Comparing Cellular Network Coverage
As the world becomes more reliant on technology, adequate cell or mobile phone coverage is needed to keep people connected and keyed into our globalized society. Still, locations worldwide are devoid of this essential internet and cellular connection. The data visualization, analysis, and viewshed tools in Global Mapper can help in comparing cellular network coverage to determine where network connection is lacking and serve as a tool for analyzing and modeling the implementation of new infrastructure.
If you have a cell phone, you are likely familiar with the cellular coverage maps produced by cell phone carriers. The intent of these maps is to show where cell phone coverage is available within their network. In reality, many factors influence coverage in a particular area, and the map only captures a snapshot of the coverage area. Networks are constantly being changed and updated with the latest available software and hardware as each carrier strives to lead the pack in coverage in their network area. The cellular coverage for a specific area can be analyzed and visualized in Global Mapper using the viewshed tool.
Current Network Coverage
In this simulation, the cell phone coverage for the upper peninsula region of the US state of Michigan will be analyzed. Beginning in Global Mapper with a simple vector outline map and a publicly available layer containing point features representing each cellular transmission tower, the distribution of towers across the study area can be explored. Since the signals from towers located beyond the extent of the study area will influence and provide a signal to the upper peninsula, a 20-mile buffer is created around the study area, and all tower points within this buffer area are selected and copied to a new layer.
Among the included attributes of the cellular tower points, the network for each tower and overall structure height are important factors to be considered in this analysis. Considering that a viewshed will eventually be created based on these tower points, the ALLSTRUC attribute, which reflects the height above the ground for each tower, is renamed TRANSMITTER_HEIGHT. The attribute name TRANSMITTER_HEIGHT is a viewshed parameter attribute that will be recognized by Global Mapper in the viewshed analysis and used to appropriately vary the height of each tower in the analysis.
Since the point layer contains tower points for all networks in the area, it needs to be split by the LICENSEE attribute. Splitting the layer by attribute creates a new layer for each network containing only the towers relevant to that particular network. Being able to easily select all the towers for a specific network allows these points to be used in Global Mapper’s Viewshed Analysis tool.
Before a Viewshed Analysis can be executed in Global Mapper, terrain data needs to be added to the workspace. Global Mapper’s Connect to Online Data tool makes it easy to stream freely available elevation data into the project. The elevation data covering the area of interest is then exported to a local Global Mapper Grid file and loaded into the workspace for faster rendering and analysis.
With terrain loaded and a tower height value included in the feature attributes, the 3D viewer can be used to visualize the terrain relief and vertical prominence of the towers. Using the Point Style settings in Global Mapper’s Configuration options, a custom tower 3D model is loaded and assigned to the existing Tower point type. The tower points, which were originally designated as Unknown Point Features, can then be assigned the Tower point type on the Feature Type tab of the Vector Layer options. When viewed in Global Mapper’s 3D Viewer, the terrain data appears in 3D, and the designated tower model shows at the point location.
To conduct the viewshed analysis, the tower features for a specific network are first selected using the Digitizer tool. After enabling the Viewshed tool and choosing the option to create a viewshed for each selected tower location, additional viewshed parameters are specified in the setup dialog box.
The height of each tower or transmitter does not need to be specified in the setup, as the presence of the TRANSMITTER_HEIGHT attribute for each tower location will override the value entered in the dialog. Important parameters in the viewshed setup process include the receiver height, which in this case represents the approximate height above ground of a cell phone in use, and the view radius representing the effective distance from a tower within which a signal can be received. Additional options, including atmospheric correction, Fresnel zone specification, and free space path loss, allow for more complex viewshed analyses. To consider the cellular coverage from all towers impacting the study area, the option to combine individual viewshed layers is enabled to generate a single layer mapping the total coverage.
The viewshed analysis process creates several layers. A separate viewshed layer containing both raster and vector coverage data for each tower is generated, along with a combined gridded layer showing the overlap in coverage from all the towers in the area. Using these two layers, the coverage provided by each tower and the combined coverage for Michigan’s upper peninsula can be explored.
Not only does this coverage map show the covered and uncovered areas, the combined viewshed layer shows the strength of the signal based on how many towers provide coverage at any given location. Because this combined layer is a gridded layer, a custom shader can be designed to better visualize the coverage in this area.
Completing the viewshed coverage analysis for a second prominent cellular network in Michigan’s upper peninsula, the difference in coverage reach can be analyzed. Using the Image Swipe tool, the shaded raster coverage grids are visually compared to show common dead zones between the networks as well as overall differences in coverage.
In order to compute the total area with cellular service in Michigan’s upper peninsula, the areas of the gridded coverage layer are vectorized using Global Mapper Pro’s Vectorize Raster tool. This process involves the creation of polygons enclosing all areas with coverage from at least one tower in the network. After completing this data conversion process for both networks #1 and #2, the polygon coverage can be compared.
To summarize the coverage comparison as a percent of the entire study area, the Digitizer Measurement tools are utilized to determine the total area of the upper peninsula, and the areas of the network coverage polygons for each network. Summing the areas of network coverage for each network and comparing this to the total peninsula area, it is determined that network #1 has a coverage of 71% and network #2 has a coverage of 73%.
New Tower Placement
By focusing the analysis on Marquette County, one of the more densely populated counties in the large study area, significant dead zones in cellular coverage for network #2 are identified. Using the Difference operation in Global Mapper’s Spatial Operations tool, the coverage areas are inverted and cropped, creating polygons that show the dead zones in this county.
To improve the network availability in this area, a new cellular tower needs to be added. To determine the optimal location for a new tower, the local terrain is analyzed to identify local high spots or peaks within the current dead zones, since placing a tower at a higher elevation will increase the signal’s reach. After cropping the terrain layer to the area of the dead zones in the county, the Find Local Peaks and Depressions option in Global Mapper’s Contour generation tool, creates a series of vector points representing the local high spots. This process involves the identification of locations enclosed by a specified number of nested or concentric contours, so a smaller contour interval is chosen to identify additional local peaks in flatter terrain.
Each of the point features represents a potential location for the new transmission tower. In order to uniquely label these points, the Attribute Calculator is used to create a new Tower ID attribute derived from the automatically generated Index in Layer value. This unique identifier is applied as the point name and label, and will also be inherited by layers generated in the multiple-point viewshed analysis.
To narrow down the selection to locations that are likely to be buildable, the points are filtered by the average slope value, which was automatically applied to each identified peak during the contour creation process. Using the Search Vector Data tool, the points with an average slope below 10% are selected.
After restoring the terrain layer to encompass the full extent of the county, a Viewshed Analysis is then executed for each selected point using an average transmitter height value and the same receiver height and radius used in the previous viewshed analysis. In this multiple point viewshed analysis, the individual tower coverage areas are not combined because only one new tower will likely be added to the network.
As a result of this viewshed analysis, a new layer containing the viewshed coverage from each potential tower location is created. Since the points used in the viewshed analysis were named with the Tower ID value, each generated layer includes the corresponding tower ID value in the layer name. Viewshed layers in Global Mapper are unique as they have the ability to contain both vector and raster coverage data. In this new tower analysis scenario, the viewshed was set up to generate only the raster coverage map for each tower so no vector polygons were created.
To measure and determine the coverage area within existing dead zones for each potential new tower, vector features are generated from each viewshed layer using the Create Areas from Equal Values tool and cropping the bounds of this operation to the identified dead zones. This generates a layer of vector polygons for each viewshed that show the coverage from a tower within the identified dead zones in the network.
To determine which prospective tower location best covers the existing dead zones, the total area of the dead zones and the total coverage area for each tower within the dead zones need to be calculated. Individual enclosed area measurement for each polygon can easily be generated in Global Mapper by selecting all the areas and using the digitizer to Add/Update Feature Measurement Information. This action adds a new set of attributes to all selected features that includes an enclosed area measurement. Since the dead zones and the coverage polygons for each potential tower are contained in separate layers, a Layer Statistics Report can be created to sum the enclosed area values within each layer.
When creating a layer statistics report from Global Mapper, the input layers can be specified, and in this example, the dead zones layer and all the proposed tower coverage area layers are selected. Next, a grouping can be applied based on the feature layer name. When completed, this statistics report is a CSV file containing a feature count and total enclosed area for each group of features, in this case, for each layer. The total enclosed areas for each proposed tower coverage can be compared with the total enclosed dead zone area to determine the most effective new locations for a cellular tower.
Completing a percent coverage calculation by comparing the enclosed area of each proposed tower viewshed to the enclosed dead zone area, the top three proposed tower locations are identified. Since the originally identified potential tower locations were assigned a unique Tower ID value as a name, this identifier has been carried through all generated layers and reports making it easy to identify the points and viewshed layer for the top identified proposed towers.
WORK MADE EASY WITH GLOBAL MAPPER
Beginning with a layer of existing cellular tower points and freely available terrain data, a network coverage comparison and new tower analysis were completed in Global Mapper. With the top tower locations identified in Global Mapper, these locations, along with any other layers, like the selected tower viewshed layers or existing coverage, can be exported to any supported format. Using the wireless data transfer to Global Mapper Mobile, the tower locations can be loaded onto a mobile device for further data collection in the field as the potential new tower locations are further explored and analyzed.
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