Fundamentals of Data and Signals

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• Fundamentals of Data and Signals
• Dr. Roger G. Clery
• Roosevelt University
• (cc) Clery 2007

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The Communication Process
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What Is Communication?

• Symbolic ? ?? (Which is God which is dog?)
• Representational
• The map is not the territory, the thing is not
  the thing named.
• Communication is only as good as the
  representation
• Examples
• spoken language, gestures, actions, icons

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• What is this?

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What is this?

• Where / When is the thought?
• When this is scanned is there thought?
• How might is data be communicated?
• How might this data be processed?

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Human Communication v. Data Communication

• Human communication is richer, less predictable
• Words vary in meaning with context
• Many factors influence meaning and perception of
  message
• Data communication is more precise
• Exact replication of information
• Computers do not interpret, they simply relay

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Communication Limitations

• Time
• Distance
• Bandwidth / Mindwidth
• Noise

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Communication

• Text
• Voice
• Image
• Video
• Data

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Data Information

• What is data?
• Elements that can be represented by a finite set
  of symbols, such as digits or alphabets
• What is information?
• a tangible, measurable thing
• a subjective construction

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CODE schemes for the letter A

• Morris .
• Baudot 00011
• ASCII 1000001
• EBCDIC 1100001
• Unicode (sort of 16 bits)

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ASCII



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EBCDIC




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4 Zone Hollerith

• The one is also a zone punch

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Unicode

• In Unicode, a letter maps to something called a
  code point which is still just a theoretical
  concept. How that code point is represented in
  memory or on disk is a whole nuther story.
• In Unicode, the letter A is a platonic ideal.
  It's just floating in heaven
• 
  A
• This platonic A is different than B, and
  different from a, but the same as A and A and A.
  The idea that A in a Times New Roman font is the
  same character as the A in a Helvetica font, but
  different from "a" in lower case, does not seem
  very controversial, but in some languages just
  figuring out what a letter is can cause
  controversy. Is the German letter ß a real letter
  or just a fancy way of writing ss? If a letter's
  shape changes at the end of the word, is that a
  different letter? Hebrew says yes, Arabic says
  no. Anyway, the smart people at the Unicode
  consortium have been figuring this out for the
  last decade or so, accompanied by a great deal of
  highly political debate, and you don't have to
  worry about it. They've figured it all out
  already.
• Every platonic letter in every alphabet is
  assigned a magic number by the Unicode consortium
  which is written like this U0645.  This magic
  number is called a code point. The U means
  "Unicode" and the numbers are hexadecimal. UFEC9
  is the Arabic letter Ain. The English letter A
  would be U0041.

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Data Codes

• The set of all textual characters or symbols and
  their corresponding binary patterns is called a
  data code.
• There are two basic data code sets plus some
  others code sets that have interesting
  characteristics
• ASCII (most common)
• EBCDIC (IBM mainframe standard)
• Baudot Code 5 bits (plus letters-shift and
  figures-shift
• Unicode (has all characters in every language)

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Baudot Code
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Paper Tape
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Current Loop
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Telecommunication

• Uses electricity to transmit messages
• Speed of electricity dramatically extends reach
• Sound waves 670 mph
• Light in a vacuum 186,000 mph (c)
• Bandwidth information-carrying capacity of a
  channel (measured in bits per second)

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Signal Velocity
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The Analog Digital Divide

• Analog is continuously variable
• Analog data - voice, NTSC television signals
• Analog signals telephone AM radio
• Digital is discrete steps or states
• Digital data text message jpeg file
• Digital signals Ethernet

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Analog

• Voice Frequency As in Telephone
• Radio as in radio and TV

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Analog Wave Form

• Frequency or Cycles per second is an attribute of
  analog waves
• Measured as Hz
• KHz, MHz, GHz
• Analog waves can be combined to form a composite
  signal

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An Analog Wave Form

• Continuously variable with time
• Examples Sound, Telephone voice signal, AM radio

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Amplitude

The amplitude of a signal is the height of the
wave above or below a given reference point.


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Basic Analog Terms

• Wave frequency Number of times a cycle occurs in
  given time period
• Hertz (1 Hz 1 cycle per second) The number of
  times a wave cycle occurs in one second (commonly
  used measure of frequency)
• Wave amplitude Height of a wave cycle

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Frequency Example

• For example, consider an average voice
• The average voice has a frequency range of
  roughly 300 Hz to 3100 Hz.
• The spectrum would thus be 300 - 3100 Hz
• The bandwidth would be 2800 Hz

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Analog Signaling

• represented by sine waves

phase difference
1 cycle
amplitude (volts)
time
(sec)
frequency (hertz)
cycles per second
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Data and Signals


Data are entities that convey meaning (computer
file, music on a CD, results from a blood gas
analysis machine) Signals are the electric or
electromagnetic encoding of data (telephone
conversation, web page download) Computer
networks and data / voice communication systems
transmit signals Data and signals can be analog
or digital

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Analog versus Digital

Analog is a continuous waveform, with examples
such as (naturally occurring) music and voice.


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Analog versus Digital

Digital is a discrete or non-continuous waveform
with examples such as computer 1s and 0s.


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Analog Wave Form

• Sound is from 10 Hz to 20,000 Hz
• AC power in the US is 60 Hz
• AM radio is from 540 KHz to 1.710 MHz

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Analog versus Digital - Noise

It is harder to separate noise from an analog
signal than it is to separate noise from a
digital signal.


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Frequency

• The frequency is the number of times a signal
  makes a complete cycle within a given time frame.
• Bandwidth - The absolute value of the difference
  between the lowest and highest frequencies of a
  signal.

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Analog versus Digital - Noise

Noise in a digital signal. You can still discern
a high voltage from a low voltage.


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Amplitude Modulation

• AM Radio
• Simple
• Subject to noise

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Digital
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Basic Digital Terms

• Bit digit in a binary number
• 1 is a 1-bit number (1 in base 10)
• 10 is a 2-bit number (2 in base 10)
• 10011001 is an 8-bit number (153 in base 10)
• Byte eight bits

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Digital Data

• Represented as a sequence of discrete symbols
  from a finite alphabet of text and/or digits
• Rate and capacity of a digital channel measured
  in bits per second (bps)
• Digital data is binary uses 1s and 0s to
  represent everything
• Binary digits can be represented as voltage pulses

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Analog versus Digital -Noise

Noise in a digital signal. Too much noise - you
cannot discern a high voltage from a low voltage.


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All Signals Have Three Components

• Amplitude
• Frequency
• Phase

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Frequency

The frequency is the number of times a signal
makes a complete cycle within a given time
frame. Spectrum - The range of frequencies that a
signal spans from minimum to maximum. Bandwidth -
The absolute value of the difference between the
lowest and highest frequencies of a signal.


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Three Analog signals



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Encoding
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Non-Return to Zero Level

• Simple
• Used in computer and electronic devices
• Degrades over distance
• Starts out nice and square
• Ends up lumly

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Non-Return to Zero Inverted

• Sending all zeros is a problem
• How many zeros is this

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Manchester

• Self-clocking
• Used in magnetic tape

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Differential Manchester
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AMI Alternate Mark(one) Inversion

• Must have some ones for synchronization
• Good over long distance 2 or 3 miles
• Basic digital telephone signal T1 (1.544 Mbps)

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4B/5B Encoding
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ASCII Code using Differential Manchester encoding
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Frequency For example, consider an average
voice The average voice has a frequency range of
roughly 300 Hz to 3100 Hz. The spectrum would
thus be 300 - 3100 Hz The bandwidth would be 2800
Hz


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Phase The phase of a signal is the position of
the waveform relative to a given moment of time
or relative to time zero. A change in phase can
be any number of angles between 0 and 360
degrees. Phase changes often occur on common
angles, such as 45, 90, 135, etc.


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Signal Strength

All signals experience loss (attenuation). Attenu
ation is denoted as a decibel (dB) loss. Decibel
losses (and gains) are additive.


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Signal Strength

So if a signal loses 3 dB, is that a lot? A 3 dB
loss indicates the signal lost half of its
power. dB 10 log10 (P2 / P1) -3 dB 10 log10
(X / 100) -0.3 log10 (X / 100) 10-0.3 X /
100 0.50 X / 100 X 50


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Converting Digital Data into Digital Signals

• There are numerous techniques available to
  convert digital data into digital signals.
• Lets examine four techniques
• NRZ-L
• NRZ-I
• Manchester
• Differential Manchester

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Note how with a Differential Manchester code,
every bit has at least one signal change. Some
bits have two signal changes per bit (baud rate
is twice the bps).


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4B/5B Digital Encoding Yet another encoding
technique that converts four bits of data into
five-bit quantities. The five-bit quantities are
unique in that no five-bit code has more than 2
consecutive zeroes. The five-bit code is then
transmitted using an NRZ-I encoded signal.


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Converting Digital Data into Analog Signals

• Three basic techniques
• Amplitude modulation
• Frequency modulation
• Phase modulation

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Amplitude Modulation

One amplitude encodes a 0 while another amplitude
encodes a 1 (amplitude shift keying).


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Amplitude Modulation

Some systems use multiple amplitudes.


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Multiple Signal Levels



Why use multiple signal levels? We can represent
two levels with a single bit, 0 or 1. We can
represent four levels with two bits 00, 01, 10,
11. We can represent eight levels with three
bits 000, 001, 010, 011, 100, 101, 110, 111 Note
that the number of levels is always a power of 2.
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Frequency Modulation

One frequency encodes a 0 while another frequency
encodes a 1 (frequency shift keying).


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Phase Modulation

One phase change encodes a 0 while another phase
change encodes a 1 (differential phase shift
keying).


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Quadrature Phase Modulation



Four different phase angles are used 45
degrees 135 degrees 225 degrees 315 degrees
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Four Phase Angles



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Quadrature Amplitude Modulation QAM



In this technology, 12 different phases are
combined with two different amplitudes. Since
only 4 phase angles have 2 different amplitudes,
there are a total of 16 combinations. With 16
signal combinations, each baud equals 4 bits of
information. (2 4 16)
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QAM



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Higher Data Transfer Rates



How do you send data faster? 1. Use a higher
frequency signal (make sure the medium can handle
the higher frequency) 2. Use a higher number of
signal levels In both cases, noise can be a
problem.
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Shannons equation

Maximum Data Transfer Rates How do you calculate
a maximum data rate? Use Shannons equation bps
f log2 (1 S/N) Where f signal frequency,
S is signal power, and N is noise power


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Maximum Data Transfer Rates

For example, what is the data rate of a 3400 Hz
signal with 0.2 watts of power and 0.0002 watts
of noise? bps 3400 x log2 (1
0.2/0.0002) 3400 x log2 (1001) 3400 x
9.97 33898 bps


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Converting Analog Data into Digital Signals

• To convert analog data into a digital signal,
  there are two basic techniques
• Pulse code modulation (used by telephone
  systems)
• Delta modulation

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PCM

Pulse Code Modulation The analog waveform is
sampled at specific intervals and the snapshots
are converted to binary values.


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Pulse Code Modulation

When the binary values are later converted to an
analog signal, a waveform similar to the original
results.


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PCM quantization levels

Pulse Code Modulation The more snapshots taken in
the same amount of time, or the more quantization
levels, the better the resolution.


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Analog wave form

• Amplitude or strength is one attribute of analog
  waves

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Digital Wave Form

• Desecrate steps /states

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Digital Wave Form

• Binary is always digital
• Digital is NOT necessarily Two states

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Analog Wave Form

• Phase is another attribute of an analog wave
• The phase of a signal is the position of the
  waveform relative to a given moment of time or
  relative to time zero.
• One Complete cycle is 360 degrees

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Pulse Code Modulation

Since telephone systems digitize human voice,
and since the human voice has a fairly narrow
bandwidth, telephone systems can digitize voice
into either 128 levels or 256 levels. These
levels are called quantization levels. If 128
levels, then each sample is 7 bits (2 7
128). If 256 levels, then each sample is 8 bits
(2 8 256).


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Nyquist Law

Pulse Code Modulation How fast do you have to
sample an input source to get a fairly accurate
representation? Nyquist says 2 times the
bandwidth. Thus, if you want to digitize voice
(4000 Hz), you need to sample at 8000 samples per
second.


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Delta Modulation

An analog waveform is tracked, using a binary 1
to represent a rise in voltage, and a 0 to
represent a drop.


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Converting Analog Data into Analog Signals



Many times it is necessary to modulate analog
data onto a different set of analog
frequencies. Broadcast radio and television are
two very common examples of this.
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Spread Spectrum Technology

• A secure encoding technique that uses multiple
  frequencies or codes to transmit data.
• Two basic spread spectrum technologies
• Frequency hopping spread spectrum
• Direct sequence spread spectrum

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Frequency Hopping Spread Spectrum



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Direct Sequence Spread Spectrum

This technology replaces each binary 0 and binary
1 with a unique pattern, or sequence, of 1s and
0s. For example, one transmitter may transmit the
sequence 10010100 for each binary 1, and 11001010
for each binary 0. Another transmitter may
transmit the sequence 11110000 for each binary 1,
and 10101010 for each binary 0.


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Data and Signal Conversions in Action


Data and Signal Conversions in Action Let us
transmit the message Sam, what time is the
meeting with accounting? Hannah. This message
first leaves Hannahs workstation and travels
across a local area network.

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Frequency Modulation ASCII letter S

Data and Signal Conversions in Action


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end
END of presentation

• (cc) Roger Clery 2007