02. radio propagation fundamentals

7/30/2019 02. Radio Propagation Fundamentals

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1 Nokia Siemens Networks Presentation / Author / Date

Radio propagation fundamentals

MODULE 2


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Module 2 Radio propagation fundamentals

Objectives

After this module the participant shall be able to:-

Understand basic radio propagation mechanisms

Understand fading phenomena

Calculate free space loss


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Module Contents

Propagation mechanisms

Multipath And Fading

Propagation Slope And Different Environments


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Module Contents

Propagation mechanisms

Basics: deciBel (dB) Radio channel

Reflections

Diffractions

Scattering




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deciBel (dB) Definition

Power

Voltages

dB PP

PlinP dB

10 10

0

10log [ ].( )

dBE

E Elin

E dB

20 10020log [ ].

( )

Plin.=Elin.

/ 2



deciBel (dB) Conversion

Calculations in dB (deciBel)

Logarithmic scale

Always with respect to a reference dBW = dB above Watt

dBm = dB above mWatt

dBi = dB above isotropic

dBd = dB above dipole

dBmV/m = dB above mV/m

Rule-of-thumb: +3dB = factor 2

+7 dB = factor 5

+10 dB = factor 10

-3dB = factor 1/2

-7 dB = factor 1/5

-10 dB = factor 1/10

-30 dBm = 1 mW-20 dBm = 10 mW

-10 dBm = 100 mW-7 dBm = 200 mW-3 dBm = 500 mW0 dBm = 1 mW+3 dBm = 2 mW

+7 dBm = 5 mW+10 dBm = 10 mW

+13 dBm = 20 mW

+20 dBm = 100mW

+30 dBm = 1 W

+40 dBm = 10W+50 dBm = 100W



Radio Channel Main Characteristics

Linear

In field strength Reciprocal

UL & DL channel same (if in same frequency)

Dispersive

In time (echo, multipath propagation)

In spectrum (wideband channel)

amplitude

delay time

direct path

echoes


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Propagation Mechanisms (1/2)

Free-space propagation

Signal strength decreases exponentially with

distance

Reflection

Specular reflection

amplitude A a*A (a < 1)

phase f - f

polarisation material dependant

phase shift

Diffuse reflection

amplitude A a *A (a < 1)

phase f random phase

polarisation random

specular reflection

diffuse reflection

D


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Propagation Mechanisms (2/2)

Absorption

Heavy amplitude attenuation Material dependant phase shifts

Depolarisation

Diffraction

Wedge - model Knife edge

Multiple knife edges

A A - 5..30 dB


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Scattering Macrocell

Scattering local to mobile

Causes fading

Small delay and angle spreads

Doppler spread causes time varying

effects

Scattering local to base station

No additional Doppler spread

Small delay spread

Large angle spread

Remote scattering

Independent path fading

No additional Doppler spread

Large delay spread Large angle spread

Scattering to mobile

Scattering to base station

Remote scattering


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Scattering Microcell

Many local scatterers: Large angle spread

Low delay spread Medium or high Doppler spread


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Module Contents

Reflections, Diffractions And Scattering

Multipath and Fading

Delay Time dispersion

Angle Angular Spread

Frequency Doppler Spread

Fading

Slow & Fast



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Multipath propagation

Radio signal propagates from A to B over multiple paths using different

propagation mechanisms

Multipath Propagation

Received signal is a sum of multipath signals

Different radio paths have different properties

Distance Delay/Time Direction Angle

Direction & Receiver/Transmitter Movement Frequency


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Delay Time dispersion

Multipath delays due to multipath propagation

1 ms 300 m path difference

WCDMA Rake receiver to combine multipath components

Components with delay separation more than 1 chip (0.26 ms = 78 m) can beseparated and combined

Standardized delay profiles in 3GPP specs: TU3 typical urban at 3 km/h (pedestrians)

TU50 typical urban at 50 km/h (cars)

HT100 hilly terrain (road vehicles, 100 km/h)

RA250 rural area (highways, up to 250 km/h)


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t

P

4.3.2.

1.1.

2.

=>

f1

f1

f1

f1

BTS

1st floor

2nd floor

3rd floor

4th floor

Delay Spread

Multipath

propagation

Channel impulse

response

Delayed components in DAS

(Distributed antenna systems)


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Delay Spread

Typical values

Environment Delay Spread (ms)

Macrocellular, urban 0.5-3

Macrocellular, suburban 0.5

Macrocellular, rural 0.1-0.2

Macrocellular, HT 3-10

Microcellular < 0.1

Indoor 0.01...0.1


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Angle Angular Spread

Angular spread arises due to multipath, both from local scatterers near the

mobile and near the base station and remote scatterers

Angular spread is a function of base station location, distance and environment

Angular Spread has an effect mainly on the performance of diversity reception

and adaptive antennas


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Macrocellular Environment

= Macrocell Coverage Area

Microcellular Environment

= Microcell Coverage Area

Microcell Antenna

Macrocell Antenna

a

Angular Spread

5 - 10 degrees in macrocellular environment

>> 10 degrees in microcellular environment

< 360 degrees in indoor environment


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Frequency Doppler Spread

With a moving transmitter or receiver, the frequency observed by the receiver will

change (Doppler effect)

Rise if the distance on the radio path is decreasing

Fall if the distance in the radio path is increasing

The difference between the highest and the lowest frequency shift is called

Doppler spread

fc

vvfd

v: Speed of receiver (m/s)c: Speed of light (3*10^8 m/s)

f: Frequency (Hz)


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Fading

Fading describes the variation of the total pathloss ( signal level) when

receiver/transmitter moves in the cell coverage area

Fading is commonly categorised to two categories based on the phenomena

causing it

Slow fading: Caused by shadowing because of obstacles

Fast fading: Caused by multipath propagation

Time-selective fading: Short delay + Doppler

Frequency-selective fading: Long delay

Space-selective fading: Large angle


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time

power

2 sec 4 sec 6 sec

+20 dB

meanvalue

- 20 dB

lognormal

fading

Rayleighfading

Fading Slow & Fast


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Slow Fading Gaussian Distribution

Measurement campaigns have shown that slow fading follows Gaussian

distribution

Received signal strength in dB scale (e.g. dBm, dBW)

Gaussian distribution is described by mean value m, standard deviation 68% of values are within m

95% of values are within m 2

Gaussian distribution used in planning margin calculations


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Slow Fading Gaussian Distribution

d

Normal / Gaussian Distribution

Standard Deviation, = 7 dB

0.00000

0.01000

0.02000

0.03000

0.04000

0.05000

0.06000

0.07000

-25 -20 -15 -10 -5 0 5 10 15 20 25

Normal / Gaussian Distribution

22

1

m


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Fast Fading

Different signal paths interfere and affect the received signal

Rice Fading the dominant (usually LOS) path exist

Rayleigh Fading no dominant path exist


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Fast Fading Rayleigh Distribution

It can be theretically shown that fast fading follows Rayleigh Distribution when

there is no single dominant multipath component

Applicable to fast fading in obstructed paths

Valid for signal level in linear scale (e.g. mW, W)

+10

0

-10

-20

-300 1 2 3 4 5 m

level (dB)

920 MHz

v = 20 km/h


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Fast Fading Rician Distribution

Fast fading follows Rician distribution when there is a dominant multipath

component, for example line-of-sight component combined with in-direct

components

Sliding transition between Gaussian and Rayleigh

Rice-factor K = r/A: direct / indirect signal energy

K = 0 RayleighK >>1 Gaussian

K = 0(Rayleigh)

K = 1

K = 5


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Module Contents

Reflections, Diffractions And Scattering



Free Space Loss

Received power with antenna gain

Propagation slope

F S L


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Free Space Loss

Free space loss proportional to 1/d2

Simplified case: isotropic antenna

Which part of total radiated power is found within surfaceA?

Power density S = P/A = P/ 4 d2

Received power within surfaceA : P = P/A * A Received power reduces with square of distance

d

SurfaceA = 4 * d2

assume surface

A= 1m

2

2d

4d

A = 4*AA = 16*A

A

d

R i d ith t i


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Received power with antenna gain

Power density at the receiving end

Effective receiver antenna area

Received power

Reff GA

4

2

s

s

Gd

P

S 24

P

PG G

d

r

s

s r

4

2

Ps

As

Gs

Pr

Ar

Gr

d

SAP effr

P ti l


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Propagation slope

The received power equation can be formulated as

Where

C is a constant

is the slope factor

Free space = 2

Practical propagation = 2.5 ... 5

2

4

C

dCGGPP rssr

M d l 2 R di P ti F d t l


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Module 2 Radio Propagation Fundamentals

Summary

Radio signal propagates with multiple propagation

mechanisms

Radio signal strength varies between locations Fading

Fading is caused by shadowing and multipath propagation

Received radio signal power attenuates with increasing

distance Propagation slope

02. radio propagation fundamentals

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