Radio Propagation Basics - Wirelesswireless.ictp.it/school_2005/lectures/struzak/R_Propg_Basics.pdfQuiz • Imagine 2 persons at 1 m distance. Their bodies consist of balanced set

ICTP-ITU/BDT-URSI School on Radio-Based Computer Networking for Research and Training in Developing Countries The Abdus Salam International Centre for Theoretical Physics ICTP, Trieste (Italy), 7th February - 4th March 2005

Radiopropagation basicsRyszard Struzak

[email protected]

Note: These are preliminary notes, intended only for distribution to participants. Beware of misprints!

Purpose

• To refresh basic physics of EM fields and propagation of radio waves to better understand the operation of wireless (microwave) LAN/ WAN systems

Property of R. Struzak 2

Outline

• Introduction• Some simple models• Propagation effects• Site-specific models and digital maps• Time response of propagation channel• Summary


What is EM field?• A spatial distribution of forces acting on

an electric charge• A vector field, described by six numbers at

every point:– Ex(x,y,z,t), Ey(x,y,z,t), Ez(x,y,z,t)– Hx(x,y,z,t), HY(x,y,z,t), HZ(x,y,z,t)

• EM fields interact with the matter • Electric component (E) interacts with electric

charges (fixed and moving) • Magnetic component (H) interacts only with

moving electric charges

• Electricity and magnetism were considered as separate (and mysterious) phenomena until Maxwell’s theory

E

E

H


Example of EM interaction• Lightning: Natural electrical

discharge known from the beginning of human existence

• Lightning flash, Acoustic pulse, Heat stroke, EM pulse, RF wave

• Can destroy electronic and electric networks, trees, buildings, etc.

• Artificial lightning provoked to facilitate observations and measurements

Source: Wikipedia

•http://en.wikipedia.org/wiki/Lightning


Classic EM theory• James Clerk Maxwell (1831-

1879) created a unified theory of electricity and magnetism

• He showed that light is an electromagnetic (EM) wave, and that all EM waves propagate through space with the same speed, which depends on the dielectric and the magnetic properties of the medium– http://www.amanogawa.com/archive/w

avespdf.html– http://www.amanogawa.com/archive/w

avesA.html


Quiz• Imagine 2 persons at 1 m distance.

Their bodies consist of balanced set of electrons & protons

• By some magic, we decrease the number of protons by 1% in each, so that they now have more electrons than protons and repulse each other

• How strong is the repulsive force?• Is it strong enough to move a hair? Or a sheet of

paper? Or this table?


How strong?

• The force would be strong enough to lift the whole Earth!

• Richard Feynman calculated


Richard Feynman (1918-1988) • American physicist, a

grandson of Polish Jews. • 1965 Nobel Prize • Showed that classic

electromagnetics does not apply to small-scale events

• that Maxwell theory is a simplified case of more general laws of quantum electrodynamics


Abdus Salam (1926-1996)• Pakistani physicist (1979

Nobel Prize Laureate and co-founder of ICTP) generalized further the Feynmann’s work.

• Showed that electro-magnetism and weak nuclear interactions known from quantum physics are various facets of the same phenomenon.– http://www.ictp.trieste.it/ProfSalam/


Why consider propagation?1. Could my system operate correctly?

– Wanted signal intensity/ range/ coverage?– Accounting for

• Required quality• Required distance/ area/ volume• Required geographic/ climatic region• Required time period

(Other radio-systems ignored)


2a. Could my system suffer unacceptable interference from other systems?

2b. Could my system produce such interference to other systems?– Strength of unwanted interfering signals?

• Received by the system at hand• Radiated by the system at hand

– Physical area of interference?– Time period of interference?– Degradation in quality of wanted signals?


Why various propagation models?

• Generally, different models are used for:– different applications– different environments (urban – rural,

equatorial – temperate, etc)– the wanted signal and for interfering signals– different dominating propagation mechanism - different

frequency ranges– answering different questions

• Some models include a variability due to randomly changing factors that require probabilistic approach (time, temperature, pressure, water vapor, rain intensity, cloud cover, etc.)


Outline



The simplest model: Free-space


2

2

1 0

4

1 0 lo g4

R T T R

R d B T d B T d B R d B

P P G Gd

P P G Gd

λπ

λπ

⎛ ⎞= ⋅ ⋅ ⋅ ⎜ ⎟⎝ ⎠

⎛ ⎞= + + + ⎜ ⎟⎝ ⎠

Notes: 1. Propagation of a plane EM wave in a homogeneous ideal absorption-less medium (vacuum) with no limits in all directions.2. Doubling the distance results in four-times less power received; the frequency-dependence is involved (antenna gains vary with frequency)3. Matched polarizations4. Specific directions

PT = transmitted power [W]d = distance between

antennas Tx and Rx [m]PR = received power [W]GT = transmitting antenna power gainGR = receiving antenna power gainPR/PT = free-space propagation (transmission) loss (gain)

Avaya

Time delay

Okumura-Hata model

Distance (log)

Sig

nal s

treng

th (l

og)

Free space

Open area (LOS)

Urban Suburban

Microwave transmission gain up to the radio horizon:

Gavrg = Kd-n

Typically: 3≤ n≤ 5n = 2: free spacen = 4: two-ray

model

Long-term average


• Max. Allowable Path LossMAPLdB = PTmaxdb – PRmindB

• Max range estimation from:

( )

4

4

n

R T T R

nn T T R

R

P P G Gd

P G GdP

λπ

λπ

⎛ ⎞≅ ⎜ ⎟⎝ ⎠

⎛ ⎞= ⎜ ⎟⎝ ⎠


MAPL & max rangen PTdBm PRdBm MAPL

dB2.4 GHz range m

5 GHz range m

2 0 -80 80 100 45

2 +20 -80 100 1000 450

4 0 -80 80 6 4

4 +20 -80 100 32 21


LOS model• LOS model

approximates the free-space model if:– 1st Fresnel zone

unobstructed – no reflections,

absorption & other propagation effects

• Power flow from T to R concentrates in the 1st

Fresnel zone

Direct Path Length = L

First Fresnel Zone

Path Length = L + λ/2

Avaya


Fresnel Zone • Fresnel zones are loci of points of constant path-length difference of λ/2

– constant phase difference of 1800

– The n-th zone is the region enclosed between the 2 ellipsoides giving path-length differences n(λ/2) and (n-1)(λ/2)

• The 1st Fresnel zone corresponds to n = 1

T R

1 21

1

1 2

1 2

12

: radius of the 1st Fresnel zone, m: distance T-R, m

: wavelength, m, : distance to R and to T, m

d dr dd

rd d d

d d

λ λ

λ

= ≤

= +

d1 d2

Example: max. radius of the 1st Fresnel zone at 3 GHz (λ= 0.1m) with T – R distance of 4 km:= (1/2)sqrt(0.1*4000) = 10m


Non-LOS propagation

• – when the 1st Fresnel zone is obstructed and/ or the signal reached the receiver due to reflection, refraction, diffraction, scattering, etc.– An obstruction may lie to the side, above, or

below the path. » Examples: buildings, trees, bridges, cliffs, etc. » Obstructions that do not enter in the 1st Fresnel

zone can be ignored. Often one ignores obstructions up to ½ of the zone


Reflection

• = the abrupt change in direction of a wave front at an interface between two dissimilar media so that the wave front returns into the medium from which it originated.

• Reflecting object is large compared to wavelength.


Scattering

• - a phenomenon in which the direction or polarization of the wave is changed when the wave encounters propagation medium discontinuities smaller than the wavelength (e.g. foliage, street signs, …)

• Results in a disordered or random change in the incident energy distribution


Reflection: what it does?• changes the magnitude and phase of the

reflected wave depending on:– The nature of the media (reflection coefficient)– The wave polarization– The shape of the interface

• Reflection may be specular (i.e., mirror-like) or diffuse (i.e., not retaining the image, only the energy) according to the nature of the interface.

• Demonstration with the laser pointerProperty of R. Struzak 24

Reflection coefficient

• = The ratio of the complex amplitudes of the reflected wave and the incident wave

2

2

2

2

sin cos

sin cos

sin cos

sin cos60 (complex dielectric const.)

: grazing angle (complementary angle of incidence): dielectric const. of reflection surface:

cHP

c

c cVP

c c

c r

r

R

R

j

ψ ε ψ

ψ ε ψ

ε ψ ε ψ

ε ψ ε ψε ε σλψεσ

− −=

+ −

− −=

+ −

= −

conductivity of reflection surface, 1/ohm.m: wavelength, mλ


2 ray propagation model • The received direct

and reflected waves differ due to path-lengths difference

• Significant phase change: at distance difference of λ/2 (6 cm at 2.4 GHz), the phase change is 180 deg!

• Usually insignificant amplitude change at (λ/2) distance

T R

Note: The transmitting antenna gain and the receiving antenna gain may have different magnitudes and phases for the direct ray and for the reflected ray


2 Rays: Path-length Difference


h2

D

( ) ( )

22 2 1 2

1 2

22 2 1 2

1 2

2 3

2 21 2 1 2 1 2 1 2

Direct ray: ( ) 1

Reflected ray: ( ) 1

1 1 1 1 1 3(1 ) 1 ...2 2 4 2 4 6

2 if 12 2

d

r

r d

h hd D h h DD

h hd D h h DD

x x x x

h h h h h h h hd dD D D D

−⎛ ⎞= + − = + ⎜ ⎟⎝ ⎠

+⎛ ⎞= + + = + ⎜ ⎟⎝ ⎠

+ = + − + −

+ − +∆ = − ≈ − =

h1

h1

2 rays: resultant field strength( )2

0

2

0

Plane TEM wave: 4

120 30

: free-space power flux density, W/m: power radiated (isotropic antenna), W: distance between antennas, m: free space field strength (isotropic a

T

T

T

PFD P D

E PFD P D

PFDPDE

π

π

=

= =

ntenna), V/mNote: With real antennas, use e.i.r.p. instead of P

δ

φR

Edir

Erefl

E

2 2 22 cos( ) 1 2 cos( )

; 2 (= lagging angle due to path-length difference )

= length difference = (reflected path) - (di

R

direct refl direct refl R direct R

refl j

direct

E E E E E E R R

ER e

Eφ

δ φ π δ φ π

δ π λ−

= + − + − = + − + −

= = ∆

∆

1 2 1 2

rect path)4 , if /( )h h D D h hδ π λ→ + →∞


2-ray model: analysis2

2

2

1 2 cos( )max : cos( ) 1

1 2 (1 )( ) (2 1)

2min : cos( ) 1

1 2 (1 )( ) 2

(2 1)

direct R

R

direct direct

R

R

R

direct direct

R

R

E E R R

E E R R E Rk

k

E E R R E Rk

k

δ φ πδ φ π

δ φ π πδ π φ

δ φ π

δ φ π πδ π φ

= + − + −

+ − = −

= + + = +

+ − = += −

+ − =

= + − = −

+ − == + −


Distance DependenceDoubled power received!

Leve

l rel

ativ

e to

Fre

e-sp

ace,

dB


Log. distance

Slope (absolute): -40 dB/decField-strength ~d-2

Power ~d-4

0 dB relative to free-space6 dB

d = 2πh1h2/λd = 4h1h2/λd = 2h1h2/λ

Simulated Experiments

• Distance dependence • Height dependence• Frequency dependence


Example 1: distance


Variable:d = 500-1000m Step = 10m

Fixed parameters:F = 2.4 GHzH1 = 11mH2 = 10m|R| = 1Arg(R) = 1800

0

0.5

1

1.5

2

500 600 700 800 900 1000

d, DISTANCE, m

FIEL

DST

REN

GTH

REL

. TO

FR

EE S

PAC

E

Example 2: heigth

Variable:H2 = 2 - 3mStep = 1 cm

Fixed parameters:F = 2.4GHzH1 = 1mD = 3m|R| =1Arg(R) = 1800

2.00

2.10

2.20

2.30

2.40

2.50

2.60

2.70

2.80

2.90

3.00

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Field strength relative to Free-space

Ante

nna

heig

ht, m


Example 3: frequencyVariable:

F = 2.4 - 2.6 GHz Step = 2 MHz

Fixed parameters:H1 = 14 mH2 = 12 mD = 104 m|R| =1Arg(R) = 1800

0

0.5

1

1.5

2

2.4 2.42 2.44 2.46 2.48 2.5FREQUENCY, GHz

FIEL

DST

REN

GTH

REL

AT.

TO

FR

EE S

PAC

E


Field-strength measurements


• The field strength strongly depends on local environment

• Measurement results depend strongly on the antenna location/ orientation, local cables, etc.

• Measurement uncertainty can be reduced by statistical evaluation of many measurements at slightly changed antenna positions

Avoiding negative reflection effects

• Controlling the directive antenna gain at the transmitter and/or receiver

• Blocking the reflected ray at the transmitter-reflector path and/or reflector –receiver path

• Combine constructively the signals using correlation-type receiver – Antenna diversity (~10 dB)– Dual antennas placed at λ/2

separation

T RR

T R


Absorbing reflections• Absorbing the

reflected wave• Covering

reflecting objects by absorbing material (Black-body in optics)

Property of R. Struzak 37Source: Rohde & Schwarz

• Variations

( ) ( )

( )

2

2

Shadowing: log-normal distribution

1 exp22

: probability density function

: standard deviation (8 12 )

Multipath fading: Rayleigh, Rice, and/or Nagakami-Rice distribution

s avrgs

ss

s

s

G Gp G

p G

dB

σσ π

σ

⎡ ⎤−⎢ ⎥= −⎢ ⎥⎢ ⎥⎣ ⎦

−

s


Outline



Principal propagation effects1. Effects of obstructions (indoor) 2. Effects of the ground and obstructions (outdoor)2. Tropospheric effects (outdoor)

– clear air– non-clear air

3. Ionospheric effects (outdoor)

Generally, dependence on- Wavelength (frequency) & polarization- Environment/ climate/ weather - Time



0452-01

FIGURE 1Long-term interference propagation mechanisms

Tropospheric scatter

Diffraction

Line-of-sight

Long-term propagation modes

ITU

Reflection

Troposphere

• = the lower layer of atmosphere (between the earth surface and the stratosphere) in which the change of temperature with height is relatively large. It is the region where convection is active and clouds form.

• Contains ~80% of the total air mass. Its thickness varies with season and latitude. It is usually 16 km to 18 km thick over tropical regions, and less than 10 km thick over the poles.


Troposphere effects (clear air)• absorption by atmospheric gases

– molecular absorption by water vapour and O2

– important bands at ~22 and ~60 GHz• refractive effects

– ray bending– super-refraction and ducting– multipath– Scintillation

» scintillation: a small random fluctuation of the received field strength about its mean value. Scintillation effects become more significant as the frequency of the propagating wave increases.


Refraction

• = redirection of a wavefront passing through a medium having a refractive index that is a continuous function of position (e.g., a graded-index optical fiber, or earth atmosphere) or through a boundary between two dissimilar media – For two media of different refractive indices,

the angle of refraction is approximated by Snell's Law known from optics


LOS – Radio Horizon• Earth curvature

• Radio waves go behind the geometrical horizon due to refraction: the air refractivity changes with height, water vapor contents, etc.

• In standard conditions the radio wave travels approximately along an arc bent slightly downward.

• K-factor is a scaling factor of the ray path curvature. K=1 means a straight line. For the standard atmosphere K=4/3. An equivalent Earth radius KRearth ‘makes’ the path straight

• Departure from the standard conditions may led to subrefraction, superrefractionor duct phenomena.

• Strong dependence on meteorological phenomena.

Geometrical horizon

Radio horizon

•Optics: Snell’s law


Diffraction • = the mechanism the waves spread as they pass

barriers in obstructed radio path (through openings or around barriers)

• Diffraction - important when evaluating potential interference between terrestrial/ earth stations sharing the same frequency.– Mechanism: Each point on a wave front acts as a source of

secondary spherical wavelets. When the wave front approaches an opening or barrier, only the wavelets approaching the unobstructed section can get past. They emit new wavelets in alldirections, creating a new wave front, which creates new wavelets and new wave front, etc. - the process self-perpetuates.

• [Huygens, 1629-1695].


Absorption

• = the conversion of the transmitted EM energy into another form, usually thermal. – The conversion takes place as a result of

interaction between the incident energy and the material medium, at the molecular or atomic level.

– One cause of signal attenuation due to precipitations (rain, snow, sand) and atmospheric gases


Atmospheric Absorption• Important at

frequencies >10 GHz• The atmosphere

introduces attenuation due to interaction of radio wave at molecular/ atomic level

• Exploited in Earth-exploration passive applications

• New wideband short-distance systems

10 100 GHz

0.1

10

10

H2O

O2

Spe

cific

Atte

nuat

ion

dB

/km


Ground and obstacles• terrain (smooth Earth, hills and mountains)

– diffraction, reflection and scattering• buildings (outside and inside)

– diffraction, reflection and scattering• vegetation

– attenuation– scattering


Effects of Buildings - inside• Important for the planning of indoor LAN’s and

wireless private business exchanges for high data rate services– Reflection, multipath and diffraction from objects

• delay spread 70 - 150 ns (~2 GHz; residential – commercial; compare with symbol length)

• statistical or site-specific propagation models

– Path loss through walls and floors• frequency re-use?

– Channelling of energy along the building structures


Effects of Buildings - outside

• Important in the planning of short-range mobile and personal communication systems, LAN’s and Wireless Local Loop systems– Wall/ roof attenuation if antennas located in the

building– Line-of-sight path outside

• Attenuation (free-space, atmospheric gases, rain, etc.)– Non line-of-sight path

• reflection, diffraction and scatter– building height, density, street width, orientation– crossing streets, corner angle (street canyon)

• Multipath delay spread e.g. 0.8 - 3 µs (urban - suburban)


Short-term propagation modes

Property of R. Struzak 520452-02

FIGURE 2

Anomalous (short-term) interference propagation mechanisms

Hydrometeor scatter

Elevated layerreflection/refraction

Ducting

Line-of-sight withmultipath enhancements

ITU

Troposphere effects (non-clear air)• rain effects

– attenuation– depolarisation– scattering

• cloud effects– attenuation

• system availability considerations99.9 % availability (rain at 0.1 % time)90 % availability (cloud at 10 % time)


Super-refraction and ducting


Actual Earth with radius 6 370 km

Standard atmosphere(– 40 N units/km)

(– 157 N units/km)

Ducting(– 157 N units/km)

More negative

Less negative

Atmospheric refraction effects on radio signal propagation

ITU

Standard atmosphere: -40 N units/km (median), temperate climatesSuper-refractive atmosphere: < -40 N units/km, warm maritime regions Ducting: < -157 N units/km (fata morgana, mirage)

Important when evaluating potential interference between terrestrial/ earth stations sharing the same frequency– coupling losses into

duct/layer• geometry

– nature of path (sea/land)

– propagation loss associated with duct/layer

• frequency• refractivity gradient• nature of path (sea,

land, coastal)• terrain roughness

Effects of vegetation shadowing


-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

0 10 20 30 40 50 60 70 80

Sig

nal p

ower

[dB

]

Vehicle distance [m]

TrunkTrunk Trunk

2 Trunks Trunk5 Trunks+ Limbs

-8

-6

-4

-2

0

2

4

0 5 10 15 20 25 30 35 40

Sig

nal p

ower

[dB

]

Vehicle distance [m]

PalmCrown

PalmTrunk

PalmTrunk

Pine tree

Palm tree

ITU

Attenuation up to 20 dB

Depends on the species of tree, density and structure of foliage, movement of branches and foliage, etc.

Important for the planning of microwave propagation path over wooded areas

Ionospheric propagation• The ionosphere is

transparent for microwaves but reflects HF waves

• There are various ionospheric layers (D, E, F1, F2, etc.) at various heights (50 – 300 km)

• Over-horizon commu-nication range: several thousand km

• Suffers from fading Ionospheric reflectivity depends on time, frequency of incident wave, electron density, solar activity, etc. Difficult to predict with precision.


Fading

• Case of more than one propagation path (mode) exists between T and R

• Fading = the result of variation (with time) of the amplitude or relative phase, or both, of one or more of the frequencycomponents of the signal.

• Cause: changes in the characteristics of the propagation path with time.


Outline



SISP• SISP – Site Specific propagation models based

on an analysis of all possible rays between the transmitter and receiver to account for reflection, diffraction & scattering

• Requires exact data on the environment – Indoor: detailed 3D data on building, room, equipment– Outdoor: 3D data on irregular terrain infrastructure,

streets, buildings, etc. (Fresnel-Kirchoff or Deygouttheoretical constructions)

– Large databases• Satellite/ aerial photographs or radar images,


Signal coverage map


• Example of computer-generated signal-level distribution superimposed on a terrain map – Light-blue =

strong signal

DTM• Application of

detailed propagation prediction models requires topographical information: Digital Terrain Model (DTM) or Digital Terrain Elevation Data (DTED)


Digital terrain elevation maps

Most of DTM & DTEDwere created from paper maps

Recently, they were also produced from radar data collected from satellite

Best resolution: 1 arc-sec (~30 m)30 times as precise as the best global maps in use today. First such maps were planned for 2004.

Source: NASA (http://www2.jpl.nasa.gov/srtm/)


Radar Topography

Radar interferometry compares two radar images taken at slightly different locations

Combining the two images produces a single 3-D image.

Shuttle Radar Topographic Mission (SRTM) used single-pass interferometry: the two images were acquired at the same time -- one from the radar antennas in the shuttle's payload bay, the other from the radar antennas at the end of a 60-meter mast extending from the shuttle.

Source: NASA


Shuttle Radar Topography Mission 2000

•Mission: 11-22 Feb. 2000•Collected: 9 terabytes of raw data (~15,000 CDs)

• More than 80 hours data recording

• Orbiter: Shuttle Endeavour (7.5km/sec)

• Nominal altitude: 233 km (with orbital adjustment once per day)

• Inclination:57 degrees• 6-member crew

• to activate payload, deploy and stow mast, align inboard and outboard structures, monitor payload flight systems, operate on-board computers & recorders, & handle contingencies

Source: NASA


Outline



Multipath propagation

T

R

R

S

D

Indoor Outdoor: reflection (R), diffraction (D), scattering (S)


Time – Frequency Characteristics• Radio channel can be treated as a linear two-terminal-pair transmission

channel (input port: transmitting antenna; output port: receiving antenna). ( ) ( ) ( )

( ) ( ) ( ) ( ) ( )

( ) ( ) (frequency transfer function of the channel)

1( ) ( ) (impulse response of the channel)2

2( ), ( ) : input signal time

j t

j t

Y X H

y t x t h t d x t h t

H h t e dt

h t H e d

fx t X

ω

ω

ω ω ω

τ τ

ω

ω ωπ

ω πω

∞

−∞

∞−

−∞

∞

−∞

=

= − = ⊗

=

=

=

∫

∫

∫

and spectral representation( ), ( ) : output signal time and spectral representationy t Y ω


Direct RF Pulse Sounding

Key BPF

Direct ray

Pulse Generator

Detector

Digital Storage Oscilloscope

Reflected ray


Frequency Domain Sounding

S-Parameter Test Set

Vector Network Analyzer &Swept Frequency Osillator

Inverse DFT Processor

X(ω) Y(ω)

S21(ω) ≈ H(ω) = [X(ω)] / [X(ω)]

Port 2

h(t)

Port 1

h(t) = Inverse Fourier Transform of H(ω)


Time Response, 2 RaysReceived signal


Am

plitu

de

Time

Reflected rayDirect ray

∆τ = c(dreflect – ddirect)

Light velocity

Path-length difference

a1

a2 ∆τ

+x(t) y(t)

Am

plitu

de

Transmitted signal

Time

Power Delay Profile

Time

Rel

ativ

e P

ower

( )

2

1

2

1

2 2

1

2

1

N

k kk

aver N

kk

N

k aver kk

rms N

kk

τ ατ

α

τ τ ατ

α

=

=

=

=

=

−=

∑

∑

∑

∑• If an impulse is sent from transmitter in a multiple-reflection environment,

the received signal will consist of a number of impulse responses whose delays and amplitudes depend on the reflecting environment of the radio link. The time span they occupy is known as delay spread

• The dispersion of the channel is normally characterized using the RMS Delay Spread, or standard deviation of the power delay profile


Inter-symbol Interference

Symbols Sent Symbols Received

• The delay spread limits the maximum data rate: no new impulse should reach the receiver before the last replica of the previous impulse has perished.

• Otherwise the symbol spreads into its adjacent symbol slot, the two symbols mix, the receiver decision-logic circuitry cannot decide which of the symbols has arrived, and inter-symbol interference occurs.


Error Bursts

• When the delay spread becomes a substantial fraction of the bit period, error bursts may happen.

• These error bursts are known as irreductible since it is not possible to reduce their value by increasing the transmitter power.


Error Reduction

• Elimination of reflections as discussed earlier, plus

• Applying error- resistant modulations, codes, and communication protocols

• Applying Automatic Repeat Request (ARQ)

• Retransmission protocol for blocks in error


Microcell vs Macrocell

Microcell MacrocellCell radius 0.1-1 km 1-20 kmTx power 0.1-1 W 1-10 WFading Ricean RayleighRMS delay spread 10-100 ns 0.1-10usBit Rate 1 Mbps 0.3 Mbps

After R.H.Katz CS294-7/1996


Outline



Radio Wave Components

Component CommentsDirect wave Free-space/ LOS propagation

Reflected wave Reflection from a passive antenna, ground, ionosphere (<~100MHz), wall, object, etc.

Refracted wave Standard, Sub-, and Super-refraction, ducting, ionized layer refraction (<~100MHz)

Diffracted wave Ground-, mountain-, spherical earth- diffraction (<~5GHz)

Surface wave (<~30 MHz)

Scatter wave Troposcatter wave, precipitation-scatter wave, ionized-layer scatter wave


Power budgetExample of the link budget spreadsheet

Parameters To access Peer to peer at different data rate point 11 Mbps 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps

Frequency (GHz) 2.45 2.45 2.45 2.45 2.45Transmit power (W) 0.032 0.020 0.020 0.020 0.020Transmit power (dBW) 15.0 16.9 16.9 16.9 16.9Transmit antenna gain (dBi) 0.0 2.0 2.0 2.0 2.0Polarization loss (dB) 3.0 3.0 3.0 3.0 3.0EIRP (dBW) 18.0 21.9 21.9 21.9 21.9

Range (m) 32.4 25.1 37.3 60.6 90.1 Path loss exponent (dB) 3.5 3.5 3.5 3.5 3.5Free-space path loss (dB) 88.6 84.7 90.7 98.1 104.1

Rec. antenna gain (dBi) 2.0 2.0 2.0 2.0 2.0Cable loss (dB) 1.9 1.9 1.9 1.9 1.9Rake equalizer gain (dB) 0.5 0.5 0.5 0.5 0.5Diversity gain (dB) 5.5 5.5 5.5 5.5 5.5Receiver noise figure (dB) 13.6 13.6 13.6 13.6 13.6Data rate (Kbps) 11000 11000 5500 2000 1000 Required Eb/No (dB) 8.0 8.0 5.0 2.0 1.0 Rayleigh fading (dB) 7.5 7.5 7.5 7.5 7.5Receiver sensitivity (dBm) 80.1 80.1 86.1 93.5 99.5 Signal-to-noise ratio (dB) 8.0 8.0 5.0 2.0 1.0 Link margin (dB) 0.0 0.0 0.0 0.0 0.0

Source: D. Liu et al.: Developing integrated antenna subsystems for laptop computers; IBM J. RES. & DEV. VOL. 47 NO. 2/3 MARCH/MAY 2003 p. 355-367


Summary• Propagation analysis is a vital part of

system design, planning and management• The best equipment may not operate

correctly if deployed disregarding significant propagation effects!


Selected references• Some software available at ICTP:

– MLINK– RadioMobile– ITS Irregular Terrain Model – SEAMCAT

– Major propagation models & related computer programs (free): http://www.ero.dk/seamcat

• International recommendations– ITU-R recommendations series SG3

– http://www.itu.int/; publications/main_publ/itur.html• Books:

– Shigekazu Shibuya: A basic atlas of radio-wave propagation; Wiley– Freeman RL: Radio System Design for Telecommunications, Wiley– Coreira LM: Wireless Flexible Persdonalised Communications, Wiley


Copyright note

• Copyright © 2004 Ryszard Struzak. All rights are reserved. • These materials and any part of them may not be published,

copied to or issued from another Web server without the author'swritten permission.

• These materials may be used freely for individual study, research, and education in not-for-profit applications.

• If you cite these materials, please credit the author. The author will appreciate letting him know that fact.

• If you have comments or suggestions, you may send these directly to the author at [email protected].

– Acknowledgment: Some of the material is based on Dr. Kevin Hughes’ presentations at previous ICTP Schools


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