04 ra41204en30gla0 radio propagation fundamentals v03

7/28/2019 04 RA41204EN30GLA0 Radio Propagation Fundamentals v03

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1 Nokia Siemens Networks RA41204EN20GLA0

LTE RPESSRadio Propagation Fundamentals


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Nokia Siemens Networks Academy

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Module Objectives

After completing this module, the participant should 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

dBP

P P

lin

P dB

10 100

10log [ ].( )

dB E

E E

lin

E dB

20 100

20log [ ].( )


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deciBel (dB) Conversion

Calculations in dB (deciBel)

Logarithmic scalealways with respect to a reference

dBW = dB above Watt dBm = dB above mWatt dBi = dB above isotropic

dBd = dB above dipole dB mV/m = dB above mV/mRule-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 mW

0 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

LTE:UE: max. 23 dBm

eNB: typ. 43 / 46 dBm



Radio Channel Main Characteristics

Linear

In field strengthReciprocal UL & DL channel same (if in same frequency)Dispersive In time (echo, multipath propagation) In spectrum (wideband channel)

am pl i t u

d e

delay time

direct path

echoes

Remember:

Multipath EffectsNormal / Extended CP



Propagation Mechanisms (1/2)

Free-space propagation

Signal strength decreasesexponentially with distance

ReflectionSpecular reflection

amplitude A a*A (a < 1)phase f - f polarisation material dependant

phase shift

Diffuse reflectionamplitude A a *A (a < 1)phase f random

phasepolarisation random

specular reflection

diffuse reflection

D



Propagation Mechanisms (2/2)

Absorption Heavy amplitudeattenuation Material dependant phaseshifts Depolarisation

Diffraction Wedge - model Knife edge Multiple knife edges

A A - 5..30 dB



Scattering Macrocell

Scattering local to mobile

Causes fading Small delay and angle spreads Doppler spread causes time varying

effectsScattering local to base station

No additional Doppler spread Small delay spread Large angle spreadRemote scattering Independent path fading

No additional Doppler spread Large delay spread Large angle spread

Scattering to mobile

Scattering to base station

Remote scattering



Scattering Microcell

Many local scatterers: Large angle spread

Low delay spreadMedium 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

LTE CP to mitigate multipath effects CP (normal or extended) covers some 1.4 km or 20 km delay respectively

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

Multipathpropagation Channel impulseresponse

Delayed components inDAS

(Distributed antennasystems)


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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

HT: hilly terrain


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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 increasingThe difference between the highest and the lowest frequency shift is called Doppler spread

f cvv

f d

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 causingit Slow fading: Caused by shadowing because of obstacles

Fast fading: Caused by multipath propagation

Time-selective fading: Short delay + Doppler Frequency-selective fading: Long delaySpace-selective fading: Large angle


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time

power

2 sec 4 sec 6 sec

+20 dB

meanvalue

- 20 dB

lognormalfading

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 theoretically 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 MHzv = 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


Propagation Slope And Different Environments Free Space Loss Received power with antenna gain Propagation slope


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Free Space Loss

Free space loss proportional to 1/ d 2

Simplified case: isotropic antenna Which part of total radiated power is found within surface A ? Power density S = P/A = P / 4 d 2

Received power within surface A

: P

= P/A * A

Received power reduces with square of distance

dSurface A = 4 * d 2

assume surface A = 1m 2

2d4d

A = 4*A A = 16*A

A

d


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Received power with antenna gain

Power density at the receiving end

Effective receiver antenna area

Received power

Reff G A

4

2

s s Gd

P S

24 P P

G Gd

r

s s r

4

2

P s

A sG s

P r A r G r

d

S A P eff r


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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

d C GG P P r s sr

04 ra41204en30gla0 radio propagation fundamentals v03

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