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Classifications of Transmission

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Transmission Media, Antennas and „ Physical path between and receiver Propagation „ Guided Media „ are guided along a solid medium

„ E.g., copper , copper , Chapter 5 „ Unguided Media

„ Provides means of transmission but does not guide electromagnetic

„ Usually referred to as transmission

„ E.g., atmosphere, outer space

Unguided Media General Ranges

„ frequency range „ Transmission and reception are achieved by „ 1 GHz to 40 GHz

means of an „ Directional beams possible „ Configurations for wireless transmission „ Suitable for point-to-point transmission „ Used for satellite communications „ Directional „ frequency range „ Omnidirectional „ 30 MHz to 1 GHz

„ Suitable for omnidirectional applications „ frequency range 11 14 „ Roughly, 3x10 to 2x10 Hz

„ Useful in local point-to-point multipoint applications within confined areas

Terrestrial Microwave Satellite Microwave

„ Description of common „ Description of communication satellite

„ Parabolic "dish", 3 m in diameter „ Microwave relay station „ Used to link two or more -based microwave „ Fixed rigidly and focuses a narrow beam transmitter/receivers „ Achieves line-of-sight transmission to receiving „ Receives transmissions on one frequency band (uplink), antenna amplifies or repeats the , and transmits it on „ Located at substantial heights above ground level another frequency (downlink) „ Applications „ Applications

„ Long haul service „ Television distribution

„ Short point-to-point links between buildings „ Long-distance telephone transmission „ Private business networks

1 Broadcast Radio Introduction to Antenna

„ Description of broadcast radio antennas „ An antenna is an or

„ Omnidirectional system of conductors

„ Antennas not required to be dish-shaped „ Transmission - radiates electromagnetic energy „ Antennas need not be rigidly mounted to a precise into space

alignment „ Reception - collects electromagnetic energy „ Applications from space „ Broadcast radio „ In two-way communication, the same „ VHF and part of the UHF band; 30 MHZ to 1GHz antenna can be used for transmission and „ Covers FM radio and UHF and VHF television reception

Radiation Patterns Types of Antennas

„ pattern „ Isotropic antenna (idealized) „ Graphical representation of radiation properties of an „ Radiates power equally in all directions antenna „ „ Depicted as two-dimensional cross section Dipole antennas

„ Beam width (or half-power beam width) „ Half- (or Hertz antenna)

„ Measure of of antenna „ Quarter-wave vertical antenna (or Marconi

„ Reception pattern antenna) „ Receiving antenna’s equivalent to „ Parabolic Reflective Antenna

Antenna

„ Antenna gain „ Relationship between antenna gain and effective area „ Power output, in a particular direction, compared to that produced in any direction by a 4πA 4πf 2 A G = e = e perfect (isotropic λ2 c2 antenna) „ G = antenna gain

„ Effective area „ Ae = effective area „ f = carrier frequency „ Related to physical size and shape of antenna 8 „ c = speed of (» 3 ´ 10 m/s)

„ λ = carrier

2 Propagation Modes Ground

„ Ground-wave propagation

„ Sky-wave propagation

„ Line-of-sight propagation

Ground Wave Propagation Sky Wave Propagation

„ Follows contour of the earth

„ Can Propagate considerable distances

„ up to 2 MHz

„ Example

„ AM radio

Sky Wave Propagation Line-of-Sight Propagation

„ Signal reflected from ionized layer of atmosphere back down to earth „ Signal can travel a number of hops, back and forth between and earth’s surface „ effect caused by „ Examples

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„ CB radio

„ Voice of America

3 Line-of-Sight Propagation Line-of-Sight Equations

„ Transmitting and receiving antennas must be „ Optical line of sight within line of sight d = 3.57 h „ Satellite communication – signal above 30 MHz not reflected by ionosphere „ Effective, or radio, line of sight „ Ground communication – antennas within effective line of site due to refraction d = 3.57 Κh „ Refraction – bending of by the atmosphere „ d = distance between antenna and horizon (km) „ h = antenna height (m) „ Velocity of electromagnetic wave is a function of the density of the medium „ K = adjustment factor to account for refraction,

„ When wave changes medium, speed changes rule of thumb K = 4/3

„ Wave bends at the boundary between mediums

LOS Wireless -of-Sight Equations Impairments

„ Maximum distance between two antennas „ and attenuation

for LOS propagation: „ Free space loss: signal disperses with distance

„

3.57( Κh1 + Κh2 ) „ Atmospheric absorption „ Multipath „ h1 = height of antenna one

„ h2 = height of antenna two „ Refraction „ Thermal noise

Acrobat Document

Attenuation Free Space Loss

„ Strength of signal falls off with distance over „ Free space loss, ideal isotropic antenna transmission medium P (4πd )2 ()4πfd 2 „ Attenuation factors for unguided media: t = 2 = 2 „ Received signal must have sufficient strength so that Pr λ c circuitry in the receiver can interpret the signal „ Pt = signal power at transmitting antenna

„ Signal must maintain a level sufficiently higher than „ Pr = signal power at receiving antenna noise to be received without error „ λ = carrier wavelength „ d = propagation distance between antennas „ Attenuation is greater at higher frequencies, causing distortion „ c = (» 3 ´ 10 8 m/s) where d and λ are in the same units (e.g., meters) „ are introduced to amplify high frequences

4 Free Space Loss Free Space Loss

„ Free space loss equation can be recast: „ Free space loss accounting for gain of other antennas 2 2 2 2 P ⎛ 4πd ⎞ L =10log t = 20log Pt (4π ) (d ) ()λd (cd ) dB ⎜ ⎟ = = = Pr ⎝ λ ⎠ 2 2 Pr GrGtλ Ar At f Ar At = −20log(λ)+ 20log(d )+ 21.98 dB „ Gt = gain of transmitting antenna

„ G = gain of receiving antenna ⎛ 4πfd ⎞ r = 20log⎜ ⎟ = 20log()f + 20log ()d −147.56 dB „ At = effective area of transmitting antenna ⎝ c ⎠ „ Ar = effective area of receiving antenna

Free Space Loss Categories of Noise

„ Free space loss accounting for gain of other „ Thermal Noise

antennas can be recast as „ Intermodulation noise

„ LdB = 20log()λ + 20log ()d −10log (At Ar ) „ Impulse Noise

= −20log()f + 20log ()d −10log (At Ar )+169.54dB

Thermal Noise Thermal Noise

„ Amount of thermal noise to be found in a „ Thermal noise due to agitation of of 1Hz in any device or „ Present in all electronic devices and transmission conductor is: media

„ Uniformly distributed across the frequency N0 = kT ()W/Hz spectrum and hence is often referred to as white noise „ N0 = noise power density in watts per 1 Hz of bandwidth „ Cannot be eliminated -23 „ k = Boltzmann's constant = 1.3803 ´ 10 J/K

„ Function of temperature „ T = temperature, in kelvins (absolute temperature)

„ Particularly significant for satellite communication

5 Thermal Noise Noise Terminology

„ Noise is assumed to be independent of frequency „ Intermodulation noise – occurs if signals with

„ Thermal noise present in a bandwidth of B Hertz different frequencies share the same medium (in watts): „ Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies N = kTB „ Due to the nonlinearity of the transmission sytem „ Crosstalk – unwanted between signal or, in -watts paths N =10log k +10 log T +10log B „ Impulse noise – irregular pulses or noise spikes = −228.6 dBW +10 log T +10log B „ Short duration and of relatively high amplitude „ Caused by external electromagnetic disturbances, or faults and flaws in the

„ A primary source of error for digital data transmission

Other Impairments

„ Atmospheric absorption – vapor and oxygen contribute to attenuation

„ Multipath – obstacles reflect signals so that multiple copies with varying delays are received

„ Refraction – bending of radio waves as they propagate through the atmosphere

The Effects of Multipath Multipath Propagation Propagation

„ Reflection - occurs when signal encounters a „ Multiple copies of a signal may arrive at surface that is large relative to the wavelength of different phases

the signal „ If phases add destructively, the signal level „ - occurs at the edge of an impenetrable relative to noise declines, making detection body that is large compared to wavelength of radio more difficult wave „ Intersymbol interference (ISI)

„ – occurs when incoming signal hits an „ One or more delayed copies of a pulse may object whose size in the order of the wavelength arrive at the same time as the primary pulse for of the signal or less a subsequent bit

6 Types of

„ Fast fading

„ Slow fading

„ Flat fading

„ Selective fading

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„ Rician fading

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