Basic Principle of Radio PropagationBasic Principle of Radio Propagation

Prepared by WCDMA RNP

Radio Waveband ClassificationRadio Waveband Classification

Frequencies in different bands have different propagation characteristics.

Waweband Frequency Wavelength Extremely long wave

(EFL, extremely low frequency) 3～ 30Hz 10 5～ 10 4 km

Special long wave (SLF, special low frequency) 30 ～ 300Hz 10

4～ 103 km

Ultra long wave(ULF, ultra low frequency 300 ～ 3000Hz 10 3～ 10 2 km

Very long wave (VLF, very low frequency) 3～ 30 kHz 10 2～ 10 km

Long wave (LF, low frequency 30 ～ 300 kHz 10 ～ 1 km

Medium wave (MF, medium frequency) 300 ～ 3000 kHz 10 3～ 10 2 m

Short wave (HF, high frequency) 3～ 30MHz 10 2～ 10 m

Very short wave (VHF, very high frequency 30 ～ 300MHz 10 ～ 1 m

Decimetric wave (UHF, ultra high frequency) 300 ～ 3000MHz 10 2～ 10 cm

Centimeter wave (SHF, special high frequency)

3～ 30GHz 10 ～ 1 cm

Millimeter wave (EHF, extremely high frequency) 30 ～ 300GHz 10 ～ 1 mm

Microwave

Submillimeter wave (ultra extremely high frequency) 300 ～ 3000GHz 1～ 0.1 mm

Note: The above table is from Electromagenetic, Antenna and Electric Wave Propagation, written by Pan Zhongying.

Electric field Electric fieldElectric field

Oscillato

r

Transmission direction of electric wave

Magnetic fieldMagnetic field

Generation of Electromagnetic WaveGeneration of Electromagnetic Wave

Based on Maxwell equations set:

The variable magnetic field can excite eddy electric field and variable electric field can also excite eddy

magnetic field.

Continuous electromagnetic oscillation (electromagnetic wave) forms due to mutual excitation of alternating

electric and magnetic field.

The speed of electromagnetic wave only varies with electric and magnetic characteristics of medium. The

propagation speed of electric microwave in vacuum equals that of light in vacuum.

Light and electromagnetic wave are essentially the same. Light is electromagnetic wave of a certain

wavelength.

Propagation of Electromagnetic WavePropagation of Electromagnetic Wave

Ripple in the pond: Energy is propagated around from the source point and gradually weakens.

Electromagnetic wave is similarly propagated except that (when the radiation source is isotropically effec

tive ideal point source):

It is propagated in the form of spherical wave in three-dimension space.

The propagation media are different, including air, obstacle and reflector.

Theory of Radio PropagationTheory of Radio Propagation

In the free space, sine wave emitted by point source radiates spherical waves in all directions. This po

int source is called isotropically effective radiation one.

Suppose transmitted power of point source is Prad (W), the power of unit area d (m) away (namely, Poy

nting vector) is:

For actual antennas, if radiated power is Pt (W) and antenna gain is Gt (dBi) ,

Poynting is:

)(W/m 4

22d

PP radfs

)(W/m 4

22d

GPP ttfs

Theory of Radio PropagationTheory of Radio Propagation

Suppose effectively received area of the Rx antenna is Ae (m2) and the gain is Gr (dBi), they satisfy the following equation:

)(m G4

2r

2

eA

Therefore, the received power at the place d (m) away is:

)(W GGPd)(44

4 rtt2

22

2

rtt

efsr

G

d

GPAPP

Radio network planning and design are based on propagation loss. Free space propagation loss is:

)(dB )d4

log(20)GG

1log(10

rt

t

rfs P

PL

)(dB log20log204532 )(f)(d.L MHzkmfs Other propagation models are developed on the basis of free space propagation model.

①Reflected wave of building②Diffracted wave③Direct wave④Reflected wave on the ground

Characteristics of Radio PropagationCharacteristics of Radio Propagation

Electric wave propagation system

of Land Mobile Communications

Radio propagation in actual

environment

LOS and NLOS

Characteristics of Radio ChannelsCharacteristics of Radio Channels

d (m)

Pr (dBm)

10 20 30

-20

-40

-60

Slow fading

Fast fading

Radio channels vary with user’s position and time.

Multipath scattering and obstruction result in acute changes to received power.

Slow fading• Attenuation: Pr is in direct proportion to

1/dn.

• Shadow: obstructed by barriers

Fast fading• Multipath effect

Fast changes to signal strength at small distance and time interval

Doppler frequency shift Delay spread

Diversity TechnologyDiversity Technology

Measures against fast fading- diversity technologies

－ Explicit diversity• Space diversity• Polarization diversity• Frequency diversity ： GSM-frequency hopping; WCDMA-

spread spectrum• Others: directional diversity, field diversity and transmit div

ersity

－ Implicit diversity• Implicit diversity uses signal processing technologies to hid

e diversity functions into signals under transmission, such as RAKE reception technology, channel interlacing and error code correction.

• Regarded as time diversity

Delay SpreadDelay Spread

Multipath propagation: Signals on different paths reach the receiver at different time.

When the receiver fails to differentiate multipath signals, co-channel interference (CCI) occurs. In the WCDMA system, only the multipath delay larger than one chip period (0.26µs)can be recognized.

Typical value (µs): Open < 0.2, Suburban = 0.5, Urban = 3

Solutions Equalization and RAKE technologyEqualization and RAKE technology

Doppler Frequency ShiftDoppler Frequency Shift

Example of Doppler effect: A train is passing by you.

f1

f2

f3

V(km /h)

Doppler frequency shift in Mobile Communications

V ： speed of MS

： angle where signals arrives

T

R

T

R

• Diffraction loss• Penetration loss

• Clutter loss

LossLoss

Characteristics:Electromagnetic wave is diffused around at the diffraction point.Diffracted wave covers all directions except for barriers.Diffusion loss is the most serious.Calculation formula is complicated, varying with different diffraction constants.

Diffraction LossDiffraction Loss

¦ È

¦ Ȧ Å0¦ Ì 0 ¦ Ŧ Ì ¦ Å0¦ Ì 0

d

Dw1 w2

E1

E2

XdBmWdBm

Penetration loss=X-W=B dBPenetration loss=X-W=B dB Reflection and refraction of electromagnetic wave through the wall

Indoor signals depend on penetration loss of building.

Signals are different at the indoor window and in the middle of room.

Building materials have great effect on penetration loss.

The reference angle of electromagnetic wave have great effect

on penetration loss.

Penetration LossPenetration Loss

• Obstacle/penetration loss is: Partition obstruction: 5 ～ 20dB Floor obstruction: ＞ 20dB ， Indoor loss value is function of floor height: -1.9dB/floor Obstruction of furniture and other barriers: 2 ～ 15dB Thick glass: 6 ～ 10dB Penetration loss of the carriage of the train: 15 ～ 30dB Penetration loss of lift: 30dB or so Loss of thick leaves: 10dB

Penetration LossPenetration Loss

Ground type Water Rice paddy Field City, mountain

and forest

Equivalent ground

reflection coefficient

0.9 ～ 1 0.6 ～ 0.8 0.3 ～ 0.5 0.1 ～ 0.2

Reflection loss (dB) 0 ～ 1 2 ～ 4 6 ～ 10 14 ～ 20

Reflection LossReflection Loss

Radio Propagation EnvironmentRadio Propagation Environment

Radio propagation environment determines the propagation models directly. And propagation environment is impacted by the following factors:• Landform: high mountain, hill, plain, waters, and vegetation •Clutter: building, road and bridge• Noise: natural noise and artificial noise• Climate: rain, snow and ice (tiny effect on UHF band)

Radio Propagation EnvironmentRadio Propagation Environment

Type of radio environment

Radio environment is classified as follows, according to ITU-R P.1411-1 and specific

conditions in China.

Propagation

environment

Description

Dense urban Many tall buildings, signals fail to diffract from the roof

of building .

Urban Signals can diffract from the roof due to low buildings

and wide streets.

Suburban Low and sparse buildings

Rural Low and sparse buildings, but with lots of vegetation

Mountainous

areas

Road

Indoor

Radio Propagation EnvironmentRadio Propagation Environment

Type of propagation environment

The corresponding cell type is as follows:

Cell type Cell type Typical antenna installation

Macro-cell >500 m Installed outdoors, higher than average height of

surrounding roofs

Micro-cell 100~500m Installed outdoors, lower than average height of

surrounding roofs

Pico-cell <100m Installed outdoors or indoors, lower than height of

all roofs

Type of other new cells, such as Mini-cell…

Th

ank yo

u!