Download - Guided & Unguided
-
8/13/2019 Guided & Unguided
1/63
Electromagnetic Spectrum
The electromagnetic (EM) spectrum is the rangeof all types of EM radiation . Radiation isenergy that travels and spreads out as it goes the visible light that comes from a lamp in yourhouse and the radio waves that come from aradio station are two types of electromagnetic
radiation. The other types of EM radiation thatmake up the electromagnetic spectrum aremicrowaves , infrared light , ultraviolet light , X-
rays and gamma-rays .
http://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_jp.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ei.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_jp.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_qz.html -
8/13/2019 Guided & Unguided
2/63
Electromagnetic Spectrum
Figure 7-1
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
3/63
Electromagnetic Spectrum
Propagation characteristics are different in each frequency band Licensed and Unlicensed bands
UV
1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz
infrared visible
X raysGamma rays
LF HF VHF UHF SHF EHF MF
902 928 Mhz2.4 2.4835 Ghz
5.725 5.785 Ghz
30kHz 300kHz 3MHz 30MHz 300MHz 30GHz 300GHz
10km 1km 100m 10m 1m 10cm 1cm 100mm
3GHz
-
8/13/2019 Guided & Unguided
4/63
Transmission Impairment
With any communications system, thesignal that is received may differ from thesignal that is transmitted, due to varioustransmission impairments.
-
8/13/2019 Guided & Unguided
5/63
Transmission Impairment
Attenuation Delay distortion Noise
-
8/13/2019 Guided & Unguided
6/63
Attenuation
Attenuation means loss of energy.
-
8/13/2019 Guided & Unguided
7/63
-
8/13/2019 Guided & Unguided
8/63
Attenuation
Bel deciBel
Pin = 100mW, P out = 10mW, attenuation =10 dB
-
8/13/2019 Guided & Unguided
9/63
Delay Distortion
Delay distortion is due to velocity of propagation that varies withfrequency. Thus, various frequency components of a signal arrive atthe receiver at different times.
Critical in particular for digital data, because signal components of bit positions spill into other bit positions, and so limiting the allowed rateof transmission.
-
8/13/2019 Guided & Unguided
10/63
Noise
Noise
Signal
signal + noise
Several types of noise such as thermal noise,
induced noise, crosstalk and impulse noisemay corrupt the signal.
-
8/13/2019 Guided & Unguided
11/63
Noise
Thermal noise is the random motion of electrons in a wire that createsan extra signal not originally sent by the transmitter.
Induced noise comes from sources such as motors and appliances.
These devices acts as sending antenna and the transmission mediumacts as receiving antenna. Crosstalk is a noise that is caused by the inductive coupling between
two wires that are closed to each other. Sometime when talking on thetelephone, you can hear another conversation in the background. That
is cross talk. Impulse noise is irregular disturbances, such as lightning, and flawed
communication elements. It is a primary source of error in digital data.
-
8/13/2019 Guided & Unguided
12/63
Transmission Media
Means by which a communication signal iscarried from one system to another (for
example twisted-pair wire, co axial cable,fiber-optic cable) and wireless links (forexample satellite, microwave, radio and
infrared systems.
-
8/13/2019 Guided & Unguided
13/63
Figure 7-2
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
14/63
Figure 7-3
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
15/63
Guided Transmission Media
Waves are guided along solid medium.
-
8/13/2019 Guided & Unguided
16/63
Twisted-Pair CableFigure 7-4 and 7-5
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
17/63
Twisted-Pair Cable
Pair of twisted conductors Twisting reduces interference (two parallel wires constitute a simple
antenna; a twisted pair does not.)
Cheap medium Commonly used for communications within buildings and in telephone
networks Produced in unshielded (UTP) and shielded (STP) forms, and in
different performance categories.
Cables may hold hundreds of pairs. Neighbor pairs typically havedifferent twist lengths to reduce crosstalk.
http://wagner.princeton.edu/cgi-bin/foldoc?twisted-pairhttp://wagner.princeton.edu/cgi-bin/foldoc?twisted-pair -
8/13/2019 Guided & Unguided
18/63
Effect of Noise on Parallel LinesFigure 7-6
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
19/63
Noise on Twisted-Pair LinesFigure 7-7
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
20/63
Unshielded Twisted-Pair Cable
Figure 7-8
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
21/63
UTP ConnectorsFigure 7-9
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
22/63
Shielded Twisted-Pair Cable
Figure 7-10
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
23/63
Shielded Twisted-Pair Cable
STP has a metal foil or braided-mesh covering that encases each pairof insulated conductors.
The metal casing prevents the penetration of electromagnetic noise.
Shielding each pair of a twisted- pair cable can eliminate mostcrosstalk.
Shield must be connected to the ground. Connectors used in STP & UTP are RJ 45, RJ 11 etc. STP is more expensive than UTP but less susceptible to noise.
-
8/13/2019 Guided & Unguided
24/63
Categories of Twisted-Pair Cables
Category 1: The basic cabling used for voice. Category 2: Suitable for voice and data up to 4 Mbps. Category 3: Required to have at least three twists per foot and can
be used for data transmission of up to 10 Mbps. It is now thestandard cable for most telephone systems.
Category 4: Must also have at least three twists per foot and canbe used for data transmission of up to 16 Mbps.
Category 5: Suitable for data up to 100 Mbps
-
8/13/2019 Guided & Unguided
25/63
Coaxial CableFigure 7-11 and 7-12
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
26/63
-
8/13/2019 Guided & Unguided
27/63
Coaxial Cable Standards
Different coaxial cable designs are categorized by theirradio government(RG) ratings.
RG-8 used in thick Ethernet. RG-9 used in thick Ethernet. RG-11 used in thick Ethernet. RG-58 used in thin Ethernet.
RG-59 used for TV.
-
8/13/2019 Guided & Unguided
28/63
Coaxial Cable Connectors
To connect co-axial cable to devices, we need coaxial connectors. The mostcommon type of connector used today is the Bayone-NeiIl-Concelman, orBNC, connectors.
Fi 7 13
-
8/13/2019 Guided & Unguided
29/63
Refraction
Figure 7-13
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Fig 7 14
-
8/13/2019 Guided & Unguided
30/63
Critical Angle
Figure 7-14
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Figure 7 15
-
8/13/2019 Guided & Unguided
31/63
Reflection
Figure 7-15
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
32/63
Figure 7 20
-
8/13/2019 Guided & Unguided
33/63
Fiber Construction
Figure 7-20
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
-
8/13/2019 Guided & Unguided
34/63
Light propagation Meaning - Light travels along a fiber cable by a
process called 'Total Internal Reflection' (TIR), this is made possible byusing two types of glass which have different refractive indexes. Theinner core has a high refractive index and the outer cladding has a lowindex.
Fiber-optic cable has two propagation modes-multimode and single mode. They performdifferently with respect to both attenuationand time dispersion . The single-modefiber-optic cable provides much better
performance with lower attenuation.
Propagation Modes in Fiber optic cable
-
8/13/2019 Guided & Unguided
35/63
Multimode Fiber
Multi-mode fiber is used for communication over shortdistances, such as within a building or on a campus or a LAN.Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/sover link lengths of up to 600 meters (300 m for 10 Gbit/s) more than sufficient for the majority of premises applications.
Categories of Multimode fiber
- Step Index Fiber
- Graded Index Fiber
-
8/13/2019 Guided & Unguided
36/63
Multimode Step-Index
Multimode fiber is designed to carry multiple light rays or
modes concurrently, each at a slightly different reflection anglewithin the optical fiber core.Multimode fiber transmission
is used for relatively short distances because the modes tend to disperseover longer lengths ( this is calledmodal dispersion ).
Multimode fiber has a larger core than
single mode.
-
8/13/2019 Guided & Unguided
37/63
Multimode graded index fiber has a higher refractive index in
the core that gradually reduces as it extends from the cylindricalaxis outward.The core and cladding are essentially a single graded unit (fig).This corresponds to multimode propagation with a refractiveindex profile that is called graded index .Here the variation of the index of refraction is gradual as itextends out from the axis of the core through the core to thecladding. There is no sharp discontinuity in the indices ofrefraction between core and cladding .
Graded -Index
-
8/13/2019 Guided & Unguided
38/63
Single Mode FiberA single-mode optical fiber (SMF) is an optical fiberdesigned to carry only a single ray of light (mode).
The diagram corresponds to single-mode propagationwith a refractive index profile that is called step index .
The diameter of the core is fairly small relative to the
cladding. Because of this, when light enters the fiber-Optic cable on the left, it propagates down toward theright in just a single ray, a single mode, which is thelowest-order mode.
-
8/13/2019 Guided & Unguided
39/63
Unguided Transmission Media
Unguided media transport electromagnetic waves without using a physicalconductor. [type of communication is often referred to as wirelesscommunication.
There are three types of Unguided Media(i) Radio waves(ii) Micro waves(iii) Infrared.
-
8/13/2019 Guided & Unguided
40/63
U id d M di B d d h i
-
8/13/2019 Guided & Unguided
41/63
Unguided Media Bands and their ranges
Band Range Propagation Application
VLF 3 30 KHz Ground Long-range radio navigation
LF 30 300 KHz Ground Radio beacons andnavigational locators
MF 300 KHz 3 MHz Sky AM radio
HF 3 30 MHz Sky Citizens band (CB),ship/aircraft communication
VHF 30 300 MHz Sky andline-of-sight
VHF TV,FM radio
UHF 300 MHz 3 GHz Line-of-sight UHF TV, cellular phones,paging, satellite
SHF 3 30 GHz Line-of-sight Satellite communication
EHF 30 300 GHz Line-of-sight Long-range radio navigation
-
8/13/2019 Guided & Unguided
42/63
Radio Waves
Radio (3kHz and 1GHz) waves are omnidirectional when an antenna transmitsradio waves they are propagated in all directions. This means that sending andreceiving antenna do not have to he aligned. A sending antenna can send waves
that can be received by any receiving antenna. Radio waves particularly those waves that propagate in sky mode, can travel long
distances. This makes radio waves a good candidate for long-distance broadcasting such as AM radio.
Radio waves particularly those of low and medium frequencies can penetrate
walls. It is an advantage because; an AM radio can receive signals inside a building. It is the disadvantage because we cannot isolate a communication tofirst inside or outside a building. The radio waves band is relatively narrow justunder I GHz, compared to the microwave band.
-
8/13/2019 Guided & Unguided
43/63
Omni directional Antenna
-
8/13/2019 Guided & Unguided
44/63
Microwaves
Electromagnetic waves having frequencies between I and 300 GHz arecalled microwaves.
Microwaves are unidirectional, when an antenna transmits microwaves they
can be narrowly focused. This means that the sending and receiving antennasneed to be aligned. On the other hand microwaves propagation is line-of-sight. Since the towers
with the mounted antennas needs to be in direct sight of each other, towersthat are for apart need to he very tall, the curvature of the earth as well asother blocking obstacles do not allow two short towers to communicate usingmicrowaves, Repeaters are often needed for long distance communicationvery high frequency microwaves cannot penetrate waIls.
Parabolic dish antenna and horn antenna are used for this means oftransmission.
-
8/13/2019 Guided & Unguided
45/63
Unidirectional Antenna
Figure 7-7
-
8/13/2019 Guided & Unguided
46/63
Terrestrial microwave
-
8/13/2019 Guided & Unguided
47/63
Applications
Cellular phones Satellite networks Wireless LANs
-
8/13/2019 Guided & Unguided
48/63
Infrared
Infrared signals with frequencies ranges from 300GHz to 400 THz can be used for short rangecommunication. Infrared signals, having highfrequencies, cannot penetrate walls. This helps to
prevent interference between one system andanother. A short range communication system in
one room cannot be affected by the infrared wavesin another room.
-
8/13/2019 Guided & Unguided
49/63
Applications
There are no. of computer devices which areused to send data through infrared medium
e.g. keyboard mice, PCs and printers. Thereare some manufacturers provide a special
port called the (Infrared Data Association)
IrDA port that allows a wireless keyboardto communicate with a PC.
-
8/13/2019 Guided & Unguided
50/63
-
8/13/2019 Guided & Unguided
51/63
Satellite Systems
Cover very large areas Different orbit heights
GEOs (39000 Km) versus LEOs(2000 Km)
Optimized for one-way transmission Radio and movie (SatTV) broadcasting
Most two-way systems Expensive alternative to terrestrial system
-
8/13/2019 Guided & Unguided
52/63
Geostationary Earth Orbit (GEO)
These satellites are in orbit 35,863 km above the earths surface alongthe equator.
Objects in Geostationary orbit revolve around the earth at the samespeed as the earth rotates. This means GEO satellites remain in thesame position relative to the surface of earth.
AdvantagesA GEO satellites distance from earth gives it a large coveragearea, almost a fourth of the earths surface. GEO satellites have a 24 hour view of a particular area.These factors make it ideal for satellite broadcast and othermultipoint applications.
-
8/13/2019 Guided & Unguided
53/63
GEO (cont.)
DisadvantagesA GEO satellites distance also cause it to have
both a comparatively weak signal and a timedelay in the signal, which is bad for point to
point communication.GEO satellites, centered above the equator,have difficulty broadcasting signals to near
polar regions
h ll
-
8/13/2019 Guided & Unguided
54/63
Geosynchronous Satellite
Satellite communication
-
8/13/2019 Guided & Unguided
55/63
Satellite communication
-
8/13/2019 Guided & Unguided
56/63
Types of Telecommunications Media
SatelliteTransmission
Communications satellites arerelay stationsthat receivesignals fromone earth
station andrebroadcastthem to another.
-
8/13/2019 Guided & Unguided
57/63
-
8/13/2019 Guided & Unguided
58/63
Point-to-Point Link via Microwave
-
8/13/2019 Guided & Unguided
59/63
Latency of Satellite Systems GEO satellite systems have a high latency. Consider a transmission between two remote nodes.
The sending station transmits a message to the satellite(uplink). The satellite transmits this message to the
destination node (the downlink). The destination nodesends an acknowledgement (ACK) to the satellite. Thesatellite then transmits the ACK to the sender.
The total distance involved is 88,000 miles.
Dividing by the speed of light, we get a total propagation delay of 470 milliseconds.
-
8/13/2019 Guided & Unguided
60/63
Latency of Satellite Systems
The longer the latency, the less bandwidth thesystem can support. The bandwidth capability of satellite systems
is a function of the frequency at which thesatellites transmit. Four common frequencies are:
C-band 6GHz uplink and 4 Ghz downlink Ka-band 28 Ghz uplink, 18 Ghz downlink Ku-band 14 Ghz uplink, 12 Ghz downlink V-band above 30 Ghz
-
8/13/2019 Guided & Unguided
61/63
-
8/13/2019 Guided & Unguided
62/63
Disadvantages
expensive large propagation delay (high latency) not very secure; signals can be easily intercepted affected by atmospheric conditions
-
8/13/2019 Guided & Unguided
63/63
Advantages of Satellite
The advantages of satellite communication over terrestrialcommunication are:
The coverage area of a satellite greatly exceeds that of a terrestrialsystem.
Transmission cost of a satellite is independent of the distance fromthe center of the coverage area.Satellite to Satellite communication is very precise. Higher Bandwidths are available for use. Covers very large areas.