Transmission Media (Chapter 7) Many of the figures are from the
textbook.
Slide 2
Most of the diagrams in this powerpoint presentation (and
future ones as well) come from the powerpoint file available via
the books web site. They reflect diagrams contained in the
textbook.
Slide 3
Twisted pair Figure 7.3 Twisted-pair cable
Slide 4
Figure 7.4 UTP and STP cables
Slide 5
twisted to avoid crosstalk
[http://en.wikipedia.org/wiki/Inductance]http://en.wikipedia.org/wiki/Inductance]
[http://en.wikipedia.org/wiki/Crosstalk]
[http://en.wikipedia.org/wiki/Crosstalk
[http://en.wikipedia.org/wiki/Twisted_pair]http://en.wikipedia.org/wiki/Twisted_pair]
Optical signals are not electrical in nature and not subject to
same interference as are electrical signals less attenuation
[http://www.arcelect.com/fibercable.htm]http://www.arcelect.com/fibercable.htm]
Slide 10
LED/laser, multimode, graded index multimode, single mode
LED/laser, multimode, graded index multimode, single mode modal
dispersion (spreading of light in multimode fibers) infrared range
of E/M waves. Dark Fiber: Optical fiber thats in place but
currently not being used
Radio waves Generally between 3 KHz and 1 GHz Regulated by the
FCC Low data rates and not particularly suited for digital
communications Length of antenna proportional to the wavelength
(inversely proportional to the frequency)
Slide 16
Project ELF [http://www.fas.org/nuke/guide/usa/c3i/elf.htm
]http://www.fas.org/nuke/guide/usa/c3i/elf.htm
[http://enterprise.spawar.navy.mil/UploadedFil
es/fs_clam_lake_elf2003.pdf]http://enterprise.spawar.navy.mil/UploadedFil
es/fs_clam_lake_elf2003.pdf
[http://en.wikipedia.org/wiki/Extremely_low_f
requency]http://en.wikipedia.org/wiki/Extremely_low_f requency No
longer active [http://www.senate.gov/~feingold/statements/0
3/01/2003310D02.html].
[http://www.senate.gov/~feingold/statements/0
3/01/2003310D02.html].
Slide 17
Danish King Harald Blatand: (Danish: Harald Bltand, Old Norse:
Haraldr bltnn, Norwegian: Harald Bltann)Old Norse born around 935,
the son of King Gorm the Old, king of Jutland (that is, peninsular
Denmark) and of Thyra (also known as Thyre Danebod) a supposed
daughter of Harald Klak, Jarl of Jutland, or daughter of a noblemen
of Snderjylland who is supposed to have been kindly disposed
towards Christianity.ThyraHarald Klak He died in 986 having ruled
as King of Denmark from around 958 and king of Norway for a few
years probably around 970. Some sources state that he was
forcefully deposed by his son Sweyn as king [Wikipedia]
Slide 18
You might know Bltand by its other name Bluetooth
[http://en.wiktionary.org/wiki/Bl%C3%A5tand]http://en.wiktionary.org/wiki/Bl%C3%A5tand
[http://www.bluetooth.com] [http://www.bluetooth.com]
http://www.bluetooth.com/Pages/Fast-Facts.aspx
http://www.bluetooth.com/Pages/Fast-Facts.aspx
Slide 19
Wireless LANs: infrared vs radio waves covered later
Slide 20
Free space Optics :
[http://www.freespaceoptics.org/]http://www.freespaceoptics.org
optical technology without the fiber transmits using narrowly
focused laser beams (10 12 Hz range, which is unregulated by law)
line of sight buildings sway and can lose tracking (although can
use auto tracking receivers) after about 1-2 km signal becomes less
focused fog can disrupt public perception of birds flying into the
path of a laser, getting fried, and falling to the ground.
Slide 21
Microwaves: parabolic and horn antenna, requires
line-of-sight.
Slide 22
Satellites : Arthur C. Clarke wrote about them in 1940 Sputnik
Sputnik Interestingly part of the sputnik crashed in Manitowoc
[http://www.manitowoc.org/index.aspx?NID=1026]http://www.manitowoc.org/index.aspx?NID=1026]
[http://www.roadsideamerica.com/sights/sightstory.p
hp?tip_AttrId=%3D12959]
[http://www.roadsideamerica.com/sights/sightstory.p
hp?tip_AttrId=%3D12959]
Slide 23
Planetary Orbits: too slow and object falls to earth; too fast
and it speeds into space Keplers laws of planetary motion defines
the speed as a function of, in part, the distance from the planet
Geosynchronous (22,300 miles) orbital speed matches earths
rotation. By comparison, the space shuttle may orbit between 200
and 400 miles. 200 and 400 miles TV satellite technology uses
geosynchronous orbits
Slide 24
LEO (Low Earth orbit) Satellites Satellites move relative to
ground position Useful for surveillance
Slide 25
LEO systems Iridium Iridium Orbcomm Orbcomm GlobalStar
GlobalStar Other references Other references
Slide 26
GPS Systems GPS Systems Applications to Einsteins theory of
relativity Applications to Einsteins theory of relativity
Slide 27
Cell phones, grids Cell phones
Slide 28
Digital and Analog signals (Chapter 3 and 4) Digital signal vs
analog signal Sound and images are naturally analog Computer data
is digital
Slide 29
periodic signal: repeating signal Cycle: part that repeats
Period (p): length of a cycle Frequency (f): 1/period (1 Hertz (Hz)
= 1 cycle per second (cps) ) f = 1/p and p = 1/f KHz = 10 3 Hz; MHz
= 10 6 Hz; GHz = 10 9 Hz Bandwidth: (frequency range) bit rate: #
bits per second (bps or Kbps or Mpbs or Gbps)
Slide 30
Periodic Analog signals (Chapter 3) An analog signal is defined
by its frequency, amplitude, and phase.
Slide 31
Figure 3.3 Two signals with the same phase and frequency, but
different amplitudes
Slide 32
Figure 3.4 Two signals with the same amplitude and phase, but
different frequencies
Slide 33
Figure 3.5 Three sine waves with the same amplitude and
frequency, but different phases
Slide 34
Slide 35
Maple worksheet has some examples
Slide 36
Figure 3.7 The time-domain and frequency- domain plots of a
sine wave
Slide 37
Fourier results: a composite signal is a combination of simple
sine and cosine wave with different frequencies and amplitudes.
Applications to equalizers, filters, CATV. Ref: Maple worksheet
[http://www.falstad.com/fourier/]http://www.falstad.com/fourier/]
Skip sections 3.3 and 3.4
Slide 38
Bit rate limits: section 3.5
Slide 39
An analog signal with a fixed amplitude, frequency, and phase
can represent a number of bits. Changing the characteristics at
regular intervals can be used to transmit a bit stream bit rate:
number of bits per second baud rate: frequency with which a signals
characteristics change Higher frequency signals can have a higher
baud rate.
Slide 40
Let n = #bits per baud and L = #different signals L=2 n
Equivalently, n=log 2 (L) eg. L=8 amplitudes => n=3 bits per
baud (since 2 3 = 8) Bit rate = baud rate n = baud rate log 2
(L)
Slide 41
Nyquist result: bit rate = 2 F n = 2 F log 2 (L) where F is the
bandwidth (highest frequency minus lowest frequency) of the signal.
This implies no theoretical limit on bit rates.
Slide 42
Does not consider Noise that affects a signals characteristics
Limitations on devices to measure small differences between
signals
Slide 43
Problem: noisy channels Large L (# different signals) means
more subtle differences and more difficulty distinguishing them.
Eg. With just a few amplitudes the amplitudes need not be close
together. More amplitudes means the values are all closer
together.
Slide 44
Shannons result: S and N are signal and noise power S/N ratio:
1 Bel = log 10 (S/N); 1 decibel (db) = 0.1 Bels Bit rate =
bandwidth log 10 (1 + S/N) bps If little noise, S/N is large and
the bit rate is larger. If lots of noise, bit rate is smaller.
Slide 45
Phone system: Maximum bit rates for dial-up modemsdial-up
modems bandwidth ~ 3000 Hz S/N ratio ~ 35 db; 3.5 Bels = log 10
(S/N) S/N ~ 10 3.5 S/N ~ 3162 bit rate ~ 3000 log 10 (1 + 3162) ~
35,000 bps max. This applies to old cases where there was a modem
on each end.
Slide 46
56Kbps possible because remote end usually connected to an ISP
and theres no analog component at that end. Thus downloads do NOT
encounter an analog- digital conversion at the remote end, which
(using PCM-covered later) is susceptible to quantization
noise.
Slide 47
Can skip section 3.6
Slide 48
Digital data (Chapter 4). Can skip section 4.1 except for the
schemes below. NRZ schemes: generally 0=high or low and 1=low or
high (the opposite of 0) Ref:
[http://www.frontiernet.net/~prof_tcarr/Encodi
ngs/applet.html#APPLET]
[http://www.frontiernet.net/~prof_tcarr/Encodi
ngs/applet.html#APPLET] NRZ subject to baseline wandering or loss
of synchronization. A very long string of 0s or 1s may be difficult
to interpret correctly.
Slide 49
Manchester 1=Low-Hi, 0 = Hi-Low; Differential Manchester 1=no
change at start, 0=change at start; transition in the middle.
Manchester codes are self synchronizing frequency = 2 bit rate (an
issue). Section 4.1 has many other schemes but well skip most and
defer a couple others until later to put them into a context.
Slide 50
Analog to digital (section 4.2) Can skip material not related
to PAM or PCM Here we deal with analog data, not simple sine/cosine
waves with fixed characteristics.
Slide 51
Sampling theorem F = max frequency receiver can reconstruct a
signal by sampling it at least 2F times per second. Sample obtained
by generating a sampling signal consisting of pulses at specified
intervals.
Pulse Amplitude modulation Each pulse has analog
characteristics in that it can be any real value
Slide 54
PCM (uncompressed video and audio) Divide vertical into bit
groups Take samples and round to the nearest bit group. This
rounding is called quantization noise and results in some signal
loss.
Slide 55
[
http://en.wikipedia.org/wiki/PCM]http://en.wikipedia.org/wiki/PCM]
Digitized voice (telephone) 8000 samples (4000 Hz max frequency) 8
bits per sample 64kbps CD player tech specs: Sampling frequency
44.1 KHz, D-A conversion = 16-bit linear frequency response up to
~20,000 Hz and 64,000 signal amplitudes.
Slide 56
Transmission Modes: Section 4.3
Slide 57
Figure 4.31 Data transmission and modes
Slide 58
Digital to analog (Section 5.1) Modulation: Amplitude Shift
Keying (ASK) Frequency Shift keying (FSK) Phase shift keying (PSK)
Quadrature modulation (QAM)
Slide 59
ASK
Slide 60
FSK
Slide 61
PSK
Slide 62
Example Signal Association for Quadrature Amplitude Modulation
Bit Values Amplitude of Generated Signal Phase Shift of Generated
Signal 000A1A1 0 001A2A2 0 010A1A1 1/(4f) 011A2A2 1/(4f) 100A1A1
2/(4f) 101A2A2 2/(4f) 110A1A1 3/(4f) 111A2A2 3/(4f)
Slide 63
Phase is relative to the signal in the previous interval
Slide 64
There is a simulation at
[http://williams.comp.ncat.edu/Networks/modulate.h tm] Also look at
[http://www.mathsnet.net/graphs/cuoc3.html]http://williams.comp.ncat.edu/Networks/modulate.h
tmhttp://www.mathsnet.net/graphs/cuoc3.html]
Slide 65
Signal constellation: Each signal is represented by a point as
shown below is the phase shift r is the amplitude
Slide 66
Slide 67
Slide 68
Modems (standards defined by CCITT (now ITU) denoted by
V.xxstandards See also Section 9.2
Slide 69
Figure 9.8 The V.32 and V.32bis constellation and
bandwidth
Slide 70
Figure 9.9 Uploading and downloading in 56K modems
Slide 71
Cable modems Cable modems See also Section 9.5
Slide 72
DSL Section 9.3 DSL (Digital Subscriber Line): DSL local loop
(last mile) POTS (Plain Old Telephone system) not high quality like
CAT5 and not likely to be ripped out and new wires installed
(costly) It is capable of transferring higher frequencies than
telephone produces.
Slide 73
Discrete Multitone Discrete Multitone Divide the frequency
range from 0 Hz to 1.104 MHz into 256 separate channels Use the
five lowest channels for POTS Use the remaining channels for
upstream and/or downstream transmission with more channels reserved
for downstream
Slide 74
some channels to be used by both upstream and downstream
transfers To transmit data, divide a bit stream into smaller groups
of bits, one group for each channel Apply a QAM technique to the
bits in each channel
Slide 75
Combine the QAM-generated signals and subject the result to an
Inverse Fast Fourier Transform. (Mathematical function that is able
to determine frequency components of a complex signal) Downstream
(in theory) up to 6 Mbps. Upstream is less.
Slide 76
Figure 9.10 Discrete multitone technique
Slide 77
Multiplexing: Section 6.1 Multiplexing: combining multiple data
signals onto a single data link.
Slide 78
Figure 6.4 FDM process
Slide 79
Figure 6.5 FDM demultiplexing example
Slide 80
Figure 6.11 Prisms in wavelength-division multiplexing and
demultiplexing
Slide 81
Time Division Multiplexing
Slide 82
Figure 6.23 Digital hierarchy
Slide 83
Figure 6.24 T-1 line for multiplexing telephone lines