Mezzo radio...Fundamentals of Radio Propagation / 1 Prof. Roberto Verdone λ [ m ] f [ MHz ] LF MF...

Prof. Roberto Verdone www.robertoverdone.org

Telecomunicazioni Mezzo radio

Roberto Verdone

[email protected] www.robertoverdone.org

https://www.linkedin.com/in/roberto-verdone/

Radio Networks DEI, University of Bologna


1. Fundamentals of Radio Propagation / 1


Fundamentals of Radio Propagation / 1

T R

peak transmit power

peak receive power

Ce Cr radio space

d

transmit antenna system

gain Gt

efficiency ηta

receive antenna system

gain Gr

efficiency ηra



T R

peak transmit power

peak receive power

Ce Cr

d


gain Gt

efficiency ηta


gain Gr

efficiency ηra

Efficient antenna: radiates all the power received at its input Efficiency: ratio between the power radiated Pt and the power received at its input Ce. Efficiency is 1 for an efficient antenna, otherwise it is less than 1.

Pt



T R

peak transmit power

peak receive power

Ce Cr

d


gain Gt

efficiency ηta


gain Gr

efficiency ηra

Efficient antenna: radiates all the power received at its input Efficiency: ratio between the power provided at its output Cr and the power pressing on the antenna. Efficiency is 1 for an efficient antenna, otherwise it is less than 1.

Pt



T R

peak transmit power

peak receive power

Ce Cr

d


gain Gt

efficiency ηta


gain Gr

efficiency ηra

Isotropic antenna: radiates / receives uniformly in / from all directions (ideal) Gain: ratio between the power that an isotropic antenna should radiate to obtain the same effect in a given direction and the power radiated Pt; G > 1 for all real antennas

Pt



T R

peak transmit power

peak receive power

Ce Cr

d


gain Gt

efficiency ηta


gain Gr

efficiency ηra

Isotropic antenna: radiates uniformly in all directions (ideal) Gain: 1 à 0 dB Omnidirectional antenna: radiates uniformly over one plane Gain: few dB Directive antenna: radiates mostly in one specific direction Gain: > 5 dB Adaptive antenna: radiates according to beams the can be modified in real time

Pt


Radio à Waves



Radio à Waves Radio Communication is* the transmission, emission, reception of signs, signals, writings, images, sounds or information of whatever nature, making use of electromagnetic waves

* MIN. SV. EC – DIP. COM. IT. – Piano Naz. di ripartiz. delle frequenze – Glossario

z

x

y

E

H

λ

d



Radio à Waves

Faraday Maxwell Hertz Lodge Guglielmo Marconi: 1895 – first wideband reception at Villa Griffone (Pontecchio Marconi) 1897 – first ship-to-shore communications over a distance of 12 Kms 1901 – first transoceanic transmission



Radio à Waves

Faraday Maxwell Hertz Lodge Guglielmo Marconi: 1895 – first wideband reception at Villa Griffone (Pontecchio Marconi)


TX

RX


Radio à Waves

Faraday Maxwell Hertz Lodge Guglielmo Marconi: 1901 – first transoceanic transmission



Radio à Waves

Phase speed in clear sky c = 3 10 8 m/s = f λ

Power density in free space p(d) [W/m2] = 0.5 Em 2 / 377

= Ce Gt ηta / 4 π d2

Waves tend to interact with objects of size

equal to or larger than λ

λ [ m ]

LF HF VHF UHF SHF EHF MF

0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF f [ MHz ]

Efficient antennas have size close to λ

Received power is Cr [W] = p(d) Gr ηra / 4 π / λ2

Antenna gains depend on directivity


Mobile Radio Networks

millimetre waves THz band


Ground waves Space waves Sky waves

Near-optical propagation

λ [ m ]

LF HF VHF UHF SHF EHF MF

0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF f [ MHz ]

3 > f [ MHz ] λ [ m ] > 100 Ground Waves 3 < f [ MHz ] < 30 10 < λ [ m ] < 100 Sky Waves 30 < f [ MHz ] 10 > λ [ m ] Space Waves

Radio à Waves


millimetre waves

Mobile Radio Networks

THz band


Radio à Antennas



Radio à Antennas


Radiation diagram: a bi-dimensional plot of the gain as a function of angle -  Polar -  Cartesian

e.g. omnidirectional antenna G

x

y

α

G

Gain

- π π


Radio à Antennas


Radiation diagram: a bi-dimensional plot of the gain as a function of angle -  Polar -  Cartesian

e.g. directional antenna G’

x

y

α

G’ Gain

- π π


Radio à Antennas


3 dB aperture angle: the angle under which the gain is not less than half of the maximum

G’

x

y

α

G’ Gain

- π π

G’/2


Radio à Antennas


•  Dipoles •  Arrays •  Patch •  Aperture


Radio à Antennas



T L approx λ x

z

y

Full dipole

T L approx λ/2 Half dipole

G = 1 - 3 dB

x

y

x

z


Radio à Antennas



x

z

y

Uda Yagi

T L approx λ

G = 1 - 3 dB

z

y

x

z G = 7 - 12 dB


Radio à Antennas



x

z

y T L approx λ/2

G = 1 - 3 dB

z

y

y

z G = 5 - 10 dB

Patch


Radio à Antennas



x

z

y T

G = 1 - 3 dB

z

y

x

z G >> 10 dB

G = π2 D2 / λ2

D >> λDish

illuminator

reflector


Radio à Antennas


•  Diversity •  MIMO •  Beamforming


Radio à Antennas


•  Diversity •  MIMO •  Beamforming

T R Ce Cr


Radio à Frequency Spectrum



λ [ m ]

f [ MHz ] LF HF VHF UHF SHF EHF MF

0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF

Frequency band assignments to services are: 1) Requested by industry alliances, standardisation bodies 2) Negotiated within and recommended by ITU-R 3) Regulated on a Country basis by National Authorities 4) Released to operators / users based on National rules (context, etc.)




λ [ m ]


0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF

‘20 – radio fari ‘30 – radio a onde corte ‘50 – televisione in bianco e nero ‘60 – satelliti per telecomunicazioni ‘70 – radio FM e televisione a colori ‘80 – telefonia mobile(1G, 2G, 3G, 4G, 5G ...) ‘90 - ...




λ [ m ]


0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF

13.553 – 13.567 MHz RFid 40.66 – 40.70 MHz RFid 433 – 464 MHz Proprietary Radios 867 – 868 MHz Proprietary Radios, LoRa, … 2.4 – 2.48 GHz Proprietary Radios, Bluetooth, WiFi, Zigbee, … 5.725 – 5.875 GHz WiFi, …

Radio à Frequency Spectrum ISM Bands: Licence - Exempt in Most Countries



Radio à Unpredictable Channel



Radio à Unpredictable Channel If radio space is uniform, isotropic, perfect dielectric, without obstacles, Cr = Ce Gt Gr ηta ηra / Aio Aio = ( 4 π d / λ )2 [Friis, 1945]


T R Ce Cr

d


Radio à Unpredictable Channel If radio space is uniform, isotropic, perfect dielectric, without obstacles,

r = sqrt(d * λ / 4)


T R

First Fresnel Elipsoid

r d


Radio à Unpredictable Channel If radio space is uniform, isotropic, perfect dielectric, without obstacles, Cr = Ce Gt Gr ηta ηra / Aio Aio = ( 4 π d / λ )2 [Friis, 1945] Otherwise Aio replaced by Ai = c * dβ * x where c is constant, x is r.v.


T R Ce Cr

d


Radio à Unpredictable Channel Spatial Filtering

T R

Receiver Power [dBm]

distance

Ce Cr

Transmission Range

d-2

d-β

β > 2

R R’

Cr = Ce Gt Gr ηta ηra / Ai

Receiver Sensitivity


d


Radio à Unpredictable Channel Spatial Filtering

T R Ce Cr

d

R’

d

β > 2 β = 2 R



Radio à Unpredictable Channel Channel Gain Fluctuations

T R

Receiver Power

time

Ce Cr

outage events

d


Receiver Sensitivity

Outage Probability: probability that received power is less than receiver sensitivity


Radio à Unpredictable Channel Channel Gain Fluctuations

T R Ce Cr

d

d


d R


T R

distance

time

pdf

distance R

R

R

Radio à Unpredictable Channel Device Location

d

d

2d/R2


random uniform distribution over circle


Radio à Unpredictable Channel

T R Pt Pr

radio space

d

Cr = k d-β ξ



2. Radio Channel Characterisation


Real World

Analysis

Comprehension

Synthesis

Model

Radio Channel Characterisation

measurements or

computation

We need models that are useful for the sake of link performance analysis We do not need models that describe carefully the real world!

deterministic or

statistical

Hp(f)

st(t) sr(t)

Ce Cr



Assumptions on the radio channel: Linear Multiple sources generate received signal given by sum Far Field Planar waves at the receiver antenna (d >> λ) Time-Variant Hp(f) changes with time à Fp(f, t) Quasi-Static Hp(f, t) varies slowly with respect to channel propagation delays

(WSSUS – Wide Sense Stationary Uncorrelated Scattering)

Hp(f)

st(t) sr(t)

Ce Cr


1. Narrowband: Carrier transmitted Cr = Ce G = Ce |Hp (f, t)|2 Channel Impulse Response (CIR): h(t, τ) Hp (f, t) 2. Wideband: Impulse transmitted Power Delay Profile (PDP):

Ph(τ) = Intt [ |h(t, τ)|2 ]

Cr = Int [ Ph(τ) ]


F

PDP [W/s]

Delay (τ)


The main phenomena characterising the mobile channel can be categorised as: 1. Large Scale if observed only changing significantly the Tx-Rx relation 2. Small Scale if observed with small changes of the Tx-Rx relation


d R

d R

Large Scale Small Scale

δ << d (few λ)


3. Large Scale Phenomena


Narrowband characterisation

Large Scale: Shadowing

Tx Rx Humans, vehicles, hills, trees, …

x

Obstacles


Tx Rx Humans, vehicles, hills, trees, …

Shadowing effect: isotropic attenuation is the product of several terms:

Aim = A1 * A2 * … * An

Aim [dB] = A1 [dB] + A2 [dB] + … + An [dB] If n is large, and central limit theorem assumptions hold, then

Aim [dB] is Gaussian distributed. Standard deviation from 4 to 12 depending on environment

Large Scale Obstacles


distance

Rec

eive

d po

wer

[dB

m]

Large scale fluctuations

d0 = 10 - 100 metres

Shadowing is usually log-normally distributed, for both mobile/stationary applications Autocorrelation function is R(d) = R0 exp [ - d/d0 ] [Gudmunson’s Model]

Large Scale


4. Small Scale Phenomena


Tx Rx

Transmitted Energy

Received Energy

delay

time

Wideband characterisation Narrowband characterisation

Small Scale: Fading

Multiple Paths


Power Delay Profile: Ph(τ) = Intt [ |h(t, τ)|2 ] Mean Delay: Tm = Intτ [ τ Ph(τ) ] / Cr (Root Mean Square) Delay Spread: στ = √ [(( Intτ τ2 Ph(τ) ) / Cr ) – Tm

2 ]

PDP

delay

Small Scale: Wideband Characterisation

Tm

Delay Spread


To be compared to symbol time.



Tx Rx

τστ = τ / 2

Math. derivation



Tx Rx

τ

frequency

στ = τ / 2

|Hp(f, t)|2 notch

1 / τ

fc



Tx Rx

τστ = τ / 2

|Hp(f, t)|2

frequency

t time

fc Cr

t



Tx Rx

τ

frequency

στ = τ / 2

|Hp(f, t)|2

1 / τ

fc

Bc



Rec

eive

d po

wer

[dB

m]

Small Scale fluctuations

Large Scale fluctuations

wavelengths (λ / 2 under typical urban conditions)

Rayleigh/Rice/… distributed envelope

Small Scale: Narrowband (Mobile) Characterisation

d0 = 10 - 100 metres

distance


Pedestrian User

Small Scale: Narrowband (Mobile) Characterisation time = distance / speed

Rec

eive

d po

wer

[dB

m]



10 - 100 s

0.1 - 0.01 s Speed: 1 m/s 2G, 3G, 4G frequency bands

time



Rec

eive

d po

wer

[dB

m]


1 - 10 s


Vehicular User (Urban)


time



Rec

eive

d po

wer

[dB

m]


0.1 - 1 s


High Speed Train


time


Transmitted Carrier

Frequency fo

Spectrum

Received Carrier

Frequency fo + Δf

Spectrum

Speed v

fo

Doppler shift

Small Scale: Doppler Effect

Tx Rx

Δf is proportional to v/λ


Speed v Tx Rx

Transmitted Carrier

Frequency fo

Spectrum

Received Carrier

Frequency

fo + Δf Spectrum

fo

fo - Δf

Small Scale: Doppler Spectrum

Δf is proportional to v/λ


9. Fundamentals of Radio Propagation / 2


λ [ m ]


0,03 0,3 3 30 300 3000 30000

10 100 1000 10000 1 0.1 0.01

VLF

f [ MHz ] Spectrum usage


More than 90% is actually unutilised!



Ultra Wide Band

Cognitive Radio

f [MHz] Spectrum usage

f [MHz] Spectrum usage

[Ross, ‘60s]

[Mitola, 1991]




10. Impact of e.m. waves on human health


Impact 1.  Base stations à large distance (d >> λ)

Power density in free space:

p(d) [W/m2] = 0.5 Em 2 / 377 = Ce Gt ηta / 4 π d2 p(d) [W/m2] max = 0.05 = Ce Gt ηta / 4 π d2

à dmin = sqrt(Ce Gt ηta / 4 π 0.05)

Ce = 20 W; Gt = 10 dB; ηta = 1 à dmin = 18 m

•  Almost independent of frequencies •  To be shared among different networks

Max Electrical field (Italy): Em = 6 Volt/m


Impact 1.  Mobile stations à near field (d << λ)

Max SAR (Specific Absorpion Rate) = 2 W/Kg

•  Epidemiological studies •  Tests

Mezzo radio...Fundamentals of Radio Propagation / 1 Prof. Roberto Verdone λ [ m ] f [ MHz ] LF MF...

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