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The Physical Layer

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A binary signal and its root-mean-square Fourier amplitudes. ... Geostationary Satellites. Medium-Earth Orbit Satellites. Low-Earth Orbit Satellites ... – PowerPoint PPT presentation

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Title: The Physical Layer


1
The Physical Layer
  • Chapter 2

2
The Theoretical Basis for Data Communication
  • Fourier Analysis
  • Bandwidth-Limited Signals
  • Maximum Data Rate of a Channel

3
Bandwidth-Limited Signals
  • A binary signal and its root-mean-square Fourier
    amplitudes.
  • (b) (c) Successive approximations to the
    original signal.

4
Bandwidth-Limited Signals (2)
  • (d) (e) Successive approximations to the
    original signal.

5
Bandwidth-Limited Signals (3)
  • Relation between data rate and harmonics.

6
Guided Transmission Data
  • Magnetic Media
  • Twisted Pair
  • Coaxial Cable
  • Fiber Optics

7
Twisted Pair
  • (a) Category 3 UTP.
  • (b) Category 5 UTP.

8
Coaxial Cable
  • A coaxial cable.

9
Fiber Optics
  • (a) Three examples of a light ray from inside a
    silica fiber impinging on the air/silica boundary
    at different angles.
  • (b) Light trapped by total internal reflection.

10
Transmission of Light through Fiber
  • Attenuation of light through fiber in the
    infrared region.

11
Fiber Cables
  • (a) Side view of a single fiber.
  • (b) End view of a sheath with three fibers.

12
Fiber Cables (2)
  • A comparison of semiconductor diodes and LEDs as
    light sources.

13
Fiber Optic Networks
  • A fiber optic ring with active repeaters.

14
Fiber Optic Networks (2)
  • A passive star connection in a fiber optics
    network.

15
Wireless Transmission
  • The Electromagnetic Spectrum
  • Radio Transmission
  • Microwave Transmission
  • Infrared and Millimeter Waves
  • Lightwave Transmission

16
The Electromagnetic Spectrum
  • The electromagnetic spectrum and its uses for
    communication.

17
Radio Transmission
  • (a) In the VLF, LF, and MF bands, radio waves
    follow the curvature of the earth.
  • (b) In the HF band, they bounce off the
    ionosphere.

18
Politics of the Electromagnetic Spectrum
  • The ISM bands in the United States.

19
Lightwave Transmission
  • Convection currents can interfere with laser
    communication systems.
  • A bidirectional system with two lasers is
    pictured here.

20
Communication Satellites
  • Geostationary Satellites
  • Medium-Earth Orbit Satellites
  • Low-Earth Orbit Satellites
  • Satellites versus Fiber

21
Communication Satellites
  • Communication satellites and some of their
    properties, including altitude above the earth,
    round-trip delay time and number of satellites
    needed for global coverage.

22
Communication Satellites (2)
  • The principal satellite bands.

23
Communication Satellites (3)
  • VSATs using a hub.

24
Low-Earth Orbit SatellitesIridium
  • (a) The Iridium satellites from six necklaces
    around the earth.
  • (b) 1628 moving cells cover the earth.

25
Globalstar
  • (a) Relaying in space.
  • (b) Relaying on the ground.

26
Public Switched Telephone System
  • Structure of the Telephone System
  • The Politics of Telephones
  • The Local Loop Modems, ADSL and Wireless
  • Trunks and Multiplexing
  • Switching

27
Structure of the Telephone System
  • (a) Fully-interconnected network.
  • (b) Centralized switch.
  • (c) Two-level hierarchy.

28
Structure of the Telephone System (2)
  • A typical circuit route for a medium-distance
    call.

29
Major Components of the Telephone System
  • Local loops
  • Analog twisted pairs going to houses and
    businesses
  • Trunks
  • Digital fiber optics connecting the switching
    offices
  • Switching offices
  • Where calls are moved from one trunk to another

30
The Politics of Telephones
  • The relationship of LATAs, LECs, and IXCs. All
    the circles are LEC switching offices. Each
    hexagon belongs to the IXC whose number is on it.

31
The Local Loop Modems, ADSL, and Wireless
  • The use of both analog and digital transmissions
    for a computer to computer call. Conversion is
    done by the modems and codecs.

32
Modems
  • (a) A binary signal
  • (b) Amplitude modulation
  • (c) Frequency modulation
  • (d) Phase modulation

33
Modems (2)
  • (a) QPSK.
  • (b) QAM-16.
  • (c) QAM-64.

34
Modems (3)
(b)
(a)
  • (a) V.32 for 9600 bps.
  • (b) V32 bis for 14,400 bps.

35
Digital Subscriber Lines
  • Bandwidth versus distanced over category 3 UTP
    for DSL.

36
Digital Subscriber Lines (2)
  • Operation of ADSL using discrete multitone
    modulation.

37
Digital Subscriber Lines (3)
  • A typical ADSL equipment configuration.

38
Wireless Local Loops
  • Architecture of an LMDS system.

39
Frequency Division Multiplexing
  • (a) The original bandwidths.
  • (b) The bandwidths raised in frequency.
  • (b) The multiplexed channel.

40
Wavelength Division Multiplexing
  • Wavelength division multiplexing.

41
Time Division Multiplexing
  • The T1 carrier (1.544 Mbps).

42
Time Division Multiplexing (2)
  • Delta modulation.

43
Time Division Multiplexing (3)
  • Multiplexing T1 streams into higher carriers.

44
Time Division Multiplexing (4)
  • Two back-to-back SONET frames.

45
Time Division Multiplexing (5)
  • SONET and SDH multiplex rates.

46
Circuit Switching
  • (a) Circuit switching.
  • (b) Packet switching.

47
Message Switching
  • (a) Circuit switching (b) Message switching
    (c) Packet switching

48
Packet Switching
  • A comparison of circuit switched and
    packet-switched networks.

49
The Mobile Telephone System
  • First-Generation Mobile Phones Analog Voice
  • Second-Generation Mobile Phones Digital Voice
  • Third-Generation Mobile PhonesDigital Voice and
    Data

50
Advanced Mobile Phone System
  • (a) Frequencies are not reused in adjacent cells.
  • (b) To add more users, smaller cells can be used.

51
Channel Categories
  • The 832 channels are divided into four
    categories
  • Control (base to mobile) to manage the system
  • Paging (base to mobile) to alert users to calls
    for them
  • Access (bidirectional) for call setup and channel
    assignment
  • Data (bidirectional) for voice, fax, or data

52
D-AMPS Digital Advanced Mobile Phone System
  • (a) A D-AMPS channel with three users.
  • (b) A D-AMPS channel with six users.

53
GSMGlobal System for Mobile Communications
  • GSM uses 124 frequency channels, each of which
    uses an eight-slot TDM system

54
GSM (2)
  • A portion of the GSM framing structure.

55
CDMA Code Division Multiple Access
  • Allow each station to transmit over entire
    frequency spectrum all the time.
  • Multiple simultaneous transmissions are separated
    using coding theory.
  • Colliding frames may not be totally
    garbled.There are techniques to separate signals
    sent by different senders.
  • Similar to a party where different conversations
    use different language.Extract desired signal
    and reject others as random noises.
  • Each bit time is subdivided into m short
    intervals called chips, typically 64-128 chips
    per bit.
  • Each station is assigned a unique m-bit code or
    chip sequence.
  • To send a bit 1, a station sends its chip
    sequence.
  • To send a bit 0, a station sends the complement
    of its chip sequence.
  • For m8, A is assigned 00011011. A sends
    00011011 as bit 1, and 11100100 as bit 0.

56
Simple Analysis of CDMA
  • Assume 1 MHz band for 100 stations
  • Use FDM, one station has 10kHz and 10 kbps
    (assume 1 bit per Hz)
  • Use CDMA, one station has 1MHz, and 1Mchips per
    seconds.
  • If CDMA uses less than 100 chips per bit then
    CDMA will be more efficient.

57
CDMA Coding Theory
  • Lets use bipolar notation 1 for binary 1 (chip
    signal), -1 for binary 0.
  • A bit1, A send 00011011 or (-1 -1 -1 1 1 -1 1
    1).
  • Let S be the m-chip vector for station s and
    for its negation.
  • Two chip sequence S and T are orthogonal if
    ST0.
  • if ST0 then S 0
  • All chip sequences must be pariwise orthogonal.
  • S -1
  • CDMA Example
  • Let SA C, SC(A C)CAC
    CCC0011

58
CDMA Code Division Multiple Access
  • (a) Binary chip sequences for four stations
  • (b) Bipolar chip sequences
  • (c) Six examples of transmissions
  • (d) Recovery of station Cs signal

59
Walsh-Hadamard Matrix forOrthogonal Spreading
Sequence
  • The Walsh-Hadamard Matrix provides the Orthogonal
    Chip Sequences of length n2m. Replacing 0 with
    signal -1 and 1 with signal 1.
  • It can be recursively constructed. W10. W2n
    where contains complement
    elements of Wn.

60
CDMA Sending
  • Channel 1 110 -gt 111 -gt (-1,-1,-1,-1),(-1,-1,-
    1,-1),(1,1,1,1)
  • Channel 2 010 -gt -11-1 -gt (1,-1,1,-1),(-1,1,-
    1,1),(1,-1,1,-1)
  • Channel 3 001 -gt -1-11 -gt (1,1,-1,-1),(1,1,-
    1,-1),(-1,-1,1,1)
  • Sum Signal (1,-1,-1,-3),(-1,1,-
    3,-1),(1,-1,3,1)

Chip Sequencec1 (-1,-1,-1,-1) c2
(-1,1,-1,1) c3 (-1,-1,1,1) c4 (-1,1,1,-1)
61
CDMA Receiving/Decoding
  • Sum Signal (1,-1,-1,-3),(-1,1,-3,-1),(
    1,-1,3,1)
  • Channel 2 Sequence (-1,1,-1,1),(-1,1,-1,1),(-
    1,1,-1,1)
  • Correlator Output (-1,-1,1,-3),(1,1,3,-1),(-
    1,-1,-3,1)
  • Integrated Output -4, 4,
    -4
  • Binary Output 0, 1,
    0

62
Power Control/Assignment
  • For the CDMA to work, the power levels of signals
    from all stations should be the same (or within
    certain tolerance level) when received by the
    receiver.
  • A good heuristic Each mobile station sends
    signal with the power level inverse of that
    received from the base station.
  • The base station can tell mobile station to
    increase/decrease its power.

63
Third-Generation Mobile PhonesDigital Voice and
Data
  • Basic services an IMT-2000 network should provide
  • High-quality voice transmission
  • Messaging (replace e-mail, fax, SMS, chat, etc.)
  • Multimedia (music, videos, films, TV, etc.)
  • Internet access (web surfing, w/multimedia.)

64
Cable Television
  • Community Antenna Television
  • Internet over Cable
  • Spectrum Allocation
  • Cable Modems
  • ADSL versus Cable

65
Community Antenna Television
  • An early cable television system.

66
Internet over Cable
  • Cable television

67
Internet over Cable (2)
  • The fixed telephone system.

68
Spectrum Allocation
  • Frequency allocation in a typical cable TV system
    used for Internet access

69
Cable Modems
  • Typical details of the upstream and downstream
    channels in North America.
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