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2011-4Q: Map: Google Earth – Coverage Checker Implementation

1.     Introduction

Google Earth Plugin that was integrated into SIMPLer in the first quarter of 2011 has been enhanced with many features that allow to approximately measure Signal Propagation and Line of Sight.

Note 1) Google Earth Plugin is not supported under Linux-based operating systems

Note 2) Google Earth Plugin should be supported by all modern browsers. However there were bugs reported for GE Plugin for Mozilla Firefox version < 8.0.0. It is recommended to upgrade your browser to the latest version. The best performance is reached under Google Chrome.

2.     Site and Basestation

Each Site added to SIMPLer system (under “Network->Site Details”)  can be represented on GE Plugin as a Tower that contain multiple amount of Access Points, BackHauls and other PTP/PMP devices. Important parameters are (Fig.1):

-      height of site - represents approximate height of tower AGL (above ground level).

-      GPS coordinates - point location of the site on the map.

-      Frequency – is a default frequency that is used in point-to-point analysis


Fig. 1. Site parameters


Each Basestation added to the SIMPLer system (under “Network->Basestation Details”) is a piece of equipment mounted on a tower. Important parameters are (Fig.2):

-      frequency – is a working frequency of device

-      direction – represents azimuth of antenna

-      sector – represents span of antenna 

Fig. 2. Basestation parameters


 Each basestation can be considered as a parent or child in regards to basestation being hanged on different tower. Basestations that are associated to one site does not have parent-child association – they are connected directly or using hubs/switches/routers. Parent relationship can be setup under “Network -> Equipment Details” (Fig.3)

Fig. 3. Parent Relationship

3.     Google Earth

 To get an access to Google Earth Plugin click on “Map” on main menu. If you open this page for the first time it will show Google Map. To switch to Google Earth simply click on “Google Earth View” link on map legend (Fig.4).

Fig. 4. “Google Earth View” switch

 Most of the features that were displaying sites and customers on map were replicated on Google Earth. Latest features added (Fig. 5):

-      number of sites and customers displayed for each type.

-      parent – child association line (+ ability to hide this line)

-      ability to show/hide site name on GE

-      ability to quickly move from current position to selected site (“Go To Site”)

-      “Reload Earth View” button – to load updated site positions, coverage graphs etc


Fig. 5. Features on Google Earth

4.     Coverage Graphs

 The most powerful tool is ability to generate Coverage Graphs on GE Plugin. SIMPLer system will let you generate and view three types of graphs:

-      Line Of Sight Graph

-      Path Loss Graph

-      Field Strength Graph

To generate any of the graphs, go and click on the particular site, switch to the “coverage graph” tab and select appropriate Access Point. Then update any of the additional details and click “generate”. Graph generation will run for a couple of seconds. Generated graph should be shown on the GE. (Fig. 6)

Fig. 6. Site “balloon”

Note 1) Make sure you have appropriate user rights assigned - Map/Coverage Checker

Note 2) If graph is not updated it is a problem with caching older graphs. You would need to click “Reload Earth View” to get the updated GE.

Note 3) If you generate coverage graph for the first time it might take more time than usual, because SIMPLer needs to download SRTM digital elevation models for your region


The advantage of coverage graphs is:

-      ability to generate multiple graphs per site, i.e. graphs associated with basestation

-      ability to generate directional path loss / field strength graphs

-      ability to hide/view different types of graphs (Fig. 7)

-      ability to hide/view  particular graphs

-      ability to hide/view graph label

Fig. 7. Coverage graph options

            A. Line of Sight (LOS)

Line of Sight (LOS) graph can be generated only for Site (“generic” AP). It plots terrain visible from site (taking site height  into account). Parameters that can be modified for LOS graph:

-      RX Antenna Height - height (above ground level) of receive antenna wishing to communicate with the site in question.

-      Ground Clutter - effects in raising the overall terrain by the specified amount.

-      Maximum Coverage Radius - this is very approximate  and cuts graph that is above maximum radius

-      Earth Radius Multiplier - modifies the effects of atmospheric bending

          B. Path Loss

Here a multi-color map is generated that is illustrating expected signal levels in areas surrounding  the transmitter site. A legend at the top of the map correlates each color with a specific path loss range in decibels. Parameters that can be modified for Path Loss graph:

-      RX Antenna Height - height (above ground level) of receive antenna wishing to communicate with the site in question.
-     
Ground Clutter - effects in raising the overall terrain by the specified amount.
-     
Path Loss DB threshold - allows a threshold to be set beyond which contours will not be plotted on the map.
-     
Maximum Coverage Radius - this is very approximate  and cuts graph that is above maximum radius
-     
Terrain Type -  based on the relative permittivity and soil conductivity of the ground
-     
Atmospheric Bending Constant – surface Refractivity - the refractivity of the atmosphere determines the amount of bending of the radio waves. In other TAP models, the effect of refractivity is entered as effective earth curvature, typically 4/3 earth (1.333) = 301 N-units
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Frequency – taken from basestation details if specified; range of frequencies: 20 Mhz - 20 GHz.
-     
Radio Climite - the Continental Temperate climate is common to large land masses in the temperate zone. It is characterized by extremes of temperature and pronounced diurnal and seasonal changes in propagation. In mid-latitude coastal areas where prevailing winds carry moist maritime air inland, a Maritime Temperate climate prevails. This situation is typical of the United Kingdom and of the west coasts of the United States and Europe. For paths that are less than 100 km long, there is little difference between the Continental and Maritime Temperate climates, but for longer paths the greater occurrence of super refraction and ducting in maritime areas may result in much higher fields for periods of 10 percent or less of the year.
-     
Polarization - either horizontal or vertical polarization must be specified. The Longley-Rice model assumes that both antennas have the same polarization, either vertical or horizontal.
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Fraction of Situations - situation variability accounts for variations between 'like appearing' systems with the same system parameters and environmental conditions, including differences in the ability of individuals to accurately take field strength readings. It is at this point that 'hidden variables' enter, variables whose effects we do not understand or which we simply have not chosen to control. The values of these variables are at the whim of nature and differ between what would otherwise be identical situations. The effects of these differences produce the changes in observed statistics. Situation variability describes the effects of the changing conditions resulting from these 'hidden variables'. The situation variability for the calculation is expressed as a percentage from 0.1% to 99.9%. This value gives the fraction of 'identical' paths on which actual received field strength is expected to be equal to or higher than the field computed by the program. This variable allows you to specify how you want to deal with the 'hidden variables' that are 'at the whim of nature' as described above. Entering higher percentage confidence values effectively reduces the variability resulting from these factors. The resulting field strength predicted by the program will be lower, but with increased confidence that the actual field that could be measured would equal or exceed the computed value.
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Fraction of Time - time variability accounts for variations of hourly median values of attenuation due to, for example, slow changes in atmospheric refraction or in the intensity of atmospheric turbulence. The computed field strength value is an hourly median value; the actual field strength at the receiver location would be expected to be above that value during half of each hour and below that value for half of each hour. Time variability describes the effects of these changes over time. The time variability for the calculation is expressed as a percentage from 0.1% to 99.9%. This value gives the fraction of time during which actual received field strength is expected to be equal to or higher than the hourly median field computed by the program. This variable allows you to specify how you want to deal with the time variability of changing atmospheric (and other) effects as described above. Entering higher percentage reliability values effectively reduces the variability resulting from these factors. The resulting field strength predicted by the program will be lower, but with increased reliability that the actual field that could be measured would equal or exceed the computed value at any given time.
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Antenna - taken from basestation details if specified; select omni or directional antenna. If selected directional antenna, please enter azimuth into the field.
-     
Antenna Span - taken from basestation details if specified; specify maximum antenna span

         C.   Field Strength

 Field strength contours  are referenced to decibels over one microvolt per meter (dBuV/m). If the signal strength is greater than or equal to 128 dB over 1 microvolt per meter (dBuV/m), the color red is displayed for the region. If the signal strength is  greater than or equal to 118 dBuV/m, but less than 128 dBuV/m, then the color orange is displayed, and so on. No grsph is displayed for regions with signal strengths less than 8 dBuV/m.

 Field strength uses almost the same set of parameters as Path Loss. There are only two differences:

-      Signal Strength Down Limit [dBuV/m] instead of Path Loss DB threshold

-      Effective Radiated Power – power radiated from antenna.

-       

Legend for Field Strength will be displayed on the right hand side of the GE Plugin

5.     Point to Point Analysis

Point to Point Analysis is available under tools tab on the right hand menu (Fig. 8). It allows to do simple analysis between two points. Points can be custom points or sites. Custom Points can be moved around on a GE. Each point must contain GPS lattitude, GPS longitude and altitude (height). Frequency  and Fresnel Zone can be modified appropriately. Point to Point Analysis analyse terrain between two points and represents the results on a graph showing:

-      Point to Point Profile (of terrain)

-      Line of Sight Path

-      Earth's curvature contour

-      First Fresnel Zone (at specified frequency)

-      xx% of First Fresnel Zone

Fig. 8. Point to Point Analysis

 Analysis also allows to download detailed report that contains information like:

-       transmitter/receive site details (ground elevation, antenna height,azimuth)

-      all obstructions at the path

-      approximate calculation how high must antenna be raised to clear all obstructions

 Analysis ends with point to point red line generated between two selected  points to show breaks between them (Fig. 9). Note that you need to zoom in to see all breaks. In order to go back to the default view click on “Reload Earth View” button.

 


Fig. 9. Point to Point Analysis graph.
 
 
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