04 ra41204en10gla0 radio propagation fundamentals v02

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Radio Propagation Fundamentals

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1 Nokia Siemens Networks RA41204EN10GLA0

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

dB PP

PlinP dB

=

=10 100

10log [ ].( )

dB EE

ElinE dB

=

=20 100

20log [ ].( )

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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 dBV/m = dB above V/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 W-20 dBm = 10 W

-10 dBm = 100 W-7 dBm = 200 W-3 dBm = 500 W0 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

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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)

amplitude

delay time

direct path

echoes

Remember:Multipath Effects Normal / Extended CP

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Propagation Mechanisms (1/2)

Free-space propagation Signal strength decreases

exponentially with distance

ReflectionSpecular reflection

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

phase shift

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

phasepolarisation 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

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

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Scattering Microcell

Many local scatterers: Large angle spreadLow 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 s 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

Multipath propagation

Channel impulse response

Delayed components in DAS

(Distributed antenna systems)

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Delay Spread

Typical values

Environment Delay Spread (s)

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

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

fcvvfd ==

v: Speed of receiver (m/s)c: Speed of light (3*108 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 + DopplerFrequency-selective fading: Long delaySpace-selective fading: Large angle

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time

power

2 sec 4 sec 6 sec

+20 dB

mean value

- 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 2Gaussian 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

+

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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 = 1K = 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/d2

Simplified case: isotropic antenna Which part of total radiated power is found within surface A? Power density S = P/A = P / 4 d2

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

dSurface A = 4 * d2

assume surfaceA= 1m2

2d4d

A = 4*AA = 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 GA 4

2

=

ss GdPS 24

=

PP

G Gd

r

ss r=

4

2

PsAsGs

PrArGr

d

SAP effr =

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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

04 ra41204en10gla0 radio propagation fundamentals v02

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