Advanced Topographic Development and Images Ltd Registered in England No. 3198786

Registered Office: 19 New Road, Brighton, BN1 1EY

ATDI Ltd Kingsland Court

Three Bridges Road Crawley, West Sussex

RH10 1HL – UK Tel: + (44) 1 293 522052 Fax: + (44) 1 293 522521

www.atdi.co.uk

Author: Cyprien de Cosson

Title: Product Manager

Dated: 29 February 2008

Issue: 2.00

ITU-R P.528-2

Aeronautical

Propagation Model

Guide

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0. Contents

1. Introduction .......................................................................................................................... 3

2. ATDI Aeronautical Model ................................................................................................... 3

2.1 Core Transmission Model ........................................................................................ 3

2.1 Obstacle Diffraction Model ...................................................................................... 4

3.1. Getting Started .................................................................................................................. 5

3.1. Software Installation ................................................................................................ 5

3.2 ICS Telecom & HTZ Warfare .................................................................................. 5

4. Technical Support ................................................................................................................ 7

5. Further Information ............................................................................................................. 7

6. References ............................................................................................................................. 7

Appendix (i) – Core Model Validation ................................................................................... 8

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1. Introduction

The ATDI Aeronautical Propagation Model is an extension model to ATDI planning tools for

use in the planning and coordination of aeronautical mobile systems. The model is compliant

with ITU-R P.528-2 and includes an optional model in order to account for terrain

obstructions that give rise to excess losses with respect to smooth earth conditions.

2. ATDI Aeronautical Model

The model is an hybrid based upon a core transmission model and an optional obstacle

diffraction algorithm. The core model reproduces the published set of reference curves in

ITU-R recommendation entitled Propagation Curves for Aeronautical Mobile and

Radionavigation Services using the VHF, UHF and SHF bands. The obstacle model is based

upon the recommendation ITU-R P. 526-10 Propagation by Diffraction, and if selected will

be added to the loss of the core transmission loss. The model manifests itself as a dll that may

be used in conjunction with ATDI planning tools.

2.1 Core Transmission Model

The core transmission loss model is based upon an implementation of the IF-77 propagation

algorithm, from which the original curves of ITU-R P. 528-2 were obtained. This means that

heights and frequencies that do not exist in the published curves are computed rather than

interpolated. The model is constrained to give basic transmission loss for 5%, 50% and 95%

of the time for antenna heights in the range 0.5 to at least 50,000m. The frequency range of

the implementation is limited from 100MHz to 20GHz and is applicable to paths of up to

1800km.

The core loss is calculated using a smooth (terrain parameter h 0) earth with an effective

Earth radius factor k of 4/3 (surface refractivity Ns 301) along with compensation for the

excessive ray bending associated with the k 4/3 model at high altitudes. Constants for

average ground, horizontal polarization, isotropic antennas, and long-term power fading

statistics for a continental temperate climate are specified, which may be considered either

reasonable or worst-case for many applications. With the exception of a region near the radio

horizon, values of median basic transmission loss for within-the-horizon paths are obtained by

adding the attenuation due to atmospheric absorption to the transmission loss corresponding to

free-space conditions. Within the region near the radio horizon, values of the transmission loss

are calculated using geometric optics, to account for interference between the direct ray and a

ray reflected from the surface of the Earth. The two-ray interference model is not used

exclusively for within-the-horizon calculations, because the lobing structure obtained from it

for short paths is highly dependent on surface characteristics (roughness as well as electrical

constants), atmospheric conditions (the effective Earth radius is variable in time), and antenna

characteristics (polarization, orientation and gain pattern). Such curves would often be more

misleading than useful, i.e., the detailed structure of the lobing is highly dependent on

parameters that are difficult to determine with sufficient precision. However, the lobing

structure is given statistical consideration in the calculation of variability. For time

availabilities other than 50%, the basic transmission loss, does not always increase

monotonically with distance. This occurs because variability changes with distance can

sometimes overcome the median level changes. Variability includes contributions from both

hourly-median or long-term power fading and within-the-hour or short-term phase

interference fading. Both surface reflection and tropospheric multipath are included in the

short-term fading.

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2.1 Obstacle Diffraction Model

The core model accounts for smooth earth diffraction and no account is taken of irregular

terrain obstacles. Whilst IF-77 has an obstacle model, this is not applied, because it is a simple

model that suffers from a limitation that the highest antenna height must be greater in altitude

than the highest obstacle. This constraint makes the model of limited use where low altitude

aeronautical platforms are to be modelled. In order to overcome this limitation, the ATDI

Aeronautical Propagation Model contains an optional algorithm based upon the cascaded

knife edge method as specified in §4.4.2 of ITU-R P.526-10 to account for the excess

diffraction loss attributable to irregular terrain effects.

This model upon the geometry of the terrain profile between the ends of the path and is based

on the Deygout method limited to a maximum of 3 edges. For line-of-sight paths it differs

from the Deygout construction in that two secondary edges are still used in cases where the

principal edge results in a non-zero diffraction loss.

In order to avoid the double counting of smooth earth diffraction losses, the diffraction

method is applied twice, once to a smooth earth profile, and the second time to an irregular

terrain profile. The excess irregular terrain diffraction loss is taken as the difference between

the diffraction losses computed in the two different cases.

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3.1. Getting Started

3.1. Software Installation

This software is currently targeted for use with ATDI planning tools running under Windows

2000, 2003, XP or Vista. Other hardware and software requirements are as per these tools.

This version is currently compatible with ICS Telecom and HTZ Warfare.

To install the model run the setup on the supplied disk. This will install the ATDI

Aeronautical Propagation Model to the default locations for ICS Telecom and HTZ Warfare.

The installer creates shortcuts to ITU-R P.528-2 Curve Viewer application and to this guide

under Programs > ATDI Software > Aeronautical Model.

Please ensure that you have read and agreed to the software licence agreement shown on the

splash screen of any installed software prior to use.

3.2 ICS Telecom & HTZ Warfare

In order to use the model in ICS Telecom or HTZ Warfare, the model must be loaded using

the Propagation Models dialog by clicking on the small button near the end of the models list

and selecting prop528.dl from the files listed.

. This should display the following splash screen which contains the licence agreement.

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After accepting the agreement, this screen disappears and the model specific settings will be

displayed as shown following.

This dialog contains few options which must be selected as appropriate to the task in hand.

The Time availability should be selected as recommended by the ITU. Typically an

availability of 95% should be specified for wanted services and 5% for unwanted services.

The height reference should normally be set to sea level. Where ground level is specified the

Fast mode option performs an interpolation between curves rather than an exact calculation

and should be used for coverage calculations where a speed gain of several orders of

magnitude may be obtained. This mode normally yields an error of a fraction of a decibel, but

may be greater in the transition region from the line of sight to diffraction region. The height

reference should be synchronised with the options on the left hand side of the main screen of

ICS Telecom. The LND setting is for all heights referenced to ground level and the R/S option

for the receiver referenced to sea level.

Once the model specific settings have specified, then click OK to save them. They may be

recalled by the user at any time by clicking on the prop528 label from the Propagation models

screen. The settings are saved in the file prop528.cfg which is stored in the same directory as

the dll and not in the main parameter file of the planning tool. In order to copy the setting

from one machine to another, then this file must be copied.

Once the model specific settings have been selected, the other options in the main propagation

dialog should be set. The most important option to check is the Flat earth profile sent to DLL.

This must be ticked for correct operation as shown below.

All other diffraction, sub path and climate models should be disabled. Clutter options may be

set from Tools > Clutter options... by setting clutter excess height for each category, which

will be used to modify the path profile altitudes used by the ATDI Aeronautical Model.

Clutter attenuations should not be specified, since these are generally only applicable where

the receiver is located in or just above ground clutter such as in land mobile systems.

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4. Technical Support

To obtain technical support please make a note of the operating system in use, hardware

components together with a brief description of the issue and how to reproduce it if there is a

fault. If possible please include sample files and screen shots and send them via email to:

technical.support@atdi.co.uk Support may also be obtained by telephone on +44 (0)1293

522052 and fax +44 (0)1293 522521.

5. Further Information

For further information on this product or other propagation models, including the supply of

this model as a component for use in other systems, then please contact the author by

telephone on +44 (0)1293 522052 or by using the email address cyprien.de.cosson@atdi.co.uk

6. References

(i) Recommendation ITU-R P. 528-2 Propagation Curves for Aeronautical Mobile

and Radionavigation Services using the VHF, UHF and SHF bands, International

Telecommunications Union, Geneva, Switzerland

(ii) Recommendation ITU-R P. 526-10 Propagation by Diffraction, International

Telecommunications Union, Geneva, Switzerland

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Appendix (i) – Core Model Validation

This section contains a series of comparisons between values derived from the ATDI

implementation of the aeronautical curves and those found in Annex II of ITU-R P.528-2.

The curves in the ITU recommendation were derived from the IF-77 propagation model upon

which the ATDI implementation is based. These curves were originally produced by the

Institute of Telecommunication Science and appear in a document entitled ‘An Atlas of Basic

Transmission Loss for 0.125 to 15.5GHz’ published in 1980. This document describes a

number of limitations of published curves which are related to the fact that the IF-77 is an

hybrid model that accounts for a number of factors that affect propagation including long-term

power fading, surface reflection multi-path and tropospheric multi-path. The model is

therefore blended at the transitions between the line-of-sight, diffraction and scatter regions.

These complications and the use of simple linear interpolation to obtain the plotted curves

result in some bumps and discontinuities. For the most part these are minor, but some are

severe enough to have been manually smoothed in the published document, particularly at

higher frequencies. Furthermore, the curves do not exist in tabular format and capture of them

in tabular form is difficult due to the skewed graphics. Therefore the curves have been

validated with the ATDI implementation, by overlaying the calculated values from IF-77 onto

the published graphics. These following pages show the curves plotted from IF-77 on the left-

hand side, and then overlaid onto of each of the graphs from Annex II of ITU-R P. 528-2 on

the right-hand side. Bearing in mind all of these limitations, there is generally excellent

agreement.

Height code h1 (m) h2 (m)

A 15 1000

B 1000 1000

C 15 10000

D 1000 10000

E 15 20000

F 1000 20000

G 10000 10000

H 10000 20000

I 20000 20000

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