2 It defines the mechanical, electrical, and timing interfaces
to the network. Purpose: To transport a raw bit stream Each one has
its own function in terms of bandwidth, delay, cost, ease of
installation and maintenance
Slide 3
Max Data Rate of a Channel Nyquist Theorem noiseless channel
Max Data Rate = 2Hlog 2 V bits/sec H : Bandwidth V : V discrete
levels of a signal For binary = 2 levels Ex: for 3KHz channel, Max
data rate 6000 bps Signal to Noise Ratio (SNR) SNR = Signal Power /
Noise Power Measured in decibels (db) 10log 10 S/N For Noisy
channel Shanon theorem Maximum number of bits/sec = Hlog 2
(1+S/N)
Slide 4
4 Physical Media Groups Roughly grouped into Guided media,
copper wire and fiber optics, Unguided media, radio and lasers
Slide 5
5 Guided Transmission Media Magnetic Media Twisted Pair
Co-axial cable Fiber optics
Slide 6
6 Guided Transmission Media Magnetic media It is the most
common way of transferring data Transmission time is measured in
minutes or hours Used Where very less frequent transportation is
needed Where amount of data is very high Cost effective, especially
for applications in which high bandwidth or cost per bit
transported is the key factor. Ex.Ultrium Tape-200 Gigabytes.
Slide 7
7 Twisted Pair Transmission time is measured in milliseconds.
Consisting of two insulated copper wires. Thickness = 1 mm Wires
are twisted together in a helical form like DNA molecule. To remove
electro-magnetic effect on data
Slide 8
8 Twisted-Pair Cable
Slide 9
9 Twisted Pair The most common application is telephone system
Can transfer data for several kilometers without amplification But
for very long distances amplification is needed Repeaters are used
Many TP cables grouped together and covered by protected material.
They can be used for digital as well as analog transmission. The
bandwidth depends on the thickens of the wire and the distance
traversed. It is the cheapest solution
Slide 10
10 Twisted Pair - Types Two types Category 3,4 pairs 16 MHz
Gently twisted Category 5,4 pairs 100 MHz More twists Less
crosstalk, better signal quality Category 6 (250 MHz) and 7 (600
MHz) are also coming It is also called UTP (Unshielded Twisted
pair) cable.
Slide 11
11 Twisted-Pair Cable Figure 7-8
Slide 12
12 A Coaxial Cable
Slide 13
13 Coaxial cable Construction stiff copper wire as the core
surrounded by an insulating material The insulator is encased by a
cylindrical conductor a closely-woven braided mesh The outer
conductor is covered in a protective plastic sheath
Slide 14
14 Coaxial Cable Advantages Better shielding than twisted pairs
High bandwidth (1 GHz) [600 MHz] Excellent noise immunity Use
Within the telephone system for long-distance lines For cable
television For metropolitan area networks
Slide 15
15 Coaxial cable Two kinds of coaxial cable 50-ohm cable used
for digital transmission 75-ohm cable used for analog transmission
and cable television
Slide 16
16 Fiber Optics It transmit data by pulses of light A pulse of
light indicates a 1 bit and the absence of light indicates a 0 bit
Optical transmission system has three components The light source
The transmission medium The detector
Slide 17
17 Working of Fiber Optics Light source is either LED or a
laser diode. The transmission medium is ultra thin fiber of glass
The detector is a Photodiode which emits electric pulse when light
falls on it. Attaching a light source to one end of an optical
fiber and a detector to the other, we have a unidirectional data
transmission system that accepts an electrical signal, converts and
transmits it by light pulses, and then reconverts the output to an
electrical signal at the receiving end. Data rate = 10 Gbps
Slide 18
18 Example a) Three examples of light rays from inside a silica
fiber impinging on the air/silica boundary at different angles b)
light trapped by total internal reflection
Slide 19
19 The Single Mode Fiber Fiber with core diameter less than
about ten times the wavelength of light then it is known as single
mode fiber Single mode fiber acts like a wave guide, and the light
propagates in a straight line They require expensive laser diodes
but are more efficient and run for longer distances It can transmit
data at 50 Gbps for 100 km without amplification The most common
type of single-mode fiber has a core diameter of 8 to 10 m
Slide 20
20 Single-mode fibers are more expensive but are widely used
for longer distances. Fiber with large (greater than 10 m ) core
diameter called multimode fiber. A fiber can pass more than one
rays at a time, at different angles then it is known as multimode
fiber. The Single Mode Fiber
Slide 21
(a) Multimode fiber: multiple rays follow different paths (b)
Single mode: only direct path propagates in fiber direct path
reflected path
Slide 22
22 Transmission of Light Through Fiber Glass used is Very
transparent! Attenuation of light passing thru glass depends on the
wavelength of it Attenuation = reduction in power
Slide 23
23 Attenuation of Light Thru Fiber in the Infrared Region
Slide 24
24 The Spectrum Used Three wavelengths are used for optical
communication. 0.85 micron, 1.30, 1.55 microns are centers Later
two have less then 5% loss per km
Slide 25
25 Dispersion and Solution Light pulses spread out in length as
they propagate, This spreading is known as chromatic dispersion The
amount of dispersion is Wavelength dependent. Dispersion results in
overlapping of light waves in multimode fiber To stop spread out
pulses overlapping, is to increase the distance between them. This
can be done only by reducing the signaling rate.
Slide 26
26 The Fiber Cable At the center is the glass core through
which the light propagates. In multimode fiber, the core is about
50 microns thick,( thickness of human hair) In single mode fiber,
the core is 8 to 10 microns wide
Slide 27
27 The Fiber Cable The core is surrounded by a glass cladding
with a lower index of refraction Next comes a thin plastic jacket
to protect the cladding Fibers are typically grouped together in
bundles, protected by an outer sheath
Slide 28
28 Fiber Cables a) Side view of a single fibre b) End view of a
sheath with three fibres
Slide 29
29 Light Sources A Comparison of LED and Semiconductor diodes
as Light sources
Slide 30
30 Interfaces (With Computers) The connector is very difficult
to make and substantial light is lost Two type of interfaces are
used first one is called the Passive Interface second one is called
Active repeater Both of them, at each computer, serves as a T
junction to allow the computer to send and accept messages, and
pass data through
Slide 31
31 A Fiber optic Ring With Active repeaters
Slide 32
32 The Active Repeater In the Active repeater the incoming
light is converted to an electric signal It is regenerated to the
full strength and retransmitted as light connector is a simple
copper wire If an active repeater fails, the ring gets broken and
the network goes down There is no virtual limit on the size of
ring
Slide 33
33 Passive Interfaces: Passive interface consists of two tapes
fused onto main fiber One tap has LED or Laser diode at the end of
it and the other has the Photodiode It is extremely reliable
because a broken LED or photodiode does not break the ring. It just
takes one computer off-line.
Slide 34
34 A Passive Star Connection
Slide 35
35 Comparing Fiber and Copper High bandwidth with min loss of
power Not affected by power line surges, Electromagnetic
interference Repeaters are needed every 50km compared to 5 km in
copper wire They are very thin and light weight
Slide 36
36 Comparing Fiber and Copper One thousand twisted pairs 1 km
long weigh 8000 kg. Two fibers have more capacity and weigh is only
100 kg. Fibers do not leak light and are quite difficult to tap
Since optical transmission is inherently unidirectional, two-way
communication requires either two fibers or two frequency bands on
one fiber It is an less familiar technology for most Engineers. Can
be damaged easily by being bent too much Fiber interfaces cost more
than electrical interfaces
Slide 37
37 Wireless Transmission For people who need to be on-line all
the time For mobile users. Running a fiber to a building is
difficult due to the terrain (mountains, jungles, etc.)
Slide 38
38 The Electromagnetic Waves When electrons move, they create
EM waves that can propagate thru free space Frequency( f ) The
number of oscillations per second of wave measured in Hz Wavelength
() The distance between consecutive maxima or minima By attaching
an antenna to an Electric Circuit, the EM Wave can be broadcasted
and can be received by receiver some distance away.
Slide 39
39 The Properties of EMWs In Vacuum all EMWs travel at the same
speed even though different frequency- 3 * 10 8 m/sec or 30 cm/nano
sec In copper or fiber, it slows about 2/3 rd of above value and
become slightly freq dependent.
Slide 40
40 The EM Spectrum
Slide 41
41 The EM Spectrum The Radio, microwave, infrared and visible
light, all can be used for transmission Transmission can be done by
modulating either amplitude, frequency or phase UV, X-rays, and
gamma rays are hard to produce, do not propagate well thru
buildings and are dangerous to living things
Slide 42
42 The Capacity of Transmission The amount of info an EMW can
carry is related to its bandwidth It is possible to encode few bits
per Hz at lower freqs but nearly 8 at high freqs
Slide 43
43 Transmission Methods Direct Sequence spread spectrum &
Frequency hopping spread spectrum The transmitter and receiver hops
from frequency to frequency hundreds of times per second makes
transmissions hard to detect which spreads the signal over a wide
frequency band good efficiency high noise immunity Used in military
and commercial world
Slide 44
44 Radio Waves They are easy to generate, can travel long
distances, penetrate buildings easily They are omni directional (
can travel in all directions) so transmitter and receiver are not
needed to be aligned Radio waves are frequency dependent At low
freq, power falls off sharply with distance from the source. At
higher freq, they tend to travel in straight lines and bounce of
obstacles
Slide 45
45 Continue In VLF, LF and MF bands radio waves follow the
ground Easily pass through buildings These bands offer relative low
bandwidth for data communication
Slide 46
46 Continue In HF and VHF bands, the ground waves tends to be
absorbed by earth The waves that reach ionosphere, are refracted by
it and sent back to earth military operates on these bands for long
distance talks
Slide 47
47 Transmission of Radio Waves In the VLF, LF and MF bands,
radio waves follow the Curvature of the earth In the HF, and VHF
they bounce of The ionosphere
Slide 48
48 Microwave Transmission Microwave = Wave above 100 MHz Travel
in Straight line Transmitting and receiving antennas must be
accurately aligned with each other Repeaters are needed If towers
are too far, the earth will get in the way Height : distance Ratio
= r:r 2 Higher the tower, farther apart they can be.
Slide 49
49 Terrestrial Microwave
Slide 50
50 Microwave Transmission To achieve high data rate -10GHz,
microwave is in routine use but At about 4 GHz, MW absorbed by
water and generate hit These waves are only a few centimeters long
and are absorbed by rain Sol n :- Shut off links where rain is
falling & take another route
Slide 51
51 MW use microwave communication is so widely used for
long-distance telephone communication, mobile phones, television
distribution
Slide 52
52 Comparison with Fiber optics Inexpensive Putting up two
simple towers may be far cheaper than buying 50 km of fiber through
a congested urban area or up over a mountain
Slide 53
53 Infrared and Millimeter Waves Used for short range
communication Remote control of electronic products Can not pass
through solid objects due to high freq infrared system in one room
will not interfere with a similar system in adjacent rooms No need
of government license
Slide 54
54 Light Wave Transmission Lasers can connect two LANs Coherent
optical signaling using lasers is inherently unidirectional Each
one need its own laser and photo detector It offers very high
bandwidth at very low cost
Slide 55
55 Continue Advantage : It is relatively easy to install, and
no licensing is needed Disadvantage : It can not penetrate even a
rain or thick fog Heat generated by sun can defocus the beam
Slide 56
56 A Bi-directional System With Two Lasers
Slide 57
Communication satellites Contains several transponders which
listens to some portion of the spectrum, amplifies the incoming
signal, rebroadcasts it at another frequency to avoid interference
with the incoming signal.
Slide 58
Communication Satellites GEO (Geostationary Satellite) Orbit
slots allocation is done by the ITU Min 2 degrees distance between
satellites 360/2 = 180 satellites The effects of solar, lunar, and
planetary gravity tend to move them away from their assigned orbit
slots and orientations, an effect countered by on-board rocket
motors. This fine-tuning activity is called station keeping.
Slide 59
Satellite Bands Ku = commercial telecommunication carriers Ka =
commercial Many government and military bands also exists
Slide 60
Communication satellites A modern satellite has around 40
transponders, each with an 80-MHz bandwidth. Spot Beams - Each
downward beam can be focused on a small geographical area
elliptically shaped, and can be as small as a few hundred km in
diameter. VSATs (Very Small Aperture Terminals) 1-meter or smaller
antennas (versus 10 m for a standard GEO antenna) and can put out
about 1 watt of power. uplink -19.2 kbps, downlink - 512 kbps.
Microstations do not have enough power to communicate directly with
one another (via the satellite). Instead, a special ground station,
the hub, with a large, high-gain antenna is needed to relay traffic
between VSATs,
Slide 61
VSAT VSATs have great potential in rural areas.
Slide 62
Communication satellites - Properties Broadcast media
Propagation delay 3 sec (fibre optic 5 sec) Because electromagnetic
waves travel faster in air than in solid materials Satellites are a
complete disaster: everybody can hear everything. Encryption is
essential when security is required. High error rates Cost to any
place is same
Slide 63
Satellites versus Fiber High bandwidth via satellite than Fiber
Communication on move (mobile) Broadcasting A message sent by
satellite can be received by thousands of ground stations at once.
Launching one satellite was cheaper than stringing thousands of
undersea cables Satellites is to cover areas where laying fiber is
difficult or unduly expensive. Military communication systems in
time of war, satellites win easily.
Slide 64
The Public Switched Telephone Network Structure of the
Telephone System 64
Slide 65
8/30/201565 How TN is used for data communication.
Slide 66
Transmission line suffers from 3 problems Attenuation-it is
loss of energy as signal propagates outward (db/km) Distortion-
speed difference leads to distortion of received signal
Noise-unwanted energy from sources other than transmitter. 66
Slide 67
8/30/201567 MODEM Aim = To transfer digital data in existing
analog twisted pair cable Achieved through modulation of one or
more properties of analog signal such as Amplitude Frequency
Phase
Slide 68
Modulation (b) AM (c) FM (d) PM 68
Slide 69
AM, FM, PM AM PM FM
Slide 70
8/30/201570 Speed Modem can sample 2400 times per second Each
sample is called baud During each baud one symbol is transmitted
Symbol may carry one or more bits If the symbol consists of 0 volts
for a logical 0 and 1 volt for a logical 1(or one bit per symbol),
than bit rate is 2400 bps (2.4kbps)
Slide 71
8/30/201571 Baud Rate / Bit Rate voltages 0, 1, 2, and 3 volts
are used, every symbol consists of 2 bits, so a 2400-baud line can
transmit 2400 symbols/sec at a data rate of 4800 bps. Similarly,
with four possible phase shifts, there are also 2 bits/symbol, so
again here the bit rate is twice the baud rate. The latter
technique is widely used and called QPSK (Quadrature Phase Shift
Keying).
Slide 72
8/30/201572 Continue To improve the speed from one bit, we can
use modulation techniques Using 4 voltage level (2 bit per symbol)
Using 4 phase shifts (2 bit per symbol) Combination of both (4 bit
per symbol)
Slide 73
8/30/201573 QPSK All advanced modems use a combination of
modulation techniques to transmit multiple bits per baud. Often
multiple amplitudes and multiple phase shifts are combined to
transmit several bits/symbol. Fig- (a) has four valid combinations
and can be used to transmit 2 bits per symbol. It is QPSK
(Quadrature Phase Shift Keying).
8/30/201575 QAM-16 In Fig-(b) we see a different modulation
scheme, in which four amplitudes and four phases are used, for a
total of 16 different combinations. This modulation scheme can be
used to transmit 4 bits per symbol. It is called QAM-16 (Quadrature
Amplitude Modulation). Sometimes the term 16-QAM is used instead.
QAM-16 can be used, for example, to transmit 9600 (2400*4) bps over
a 2400-baud line.
Slide 76
8/30/201576 QAM-64 Fig- (c) is yet another modulation scheme
involving amplitude and phase. It allows 64 different combinations,
so 6 bits can be transmitted per symbol. It is called QAM-64.
Higher-order QAMs also are used. Each high-speed modem standard has
its own constellation pattern and can talk only to other modems
that use the same one
Slide 77
Modems types Extra bit for error detection V.32 => 4+1 = 5
v.90 => 33.6 kbps V.32 bis => 6+1 = 7 V.92 => 48 kbps V.34
=> 28800 bps V.32 bis => 33600 bps
Slide 78
8/30/201578 Asymmetric Digital Subscriber Lines The maximum
speed possible by modems is 56 kbps To start Services with more
bandwidth than standard telephone service
Slide 79
8/30/201579 ADSL - Two Approaches Dividing the spectrum of 1.1
MHz into three frequency bands: POTS (Plain Old Telephone Service)
Upstream (user to end office) and Downstream (end office to user).
The alternative approach, called DMT (Discrete MultiTone )
Slide 80
8/30/201580 DMT Divide the available 1.1 MHz spectrum on the
local loop into 256 independent channels of 4312.5 Hz each Channel
0 is used for POTS. Channels 15 are not used Of the remaining 250
channels, one is used for upstream control and one is used for
downstream control. So rest(248) are available for user data.
Slide 81
8/30/201581 Operation of ADSL using discrete multitone
modulation. 80%90% of the bandwidth is allocated to the downstream
channel since most users download more data than they upload
Slide 82
8/30/201582 ADSL Arrangement DSLAM DSL Access Multiplexer
Consists of DSP
Slide 83
8/30/201583 ADSL Arrangement NID (Network Interface Device) To
interface with Telephone Network At customer premises
Splitter(Analog filter) separates the 0-4000 Hz band (voice from
the data) POTS signal routed to telephone network Data signal
routed to ADSL modem Disadvantage: presence of the NID and splitter
on customer premises required ADSL is physical layer standard.
Slide 84
8/30/201584 Wireless Local Loops What is the need of WLL ? Any
company wishing to get into the local phone business in some city
must do the following things First it must buy or lease a building
for its first end office Second it must fill the end office with
telephone switches and other equipment
Slide 85
8/30/201585 Continue Third, it must run a fiber between the end
office and its nearest toll office so the new local customers will
have access to its national network. Fourth it must acquire
customers, typically by advertising better service or lower prices
than those of the Existing companies. Fifth and hardest path is
installing local loop So WLL, a cheaper solution was
discovered
Slide 86
8/30/201586 Expectation of customer Fixed Wireless Gives
high-speed Internet connectivity New customer should not have an
objection with a large directional antenna on his roof Customer can
not be mobile
Slide 87
8/30/201587 Freq Spectrum Allocation The 198 MHz of new
spectrum was allocated for the use of WLL This service called MMDS
(Multichannel Multipoint Distribution Service). Low bandwidth of
MMDS limits the no of users because Allocated spectrum is shared by
many users gave birth to LMDS (high BW service)
Slide 88
8/30/201588 LMDS ( Local Multipoint Distribution Service ) 1.3
GHz BW At frequencies of 2831 GHz in the U.S. and 40 GHz in
Europe
Slide 89
8/30/201589 Architecture of an LMDS system
Slide 90
8/30/201590 Architecture of an LMDS system Tower is shown with
multiple antennas on it, each pointing in a different direction.
Each antenna defines a sector, independent of the other ones. Range
is 25 km, which means that many towers are needed to cover a city.
36 Gbps downstream and 1 Mbps upstream, shared among all the users
in that sector A single tower with four antennas could serve
100,000 people within a 5-km radius of the tower.
Slide 91
8/30/201591 Few problems with LMDS Waves propagate in straight
lines Leaves absorb these waves well Rain also absorbs these
waves
Slide 92
Circuit Switching and Packet Switching 92
Slide 93
93
Slide 94
Comparison 94
Slide 95
8/30/201595 The Mobile Telephone System Wireless telephones
come in two basic varieties: Cordless phones consisting of a base
station and a handset sold as a set for use within the home. Mobile
phones (sometimes called cell phones).
Slide 96
8/30/201596 Three Generations Mobile phones Generations: 1.
Analog voice. 2. Digital voice. 3. Digital voice and data
(Internet, e-mail, etc.).
Slide 97
8/30/201597 Analog Voice (First-Generation Mobile Phones )
Mobile radio telephones used for maritime and military
communication In 1946, the first system for car-based telephones
was set up in St. Louis Single large transmitter on top of a tall
building and had a single channel, used for both sending and
receiving. To talk, the user had to push a button that enabled the
transmitter and disabled the receiver Known as push-to-talk
systems
Slide 98
8/30/201598 IMTS Improved Mobile Telephone System Was installed
in the 1960s two frequencies, one for sending and one for receiving
IMTS supported 23 channels spread out from 150 MHz to 450 MHz
Slide 99
8/30/201599 Disadvantages Small number of channels, users often
had to wait a long time before getting a dial tone. The large power
of the transmitter adjacent systems had to be several hundred
kilometers apart to avoid interference The limited capacity made
the system impractical
Slide 100
8/30/2015100 Advanced Mobile Phone System Invented by Bell Labs
first installed in the United States in 1982 & was also used in
England called TACS in Japan called MCS-L1
Slide 101
8/30/2015101 Implementation Geographic region is divided up
into cells Area = 10 to 20 Km Each cell uses some set of
frequencies not used by any of its neighbours
Slide 102
8/30/2015102 Same group of Freqs
Slide 103
8/30/2015103 Cells are divided in micro cells
Slide 104
8/30/2015104 Continue At the center of each cell is a base
station to which all the telephones in the cell transmit The base
station consists of a computer and transmitter/receiver connected
to an antenna base stations are connected to an MTSO (Mobile
Telephone Switching Office) or MSC (Mobile Switching Center) The
MTSOs are connected to at least one telephone system end
office
Slide 105
8/30/2015105 Handoff When phone moves from one cell to another
cell, base station changes, It takes about 300 ms Two types of
Handoff Soft Handoff :- Telephone is acquired by the new base
station before the previous one signs off. In this way there is no
loss of continuity. Telephone needs to be able to tune to two
frequencies at the same time (the old one and the new one). Neither
first nor second generation devices can do this
Slide 106
8/30/2015106 Continue Hard Handoff With breaking continuity Old
base station drops the telephone before the new one acquires it. If
the new one is unable to acquire it (e.g., because there is no
available frequency), the call is disconnected abruptly. Users tend
to notice this
Slide 107
8/30/2015107 Communication Channels Freq Spectrum divided in
832 full- duplex channels 832 simplex transmission channels from
824 to 849 MHz 832 simplex receive channels from 869 to 894
MHz
Slide 108
8/30/2015108 Channels The 832 channels are divided into four
categories: 1. Control (base to mobile) to manage the system. 2.
Paging (base to mobile) to alert mobile users to calls for them. 3.
Access (bidirectional) for call setup and channel assignment. 4.
Data (bidirectional) for voice, fax, or data.
Slide 109
8/30/2015109 Call Management Each mobile has a 32-bit serial
number and a 10-digit(34-bit) telephone number. When a phone is
switched on, it scans a preprogrammed list of 21 control channels
to find the most powerful signal. The phone then broadcasts its
32-bit serial number and 34-bit telephone number base station hears
the announcement, informs the MTSO, and customer's home MTSO
Slide 110
8/30/2015110 Call Management To make a call User dial a no and
press send button No. is sent (on access channel) to base station
On getting request base station informs MTSO MTSO allot free
channel Channel no is sent back (on control channel) to mobile
Mobile switches to that voice channel
Slide 111
8/30/2015111 Call Management Incoming calls all idle phones
continuously listen to the paging channel When a call is placed to
a mobile phone a packet is sent to the callee's home MTSO to find
out where it is Packet sent to callees current base station Base
station broadcast are you there Callees phone responses Base
station send channel no Callees phone switches to that channel and
ringing starts
Slide 112
8/30/2015112 Second-Generation Mobile Phones: Digital Voice Due
to the lack of world wide standardization Four systems are in use
now D-AMPS, (used in US) GSM, (Everywhere) CDMA, PDC (used in
Japan) (almost same as first)
Slide 113
8/30/2015113 D-AMPS The Digital Advanced Mobile Phone System
Frequency Allocation Upstream: 18501910 MHz Downstream: 19301990
MHz Wavelength=16 cm Antenna requirement 4 cm long
Slide 114
8/30/2015114 D-AMPS Voice signal picked up by microphone is
digitized and compressed Compression is done through circuit called
vocoder Advantage of digitization & compression: More than one
users can use same frequency channel
Slide 115
8/30/2015115 D-AMPS Each frequency pair supports 25 frames/sec
of 40 msec each Each frame is divided into six time slots of 6.67
msec each Each frame holds three users who take turns using the
upstream and downstream links Using better compression algorithms,
in which case six users can be stuffed into a frame
Slide 116
8/30/2015116 TDM Frame of D-AMPS User 1 sending User 3
receiving
Slide 117
8/30/2015117 Hand off In D-AMPS, 1/3 of the time a mobile is
neither sending nor receiving. It uses these idle slots to measure
the line quality. When it discovers that the signal is waning, it
complains to the MTSO, The mobile tuned to a stronger signal from
another base station. Takes about 300 msec to do the handoff. This
technique is called MAHO (Mobile Assisted Hand Off).
Slide 118
8/30/2015118 GSM The Global System for Mobile Communication 124
pairs of simplex channels Each simplex channel is 200 kHz wide and
supports eight separate connections on it
Slide 119
8/30/2015119 GSM uses 124 frequency channels, each of which
uses an eight-slot TDM system
Slide 120
8/30/2015120 A portion of the GSM framing structure
Slide 121
8/30/2015121 A portion of the GSM framing structure Eight data
slots make up a TDM frame 26 TDM frames = 120msec multiframe. Of
the 26 TDM frames in a multiframe, slot 12 is used for control and
slot 25 is reserved for future use, only 24 are available for user
traffic. 51-slot multiframe is also used
Slide 122
8/30/2015122 A portion of the GSM framing structure TDM slot
consists of a 148-bit data frame that occupies the channel for 577
sec Each data frame starts and ends with three 0 bits It also
contains two 57-bit Information fields, each one having a control
bit that indicates whether the following Information field is for
voice or data. Between the Information fields is a 26-bit Sync
(training) field that is used by the receiver to synchronize to the
sender's frame boundaries
Slide 123
8/30/2015123 CDMA Code Division Multiple Access D-AMPS and GSM
are fairly conventional systems. They use both FDM and TDM to
divide the spectrum into channels and the channels into time slots.
CDMA allows each station to transmit over the entire frequency
spectrum all the time. If we have a 1-MHz band available for 100
stations, with FDM each one would have 10 kHz and could send at 10
kbps (assuming 1 bit per Hz). With CDMA, each station uses the full
1 MHz, so the chip rate is 1 megachip per second. Each bit time is
subdivided into m short intervals called chips. Typically, there
are 64 or 128 chips per bit, but in the example given we will use 8
chips/bit for simplicity.
Slide 124
8/30/2015124 Example Each station is assigned a unique m-bit
code called a chip sequence. To transmit a 1 bit To transmit a 0
bit, it sends the one's complement of its chip sequence.
Slide 125
8/30/2015125 Continue Orthogonal property of chip sequences A.
A = 1 A. A = -1 A. B = 0 A. B = 0
Slide 126
8/30/2015126 Continue When two or more stations transmit
simultaneously, their bipolar signals add linearly
Slide 127
8/30/2015127 (a) Binary chip sequences for four stations. (b)
Bipolar chip sequences. (c) Six examples of transmissio ns. (d)
Recovery of station C's signal.
Slide 128
8/30/2015128 Continue
Slide 129
8/30/2015129 Third-Generation Mobile Phones: Digital Voice and
Data Expectation of Industry Experts a lightweight, portable device
that acts as a telephone, CD player, DVD player, e-mail terminal,
Web interface, gaming machine, word processor, and more, All with
worldwide wireless connectivity to the Internet at high
bandwidth.
Slide 130
8/30/2015130 To Achieve this dream The single world wide
technology was envisioned (IMT-2000) Basic services High-quality
voice transmission. Messaging Multimedia Internet access
Slide 131
8/30/2015131 Several proposals came W-CDMA (Wideband CDMA), was
proposed by Ericsson. Not backward compatibility was there with GSM
UMTS (Universal Mobile Telecommunications System). Proposed by
European Union CDMA2000, proposed by Qualcomm Handoff was
problem
Slide 132
2.5G EDGE (Enhanced Data rates for GSM Evolution) GSM with more
bits per baud GPRS (General Packet Radio Service) Packet network on
top of D-AMPS and GSM Using unused TDMA channels of GSM If SMS over
GPRS is used, an SMS transmission speed of about 30 SMS messages
per minute may be achieved. This is much faster than using the
ordinary SMS over GSM, whose SMS transmission speed is about 6 to
10 SMS messages per minute.
Slide 133
8/30/2015133 Cable television was conceived in the late 1940s
Consisted of a big antenna on top of a hill to pluck the television
signal out of the air, An amplifier, called the head end, to
strengthen it, A coaxial cable to deliver it to people's houses,
Cable Television - Community Antenna TV
Slide 134
8/30/2015134 HFC Hybrid fiber coax system (Electro optical
converter)
Slide 135
Fixed Telephone System Internet on Cable a) A single cable is
shared by many houses, whereas in the telephone system, every house
has its own private local loop One-way amplifiers have to be
replaced by 2 way amplifiers b) On the other hand, the bandwidth of
coax is much higher than that of twisted pairs, but the cable is
shared.
Slide 136
8/30/2015136 Internet over Cable
Slide 137
8/30/2015137 Cable Modems Two interfaces on it: one to the
computer and one to the cable network. The headend assigns upstream
and downstream channels for that modem Modem scans the downstream
channel for system parameters
Slide 138
8/30/2015138 Cable Modems Ranging: modem determines its
distance from the headend Typical details of the upstream and
downstream channels
Slide 139
8/30/2015139 ADSL versus Cable ADSL providers can give specific
statements about the bandwidth Increasing no of users do not affect
speed Availability : You must be near the end office if you want
ADSL More secure due to p to p connection More reliable: work even
during a power outage