4th Edition: Chapter 1 - PowerPoint PPT Presentation

Loading...

PPT – 4th Edition: Chapter 1 PowerPoint presentation | free to download - id: 771b31-OWQ4M



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

4th Edition: Chapter 1

Description:

CSCD 433 Network Programming Fall 2011 Lecture 4 Physical Layer Transmission * – PowerPoint PPT presentation

Number of Views:24
Avg rating:3.0/5.0
Slides: 38
Provided by: JimKuro116
Learn more at: http://penguin.ewu.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: 4th Edition: Chapter 1


1
CSCD 433 Network Programming Fall 2011
Lecture 4 Physical Layer Transmission

1
2
Physical Layer Topics
  • Motivation for studying this topic
  • Definitions of terms
  • Analog vs Digital
  • Line encoding
  • Characteristics of physical media


2
3
Motivation
  • Why study the physical layer?
  • Need to know basic data transmission concepts
  • Didn't really cover them in CSCD330
  • Should understand physical layer to better
    understand how various media influence network
    performance and efficiency
  • What transmission speed is possible with various
    media?
  • Where and how are errors introduced?
  • Need to know current implementations of physical
    layer and future trends

4
Physical Layer - Purpose
  • To transmit bits, by encoding them onto signals
  • To receive the signals, interpreting them as bits
  • Signal
  • 1. Mechanism used to carry information over time
  • or distance
  • 2. Sign or gesture giving information
  • 3. Sequence of electrical or optical impulses or
  • waves

5
Signals
  • Examples
  • Physical gesture, wave, hand signal
  • Flashes of light (eg, Morse code)?
  • Sound vary tone, loudness or duration
  • Flags
  • Smoke
  • Electical voltages

6
Transmission
  • 1. Action of conveying electrical or optical
    signals from 1 point to 1 or more other points in
    space
  • 2. Process of sending information from 1 point to
    another
  • What do you need for a Transmission System ?
  • Medium for signal transfer
  • Transform signal to appropriate form
  • Way to transmit the signal
  • Way to remove, receive or detect the signal

7
Digital vs. Analog Signals
  • Digital Signal
  • 1. Limited to finite number of values
  • 2. Has meaning only at discrete points in
  • time
  • Examples Text, bits, integers

8
Digital vs. Analog Signals
  • Analog Signal
  • 1. Signal that is an analog of the quantity
    being
  • represented
  • 2. Continuous range of values
  • 3. Also continuous in time, always valued
  • Examples Sound, vision, music

9
Analog vs. Digital
10
Analog Signals
  • An analog signal is continuous has infinite
    number of values in a range
  • Primary shortcomings of analog signals is
    difficulty to separate noise from original
    waveform
  • An example is a sine wave which can be specified
    by three characteristics
  • ???t??????sin (2 ? f t p)?
  • A amplitude f frequency p???phase

11
Sine Wave Examples
http//www.indiana.edu/ emusic/acoustics/phase.ht
m
12
Modems, Codecs
  • Modem (Modulator-Demodulator)?
  • What does a modem do?
  • Translates digital signal (bit) into an analog
    signal, for transmission as an analog signal
  • Receives corresponding analog signal, and
    translates back into digital (bit)?
  • Purpose Use analog medium for digital
    data/signals
  • Example PC modem, phone lines, TV cable modems

13
Modems, Codecs, Baud Rates
  • Codec (codec/decoder)?
  • Converts analog data into digital form (bits),
    and the reverse.
  • Main technique PCM
  • PCM (pulse code modulation)?
  • Absolute values, based on sampling theory
    (nearly) total information

14
Pulse Code Modulation
  • Analog signal amplitude is sampled (measured) at
    regular time intervals.
  • Sampling rate, number of samples per second,
  • Several times maximum frequency of the analog
    waveform in cycles per second or hertz
  • Amplitude of analog signal at each sampling is
    rounded off to nearest of several specific,
    predetermined levels
  • Process is called quantization

15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Spectra Bandwidth
Spectrum of x1(t)?
  • Spectrum of a Signal magnitude of amplitudes as a
    function of frequency
  • x1(t) varies faster in time has more high
    frequency content than x2(t)
  • Bandwidth Ws is defined as range of frequencies
    where a signal has non-negligible power, e.g.
    range of band that contains 99 of total signal
    power

Spectrum of x2(t)?
20
Sampling Theorem
  • NyquistShannon sampling theorem
  • Theorem shows that an analog signal that has been
    sampled
  • Can be perfectly reconstructed from an infinite
    sequence of samples if the sampling rate exceeds
    2W samples/Sec, where W is the highest frequency
    of the original signal

21
Example Telephone Speech
  • Ws 4KHz, so Nyquist sampling theorem
  • ? 2W 8000 samples/second
  • Suppose 8 bits/sample, m
  • PCM (Pulse Code Modulation) Telephone Speech
  • Bit rate 8000 x 8 bits/sec 64 kbps

22
Communications Channels
  • A physical medium is an inherent part of a
    communications system
  • Copper wires, radio medium, or optical fiber
  • Communications system include electronic or
    optical devices that are part of the path
    followed by a signal
  • Equalizers, amplifiers, signal conditioners
  • By communication channel we refer to the combined
    end-to-end physical medium and attached devices
  • Sometimes we use the term filter to refer to a
    channel especially in the context of a specific
    mathematical model for the channel

23
(No Transcript)
24
Pulse Transmission Rate
  • Objective Maximize pulse rate through a
    channel, that is, make T as small as possible

Channel
t
T
t
  • Question How frequently can these pulses be
    transmitted without interfering with each other?
  • Answer 2 x Wc pulses/second where Wc is the
    bandwidth of the channel

25
Multilevel Signaling
  • Nyquist pulses achieve the maximum signaling rate
    with zero Inter Symbol Interference (ISI)?
  • 2Wc pulses per second or
  • 2Wc pulses / Wc Hz 2 pulses / Hz
  • With two signal levels, each pulse carries one
    bit of information
  • Bit rate 2Wc bits/second
  • With M 2m signal levels, each pulse carries m
    bits
  • Bit rate 2Wc pulses/sec. m bits/pulse 2Wc
    m bps
  • Bit rate can be increased by increasing number of
    levels
  • r(t) includes additive noise, that limits number
    of levels that can be used reliably.

26
(No Transcript)
27
Shannon Channel Capacity
  • If transmitted power is limited, then as M
    increases spacing between levels decreases
  • Presence of noise at receiver causes more
    frequent errors to occur as M is increased
  • Shannon Channel Capacity
  • The maximum reliable transmission rate over an
    ideal channel with bandwidth W Hz, with Gaussian
    distributed noise, and with SNR S/N is
  • C W log2 ( 1 S/N ) bits per second
  • Reliable means error rate can be made arbitrarily
    small by proper coding

28
What is Line Coding?
  • Mapping of binary information sequence into the
    digital signal that enters the channel
  • Ex. 1 maps to A square pulse 0 to A pulse
  • Line code selected to meet system requirements
  • Transmitted power Power consumption
  • Bit timing Transitions in signal help timing
    recovery
  • Bandwidth efficiency Excessive transitions
    wastes bw
  • Low frequency content Some channels block low
    frequencies
  • Long periods of A or of A causes signal to
    droop
  • Waveform should not have low-frequency content
  • Error detection Ability to detect errors helps
  • Complexity/cost Is code implementable in chip
    at high speed?

29
Desirable Properties Line Code
  • Clock Signal Synchronization between
  • transmitter and receiver is of critical
  • importance in digital communications
  • systems
  • Ideally, spectrum of line code should
  • contain a frequency component at the clock
  • frequency to permit clock extraction
  • This avoids having to transmit a separate
  • clock signal between the transmitter and
  • receiver

30
Desirable Properties Line Code
  • Signal Interference and Noise Immunity
  • Ideally, line code should be rugged in
  • terms of exhibiting an immunity to
  • interference and noise
  • In more technical terms, line code should
  • have a low probability of error for a given
  • level of transmitted power
  • Certain line codes are more rugged than
  • others, e.g. polar codes have a better error
  • performance compared to unipolar codes.

31
(No Transcript)
32
NRZ vs RZ
NRZ
  • In telecommunication, a non-return-to-zero (NRZ)
    line code is a binary code in which
  • 1's are represented by one significant condition
    (usually a positive voltage)?
  • 0's are represented by some other significant
    condition (usually a negative voltage), with no
    other neutral or rest condition
  • Pulses have more energy than a RZ code
  • Unlike RZ, NRZ does not have a rest state.

RZ
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Summary
  • Looked at Physical layer
  • Analog vs. Digital
  • Line encoding
  • Next, we will map this knowledge to Ethernet
  • Choice of physical media in relation to
    performance and/or efficiency

37
  • New Assignment up
  • Some problems from the Book


37
About PowerShow.com