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LOS simulation using 3D Digital Maps—

Techniques and Risks

Syed Masroor Hassan 00725060

Abstract ： Line-of-Sight (LOS) survey is an integral part of Microwave Link

designing. Different techniques are used for evaluating LOS for Microwave link design.

LOS can be checked by physical methods as well as by the help of simulation. This

document is focused on the LOS simulation. Detail of physical survey is beyond the

scope of this document. This document provides basic overview to the reader about

different simulation techniques and also covers various risks which need to be

considered before hardware implementation when using these simulation methods for

LOS evaluation.

Keywords: LOS simulation, Line of sight survey, 3D digital maps

Background

Purpose of this document is to provide basic overview of different LoS simulation

techniques and make people aware of potential risks which must be analyzed before

hardware implementation.

In 2010 Huawei have purchased 3D digital map for the LOS evaluation. Initially, these

maps were purchased for only one major city K in country P for trial purposes. Main

objective of purchasing these digital maps is to eliminate the requirement of physical

LOS surveys on which Huawei spends considerable amount and time every year.

There are some facts and figures about these digital maps which I think are worth

mentioning here:

The error of LOS simulation is 3 meter.

3D satellite images have 1m or 2.5m resolution.

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The price of 2.5m resolution satellite image is XX USD / sq.km.

The price of 1m resolution satellite image is 20 times more than 2.5m

resolution maps..

LOS or line of sight surveys are the most important part of MW link design. Without

proper LOS evaluation point-to-point microwave link installation is not possible.

Normally LOS is conducted in the series of steps in-order to establish the link between

two locations. There are two types of LOS evaluation:

1- Physical LOS

2- LOS using simulation tools

Details of physical LoS is beyond the scope of this document. However, LOS simulation

methods will be discussed in the later parts.

Problem ： LOS Simulation in Fast growing Cities

These digital maps are expensive and if we want to update these maps then we have to

purchase the maps again. Therefore frequent updates of these maps are note viable. In

City X a microwave SDH link was planned in Dec 2010. Transmission design engineer

have sent the Link details to Huawei HQ for the LoS simulation. He had also check the

obstacle by using conventional satellite images. As per LoS simulation results and

satellite images line of sight was clear but there was an building which was under-

construction however as the area around that building consists of houses which are

rarely have floors more than 3 stories therefore no one have idea that this under-

construction building may obstruct the line of sight by looking at the simulation results

unless a team physically visit the construction site and ask the construction team. Later-

on implementation team went for the installation and reported the LOS issue.

Precautionary measures in-order to avoid such situations needs to be considered which

have been analyzed in later sections in detail.

Analysis, Strategies and Actions

Microwave link designers use different tools in-order to simulate line of site between two

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ends, such as:

1- Terrain database tools (Pathloss, Global Mapper etc,)

2- Satellite images (e.g., Google earth)

3- 3D Digital Maps

Different tools such as Pathloss or global Mappers utilize terrain databases in order to

show the line of sight clearance. Image 1.0 shows the example of Path profile

generated by Pathloss 4.0. This profile shows the terrain information between two sites

only and we need to insert objects above terrain such as building and trees manually.

For example: in the snapshot below an average building height have been inserted

manually. In this example minimum heights worked out to be 15m at both ends but we

have set the transmission height of 20m for safe side.

May 11 11

9014Latitude 24 56 06.54 NLongitude 067 05 59.50 EAzimuth 207.04°Elevation 38 m ASLAntenna CL 20.0 m AGL

Rim Jhim HallLatitude 24 55 36.00 NLongitude 067 05 42.40 EAzimuth 27.04°Elevation 39 m ASLAntenna CL 20.0 m AGL

Frequency (MHz) = 38000.0K = 1.33, 0.67

%F1 = 100.00, 60.00

Path length (1.06 km)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Ele

vatio

n (m

)

36

38

40

42

44

46

48

50

52

54

56

58

60

62

Image 1.0: Path-profile generated by Pathloss 4.0

Terrain database method is effective in rural areas where building heights are not more

than two stories and you also know the average heights of vegetation. In urban areas

where you have buildings of different heights, it is very difficult to perform correct

simulation using Terrain database alone. In this scenario we take help from satellite

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images such as Google earth. By using satellite images you can estimate height of the

buildings by counting floor, for example in Pakistan an average height of one floor is 3

m. This method doesn’t work when the angle of the satellite image is perpendicular and

you cannot count its floors. Sometimes we estimate from the shadow of the building but

this method is highly unreliable because at different time of the day shadows have

different lengths. As shown in the image 1.2, it is not possible to find out the height of

the building. Therefore Huawei decided to purchase 3D digital maps for cities. These

digital maps are amazing and very useful for rapid deployment of the microwave

network, where physical LOS requires too much time and old simulation methods are

difficult to manipulate or in other words not so accurate. These digital maps were placed

at the centralized locations due to high system requirements. Expert resources were

dedicated in-order to facilitate queries for LOS simulation from around various parts of

the world.

Image 1.2: Example Image taken from Google earth

These 3 dimensional digital maps contain thorough information of Buildings and

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vegetations height above terrain (HAT). That means you don’t have to insert obstacle

heights manually.

Path-profile shown in the image below have been generated for Pathloss by using

digital maps and it is showing heights of the obstacles which are present between two

sites.

May 11 11

1017ALatitude 24 55 36.00 NLongitude 067 05 42.40 EAzimuth 27.04°Elevation 57 m ASLAntenna CL 5.0 m AGL

9014ALatitude 24 56 06.54 NLongitude 067 05 59.50 EAzimuth 207.04°Elevation 36 m ASLAntenna CL 15.0 m AGL

Frequency (MHz) = 18000.0K = 1.33

%F1 = 100.00

Path length (1.06 km)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Ele

vatio

n (m

)

32

34

36

38

40

42

44

46

48

50

52

54

56

58

60

62

64

66

Image1.3: Path-profile generated using digital maps data

Although this method is more reliable than its predecessor but we have to be care-full

for few things, such as tower height which we usually use is measured above ground

level but if the tower is a rooftop tower than in this method we have to use the actual

structure height instead because it also include the building height in the profile where

the tower is installed.

Strengths and weakness of LOS simulation using digital maps:

Strengths:

1- Fast evaluation

2- Useful for high level topology planning

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3- Less amount of changes required at the time of low level network plan

4- Economical

5- Less time consuming

Weaknesses:

1- These Maps are static just like Google earth

2- We have to purchase Maps again in-case re-evaluation is required

3- Cannot be used in the area where construction of buildings is expected

4- Does not include advertising board installed on top of the building

Result

In city X, construction period of building is very short, usual time of construction of grey

structure of 8 floor building is approximately one month. This is the big problem where

we want large deployment of transmission network. Therefore we have to be extra

careful while planning a microwave point to point link because these digital maps are

static and periodic update costs a lot of dollars.

In the subjected case when team went for the installation it found that there is a building

just across the road which is under-construction and in the middle of the line of sight

reaching height of 8 stories as shown in the LOS picture shown in the image 1.4.

Image 1.4: LOS picture taken

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In this Case LOS issue was captured before the installation started therefore

dismantling therefore re-installation was not required. We only arranged the physical

LOS survey with the different far-end and completed the installation.

In such case where LOS issue would have been reported after the hardware installation

we have to go with the dismantling and re-installation and this will result in the loss of

time and capital.

Suggestion or Review

Do not rely entirely on simulation results especially for important links such as links

belong to SDH rings. Simulation results can be used for the rapid high level

transmission network planning but when preparing the actual installation it is strongly

recommended to check the path physically. In some cases where link installation is

extremely urgent and you have no time to arrange physical Line of Sight surveys you

have to be extra careful and if there is any empty plot or under-construction building is

falling in the path you should arrange physical visit.

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