csis 625 week 2 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
CSIS 625 Week 2 PowerPoint Presentation
Download Presentation
CSIS 625 Week 2

Loading in 2 Seconds...

play fullscreen
1 / 57

CSIS 625 Week 2 - PowerPoint PPT Presentation


  • 220 Views
  • Uploaded on

CSIS 625 Week 2. Encoding and Transmission of Data. Copyright 2001, 2002 - Dan Oelke Portions Copyright 2000 - Dmitry Gringauz For use by students of CSIS 625 for purposes of this class only. Overview. Analog and Digital Signals Vocabulary Analog Signals Digital Signals

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'CSIS 625 Week 2' - adamdaniel


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
csis 625 week 2

CSIS 625 Week 2

Encoding and Transmission of Data

Copyright 2001, 2002 - Dan Oelke

Portions Copyright 2000 - Dmitry Gringauz

For use by students of CSIS 625 for purposes of this class only.

CSIS 625

overview
Overview
  • Analog and Digital Signals
    • Vocabulary
    • Analog Signals
    • Digital Signals
  • Encoding and Modulation
    • Digital to Digital Conversion
    • Analog to Digital Conversion
    • Digital To Analog Conversion
    • Analog to Analog Conversion

CSIS 625

analog and digital signals
Analog and Digital Signals
  • Signal - an electromagnetic wave that transfers information
  • Analog Signal - Continuous set of data
    • Real Numbers
  • Digital Signals - Discrete set of data
    • Integer Numbers
    • Often binary (1 or 0 only)

Digital Signal

Analog Signal

CSIS 625

periodic vs aperiodic signals
Periodic vs Aperiodic Signals
  • Periodic Signal
    • A signal that completes a pattern in a measureable time frame
  • Aperiodic Signal
    • A signal that does not exhibit a pattern
    • All aperiodic signals can be shown to be a combination of periodic signals

APeriodic Signal

Periodic Signal

CSIS 625

signal definitions
Signal definitions
  • Amplitude - The “height” of a signal. Measured in Volts, Amps, Watts, etc.
  • Period - The amount of time to complete one cycle
  • Frequency - The number of periods per second. Measured in Hertz (Hz)

Amplitude

Period

CSIS 625

phase
Phase
  • The position of a sine wave relative to time zero. Measured in degrees.

0 Degrees

90 Degrees

1/4 Cycle

180 Degrees

1/2 Cycle

270 Degrees

3/4 Cycle

CSIS 625

bandwidth
Bandwidth
  • Bandwidth - A range of frequencies
  • Analog - measured in Hz
    • Bandwidth = High-Freq – Low-Freq
  • Spectrum - synonym - used only in analog measurements.
  • Bandwidth in digital realm - often used to refer to bits-per-second

CSIS 625

bit rate
Bit Rate
  • Most digital signals are aperiodic
  • Period and frequency are not appropriate to describe digital signals
  • Bit Interval - time to send one bit
  • Bit rate - number of bits send in a second. Measured in bits per second
  • bps - Bits Per Second
  • Do NOT use Hz when you mean bps or vice-versa

CSIS 625

decomposing a digital signal
Decomposing a digital signal
  • A digital signal can be decomposed into an infinite number of simple sine waves
  • It is not practical or necessary to send all of these components
  • Significant Bandwidth - Those frequencies necessary to recreate a digital bit pattern
  • Significant Bandwidth is related to bit rate
    • Greater bit rate = Greater significant bandwidth

CSIS 625

medium bandwidth and significant bandwidth
Medium Bandwidth and Significant Bandwidth
  • All transmission mediums have limited bandwidth
  • The significant bandwidth of a digital bit rate must fit within the limited bandwidth of the medium that carries it.

CSIS 625

encoding
Encoding
  • Information must often be encoded before being sent over a medium
  • Four basic types of encoding
    • Digital to Digital
    • Analog to Digital
    • Digital to Analog
    • Analog to Analog
  • Encoding schemes may be stacked
    • Voice to digital data to radio waves

CSIS 625

digital to digital encoding
Digital to Digital Encoding
  • Using a digital signal to represent digital data
  • Binary data is translated to different voltage, current, or light pulses that can be transported over the medium.
  • Types
    • Unipolar - uses 1 signal level
    • Polar - uses 2 signal levels
    • Bipolar - uses 2 signal levels and 0

CSIS 625

digital signal encoding formats
Digital signal encoding formats

0 1 0 0 1 1 0 0 0 1

Unipolar

NRZL

NRZI

RZ

Manchester

Differential Manchester

Bipolar-AMI

Pseudoternary

CSIS 625

unipolar encoding
Unipolar Encoding
  • Simplest scheme
  • Uses two signal levels
    • 1’s are encoded with signal present
    • 0’s are encoded by absence of a signal
    • (Sometimes inverse of the above)
  • Long run of 0s or 1s can’t be handled by some mediums

CSIS 625

unipolar encoding synchronization
Unipolar encoding - synchronization
  • When a signal isn’t varying, receiver can’t determine beginning and ending of each bit
  • Solutions:
    • A separate line with a clock signal
    • Asynchronzous Serial lines wrap each byte with start and stop bit
    • Scrambling of data to ensure enough transitions
    • Use of additional coding schemes like 8b10b

CSIS 625

polar encoding
Polar Encoding
  • Uses a positive and a negative signal
    • but not a zero level
  • Several types of Polar encoding
    • NRZ - Non-Return to Zero
    • RZ - Return to Zero
    • Biphase

CSIS 625

non return to zero level
Non-Return to Zero - Level
  • NRZL - Non-Return to Zero - Level
  • Simple - exactly like Polar, except
    • 1’s are encoded with positive signal
    • 0’s are encoded with negative signal
    • (Sometimes inverse of the above)
  • Same synchronization problems and solutions

CSIS 625

non return to zero invert on ones
Non-Return to Zero - Invert on Ones
  • NRZI - Non-Return to Zero - Invert on Ones
  • A change in voltage level indicates a 1
  • No change in voltage level indicates a 0
  • Synchronization less of a problem
    • Every 1 bit causes a signal change
    • A string of 0’s still causes problems
      • Same synchronization solutions

CSIS 625

return to zero
Return to Zero
  • RZ - Return to Zero
  • Not strictly polar - uses 0 in addition to positive and negative
  • Works like NRZL, except it goes to zero between each bit.
  • Transition to/from zero provides for synchronization
  • Because there are more transisitions (2 per bit time) it has a higher significant bandwidth than NRZ

CSIS 625

manchester coding
Manchester Coding
  • A biphase mechanism
  • Inversion of signal in middle of each bit
    • low to high transition is 1
    • high to low transition is 0
  • Mid-bit inversion provides for both data and synchronization information
  • May have transition between bits so that right transition can be made in middle of a bit

CSIS 625

differential manchester
Differential Manchester
  • A biphase mechanism
  • Always has a mid-bit inversion to provide timing information
  • Inversion at beginning of bit time provides data
    • Presence of inversion means 0
    • No inversion means 1

CSIS 625

bipolar ami
Bipolar AMI
  • Bipolar Alternate Mark Inversion
  • Mark comes from old telegraphy - means 1
  • Encoding
    • 0 = lack of signal (0)
    • 1 = positive or negative values alternating for successive ones

CSIS 625

pseudoternary
Pseudoternary
  • Same as Bipolar AMI, but inverts 1s and 0s
  • Encoding
    • 0 = positive or negative values alternating for successive zeros
    • 1 = lack of signal (0)

CSIS 625

slide24

1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0

Binary-AMI

V

V

B8ZS

V = Bipolar AMI Violation

B8ZS
  • Bipolar 8-Zero Substitution
  • A modification of Bipolar AMI to solve the synchronization problem that occurs when a long string of 0s occurs
  • Substitutes 8 consecutive 0s with fixed pattern that contains 2 AMI violations

CSIS 625

slide25

1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0

Binary-AMI

V

V

V

HDB3

V = Bipolar AMI Violation

HDB3
  • High Density Bipolar - 3 Zeros
  • Similar to B8ZS
  • Substitutes 4 zeros with a pattern that contains 1 AMI violation

CSIS 625

analog to digital encoding
Analog to Digital Encoding
  • Digitizing - analog to digital conversion
  • Approximate analog information with a digital signal
  • Reduces infinite number of analog values to a finite number of digital values.
  • Codec - Coder-Decoder
    • Analog to digital converter

CSIS 625

pulse amplitude modulation pam
Pulse Amplitude Modulation (PAM)
  • First step to analog to digital encoding
  • Sample analog amplitude information at equal intervals
  • PAM alone not useful as measurements are still analog values

CSIS 625

pulse code modulation pcm
Pulse Code Modulation (PCM)
  • Modifies PAM output to create completely digital signal
  • PCM quantizes Take the samples from PAM and assigns digital values to each measurement.
  • Nyquist theorem - To ensure accurate reproduction of a signal, the sample rate must be twice the highest frequency of the original signal

CSIS 625

pcm telephony
PCM & Telephony
  • Telephony system uses 8 bits (256 levels) when quantizing
  • A non-linear set of quantizing levels is used so that quiet sounds are accurately reproduced
  • 300-3300Hz is voice range.
  • 8kHz sample rate is used to cover this range
  • 8kHz * 8 bits/sample = 64,000 bps

CSIS 625

dm delta modulation
DM - Delta Modulation
  • Analog data is approximated using a staircase function that moves up or down by one level each sampling time.
  • Digital data is a stream of 1s and 0s that specify the up and down steps.
  • Can be implemented using simple components.
  • Not as good quality as PCM
    • Quantizing noise when slope changes slowly
    • Slope overload noise when slope changes fast

CSIS 625

digital to analog conversion
Digital to Analog Conversion
  • ASK - Amplitude Shift Keying
  • FSK - Frequency Shift Keying
  • PSK - Phase Shift Keying
  • QAM - Quadrature Amplitude Modulation
    • combination of ASK & PSK

CSIS 625

bit rate vs baud rate carrier signal
Bit rate vs. Baud Rate & Carrier Signal
  • Bit rate is Bits per Second
  • Baud Rate is number of signal units per second
    • Baud rate is less than or equal bit rate
  • Don’t mix them up!
  • Carrier Signal
    • high frequency signal that is modified to carry digital signal

CSIS 625

ask amplitude shift keying
ASK - Amplitude Shift Keying
  • Amplitude of signal varied for 1 or 0
  • Frequency and phase remain constant
  • Very susceptible to noise
  • On-Off-Keying - signal and no-signal
  • Example:

1 BIT

0

1 BIT

1

1 BIT

0

1 BIT

1

CSIS 625

fsk frequency shift keying
FSK- Frequency Shift Keying
  • Frequency of the carrier signal is varied to represent a 1or 0.
  • Avoids many of the noise problems of Amplitude Shift keying
  • Example:

1 BIT

0

1 BIT

1

1 BIT

0

1 BIT

1

CSIS 625

psk phase shift keying
PSK - Phase Shift Keying
  • The phase of the carrier signal is varied to represent a 1 or 0.
  • Avoids noise problems of ASK
  • Uses less bandwidth than FSK
  • Example:

1 BIT

0

1 BIT

1

1 BIT

0

1 BIT

1

CSIS 625

qpsk quadrature psk
QPSK - Quadrature PSK
  • A type of PSK that uses 90° shifts instead of 180° shifts.
  • Allows for 2 bits per baud to be encoded.

CSIS 625

dpsk differential psk
DPSK - Differential PSK
  • The bit pattern defines the phase change, instead of the current phase
  • V.22bis standard at 1200 bps uses:
    • 00  90 Degree phase change
    • 01  0 Degree phase change
    • 10  180 Degree phase change
    • 11  270 Degree phase change

CSIS 625

quadrature amplitude modulation
Quadrature Amplitude Modulation
  • The phase and amplitude of the carrier signal is varied to give several bits per baud
  • Number of different phases is greater than number of amplitudes
  • Example: 2 amplitudes & 4 phases

3 BITS

000

3 BITS

010

3 BITS

001

3 BITS

111

CSIS 625

trellis coded modulation
Trellis Coded Modulation
  • Uses QAM, but includes extra data
  • Trellis coding is a specific type of convolutional encoding
  • Viterbi Decoder - a specific algorithm for decoding convolutionally encoded data.
  • Convolutional codes add redundancy to the data, which makes it more resistant to noise.
  • Resistance to noise is more important as data rates get higher.

CSIS 625

constellation diagrams
Constellation diagrams
  • Constellation diagram shows relationship between amplitude and phase of different signal levels
  • polar diagram,
    • amplitude shown as distance from center
    • phase shown as degrees around circle

011

010

0

1

0

1

101

100

000

001

110

ASK

PSK

111

8-QAM

16-QAM

CSIS 625

bandwidth required
Bandwidth required
  • Amplitude Shift Keying
    • bandwidth = baud rate * (1 + noise factor)
      • noise factor is 0 in ideal world
  • Frequency Shift Keying
    • bandwidth = (fc1 - fc0) + baud rate
  • Phase Shift Keying & QAM
    • bandwidth = baud rate * (1 + noise factor)
    • but bit rate is higher because more than one bit per baud

CSIS 625

analog to analog encoding
Analog to Analog Encoding
  • AM - Amplitude Modulation
    • The amplitude of the carrier is modified
    • Bandwidth = 2x Bandwidth of modulating signal
  • FM- Frequency Modulation
    • The frequency of the carrier is modified
    • Bandwidth = 10x Bandwidth of modulation signal

CSIS 625

analog to analog encoding43
Analog to Analog Encoding
  • Phase Modulation
    • The phase of the carrier is modified
  • Phase Modulation and FM are a special case of Angle modulation
    • Observing the signal, it is impossible to tell apart FM and phase modulation

CSIS 625

parallel serial transmission of data
Parallel/Serial Transmission of Data
  • Transmission of Digital Data
    • Serial & Parallel transmission
    • Serial interfaces - DTE & DCE - Modems

CSIS 625

parallel transmission of data
Parallel Transmission of Data
  • Send several bits of data at the same time, each one over a separate media link.
    • Typically 8 bits of data sent over 8 wires
    • Examples: Printer cables, SCSI, PCI bus
  • Allows faster transmission of data, but at the cost of multiple wires, multiple transmitters, and multiple receivers
  • Must keep all bits in sync
  • Typically uses a separate clock line

CSIS 625

serial transmission of data
Serial Transmission of Data
  • Sends all bits from node to node over a single media link.
  • Bits are sent one after another - or “serially”
  • May or may not have additional media links for clock, frame, or flow control.
  • Need some method of keeping track of when a byte starts and ends.
    • Asynchronous or Synchronous

CSIS 625

serial asynchronous transmission
Serial - Asynchronous transmission
  • Bits are grouped together into characters
  • Start and stop bits frame the data bits
    • A start bit is sent first
    • Followed by the data bits
    • Followed by a stop bit or bits
  • Variable number of idle bits between characters

CSIS 625

serial asynchronous transmission48

Start

Start

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Stop

Stop

Serial - Asynchronous transmission
  • At best - 80% efficient
    • 8 data bits
    • 1 start bit
    • 1 stop bit
  • Allows for about a lot of timing error
  • Example:

CSIS 625

serial synchronous transmission
Serial - Synchronous transmission
  • Each byte of data is sent with no extra gaps between bytes.
  • Data is grouped into frames
    • Frame contains
  • Between frames, special idle patterns used
  • Much less overhead that asynchronous
  • Can achieve faster bit rates than asynchronous
  • Requires synchronization method

CSIS 625

data transparency on serial links
Data transparency on serial links
  • Data transparency - the ability of a link to send any data pattern
  • Bit stuffing - insertion of extra bits to change a flag pattern so that data transparency is achieved
  • Byte stuffing - insertion of extra bytes to change a flag pattern so that data transparency is achieved
  • Flag character - special bit pattern to show start or end of a frame

CSIS 625

serial synchronous transmission51
Serial - Synchronous transmission
  • Bit-oriented synchronous transmission
    • Uses a special bit pattern at the start and end of the frame (flag character)
    • Data may be any number of bits
    • Uses bit stuffing to replace flag pattern in data
    • Bit stuffing is slightly more efficient than byte stuffing
    • Easier to implement in hardware

CSIS 625

serial synchronous transmission52
Serial - Synchronous transmission
  • Character oriented synchronous transmission
    • Uses a special byte at the start and end of the frame
    • Data must be an even number of 8-bit bytes
    • Uses byte stuffing to replace flag byte in data
    • Byte stuffing makes this slightly less efficient
    • Easier to implement in software

CSIS 625

dte dce interface
DTE-DCE interface
  • DTE - Data Terminal Equipment
    • A device that is a source or destination for binary digital data
  • DCE - Data Circuit-terminating Equipment
    • A device that interfaces between a DTE and a network
    • Modem is classic DCE example
  • Lots of standards specify DTE to DCE interface
  • More standards for DCE to DCE interface

CSIS 625

rs 232 interface
RS-232 Interface
  • Specifies the mechanical, electrical & functional characteristics of DTE-DCE interface
  • EIA-232 is now the official name
  • Tailored to Computer to modem interface
  • Limited to about 20 Kbps
  • Mechanical
    • less than 50 feet long cable
    • DB-25 connector original standard
    • DB-9 connector now standardized

CSIS 625

rs 232 interface55
RS-232 Interface
  • Electrical - Uses NRZL
    • 0 = +3 to +15 volts
    • 1 = -3 to -15 volts
  • 3 pins are all that are necessary
    • Receive Data
    • Transmit Data
    • Ground
  • Other pins are often ignored
  • Null modem - a device that flips receive and transmit lines

CSIS 625

other serial interfaces
Other serial interfaces
  • RS-449 - uses 37 pin connector
  • RS-423 - uses 2-6 volt levels
    • 40 feet - 100 Kbps
    • 4000 feet - 1 Kbps
  • RS-422 - 2-6 Volt balanced transmission
    • 40 feet - 10 Mbps
    • 4000 feet - 1 Kbps

CSIS 625

balanced transmission
Balanced transmission
  • Uses two wires with a positive or negative voltage put on the line
  • Compared to unbalanced which using two wires, one as ground and the other as signal.
  • Better noise resistance than unbalanced

CSIS 625