wireless communication basic knowledge

7/31/2019 Wireless Communication Basic Knowledge

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Wireless Communication Basic

Knowledge


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Wireless Communication Basic Knowledge

Applicable to:junior wireless communication engineers

Proposal: Before reading this document, you had better have the following knowledge and skills.SEQ Knowledge and skills Reference material

1 Communication basic knowledge Communication principle

2

3

Follow-up document: After reading this document, you may need the following informationSEQ Reference material Information

1 LTE principle and key technologyWireless communication development and thelatest wireless communication technology

2

3


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About This Document

Summary

Chapter Description

1 Basic Conception of

Communications

Briefly describes the conception of system bandwidth, signal

bandwidth, Erlang, Blocking rate, GoS, dB, dBm, dBd, dBi,dBc, dBW, bit, and Byte.

2 Radio Propagation Briefly describes the radio propagation theory, Radiopropagation model.


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TABLE OF CONTENTS1 ............................................ Basic Conception of Communications1

1.1 System Bandwidth and Signal Bandwidth ......................................................... 1

1.1.1

System Bandwidth ............................................................................................ 1

1.1.2 Signal Bandwidth .............................................................................................. 31.2 Definition of Erlang ........................................................................................... 31.3 Blocking Rate ................................................................................................... 41.4 GOS ................................................................................................................. 51.5 Definitions of dB, dBm, dBi, dBd, dBc, and dBW .............................................. 6 1.6 Comparison Between Bit and Byte ................................................................... 7

2 Radio Propagation .......................................................................................... 72.1 Radio Propagation Theory ................................................................................ 72.1.1 Overview .......................................................................................................... 72.1.2 Free Space Propagation ................................................................................... 82.1.3

Relation Between Electric Field and Power .................................................... 11

2.1.4 Three Fundamental Propagation Mechanisms................................................ 142.2 Introduction to Radio Propagation Models ...................................................... 192.2.1 Overview ........................................................................................................ 192.2.2 Categories of Propagation Models .................................................................. 192.2.3 Macro Cell Propagation Model ........................................................................ 212.2.4 Micro Cell Propagation Model ......................................................................... 312.2.5 Indoor Propagation Model............................................................................... 332.2.6 Application of Propagation Model in Cellular Design ....................................... 34


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FIGURES

Figure 1-1 Equivalent noise bandwidth of low-pass filter ...................................................... 1

Figure 1-2 Equivalent noise bandwidth of band-pass filter.................................................... 2

Figure 1-3 Half-power point bandwidth ................................................................................. 2

Figure 1-4 System bandwidth Beof band-pass filter ............................................................. 3

Figure 2-1 Small-metric fading and large-metric fluctuation .................................................. 8

Figure 2-2 Energy stream density and input voltage of the receiver in the place with adistance d from point source ................................................................................................. 12

Figure 2-3 Sketch diagram of calculating reflectance between two medias ........................ 15

Figure 2-4 Landform wave height ....................................................................................... 23

Figure 2-5 common slope landform .................................................................................... 24

Figure 2-6 Diffraction over ridge ......................................................................................... 25

Figure 2-7 Sea-lake mixing path......................................................................................... 26

Figure 2-8 Environment parameters and street parameters ............................................... 30

Figure 2-9 Multi-slot wave-guide model .............................................................................. 33

Figure 2-10 Digital map of one certain area........................................................................ 35

Figure 2-11 Forward receiving powers in one certain city ................................................... 36

Figure 2-12 Reverse receiving powers in one certain city ................................................... 37


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1 Basic Conception of Communications

1.1 System Bandwidth and Signal Bandwidth

1.1.1 System Bandwidth

In the communication system, all signals transmitted have certain bandwidth (that is,

occupy some band resources). To process the signals for a specific purpose, the system

bandwidth, that is, the band resource provided by the system, is a key performance

parameter. The following are the three ways that a system bandwidth can be defined:

1. Define the system bandwidth by the equivalent noise bandwidth: Suppose the

systems transmission function is H(f), then the equivalent noise bandwidth is given

by:

0

2

2

max

|)(|||

1dffH

HW

n

Where Hmax is the maximum amplitude of H(f).

For example, the equivalent noise bandwidth Wnof the low-pass filter is illustrated inFigure 1-1

Figure 1-1 Equivalent noise bandwidth of low-pass filter

Definition of the equivalent noise bandwidth Wnis:

average power of the white noise passing Wn= power of the white noise passing the

actual filter

For the band-pass filter with 0f

as the center frequency as shown in Figure 1-2,

the definition of the equivalent noise bandwidth Bn is: average power of the white

noise passing Bn = power of the white noise passing the actual filter.


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2

Figure 1-2 Equivalent noise bandwidth of band-pass filter

2. Definition of the half-power point bandwidth or the so-called 3dB bandwidth byh the

half-power point of the power transfer function:

For the low-pass filter, the power transfer function at the half-power point W1/2 is:

2

0

2 |)(|2

1|)(|

2/1fHfH W

For the band-pass filter, the power transfer function at the half-power point W1/2 is:

22

02/1|)(|

2

1|)(| fB fHfH

Figure 1-3 Half-power point bandwidth

For the amplitude

frequency curve, it is

0.71

3. Definition of the system bandwidth Beby percentage of the total passed energy:

For the band-pass filter:

2/

2/

220

0

|)(|)1(|)(|e

e

Bf

Bf

dffHedffH


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Figure 1-4 System bandwidth Beof band-pass filter

|H(f)|2(dB)

In this case, bandwidth is also defined with respect to the power declinnation, with

the only exception that the declination is not fixed to 3dB, but at random, such as

1dB, 2dB, and so onand so on

For some low-pass filters such as the loop filter, the bandwidth is usually defined

with respect to the equivalent noise; for the band-pass filters, the bandwidth is

usually defined with a fixed 3dB declination or energy percentage.

1.1.2 Signal Bandwidth

As discussed above, bandwidth can be defined by the declination of a certain percentage

(dB) of the power transfer function. This concept can also be used to define the signal

bandwidth if2|)(| fH is replaced by the signals Fourier Transformation (FT)

2

|)(| fX . For the average power of random signals, use the frequency density )( fSx

to replace2|)(| fX . And similarly, the signal may have bandwidths of 1dB, 2dB, or 3dB,

or a 90% power (energy) or 95% power (energy) bandwidth.

The system bandwidth is to the signal bandwidth as the car is to the road.

A certain main lobe bandwidth is the requirement on the system bandwidth of the signal

bandwidth. For example, to transmit voice signals with a rate of 32Kbps through BPSK,

the system bandwidth should be 64kHz or above; another example is that the system

bandwidth determines the bandwidth of signals that can be transmitted. For example, the

ordinary digital voice channel cannot transmit digital color signals, and a 14kHz systemcan transmit 216Kbps voice signals.

1.2 Definition of Erlang

In the telephone switching system, demand of the source for the server is called the

traffic, whereas the traffic on the server is called the traffic load. The definition of traffic or

traffic load is as follows:

The traffic load produced (or shouldered) by a source (or a server) during the period T is

the total sum of the lasted time of all services during this period. Two factors are related


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4

to the traffic load: the call intensity (degree of demand frequency) and call duration (time

lasted for each service).

Suppose n calls occur during the period T, and the average call duration of the calls is

hav, then the traffic load is: AT=n*hav. In order to calculate the traffic density, first define

he

source or the average calls within a unit period. The traffic flow is the total of service time

within the unit period, which represents the occupation ratio of a single source or server.

The occupation ratio is forever less than or equal to 1. The unit of the traffic flow is Erlang.

In practice, the traffic flow is usually called the traffic.

Note: The dimension of traffic is time, but the traffic flow has no dimension.

If the unit of the call intensity is call/hour, and the unit of the call duration is 100s, then

another unit of the traffic flow is hundred call seconds (ccs), which is a unit frequently

used in North American countries. The unit of call duration in Erlang definition is hour,

therefore: 1erl=36ccs.

1.3 Blocking Rate

Due to economic reasons, links that can be provided in a given area are usually much

fewer than the telephone subscribers. When someone makes a call, it might be possible

for all links to be busy, which is called blocking or time blocking. The more the links

can be provided, the lower the blocking rate of the system and the better the QoS

provided to the subscribers. That is, the bearing capabilities of the telephone system

decide the number of links, which in turn decides the blocking rate of the system.

The call blocking rate is given by:

S

k

K

S

blocking

K

SP

0

!

!

Where, the unit of / is Erlang. In physics, / means the number of simultaneous call

links. In Poisson distribution, / means the frequency of occurrence of a certain

parameter. For example, in the queue events, the physical meaning of / is the amo unt

of increased queue length in a unit time. Another example can also explain the Poisson

distribution.

Suppose that during a given period of time [0, 1], the number of accidents at a crossroad

is . Now divide the time equally into n parts, n

1 2[0,1 ], [1 ,2 ],l n l n n

Supposition 1: The probability of having one accident within li is proportional to length of

time, and the probability of having two accidents within liis zero. is a constant, and the

probability of the accident within liis /n.


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Supposition 2: Within each part of the period, events of accident occurrence are mutually

independent.

Then, how is the probability of having i accidents?

Obviously, the probability of having i accidents is in binomial distribution.

ini

nni

nixP

1)(

When ,

e

nnn

i

nn

1,!1!

!)( ieixPi

In the above formula, the meanings of the various parameters of the Poisson distribution

are: is the frequency of occurrence, the index i means that the same event occurs i

times within a given period of time, and the formula gives the probability of having i

events within a given period of time.

The trunk seizure in fixed line communication can be described with the Poisson

distribution. Suppose that, in a given period, the average call duration is 1/. Now divide

the duration equally into n parts, then each part is 1/(n). Now, repeat the same analysis,

hence:

!)( ieixP i

When there are only n trunk lines, the concept of i=n is the blocking rate. Hence:

ni

n

ni

n

blocking

i

n

ie

neP

00

!

!

!

!

Where / is the traffic in Erlang within the unit period of time.

Given the same capacity in Erlang, the higher the allowed blocking rate is, the fewer the

required links.

1.4 GOS

GOS means Grade of Service (Quality of Service). The blocking rate, together with other

performance indexes of system quality, constitutes the GOS provided by the system to

the subscribers.


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6

1.5 Definitions of dB, dBm, dBi, dBd, dBc, and dBW

1. dBm

dBm is the absolute value of power, equivalent to 1mW. Calculation of 1dBm is 10lg

(P value /lmW).

For example, if the transmitting power P is 10W, then, in dBm: 10lg(10W/1mW)

=10lg(10000)=40dBm. Therefore it can be said the transmitting power P is 40dBm.

2. dBi, dBd

dBi and dBd are both relative values for power gain, but have different references.

The reference of dBi is the omni-antenna (isotrophic radiator), while that of dBd is

the dipole (half-wave dipole antenna). Therefore, the values of dBi and dBd are

slightly different, and the gain expressed in dBi is 2.15 larger than the same gain

expressed in dBd.

For example: the antenna gain of 16 dBd can be converted into 18.15 dBi (the

integral value is 18 dBi).

3. dB

For voltage V, current I and field intensity E: 20logdB

For power P: 10logdB

dB is the relative value of power. To calculate how much dB power A is more or less

than power B, use the formula: 10lg (power A/power B).

For example, if the gain of antenna A is 20dBd, and that of antenna B is 14dBd, then

the gain of antenna A is 6dB larger than that of antenna B.

4. dBc

dBc is usually used to describe the performance of RF components. dBc is also a

relative value of power that has the same calculation method as that of dB.

Generally speaking, dBc is a relative value used on many occasions for describingthe carrier power, such as measuring the interference (co-frequency interference,

intermodulation interference, cross-modulation interference, and out-of-band

interference), coupling, and scattering, and so on. In principle, where dBc is applied,

dB can replace it.

5. dBW

Similar to dBm, dBW is an absolute value of power. The formula is 10log(W).

For example, power of 1W can be converted to dBW by: 10log1=0dBW, power of

2W can be converted to: 10log=3dBW.


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1.6 Comparison Between Bit and Byte

1. Bit is 0 or 1 carried in the baseband signal. Each digit represents 1 bit;

2. 1 byte=8 bits. At the earlier stage, the AUX adder uses 8 bits for one calculating

action. Therefore, it is called the eight-bit system. The concept byte is seldom used

in CDMA baseband processing;

2 Radio Propagation

2.1 Radio Propagation Theory

2.1.1 Overview

Mechanisms of electromagnetic wave propagation are diverse, but in general the

electromagnetic waves can be propagated through reflection, diffraction, and scattering.

The majority of cellular wireless systems operate in urban areas where there is no LOS

path between the transmitter and the receiver and the high-rises cause strong diffraction

loss. Besides, as there are multiple paths of propagation through different materials and

the paths have varying lengths; electromagnetic waves propagated along such paths

interact with each other and this causes multi-path loss. As the distance between the

transmitter and the receiver increases, the electromagnetic intensity decreases.

Traditionally, research on the propagation model focuses on predicting the mean

receiving field intensity within a given area and the fluctuation of the field intensity. The

propagation model for predicting the mean field intensity and estimating the wireless

coverage is called the large-metric propagation model due to the fact that it deals with the

intensity fluctuation over a long distance (of several hundred or several thousand meters)

between the transmitter and the receiver (T-R). The propagation model for predicting the

rapid fluctuation of the receiving field intensity over a short distance (of several wave

lengths) or a short period of time (in seconds) is called the small-metric fading model.

When the mobile station moves within an extremely small area, it may cause rapid

fluctuation in the instant receiving field intensity, which is called small-metric fading. Thereason is that the phase changes in random, which in turn causes synthesis of received

signals from different directions to fluctuate greatly. For the small-metric fading, the

receiving field intensity may change by 3 or 4 levels (30dB or 40dB) if the length of the

mobile station movement equals to the wave length. As the mobile station moves away

from the transmitter and the local field intensity decreases, the mean receiving field

intensity should be predicted by applying the large-metric propagation model. Typically,

the local field intensity is calculated with the mean value of signal measurements within 5

- 40. For the cellular system with a frequency range between 1 GHz and 2 GHz, the

measuring range should be between 1m and 10m.


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8

Figure 2-1 shows the rapid small-metric fading and slow large-metric fluctuation of an

indoor wireless communication system.

Figure 2-1 Small-metric fading and large-metric fluctuation

Receivingpow

er(dBm)

T-R distance (m)

2.1.2 Free Space Propagation

The free space propagation model is used for predicting the receiving field intensity

between the transmitter and the receiver where there are completely free LOS paths.

Satellite communication and microwave wireless LOS links have typical free space

propagation. Similar to the majority of large-metric radio wave propagation models, the

free space propagation model predicts that fading of the receiving power is a function of

the T-R distance (an idempotent function). The receiving power of the antenna in free

space at a distance d from the transmitter is shown by the Friis formula:

Ld

GGPdP rttr 22

2

)4()(

(1)

Where tP is the transmitting power; )(dPr is the receiving power, a function of the

T-R distance; tG is the gain of the transmitting antenna; rG is the gain of the

receiving antenna; d, in meters, is the T-R distance; L is the system loss factor which is

independent of propagation; , in meters, is the wave length.

The antenna gain is subject to the effective section area of the antenna:


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2

4

eAG

(2)

The effective section area eA is related to the physical dimensions of the antenna, while

is related to the frequency:

c

c

f

c

2

(3)

Where f , in Hz, is the frequency; c , in rad/s, and c, in m/s, is the light speed. tP

andrP shall have the same unit, and tG and rG are dimensionless values.

Aggregate loss L (L 1) is, typically, the total of transmitting line fading, filter loss, and

antenna loss. L=1 indicates that the system hardware has no loss.

As revealed in Formula (2.1), the receiving power decreases with the square of the T-R

distance. That is, the ratio of the fading of the receiving power to the T-R distance is

20dB/10 octave.

The ideal omni-antenna that has the same unit gain in all directions is usually used as the

reference antenna of the wireless communication system. The effective omni-directional

radiation power (EIRP) is defined as:

ttGPEIRP (4)

which is the maximum radiation power of the transmitter in the direction of maximum

antenna gain as compared with the omni-antenna.

But in practice, the effective radiation power (ERP) is usually used instead of the EIRP

to indicate the maximum radiation power against the half-wave bipolarized sub-antenna.

As the bipolarized sub-antenna has 1.64 units of gain (which is 2.15dB higher the

omni-antenna), ERP is 2.15dB lower than EIRP for the same transmission system. In

effect, the antenna gain is in dBi (the gain in dB against the isotropic radiator) or in dBd

(the gain in dB against the half-wave bipolarized sub-antenna).

The path loss, a positive value in dB indicating signal fading, is defined as the difference

between the effective transmitting power and the receiving power, including or excluding

the antenna gain. If the antenna gain is included, the free space path loss is:

22

2

)4(log10log10)(

d

GG

P

PdBPL rt

r

t

(5)

If the antenna gain is excluded and it has the unit gain, the path loss is:


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10

22

2

)4(log10log10)(

dP

PdBPL

r

t

(6)

The Friis free space propagation model applies if and only if dindicates the value of the

far field of the transmitting antenna. The far field of the antenna is defined as the area

beyond fd , the far field distance that is related to the maximum linear dimensions of the

transmitting antenna and the wave length of the carrier.

22Ddf (7)

Where, Dis the maximum physical dimension of the antenna. Also, for the far field,fd

shall meet the following condition:

Ddf and fd

Obviously, equation (1) does not allow d= 0. Therefore, the large-metric propagation

model uses the near distance 0d as the reference value of the receiving power.

When 0dd , the receiving power )(dPr is related to rP at the distance 0d .

)( 0dPr can be predicted from the equation (1) or derived from the mean measurement.

The reference distance must be in the far field, that is, fdd 0 , where 0d is smaller

than the actual distance applied in the mobile communication system. Hence, derived

from equation (1) in the distance beyond 0d , the receiving power in the free space is:

frr dddd

ddPdP

0

2

00 )()( (8)

In the wireless mobile system, it is common for rP to have changes of several quantity

levels within the typical coverage area of several square kilometers. As the receiving

level varies violently, it is usually represented in dBm or dBW. The equation (11) can

have dBm or dBW as the unit, if both ends of the equation are multiplied by 10. For

example, if rP is in dBm, the receiving power is calculated by:

fr

r dddd

d

W

dPdBmdP

0

00 log20001.0

)(log10)(

(9)

Where )( 0dPr is in watts.


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In the actual system which uses low gain antenna, if the indoor value of 0d is 1m, and

the value outdoor is 100m or 1km, the numerators in equation 8 and 9 are multiplied by

10 to make it easy to calculate the path loss in dB.

[Example 1]

If the transmitter sends 50W power, convert it to unit dBm and dBW. If the transmitter has

unit gain antenna and the frequency is 900MHz, analyze how many dBm is receiving

power at the distance 100m from free space to the antenna, and what is at the

distance of 10km (suppose that the receiving antenna has unit gain)?

Solution:

Known:

Transmitting power WPt 50 ;

Frequency MHzfc 900

a) Transmitting power

dBmmWmWPdBmP tt 0.471050log10)1/()(log10)(3

b) Transmitting power

dBWWWPdBWP tt 0.1750log10)1/()(log10)(

Receiving power at the distance 100m:

mWWLd

GGPP rttr

36

22

2

22

2

105.3105.3)1()100()4(

)3/1)(1)(1(50

)4(

dBmmWmWPdBmP rr 5.24105.3log10)(log10)( 3

Receiving power at the distance 10km:

dBmdBdBmmPkmP rr 5.64405.2410000

100log20)100()10(

2.1.3 Relation Between Electric Field and Power

In a free space, the energy stream density)( 2mWPd is:


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12

222

2244

mWE

R

E

d

GP

d

EIRPP

fs

ttd

(10)

Where fsR is inherence impedance, In free space )377(120 . Hence

energy stream density is:

2

2

377mW

EPd

(11)

Where E is electric field radiation part in remote ground field.

Figure 2-2 Energy stream density and input voltage of the receiver in the place with a

distance d from point source

Figure 2-2 (a) shows the energy stream density situation from omni-antenna in free

space. dP is EIRP insulated by a ball surface whose radius is d. The receiving power ind is the product of energy stream density and receiving antennas valid acreage:

Wd

GGPA

EAPdP rtteedr 22

22

)4(120)(

(12)

The equation (12) associates field intensity unit V/m with receiving power unit Watt, which

is the same as equation (1) when L =1.

Generally it is very useful to associate the receiving level and receiver input voltage with

induced electric field E. If the receiving antenna is modeling as a matching impedance


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load of the receiver, the receiving antenna will induce a voltage into the receiver, which is

half of open circuit voltage in antenna.

Hence, ifV isthe receivers input voltage andantR

is matching receivers impedance,

the receiving power is:

ant

ant

ant

ant

ant

rR

V

R

V

R

VdP

4

]2[)(

222

(13)

By formula (11) and formula (13), the relation between receiving power and receiving

electric field or receiving electric field and receiving antenna terminal open circuit voltage

is established. Note that Vant =V without load.

[Example 2]

Supposing the distance between receiver and transmitter is10km, the transmitters power

is 50W, carrier is 900MHz, and free space propagation exists, 1tG and

2rG ,ask:(a) the receivers power; (b) receiving antenna electric field; (c) receivers

input voltage supposing receiver antenna has 50 ideal impedance and matches with

the receiver.

Answer:

Known:

Transmitting power WPt 50 ;

frequency MHzfc 900 ;

Transmitting antenna gain 1tG ;

Receiving antenna gain 2rG ;

receiver antenna impedance 50 .

a) Using formula (5), when kmd 10 , the receiving power is:

dBmdBW

Ld

GGPdP rttr

5.615.91

10000)4(

)3/1(2150log10

)4(log10)(

22

2

22

2

b) Using formula (12), antenna receiving electric field is:


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14

V/m0039.04/33.02

120107

4/

120)(120)(2

10

2

r

r

e

r

G

dP

A

dPE

c) Using formula (13), receiver input open circuit voltage is:

mV374.05041074R)( 10ant dPV rant

2.1.4 Three Fundamental Propagation Mechanisms

In mobile communication, there are three fundamental mechanisms that affect

propagation: reflection, diffraction, and scattering. The receiving power (or its opposite:

the path loss) is the most important parameter that the reflection, diffraction, and

scattering-based large-metric propagation models predict. The three mechanisms also

describe the small-metric fading and multi-path propagation.

When the electromagnetic wave encounters obstacles such as the earth surface,

buildings, and building walls that have a much longer wave length, reflection occurs.

When the wireless link between the transmitter and the receiver is blocked by sharp

edges, diffraction occurs. The resulting secondary waves are diffracted in the space,

even to the back of the obstacle. Even if there is no LOS path between the transmitter

and the receiver, wave bending can occur around the obstacle. In the high frequency

band, diffraction, just as reflection, is subject to the shape of the obstacle as well as the

incident wave amplitude at the diffraction point, its phase, and polarization.

When the transmitting medium of the electromagnetic wave has materials smaller than

the wave length and the quantity in the unit volume is prodigious, scattering occurs. The

scattering wave is produced on the rugged surface, small materials, or other things with

irregular shapes. In the actual communication system, leaves, the street signs. and light

posts all cause scattering.

1. Reflection

In the intersecting place of media with different properties, part of electromagnetic

waves is reflected and the rest passes through. If the incident plane waves

encounter the surface of the ideal medium, and part of the energy enters the second

medium while part of it is reflected back into the first medium, then no energy is lost.

If the second medium is an ideal reflector, then all energy will be reflected back to

the first medium, and no energy is lost. The field intensities of the reflected waves

and the transmitting waves depend on Fresnel reflection coefficient ( ), which is a

function of the material and related to the polarization, incident angle, and

frequency.

In case that the electromagnetic waves penetrate into the intersecting plane of the

medium and have no reflection, such an incident angle is called Brewster Angle. In


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this case, the reflection coefficient is 0. Note that Brewster Angle only occurs in case

of vertical polarization.

i. Reflection of the electric media

As shown in Figure 2-3, an angle of incidence of electromagnetic wave isi ,

the common boundary between two electric medias is plane with a portion of

energy being reflected to the first media inr and a portion of energy going

into the second media int . Reflection property varies with electric field

polarization. The feature in special direction is researched from two different

situations, as shown in Figure 2-3. Incidence plane is defined as a plane

including incidence wave, reflection wave, and refraction wave. In Figure 2-3

(a), electric field polarization is parallel to the incidence wave plane, namely

electric field is vertical polarization wave or orthogonal part of the reflectionplane; In Figure 2-3 (b), electric field polarization is vertical to the incidence

wave plane, namely electric field is vertical to the paper and parallel to the

reflection plane and points to the reader.

Figure 2-3 Sketch diagram of calculating reflectance between two medias

In Figure 2-3, subscript i, r, and tmean incidence, reflection, and transmission

field respectively. Parameter1

, 1 , 1 and 2 , 2 , 2 mean media

constant of two medias, refractive indexes, and conductance.

Generally, ideal electric media has no spoilage and insulation constant is

relevant to media constant r , namely r 0 and mF/1085.812

0

. If

the electric media has spoilage, it will absorb a portion of energy and its

insulation constant is calculated by the below formula:

jr0 (14)

In the formula (14)


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16

f

2 (15)

is conductance (unit:S/m). When the material is a good conductor,)( 0 rf and r is relevant to . In terms of electric media with

spoilage, 0 and r dont change with frequency, but is relevant to

frequency.

To ask for reflection problems two orthogonal polarizations needs be

considered. Reflectances which is vertical or parallel with polarization field in

the media boundary are:

it

it

i

r

E

E

sinsin

sinsin

12

12

//

(16)

ti

ti

i

r

E

E

sinsin

sinsin

12

12

(17)

Where,i is implicit impedance when media ii=1, 2, is ii .

Electromagnetic wave rate is 1 , boundary condition on the incidence

plane abides by Snell theorem. See Figure 2-3, the formula is:

)90sin()90sin( 2211 ti (18)

The Maxwell formula boundary term deduces the formula (16) with (17) and

formula (18), (19) with (20).

ri (19)

And

ir EE (20)

it EE )1( (21)

(or // , or ) depends on polarization.

When the first media is free space and 21 , in vertical polarization and

horizontal polarization cases reflectance is simply:


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irir

irir

2

2

//

cossin

cossin

(22)

iri

iri

2

2

cossin

cossin

(23)

ii. Brewster angle

In case that the electromagnetic waves penetrate into the intersecting plane of

the medium and have no reflection, such an incident angle is called Brewster

Angle. In this case, the reflection coefficient is 0.

Brewster angleB fulfils:

21

1)sin(

B(24)

When the first media is free space and the second media relative coefficient is

r , formula (24) is:

1

1)sin(

2

r

r

B

(25)

Note that Brewster Angle only occurs in case of vertical polarization.

iii. Reflection of ideal conductor

Because the electromagnetic wave can't penetrate the ideal conductor, plane

wave shoots the ideal conductor and all its energy is reflected back. To abide

by Maxwell formula, anytime electric field surface of the conductor must be 0,

and the reflection wave must equal to the incidence wave. In term of electric

field polarization is on the incidence wave plane, the boundary condition

requires:

ri (26)

And

ri EE (27)

Electric field is parallel to incidence wave plane Also, Electric field is vertical

polarization, boundary condition requires:


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18

ri (28)

And

ri EE (29)

Electric field is parallel with incidence wave plane

Refers to formula (26) ~ (29), get //

=1 and = -1 in any incidence angle for

the ideal conductor.

2. Diffraction

Diffraction enables the wireless signals to propagate around the earth curve andreach the back of the obstacle. Although when the receiver moves into the shadow

of the obstacle, the receiving field intensity attenuates very rapidly, the diffraction

field still exists and usually has a strong enough intensity.

The phenomenon of diffraction can be explained with Huygens Principle. According

to Huygens Principle, the wavefront of a propagating wave of light at any point may

be regarded as the source of secondary waves and conform to the envelope of

spherical wavelets emanating from every point on the wavefront at the prior instant.

The principle was later developed by Fresnel who believed that the radiation field of

a propagating wave at any point in the space is the result of the superposition of the

waves emanated from the secondary waves of the points enveloping the wavesource. This is the Huygens-Fresnel Principle, and the secondary wave source is

called Huygens wavelet.

3. Scattering

In the actual mobile communication environment, the received signal intensity is

stronger than mere diffraction or that predicted with the reflection model. This is

because, when the electromagnetic waves encounter the rugged surface, the

reflected energy is scattered to all directions. Trees, street signs, light posts etc all

scatter energy in every direction, which provides extra energy to the signals

received by the receiver.

The smooth plane with a width much larger than the wave length can be modeled

into a reflection plane. For the rugged plane, the reflection coefficient should be

multiplied by a scattering loss coefficient s

to indicate a weakened reflection field.

The degree of ruggedness can be calculated with the Rayleigh distribution principle,

which defines the reference height ch

for ruggedness calculation with a given

incident angle i

as:


25/44


i

ch

sin8 (30)

If the maximum height h of the obtrusion of the plane is smaller than ch , then the

plane is considered smooth. Otherwise, it is considered rugged.

2.2 Introduction to Radio Propagation Models

2.2.1 Overview

During the planning and optimization phases of the mobile communication network, the

most important propagation issue is path loss that represents large-metric propagation

features and is characteristic of the idempotent law. Path loss is an important reference

for mobile communication system planning and design, and has influence on coverage,

S/N, near-far effect for cellular design. Therefore, at the initial stage of mobile

communication system design or future capacity expansion and network optimization,

anticipation of path loss should be made. The radio propagation model can be used to

anticipate the path loss in different propagation environments so as to build a better local

wireless communication network.

Introduction to the radio propagation models includes: characteristics of radio

propagation in mobile communication, macro cell propagation models, micro cell

propagation models, indoor propagation models in different application environments,

and application of the propagation models in the cellular design.

Radio waves sent from the base station suffer not only from path loss in atmospheric

transmission, but also from loss in the ground propagation path that depends heavily on

topographic conditions. The antenna of the mobile station is usually very low and close to

the ground, which is one of the causes for extra propagation loss. Generally speaking,

the ground quality and ruggedness usually cause energy loss and reduce the intensity of

signals received by the mobile station and base station. Such kind of loss, combined with

free space loss, constitutes the transmission path loss.

It is an extremely arduous task to precisely prescribe the signal change in such complex

environments. The various models introduced in the following part describe the local

radio signal changes predicted by a large amount of field data or precise theoretic

electromagnetic calculations.

2.2.2 Categories of Propagation Models

In mobile communication design, a key task is to make the network have a satisfactory

quality of service (coverage ratio, voice quality, call drop rate, and call completion rate)

while meeting the mobile users demand of traffic capacity. A considerable part of the

quality requirements are related to the quality of the received signals, which is largely


26/44


20

decided by the propagation conditions between sending and receiving ends. During the

radio wave propagation of the mobile communication, propagation path loss is one of the

major parameters that are concerned. We can use the radio propagation model-based

analytic method to predict the radio wave propagation path loss.

By the characteristics of radio propagation models, they can be divided into the following

categories:

1. Empirical model

2. Quasi-empirical or quasi-assured model

3. Assured model

The empirical model is an equation derived from statistics and analysis of a host of test

results. Prediction of path loss with the empirical model is very simple and does notrequire precise information of the related environment, but cannot produce extremely

precise value of evaluation of the path loss.

The assured model is a method that calculates the specific field environment by directly

applying the electromagnetic theory. Environment description, which may have different

levels of precision, can be made from the topographic condition database. In the assured

model, the several technologies that have been applied are usually based on radiation

tracking. They are: Geometric diffraction theory (GTD), Physical Optics (PO), and the

precision methods not frequently used, such as Integral Equation (IE) method or Finite

Differentiation of Time Domain method (FDTD). In downtown area, mountainous area

and indoor environments, assured radio propagation prediction is an extremely complex

electromagnetic task.

The quasi-empirical or quasi-assured model is an equation derived by applying the

assured method in the general downtown or indoor environments. Sometimes, to

improve compliance with the experiment result, the equation should be modified in light of

the experiment result and the resulting equation is about the function of a certain property

of the neighboring area of the antenna.

Due to the diversity of the mobile communication environments, each propagation model

is targeted for a special kind of environments. Therefore, they can be classified by the

environment where the propagation model is applied. There are three commonly seen

kinds of environments (cells): the macro cell, micro cell and Picocell.

The macro cell has a large area with a radius between 1 and 30km. In the macro cell, the

base station transmitting antenna is usually mounted on the top of neighboring building,

and there is no direct ray between the transmitting and receiving ends.

The micro cell has a radius between 0.1 and 1km, and is not necessarily round in shape.

The transmitting antenna can have the same height with, or slightly higher or lower than

the surrounding buildings. Usually, according to the position of the transmitting and


27/44


receiving antenna relative to the environmental obstacles, there are two categories: LOS

(line of sight) and NLOS (non-line of sight).

The picocell typically has a radius between 0.01 and 0.1km. It can be an indoor and an

outdoor cell. The transmitting antenna is under the roof or inside the building. Whether it

is indoor or outdoor cell, usually LOS and NLOS should be considered respectively.

Generally, the three kinds of models and the three kinds of cells are matched. For

example, the empirical and the quasi-empirical models are suitable for the uniform macro

cell, and the quasi-empirical model is suitable for uniform micro cell. In such cases,

parameters of the models can very well represent the entire environment. The assured

model is suitable for micro cells and picocells, whatever the shape is, but not suitable for

the macro cell, since the CPU time required by the macro cell makes such technologies

ineffective.

2.2.3 Macro Cell Propagation Model

2.2.3.1 Okumura-Hata Model

The Okumura-Hata model is fit with formulas by Hata who drew on the large quantity of

test data of Okumura. To apply the Okumura model, various curves should be found and

it is thus not suitable for computer-based prediction. Based on Okumuras basic mean

field intensity prediction curve, Hata matched the curves and introduced the empirical

formula of propagation loss, that is, , the Okumura-Hata model.

For simplicity, the above model makes three hypotheses:

1. Suppose it is the propagation loss processing between two omni-antennas;

2. Suppose it is a quasi-smooth topography instead of an irregular topography;

3. The propagation loss formula for urban area is taken as the standard, while the

formula for other areas is modified from the standard with the correction formula.

Applicable conditions:

1. The frequency f is between 150 and 1500MHz;

2. The effective height of the base station antenna is between 30 and 200m;

3. The height of the mobile station antenna is between 1 and 10m;

4. Distance of communication is between 1 and 35km;

Propagation loss formula:


28/44


22

g))(lglg55.69.44()(lg82.13lg16.2655.69 dhhahfLb urban bmb

Formula explanation:

The unit of d is km, and the unit of f is MHz;L

b urban is the basic mean value of

propagation loss for the urban area; hb and hm, in meters, are the effective heights of the

base station and mobile station antennas.

Calculation of the base station antenna effective height: Suppose the height of the base

station antenna from the ground is sh

, the base station ground height above sea level

is gh

, the mobile station antenna height from the ground is mh

, the mobile station

ground height above sea level is mgh

, then the effective height of the base station

antenna hb= sh

+ gh

- mgh

, and the effective height of the mobile station antenna is

mh .

Note: There are many methods for calculation of the effective height of the base station

antenna. For example, the average of the ground height above sea level within 5 to 10km

away from the base station; the topographic fitting curve of the ground height above sea

level within 5 to 10 km away from the base station and so on. Different methods of

calculation is not only related to the applied propagation model, but also related to

different calculation accuracy.

Correction factors for the mobile station antenna height:

mh

MHzfh

MHzfh

fhf

ha

m

m

m

m

m

5.10

40097.4)75.11(lg2.3

2001501.1)54.1(lg29.8

)8.0lg56.1()7.0lg1.1(

)(2

2

Large cities

Medium- and small-sized cities

Correction factors for long-distance propagation:

20)

20)(lg1007.11087.114.0(1

2018.034

dd

hf

d

b

g

There are also correction factors for various environments.

Kstreet-the correction factor for streets

Generally only the loss correction curve is given, which is horizontal or vertical with

spread direction, for the sake of calculation easily, with fitting formula of arbitrarily angle.


29/44


Supposing the clip angle between spread direction and street as , then:

1)cos6.7sin9.5(

1cos)lg

6

106.7(sin)lg

6

119.5(

d

ddd

Kstreet

In practice, the street effect will disappear at 8 km to 10 km generally, so only consider

distance shorter than 10 km.

Kmr-the correction factor for suburbs

)4.5))28/(lg(2(2 fKmr

Qo-the correction factor for open area

)94.40lg33.18][lg78.4(2 ffQo

Qr-the correction factor for quasi-open areas

5.50 QQr

Ru-the correction factor for rural areas

17.23lg17.9)(lg39.2)28

(lg 22 fff

Ru

Kh-the correction factor for

hills

1,15)2.7)lg96.6024.07.5(

1,15)2.7lg5.9()lg96.6024.07.5(

150

1

11

hhhh

hhhhh

h

Kh

landform wave height. As shown in Figure 2-4, extend 10km from MS to BTS, if less

than 10km, use actual distance to make the calculation. It is applicable to multi wave to

calculate difference between 10% and 90% of the wave height in this scope (wave

times) >3.

Figure 2-4 Landform wave height


30/44


24

min1 8/ hhhh mg , minh is the minimum landform height of the h in calculatingsection plane.

Ksp-the correction factor for slopes

Figure 2-5 common slope landform

1)

2)

3)

BTS

h1

h2

H+m

d3

d2d

MS

d2

d1

(a) positive slope+m

d1

h1

H

1)2)

3)

d2d3

d

h2

(b) negative slope-m

-m

It is possible that slope landform produces the second ground reflection. When horizontal

distance d2>d1, as shown in Figure 2-5, it is possible that the positive slope and negative

slope produce the second ground reflection.

Approximately conclude that slope correction factor is:

mmmsp ddK 44.0002.0008.02

Where,

m unit: milli radian, d unit: km;

m the average obliquity of the landform height, 1km in front of /behind MS on the

section plane of the connection line between MS and BTS.


31/44


Kimthe correction factor for independent mountains

Here, use diffraction over ridge loss to make the calculation. Though the calculated

quantity is larger, the result is exact.

Figure 2-6 Diffraction over ridge

As shown in Figure 2-6,consider single ridges 4 parameters, 1r, 2r , ph , and working

wave length ;

Calculate new parameter v with these 4 parameters:

)

11

(

2

21 rrhvp

Calculate refraction loss:

7.00

7.0)1.01)1.0(lg(209.62

v

vvvKim

Ks-the correction factor for sea (lake) mixed paths

During propagation path if there is a water area, consider two cases, as shown in Figure2-7


32/44


26

Figure 2-7 Sea-lake mixing path

BTS

MS

ds

d

BTS

MS

dds

(a)land is near BTS (b) water area is near BTS

Define that correction factor is:

)6.948.0(:)(

)81.068.0/0.7(:)(

2

2

qqdb

dqqqaKts

Where, q=ds /d%), ds is length of full water area in section plane.

Determinant method for selection formula (a) or (b):

If there is a water area, 200 m near BTS on the section plane of MS and BTS, then:

2/))()(( bKaKKs

Or else

)(bKKs

S(a)-the correction factor for building density

120

51)20lg19.0)(lg6.15(

1005)lg2530(

)( 2

a

aaa

aa

aS

where, a is building density, shown with %.

Combination usage situation of the all correction factors:

Collectivity path loss:

r

mr

u

sp

im

h

s

streetb

Q

Q

K

R

KK

K

K

aSKLL

0

0

0

)(


33/44


2.2.3.2 COST231-Hata Model

The COST231-Hata model is also based on the test results of Okumura and derived by

analyzing the Okumura propagation curve for relatively high frequency ranges.

Applicable conditions:

1. The frequency f is between 1500 and 2000MHz;

2. The effective height of the base station antenna is between 30 and 200m;

3. The height of the mobile station antenna is between 1 and 10m;

4. Distance of communication is between 1 and 35km;


mbmbbCdhhahfL lg)lg55.69.44()(lg82.13lg9.333.46

Formula explanation:

The unit of d is km, and the unit of f is MHz;

Lb is the medium value of basic propagation loss in urban;

hb, hm-BTS, MS antenna effective height, unit is m;

BTS antenna effective height: supposing BTS antenna iss

h away from ground, BTS

ground height above sea level is gh , MS antenna is mh away from ground, MS ground

height above sea level is mgh , then BTS antenna effective height is hb= sh + gh - mgh ,

MS antenna effective height is mh .

Center of the large city

The medium-sized city with an average

forest density and the suburb center

dB

dBCm

3

0

Correction factors for the mobile station antenna height:

mh

h

fhf

ha

m

m

m

m

5.10

97.4)75.11(lg2.3

)8.0lg56.1()7.0lg1.1(

)( 2 Large cities

Medium- and small-sized cities

Far distance propagation correction factor:


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28

20)

20)(lg1007.11087.114.0(1

2018.034 d

dhf

d

b

g

Other correction factors are the same as ones of Okumura-Hata model.

2.2.3.3 COST-231-Walfish-Ikegami Model

The basis of the macro cell model is that the propagation loss between the base station

and the mobile station is decided by the surrounding environment of the mobile station.

But the building and streets within 1km of the base station heavily affect the propagation

loss between the base station and the mobile station. Therefore, the above mentioned

macro cell model is not suitable for prediction of the propagation loss within 1km.

The COST-231-Walfish-Ikegami model is suitable for propagation loss prediction within

the area ranging from 20m to 5km for both the macro cell model and the micro cell model.

To predict the propagation loss for the micro cell coverage, there should be detailed data

for the streets and buildings and should not adopt approximate values.

This model is applicable for the condition that f is between 1500 MHz and 2000MHz.


1. Low BTS antenna:

The propagation feature formed in the gorge of the street is different from thepropagation feature formed in free space. If there is free view distance LOS path in

the gorge of the street, then

)()( lg20lg266.42 MHzkmb fdL Kmd 02.0

2. High BTS antenna:

In this case, OST-231-Walfish-Ikegami model consists of 3 items, it is f it for NLOS.

msdrtsb

LLLL 0

where,

)0(0

lg20lg10lg109.16

rts

MobilerooforiMobile

rtsLif

hhLhfL

oo

oo

o

oriL

9055)55(114.00.4

5535)35(075.05.2

350354.010


35/44


)0(0

lg9lglg

msd

fdabsh

msdLif

bfKdKKLL

roofBase

roofBaseBase

bshhh

hhhL

0

)1lg(18

Note:

L0- the transmitting loss in free space, calculate loss in free space from BTS to the

latest roof;

Lrts-the diffraction and scatter loss from the latest roof to street, calculate diffraction

and reflection in the street;

Lmsd-multi-screen forward diffraction loss multi-screen diffraction loss, calculate

multi diffraction over the roof;

Lori-the factor of street direction;

roofBaseBaseMobileroofMobile hhhhhh

-street width m;

f - calculating frequency MHz

Mobileh Unit is m;

-Unit is degree;


36/44


30

Figure 2-8 Environment parameters and street parameters

hMobile

hMobile

bd

hBase

hroof

hBase

BTS

Incidence

wave

building

(a)environment parameters

(b)street parameter

MS

roofBaseBase

roofBaseBase

roofBase

a

hhkmdd

h

hhkmdh

hh

K

&5.05.0

8.054

&5.08.054

54

roofBase

roof

Base

roofBase

dhh

h

h

hh

K1518

18

In the above expression, Ka means path loss when BTS antenna is lower than adjacent

roof, Kd controls the relation between Lmsd and distance d, Kf controls the relation

between Lmsd and frequency f.

Landform correction factors in Okumura-Hata model can be used.

Kh-correction factor for upland


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See Okumura-Hata model;

Ksp-correction factor for slope landform


Kim-correction factor for isolated hill


Ks-correction factor for sea-lake mixing path

See Okumura-Hata model.

2.2.4 Micro Cell Propagation Model

2.2.4.1 Double-Ray Propagation Model

When the double-ray propagation model is applied to calculate the field intensity in the

receiving end, only the contribution of the direct rays and ground reflected rays is

considered. This model is suitable for the smooth countryside environment and the micro

cell that has a low base station antenna, where there are LOS paths linking the

transmitting and receiving antennas. In this case, if walls of buildings also reflect and

diffract the radio waves, it will cause the field intensity amplitude to fluctuate rapidly in the

simple double-ray model, but will not change the prediction of the entire path loss (thevalue of power n in the idempotent law) made with the double-ray model.

The path loss equation produced with the double-ray model is represented by a function

of d, the distance between the transmitting and receiving ends. The distance can be

represented by the approximate value of two line segments with different slopes ( 1n and

2n ). The distance of the mutation point (also known as point of reflection) between the

two segments from the transmitting end is:

rt

b

hhd

4

Where,tr

hh andare the heights of the receiving and transmitting antennas

respectively.

Path loss can be represented by the following equations:


38/44


32

b

b

b

b

b

b

ddddnLL

ddd

dnLL

log10

log10

2

1

The above approximate equation is called the double-slope model. For the theoretical

double-ray ground reflection model, the values of 1n and 2n are 2 and 4, respectively.

In the downtown area micro cell with a frequency range of 1800 ~ 1900MHz, the test

result shows that the value of 1n is 2.0 to 2.3, and the value of 2n is 3.3 to 13.3.

bL is the path loss at the point of reflection derived from the following equation.

2

28log10

rt

bhhL

2.2.4.2 Multi-Ray Model

The multi-ray model is already applied in downtown micro cell where there is the LOS

path and the transmitting and receiving antennas are much lower than the roof plane.

This model assumes the so-called streets have medium valley structures (also known

as the wave-guide structures), and the field at the receiving end is composed of the direct

rays between the transmitting and receiving ends, the reflected rays along the ground,

and the rays reflected by the vertical planes (that is, , building walls) of the valley. The

double-ray model can be deemed as the multi-ray model that considers only two rays.

Four-ray and six-ray models are already introduced. The four-ray model is composed of

the direct rays, ground reflected rays and two rays reflected once by building walls. The

six-ray model has the same mechanism as the four-ray model, except that it has two rays

reflected twice by building walls.

2.2.4.3 Multi-slot Wave-guide Model

When the multi-ray model is applied to the downtown environment, the buildings along

the streets are usually supposed to be lined consecutively and without slots. The

multi-slot wave-guide model proposed by Blaunstein and Levin, on the other hand, takes

into account the actual medium property of the building walls, the actual street width and

reflections from the road, as shown in the Figure 2-9. This model assumes the city to be

composed of two parallel lines of screens (that is, , simulated building walls) with

randomly distributed slots (that is, , gaps between buildings) and takes into account the

direct signal field, multiple reflections from the building walls, multiple UTD (Uniform

Theory of Diffraction) reflections from the corners and reflections from the ground.


39/44


Figure 2-9 Multi-slot wave-guide model

Ray

xy

z

Building

Building

BuildingBuilding

Receiver

Transmitter

Mirror source

2.2.5 Indoor Propagation Model

Laboratory research finds that NLOS propagation within buildings has Rayleigh fading,

while Ricean fading in LOS propagation is independent of building types. The Ricean

fading is caused jointly by the strong LOS path and many ground paths of weak reflection.

Studies have found that materials of building, the vertical/horizontal ratio of building,

types of windows etc all have influence on RF fading between floors. Measurements

point out that fading between floors does not have a linear increase in decibel as the

distance increases. The typical fading values between floors are: for the first floor, it is

15dB, then an extra 6dB to 10dB for each floor but not exceeding 4 floors. For buildings

with 5 or more floors, increasing of the path loss for each extra floor can be only several

decibels.

Laboratory research has found that, in case that the indoor system is covered by the

outdoor base station, the intensity of signals received within buildings increases as the

floor increases. In the first floor of the building, there is considerable fading due to the

urban building blocks which make the level of signals penetrating into the building very

small. In the floors of the higher part of the building, if there are LOS paths, relatively

strong direct signals can reach the wall of the building. The penetrating loss of signals is

a function of the frequency and the interior height of the building. The penetrating loss

increases as the frequency increases. Measurements find that penetrating loss for

buildings with windows is 6dB less than that for buildings without windows.

2.2.5.1 Path Loss Model for Logarithmic Distance

The mean path loss is a function of the nth power of the distance:


40/44


34

)log(10)()(0

050d

dndLdL

Where )(50 dL is the mean path loss (in dB), d is the distance between the

transmitting and receiving ends (in meters),)( 0dL is the path loss from the transmitting

end to the reference distance 0d

(in meters), and n is the mean path loss index

subject to the environment. The reference path loss can be measured or calculated by

applying the free space path loss equation.

As shown by the above equation, the path loss has logarithmic normal distribution. The

mean path loss index n and standard dethroughtion depend on the building type,

building sidewall, and the number of floors between the transmitter and receiver. The

path loss in the distance of d from the transmitter is

)()()( 50 dBXdLdL

The above equation is an empirical model, where X

is the random variant of the

zero-mean logarithmic normal distribution with a standard dethroughtion)(dB

, which

represents the influence of the environment.

2.2.5.2 Fading Factor Model

The formula in the preceding section can also be substituted by:

FAFd

dndLdL )log(10)()(

0

10

Where 1n

is the path loss index for one entire floor, with a typical value of 2.8 but

subject to the building type. FAF is the floor fading factor, which is a function of the

number of the floor and the building type.

2.2.6 Application of Propagation Model in Cellular Design

In wireless cellular design, the coverage radius of the base station or the receiving power

of the receiver (power link budget) can be expressed as:

bfrtrttr LLLGGPP


41/44


Where rP

and tP

are receiving power and transmitting power in dBm, respectively;

rG

and tG

are the gains of the receiving and transmitting antennas in dB; rL

and

tL are the feeder loss in the uplink and downlink in dB; bfL is the propagation pathloss in dB, which can be predicted through the model described above.

To improve the accuracy of prediction and reduce the work of the wireless network

planning engineers, computer software is usually adopted to predict the propagation loss

and the coverage area. Path loss prediction is closely related to the topography, clutter

and distance etc near the base station. Therefore, we can store information of the

topography and conditions into the digital map and recall it when necessary for computer

operation. Figure 2-10 is a digital map of one certain area, with different colors

representing different topographies.

Figure 2-10 Digital map of one certain area

By inputting the digital map and base station information and selecting an appropriate

model, the software can work out and display in the screen the receiving power and other

information at different distances from the base station. Figure 2-11 shows software

prediction of the coverage area of a certain city, with different colors representing

different receiving powers.


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36

Figure 2-11 Forward receiving powers in one certain city

Legends:

The software can also carry out reverse coverage prediction, as shown in the Figure 2-12


43/44


Figure 2-12 Reverse receiving powers in one certain city

Legends:

Propagation path loss in the urban, suburb and rural area is different. In this case, we can

adopt different propagation models and correction factors. Some prediction software

provides model parameter correction function through field tests. Such a model greatly

improves the accuracy of computer-aided simulated prediction of coverage. Take the

General model as an example. The formula is:


44/44


Where

PREP

: Receiving power;

ERP: Effective transmitting power;

md : Distance of the mobile station from the base station;

effH

: Effective height of the base station antenna;

DIFFL : Loss of diffraction.

K1, K2, K3, K4, K5, and K6 are the correction factors of the above parameters

respectively. ClutterK

is the correction factor of clutter. K1 to K5 and ClutterK

can be

used by the computer for correction of the actual propagation model with the actual test

data.

wireless communication basic knowledge

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