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Module Objectives

At the end of the module you will be able to:

• Understand basic radio propagation mechanisms

• Understand fading phenomena

• Calculate free space loss

• Understand basic concepts related to Node B and UE performance

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• Propagation mechanisms

• Basics: deciBel (dB)

• Radio channel

• Reflections

• Diffractions

• Scattering

• Multipath & Fading

• Propagation Slope & Different Environments

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deciBel (dB) – Definition

Power

Voltages

dB PP

Plin

P dB=

=10 10

0

10log [ ].( )

dB EE

Elin

E dB=

=20 10

0

20log [ ].( )

Plin.~⏐Elin.⏐² / 2

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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• 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

UMTS Power Range

-50 dBm = 10 nW-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

UMTS Power → Link Budget:• min. UE Power: -50 dBm* • max. UE Power: 21 dBm / 24 dBm (UE Power Class 4 / 3)*• max. Node B Power/cell typically: 40 - 46 dBm

* 3GPP TS 25.101

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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)

direct path

echoes

Multipath Effects→ RAKE Receiver

→ α (Orthogonality)

Am

plitu

de

Delay time

α: orthogonality factorTime Dispersion / Multipath propagation Loss of Orthogonality in DL Transmission(Channelisation Codes only orthogonal when synchronised)

• α location dependent (Multi-path effect)• value α = [0..1]; typically:

- 0.4 - 0.9 (Macro Cells)- > 0.9 (Micro & Pico Cells)

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Free-space propagation• Signal strength decreases exponentially with distance

Reflection

• Specular reflectionamplitude 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

Propagation Mechanisms (1/2)

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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

Macro Cell• Scattering local to UE

• causes fading • small delay & large angle spreads• Doppler spread time varying effects

• Scattering local to BS• No additional Doppler spread• Small delay & angle spread

• Remote scattering• Independent path fading• No additional Doppler spread• Large delay spread• Large angle spread

Scatteringlocal to UE

Scatteringlocal to BS

Remote scattering

Micro Cell• local scattering:

Large angle spread• Low delay spread• Medium or high Doppler spread

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• Delay – Time dispersion

• Angle – Angular Spread

• Frequency – Doppler Spread

• Fading – Slow & Fast


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Multipath propagation: Delay – Time dispersion

• Multipath: Different radio paths have different properties• Distance → Delay/Time• Direction → Angle• Direction & Receiver/Transmitter Movement → Frequency

• Multipath delays due to multipath propagation• 1 μs ≅ 300 m path difference

• WCDMA: RAKE Receiver to combine multipath components• Components with delay separation > 1 chip (0.26 μs = 78 m) can

be separated & combined• Standardized delay profiles in 3GPP specs:

• TU3 typical urban at 3 km/h (pedestrians)• TU50 typical urban at 50 km/h (cars)• HT100hilly terrain (road vehicles, 100 km/h)• RA250 rural area (highways, up to 250 km/h)

t

P

4.3.2.

1.

1.

2.

Multipathpropagation

Channel impulse

response

Multipath delays due to multipath propagation• 1 μs ≅ 300 m path difference• 1 chip ≅ 260.4 ns ≅ 78 m (→ RAKE Receiver/Matched Filter)

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Delay Spread

• Typical valuesEnvironment Delay Spread (μs)

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

Remember:• Loss of DL Synchronisation / Orthogonality Factor α• 1 chip ≅ 260.4 ns ≅ 78 m

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Angle – Angular Spread

• Angular spread arises due to multipath, both from local scatterers near the mobile & near the base station and remote scatterers

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

• Angular Spread has an effect mainly on the performance of diversity reception & adaptive antennas

Macrocellular Environment= Macrocell Coverage Area

Microcellular Environment= Microcell Coverage Area

Microcell Antenna

Macrocell Antenna

α

• 5 - 10 degrees in macrocellular environment

• >> 10 degrees in microcellular environment

• < 360 degrees in indoor environment

Angular spread:

• function of BS location, distance & environment

• has an effect mainly on the performance of diversity reception & adaptive antenna typical no sectorisation in Micro- & Pico Cells

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Frequency – Doppler Spread

• Doppler Effect: with a moving transmitter or receiver, the frequency observed by the receiver will change

• 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

fcvvfd ==

λv: Speed of receiver (m/s)c: Speed of light (3*10^8 m/s)f: Frequency (Hz)

frec = fsource √(1-β2)/1±β; β = v/c

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Fading

time

Power

2 sec 4 sec 6 sec

+20 dB

mean value

- 20 dB

Slowfading*

FastFading

* or Lognormal 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 due to obstacles

• Fast fading: Caused by multipath propagation

• Time-selective fading: Short delay + Doppler

• Frequency-selective fading: Long delay

• Space-selective fading: Large angle

In wireless communications systems, the transmitted signal typically propagates via several different paths from the transmitter to the receiver. This can be caused, e.g., by reflections of the radio waves from the surrounding buildings or other obstacles, and is typically called multipath propagation. Each of the multipath components have generally different relative propagation delays and attenuations which, when summing up in the receiver, results in filtering type of effect on the received signal where different frequencies of the modulated waveform are experiencing different attenuations and/or phase changes. This is typically termed frequency-selective fading.

Another important characteristics is related to the relative mobility of the transmitter and receiver, or some other time-varying behavior in the propagation environment. In effect, this causes the overall radio channel to be time-variant meaning time-varying delays and attenuations for the individual multipath components. This phenomenon is generally termed time-varying or time-selective fading.

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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 σ• 68% of values are within m ±σ• 95% of values are within m ±2σ

• Gaussian distribution used in planning margin calculations

Compensation of Slow Fading in UMTS• Rel. 99 & HSUPA: by Fast Power Control & SHO• HSDPA: by Fast Link Adaptation

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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

Compensation of Fast Fading in UMTS• Rel. 99 & HSUPA: by Fast Power Control• HSDPA: by Fast Link Adaptation

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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 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 energyK = 0 RayleighK >>1 Gaussian

K = 0(Rayleigh)

K = 1

K = 5

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• 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 πd2

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

d

Surface A = 4π * 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 GAπ

λ4

2

=

ss Gd

PS 24π=

PP

G Gd

r

ss r=

λπ4

2

PsAsGs

PrArGr

d

SAP effr =

Antenna gain is normally given by how much the given antenna is better than a dipole antenna (dBd) or an isotropic (fully omnidirectional) antenna (dBi)

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Propagation slope

• The received power equation can be formulated as

• Where

• C is a constant

• γ is the slope factor

• 2 for free space

• 4 for plane, smooth, perfectly conducting terrain

• 3-3.4 for irregular terrain

2

4

=

πλC

γ−= dCGGPP rssrPropagation Models:

Statistical Path Loss

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Thank You !

02_RN31542EN30GLA0_Radio Network Planning Fundamentals

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Transcript of 02_RN31542EN30GLA0_Radio Network Planning Fundamentals