital signal processing
 Real
and complex signals
 Vector representation of phase
 Sampling capabilities and limitations
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Probability and Statistics
 Behavior
of noise in linear systems
 Effect of noise on decoding operations
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Coding, modulation, and demodulation
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History
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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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Formatting and Baseband
Modulation
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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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Sklar Chapter 2
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Baseband Signals
Definition: Data source, the signal to be
presented to data sink at receiver end
 Principal types
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 Digital
 Text
or data
 Analog
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Message, Characters and
Symbols
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Definitions
– 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
 Message
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Characters and symbols are often
different sizes
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Formatting Analog
Information
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Operations are
 Sampling – uniformly spaced captures of a
 Digitization – reduction of a data sample to
waveform
a set of
discrete levels
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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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Sampling
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Can be characterized as
 Switch
a waveform into a follower
 At the sample time
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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
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An ADC operates on the held signal
Sampling is an analog operation and has a
frequency response
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Aliasing
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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
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Usual ambiguity range is from minus half the
sample frequency to plus half the sample
frequency
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Issues With Sampling
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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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Real vs. Complex Sampling
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For real sampling at frequency fs > 2.B
 The
ambiguity range is 0 to fs
 Negative frequencies are ambiguous with
positive frequencies
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For quadrature demodulation and output
samples at frequency fqs > B
ambiguity range is –fqs/2 to +fqs/2
 Positive and negative frequencies are
unambiguous
 The
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Digital Quadrature
Demodulation
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Undersample
 Signal
at frequency f0 with bandwidth B
 Sample at rate fqs
4 f0
f qs 
B
2k  1
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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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Digitization Levels
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Uniform and non-uniform commonly used
Uniform sampling levels – used for high quality
systems
 Requires
 Music
 Radar
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more bits, typically 10 to 16 bits
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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Effects
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Both types have a “hard” ceiling
Extra ADC circuitry offers hard limiting in place
of end-around overflow
Noise floor is different
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
 Uniform
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Real-World
Sampling and ADC
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Sampling is
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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
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Dynamic range
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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
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Spurious spectral lines
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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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Trades in Quadrature
Demodulation
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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
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Traces for digital quadrature demodulator
 Ghosting
is determined by sampling and FIR
filtering/decimation scheme
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Why Digital Quadrature
Demodulation
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Advantages
 Only
one ADC, no multiplexing or matching
 Performance is determined by
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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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SystemView Overview
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Simulations of digital signal processing
operations
 Analog,
through oversampling and emulation of
analog operations
 Digital, through direct emulation
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Analysis
 Bode
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plots, root locus, other
Visualization
 Time
domain plots
 Virtual spectrum analyzer
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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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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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Feedback
Around the room
 Please let me know
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 What
your background is
EE
 Design
 SystemView
 Communications
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 What
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you expect from this course
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Text and Assignment
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Text
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Benard Sklar, Digital Communicatinons ISBN 0-13-084788-7
SystemView User's Manual, Elanix, Inc
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Assignment: Read Text
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http://www.elanix.com/
http://www.elanix.com/pdf/SVUGuide.pdf
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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http://www.temple.edu/ece/tuarc.htm
http://www.temple.edu/k3tu
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