CS-435 Network Technology & Programming Laboratoryhy435/material/CS435-lecture11.pdf · Network...
Transcript of CS-435 Network Technology & Programming Laboratoryhy435/material/CS435-lecture11.pdf · Network...
Network Technology & Programming LaboratoryCS-435spring semester 2016
Stefanos Papadakis & Manolis SpanakisUniversity of Crete
Computer Science Department
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
CS-435
• Lecture preview
• Wireless Networking
• Radio Communications Explored
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Radio transmission:
two endpoints
Tx Rx
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Tx Rx
Signal wave Propagation path
Propagation medium
Signal transformations due to natural
phenomenon; attenuation, external
noise, fading, reflection, diffraction,
refraction, and interference
Radio transmission:
two endpoints
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Interference (!)• Interference: anything which alters, modifies, or disrupts a signal during
transmission over a wireless channel.
• Superposition of unwanted signals to a useful signal.
• Examples :
• Electromagnetic interference (EMI): disturbance of an electrical circuit due to
electromagnetic induction or electromagnetic radiation emitted from an external
source
• Co-channel interference (CCI): different radio transmitters using the same
frequency
• Adjacent-channel interference (ACI) (filter interference)
• Inter-symbol interference (ISI): distortion of a signal in which one symbol
interferes with subsequent symbols
• Inter-carrier interference (ICI), caused by Doppler shift in OFDM modulation.
• Conducted interference (noise interference)• …
• Inter/Intra-flow interference refers to the interference between source sharing the
same busy channel of path.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Interference (!)
• Everything on same channel
• sum all powers
• On different channels
• inter-channel power quotient(proportion)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Thermal Noise
• Thermal noise due to agitation of electrons
• Present in all electronic devices and
transmission media
• Cannot be eliminated
• Function of temperature
• Particularly significant for satellite communication
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Noise Terminology
• Intermodulation noise – occurs if signals with different frequencies share the same medium• Interference caused by a signal produced at a
frequency that is the sum or difference of original frequencies
• Crosstalk – unwanted coupling between signal paths
• Impulse noise – irregular pulses or noise spikes• Short duration and of relatively high amplitude
• Caused by external electromagnetic disturbances, or faults and flaws in the communications system
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Other Impairments
• Atmospheric absorption – water 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
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
SNR / SIR / SINR
• What is interference?
• What is noise?
• noise floor:
• noise factor / noise figure:
• SNR / SINR / SIR:
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Sensitivity
• SINR is not the only criterion for reception!
• The Received Signal power must be over a threshold
• Vendors usually provide only RSS thresholds, not SINR
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Sensitivity
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Rates vs. Sensitivity/SINR
• Different modulation schemes have different
constellations
• Denser constellations carry more bits/point
• higher rate
• increased BER
• needs larger SINR
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
802.11a/g OFDM
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Multipath Propagation
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Multipath Propagation
• Reflection - occurs when signal encounters
a surface that is large relative to the
wavelength of the signal
• Diffraction - occurs at the edge of an
impenetrable body that is large compared to
wavelength of radio wave
• Scattering – occurs when incoming signal
hits an object whose size in the order of the
wavelength of the signal or less
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Classical two-ray
(ground model)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
The Effects of Multipath
Propagation• Multiple copies of a signal may arrive at
different phases
• If phases add destructively, the signal level relative to noise declines, making detection more difficult
• Intersymbol interference (ISI)
• One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Types of Fading
• Fast fading
• Slow fading
• Flat fading
• Selective fading
• Rayleigh fading
• Rician fading
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Fading in a mobile environment
• The term fading refers to the time variation of
received signal power caused by changes in
the transmission medium or paths.
• Atmospheric condition, such as rainfall
• The relative location of various obstacles
changes over time
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
The fading channel
• Additive White Gaussian Noise (AWGN) channel thermal noise as well as electronics at the transmitter and receiver
• Rayleigh fading there are multiple indirect paths between transmitter and receiver and no distinct dominant path, such as an LOS path
• Rician fading there is a direct LOS path in additional to a number of indirect multipath signals
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Fading: Small and Large scale
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Path Loss
• Free Space propagation model:
• Two Ray (Ground Reflection) model:
• Log Distance model
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Measured indoor path loss
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Measured large-scale path loss
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Path Loss Exponent for
Different Environments
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Signal Propagation
• Reflection
• Diffraction
• Scattering
• MultiPath
• Fading
• Shadow
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Radio Propagation Model
• An empirical mathematical formulation for the:• characterization of radio wave propagation as a
function of : • frequency, distance and other conditions
• A single model developed to • predict the behavior of propagation for similar
links under similar constraints
• formalize the way radio waves are propagated
from one place to another
• Goal : predict the path loss along a link or the
effective coverage area of a transmitter.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Propagation Modes
• Ground-wave propagation
• Sky-wave propagation
• Line-of-sight propagation
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Ground Wave Propagation• Follows contour of the earth
• Can Propagate
considerable distances
• Frequencies up to 2 MHz
• Example : AM radio
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Sky Wave Propagation• Signal reflected from ionized layer of atmosphere back
down to earth
• Signal can travel a number of hops, back and forth
between ionosphere and earth’s surface
• Reflection effect caused by refraction
• Examples
• Amateur radio
• CB radio
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Line-of-Sight Propagation
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Line-of-Sight Propagation
• Transmitting and receiving antennas must be within line of sight• Satellite communication – signal above 30 MHz
not reflected by ionosphere
• Ground communication – antennas within effectiveline of sight of each other due to refraction
• Refraction – bending of microwaves by the atmosphere• Velocity of electromagnetic wave is a function of
the density of the medium
• When wave changes medium, speed changes
• Wave bends at the boundary between mediums
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Fresnel Zone• The area around the visual line-of-sight that radio waves spread out
into after they leave the antenna.
• This area must be clear or else signal strength will weaken.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Fre’s’nell Zone (silent ‘s’) …
• We know that :
• Each wave-front point creates new circular waves
• Microwave beams widen, and
• Waves of one frequency can interfere with each other
• Fresnel zone theory: looks at a line from T to R, and at the
space around that line that contributes to what is arriving at
point R. • Some waves travel directly from T to R, while
• Others travel on paths off axis.
• their path is longer, introducing a phase shift between the direct and indirect beam
• Whenever a phase shift is one full wavelength, you get constructive interference: the
signals add up optimally
• Taking this approach and calculating accordingly, you find that:
• there are ring zones around the direct line T to R which contribute to the signal arriving at point T.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Fre’s’nell Zone (silent ‘s’) …
• There are many possible Fresnel zones, but we are concerned with zone 1.
• If this area were blocked by an obstruction, e.g. a tree or a building, the signal arriving at the far end
would be diminished.
• We need to make sure that these zones be kept free of obstructions
• usually we check that 60 percent of the first Fresnel zone is kept free.
• A formula for calculating the radius of the first Fresnel zone:
• rN is the radius of the zone in meters
• N is the zone to calculate (i.e. N=1)
• d1 and d2 are distances from the
obstructing screen at height h
• λ is the wavelength
• h<<d1,d2 and h>>λ
1 2
1 2
N
N d dr
d d
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
At the Receiver
• Signal of Interest
• Account path loss + delayed reflections
• Interference
• Transmissions in the same or neighboring
channels/frequencies
• Noise
• Thermal + System noise
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Antennas• The antenna provides three fundamental
properties
• Gain
• Direction
• Polarization
• Gain: (pos/neg) increase in power
• Direction: transmission shape/pattern
• Polarization: electric field oscillation axis
orientation
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Antennas
• Near field
• Far field / Fraunhofer region
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Antennas
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Near/Far Field
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Omni-directional Antenna
Patterns
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Directional Antennas
Patterns
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Received Power
• Effective Isotropic Radiated Power
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget
• Predict the wireless link
• Estimate the Received Power =>
• Rate
• Use dB (additions & subtractions)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget Example
• We want to estimate the feasibility of a 5km link, with one access point
and one client radio.
• The access point is connected to an omnidirectional antenna with
10dBi gain, while the client is connected to a sectorial antenna with
14dBi gain.
• The transmitting power of the AP is 100mW (or 20dBm) and its
sensitivity is -89dBm.
• Cable losses for both the Rx and the Tx are the same at 2 dBm
• The transmitting power of the client is 30mW (or 15dBm) and its
sensitivity is -82dBm.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget Example (cont.)
• Adding up all the gains and subtracting all the losses for the AP to
client link gives:
20 dBm (TX Power Radio 1)
+ 10 dBi (Antenna Gain Radio 1)
+ 14 dBi (Antenna Gain Radio 2)
- 2 dBm (Cable loses Rx)
- 2 dBm (Cable loses Tx)
--------------------------------------------------
40 dB = Total Gain
• The path loss for a 5km link, considering free space loss is:
Path Loss = 40 + 20log(5000) = 113 dB
• Subtracting the path loss from the total gain
40 dB - 113 dB = -73 dB
• Since -73dB is greater than the minimum receive sensitivity of the
client radio (-82dBm), the signal level is just enough for the client
radio to be able to hear the access point.
• There is 9dB of margin (82dB -73dB)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget Example (cont.)• Next we calculate the link from the client back to the access
point:
15 dBm (TX Power Radio 2)
+ 14 dBi (Antenna Gain Radio 2)
+ 10 dBi (Antenna Gain Radio 1)
- 2 dBm (Cable loses Rx)
- 2 dBm (Cable loses Tx)
--------------------------------------------------
35 dBm = Total Gain
• Obviously, the path loss is the same on the return trip. So our
received signal level on the access point side is: 35 dB - 113 dB =
-78 dB
• The receive sensitivity of the AP is -89dBm, this leaves us 11dB of
margin (89dB -78dB)
• For the case of 802.11b (2,4GHz) E.I.R.P is 20dBm
IS EVERYTHING OK?
ANY PROBLEMS? …. (think about it)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Link Budget (homework)
• Exercise 1:
• 802.11g , 54Mbps => -73dBm sens.
• Tx Power 20dBm
• EIRP 30dBm
• distance covered?
• Exercise 2:
• 802.11g
• 2km distance
• EIRP 20dBm
• achievable rate?
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
References
(images/material)• Wireless Communications - Principles and
Practice (Second Edition),
by Theodore S. Rappaport
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
APPENDIX
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Algebra• When using Watt:
• multiply, divide
• When using dB/dBm:
• add, subtract
• The decibel (dB) is a logarithmic unit that indicates the
ratio of a physical quantity (usually power or intensity)
relative to a specified or implied reference level
• Decibel suffix:
• dBm: indicates that the reference quantity is one milliwatt
• dBi : dB(isotropic) – the forward gain of an antenna compared
with the hypothetical isotropic antenna, which uniformly
distributes energy in all directions.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Decibel
• Relative measurement unit:
Examples
• Rule of thumb: +10dB <=> x10
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Decibel
• Rule of thumb: +3dB <=> x2
• 10 mW + 3 dB = 20 mW
• 100 mW - 3dB = 50 mW
• 10 mW + 10 dB = 100 mW
• 300 mW - 10 dB = 30 mW
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Decibel
• From dB to units:
• -3dB = half the power in mW
• +3dB = double the power in mW
• -10dB = one tenth the power in mW
• +10dB = ten times the power in mW
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
more algebra…
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Basic Encoding Techniques
• Digital data to analog signal
• Amplitude-shift keying (ASK)
• Amplitude difference of carrier frequency
• Frequency-shift keying (FSK)
• Frequency difference near carrier frequency
• Phase-shift keying (PSK)
• Phase of carrier signal shifted
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Amplitude modulation
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Basic Encoding Techniques
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Amplitude-Shift Keying
• One binary digit represented by presence of carrier, at constant amplitude
• Other binary digit represented by absence of carrier
• where the carrier signal is Acos(2πfct)
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Binary Frequency-Shift
Keying (BFSK)
• Two binary digits represented by two different
frequencies near the carrier frequency
• where f1 and f2 are offset from carrier frequency fc by equal but
opposite amounts
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Multiple Frequency-Shift
Keying (MFSK)• More than two frequencies are used
• More bandwidth efficient but more susceptible to error
• f i = f c + (2i – 1 – M)f d• f c = the carrier frequency
• f d = the difference frequency
• M = number of different signal elements = 2 L
• L = number of bits per signal element
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Phase-Shift Keying (PSK)
• Two-level PSK (BPSK)
• Uses two phases to represent binary digits
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Phase-Shift Keying (PSK)
• Differential PSK (DPSK)
• Phase shift with reference to previous bit
• Binary 0 – signal burst of same phase as
previous signal burst
• Binary 1 – signal burst of opposite phase to
previous signal burst
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Phase-Shift Keying (PSK)
• Four-level PSK (QPSK)
• Each element represents more than one bit
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Phase-Shift Keying (PSK)
• Multilevel PSK• Using multiple phase angles with each angle having
more than one amplitude, multiple signals elements can be achieved
• D = modulation rate, baud
• R = data rate, bps
• M = number of different signal elements = 2L
• L = number of bits per signal element
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
• Bandwidth of modulated signal (BT)
• ASK, PSK BT=(1+r)R
• FSK BT=2DF+(1+r)R
• R = bit rate
• 0 < r < 1; related to how signal is filtered
• DF = f2-fc=fc-f1
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
• Bandwidth of modulated signal (BT)
• MPSK
• MFSK
• l = number of bits encoded per signal element
• M = number of different signal elements
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
• Bandwidth efficiency ― The ratio of data rate to transmission bandwidth (R/BT)
• For MFSK, with the increase of M, the bandwidth efficiency is decreased.
• For MPSK, with the increase of M, the bandwidth efficiency is increased.
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
<CS-435> Network Technology and Programming Laboratory
CSD.UoC Stefanos Papadakis & Manolis Spanakis spring 2016
Performance
• Tradeoff between bandwidth efficiency and
error performances: an increase in bandwidth
efficiency results in an increase in error
probability.