Clutter Attenuations

Clutter attenuations in ICS TELECOM

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INDEX

1.- LINEAR AND FLAT ABSORPTIONS ........................................................................................................................... 3

2.- THE DIFFERENT MODES ......................................................................................................................................... 4

2.1 The “dB/km” mode .............................................................................................................................................. 4

2.2 The “Flat + absorption” mode ............................................................................................................................. 5

2.3 The “Flat + diffraction” mode .............................................................................................................................. 8

2.4 The “User” mode ................................................................................................................................................ 10

2.5 The “Tuning” mode ............................................................................................................................................ 13

2.6 The “none” mode ............................................................................................................................................... 15

2.7 The “CCIR” et “UER” modes ............................................................................................................................... 15

2.8 The "TSB-88" mode ............................................................................................................................................ 20

2.9 The "Indoor" option ........................................................................................................................................... 23

2.10 The "Indoor building additional" option ...................................................................................................... 25

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1.- LINEAR AND FLAT ABSORPTIONS

The first column is used to define the linear absorption in dB/km (a typical value is between 500 and 1000dB/km but

of course it depends on the materials, the frequency...

The second column is used to define flat absorption in dB.

For example, suppose that for a given clutter code 1000dB/km has been set in the first column and 3dB in the second

column. In that case, 3dB + 1000dB/km attenuation will be added during the calculation of the indoor coverage for

that code.

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2.- THE DIFFERENT MODES

2.1 The “dB/km” mode

The “dB/km” mode takes in account the linear and the flat absorption. The user sets the attenuation values and the

total clutter attenuation is calculated for the last clutter obstacle only.

In this mode, the field strength calculation is done on one side with the diffraction considerations and on the other

side with clutter attenuation. Then, the highest received value is returned.

Note that in the "dB/km" mode, the flat attenuation is taken into account only if the receiver is located inside a clutter

class that has a height higher than the receiving antenna, otherwise, the calculation takes in account only the

attenuations due to the diffraction.

Rx over ground spot option :

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2.2 The “Flat + absorption” mode

This option is considering a flat attenuation in dB each time the clutter class is crossed along the path. The user

chooses the attenuation values, for example, if 5dB "flat" attenuation has been set on clutter code 9 and if this code is

crossed 3 times along a given profile, the total clutter attenuation will be 15dB. This option is considered for a receiver

located anywhere (outdoor and indoor),meaning that the user can select the “Rx over ground spot” or” Rx over

clutter”.In this mode, like in the “dB/km mode”, the field strength calculation is done with the diffraction attenuation

and with clutter attenuation, then, it considers the best value.

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Rx over clutter option :

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2.3 The “Flat + diffraction” mode

This option is considering a flat attenuation in dB for the last obstacle and only if the receiver is inside a

clutter code. If the clutter obstacle is a building (from the BLG layer), the total attenuation value will be the “flat”

attenuation corresponding to the clutter plus the diffraction attenuation before entering in the building.

If the receiver is inside another clutter code, the received power will be the maximum of the diffracted path and the

diffracted path before the last clutter code plus the flat attenuation.


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2.4 The “User” mode

This option is considering a flat attenuation in dB but for the last clutter obstacle only and cannot be used with a BLG

layer. The user sets the attenuation values and the clutter attenuations are taken into account only if the receiver is

located over a clutter class that has a height different from 0. The total attenuation applied is the sum of the

diffraction on the last receiving point and the flat attenuation.

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2.5 The “Tuning” mode

The attenuation values (flat, in dB) are calculated during an automatic correlation and cannot be used with a BLG

layer. They are taken into account only if the receiver is located inside a clutter class that has a height different from

0, and for the last clutter obstacle. The total attenuation applied is the sum of the diffraction on the last receiving

point and the flat attenuation.

This option is used when the user has performed a correlation between measurements and simulations and has

defined specifics attenuation values.


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2.6 The “none” mode

In this mode, no attenuation for clutter penetration is calculated and there is no propagation result inside clutter

obstacles.

2.7 The “CCIR” et “UER” modes

These options provide standard flat attenuation values extracted from broadcast standard (to be used in

combination of the ITU-R 370-7 propagation model). In these modes, the user can select the “Rx over ground spot”

or” Rx over clutter” option. The total attenuation applied is the sum of the diffraction on the receiving point and the

flat attenuation.

These modes are genearlly considered in medium resolution DTM, with a clutter layer and cannot be used

with a BLG layer.

Clutter attenuation used in the “UER mode”

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Rx over clutter option with CCIR attenuations :

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Rx over ground spot option with CCIR attenuations :

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Rx over clutter option with UER attenuations :

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Rx over ground spot option with UER attenuations :

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2.8 The "TSB-88" mode

This mode has to be used as recommended by the NTIA (National Telecommunications and Information

Administration, US) report "TSB-88-B" (Telecommunications Systems Bulletin 88-B). It defines flat attenuation values

as follows :

Attenuation (dB) Frequency range(MHz)

[30 - 50] [136-174] [220-222] [380-512] [746-941]

Clu

tte

r co

de

1 3 3 3 3 5

2 2 3 3 4 18

3 1 9 9 10 10

5 3 8 9 12 25

6 1 3 3 3 3

7 3 14 15 16 20

8 4 15 16 17 20

9 4 14 14 15 20

The total attenuation applied is the sum of the diffraction on the last receiving point and the flat attenuation.

Note that clutter heights should be set to 0m in order to be not too pessimistic.

Notes

Two propagation models are recommended in TSB-88-B :

- The Okumura/Hata/Davidson model. TSB-88-B recommends the use of this model when terrain data is not

available but the operating environment is known (i.e., large or small city, suburban, or open environment).

Okumura’s measurement results were given in terms of a set of curves of basic median attenuation relative

to free space in an urban area over semi-smooth terrain as a function of frequency and distance for a base

antenna height of 200 meters and a mobile station antenna height of 3 meters. Okumura also developed

correction curves for other environments, terrain, and antenna heights. The Okumura/Hata Model is a

computer model based on equations derived from Okumura’s findings by Hata, for limited ranges of

frequency, distance and antenna heights for four types of environment, large and small city, suburban and

open. The Okumura/Hata/Davidson model uses equations extending ranges of frequency, distance and base

antenna height

- For detailed predictions using terrain data, TSB-88-B recommends the use of a two-ray model for line-of-sight

paths, and the Anderson 2D model for obstructed paths. As this model is not widely available, in some

applications of TSB-88-B, other more widely used models, such as Longley-Rice, based on NBS Technical Note

101, or Epstein-Peterson is also used.

TSB-88-B recommends that attenuation due to clutter be included where appropriate. Clutter losses are implicit in the

Okumura/Hata/Davidson model, whereas clutter must be added to the other propagation models. The clutter losses

are based on the United States Geological Survey (USGS), Land Use Land Cover (LULC) data and the National Land

Cover Dataset (NLCD).

Building and other expected losses or margins can be included in the interference analysis with any of the propagation

models.

TSB-88-B recommends using 30-meter terrain data, re-sampled at three arc second resolution. This is superior to the

original three arc second terrain data, as the re-sampled data has much better vertical accuracy than the original three

arc second data.

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Rx over clutter option:

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Rx over ground spot option:

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2.9 The "Indoor" option

This option is requiring a specific clutter layer where code numbers 12 to 18 are describing buildings with different

number of floors. The attenuations are calculated according to the COST recommendation and are also depending on

the frequency. The total attenuation applied is the sum of the diffraction on the last receiving point and the flat

attenuation. This option cannot be used with a BLG layer.


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2.10 The "Indoor building additional" option

This option can be used only with a BLG layer. It applies an additional flat attenuation in dB to the attenuation

calculated using one of the three following modes :

- "dB/km";

- "Flat + absorption";

- "Flat + diffraction".

For example, in “flat + absorption” mode and 5dB set for the indoor building additional attenuation :

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Documents

Clutter Attenuations