Table of Contents

 1.0  Introduction

 1.1  Location

 1.2  Cellular Phone Technology 101

 1.3  On-Line Cellular Coverage Maps

 2.0  Sources of Data

 3.0  GIS Line of Site Analysis Process

     4.0  Analysis Results

5.0  Field Validation of the Results

6.0     Conclusion

Listing of Figures

Listing of Tables

1.0  Introduction

     Cellular Phone Coverage (CPC) is dependent on optimal placement of cellular towers.   Based on experiences, as a Sprint Personal communication System (PCS) user, analysis should find that the southern area of Sarpy county is lacking in sufficient coverage.  Through the use of Geospatial Information Systems (GIS), it is possible to assess cellular coverage areas using viewshed analysis, available through three dimensional analysis functionality.  This type of functionality will be used to perform a line of site analysis of Sprint PCS coverage in the Sarpy county area of eastern Nebraska.  Field verification of the analysis will be performed using a Sprint PCS phone to measure signal strength and a GPS receiver to record locations by geographic coordinates. 

Fig. 1.  Location of Sarpy County in Nebraska

GIS data was derived from U.S. Census Bureau Tiger 2000 files available from: http://www.nrc.state.ne.us/databank/spat.html.

1.1  Location

     Sarpy county is located in the extreme eastern portion of Nebraska.  A majority of the boundary outline is defined by major Midwestern tributaries, the Missouri River and the Platte River.  To the north is Douglas county.  Most of Omaha falls within Douglas county, making it the most populous county in Nebraska.  As a result of the proximity to Douglas county, northeastern Sarpy county is densely populated.  The remainder of the county is very rural.

Fig. 2.  Sarpy County Population Density by Census Tracts. 

      Derived from 1990 U.S. Census Data (http://www.ciesin.org/)

    The physical geography of the region is predominately rolling hills, except in the extreme eastern, southern, and western areas of the county that consist of floodplain.  The most extensive floodplain is in western Sarpy county.  In this area, the Platte River has formed a broad floodplain.  As the river turns east to form the Southern boundary of the county, the floodplain narrows and the bluffs become more abrupt as a result of the sedimentary rock outcrops in this area.

Fig. 3.  Sarpy County Land Cover Diagram.

     Derived from Landsat TM imagery dated 1992.   Available from:  http://seamless.usgs.gov

1.2  Cellular Phone Technology 101

     The cellular phones that we enjoy today are the result of advancements in electronic and computer technology.  Electronic technology has enabled cell phones to become smaller yet more powerful.  Computer technology has greatly improved the signal/reception quality of the personal cellular phone.  Computers enable the processing of thousands of encoded digital signals at a given point of time.  Computers also convert the encoded signals to a discernable audible voice.  This manipulation goes undetected by cellular users.

     Cellular phones are dependent on a network of towers for receiving/sending calls.  The basic concept of cellular communication is that signals travel in a linear direction (straight line).  The influence of the ground surface enables a degraded signal to be received by a cellular user who is outside the line of site buffer of a cellular tower network.   

     Signal intensity is a function of line of site access to the cellular tower network.  As a cellular phone user travels

 away from a tower, the signal will decrease.  As you loose site of a tower, the amount of signal loss increases, until

which point the signal is lost completely. 

     Another factor that influences cellular signal intensity is land cover.  Heavily forested areas and buildings tend to

decrease (absorb) signal intensity.  In Sarpy county, tree coverage is significant along the Platte and Missouri

Rivers, as well as in established populated areas such as Papillion, LaVista, Springfield, and Bellevue.  The trees in

these areas tend to degrade signal intensity (reference Fig. 3).

     The placement of towers is directly proportional to population densities.  Transmitters/receivers that are located

on the cellular towers are limited to the number of calls that can be processed at any given time.  To compensate for

this limitation, the tower heights are decreased and the numbers of towers are increased in proportion to the

population density.  By decreasing the tower height, the area coverage and potential customer base that have access

to the tower transmitters/receivers is also decreased. 

1.3  On-Line Cellular Coverage Maps    

     A number of cellular companies have on-line services for assessing coverage in given geographical areas. 

NEXTEL 

Fig. 4.  NEXTEL Coverage Graphic (http://www.nextel.com)

SPRINT PCS

 Fig. 5.  Sprint PCS Coverage Graphic (http://www1.sprintpcs.com)

 Verizon Wireless  

Fig. 6.  Verizon Wireless Local Coverage Graphic (http://www.verizonwireless.com)

Verizon Wireless National Coverage 

Fig. 7.  Verizon Wireless National Coverage  (http://www.verizonwireless.com)

Cricket Cellular

Fig. 8.  Cricket Cellular Local Coverage (http://www.letstalk.com)

     The above maps are an example of the types of cellular coverage that is available in the greater Omaha area.  All of the on-line coverage maps provide a generalized representation of coverage areas.  The Cricket coverage map showed the most detail, listing major roads (interstates and highways) and surrounding cities in the Omaha area.   Verizon Wireless provides the most extensive communication network of all the cellular plans reviewed for this project.  Both NEXTEL and Sprint PCS networks are limited to major cities and significant transportation networks.  For this project, a more detailed coverage analysis and field validation will be performed on the Sprint PCS network in the Sarpy county region of eastern Nebraska.

2.0 Sources of Data

      The collection of source information for this project was a very time intensive process.  Of significant challenge was deriving accurate data on the Sprint PCS cellular towers in the Omaha region.  Initially, cellular tower locations were derived from the Federal Communication Commission’s (FCC) National Vertical Obstruction Database website (http://wireless.fcc.gov/cgi-bin/wtb-datadump.pl).  The initial database file contained over 750,000 records.  From this listing, Sprint PCS cellular towers in the Douglas/Sarpy county region were extracted.   The initial dataset listed geographic location in degrees, minutes, and seconds.  Locations were converted to decimal degrees in Microsoft Excel using the following formula:

Decimal Degrees=SUM(degrees+((minutes/60)+(seconds/3600))).

     A major drawback to the FCC database is that cellular towers under 33 meters are not required to be reported.  As a result, any analysis performed using this dataset would not be an accurate representation of the true line of site area.  Contact was made with the Sprint PCS technical representative for the eastern Nebraska region.  An agreement was made to provide a complete list of Sprint PCS tower locations that impact reception in Sarpy county.

                                 Listing of FCC SPRINT PCS Towers over the Greater Omaha Area

                             HGL = Ground elevation at Base of the tower    AGL = Height of tower

                   AMSL = Above Mean Sea Level     M = Meters   Note:  Tower elevations are in meters

Table 1.  FCC Sprint PCS cellular tower locations in the Douglas/Sarpy county region of eastern Nebraska.  Extraction date:  October 2003.

     The elevation of the top of the towers is necessary for performing line of site analysis.  The original dataset did not include the elevation in for the top of each tower.  Only tower height information was provided.  To establish the elevation at the top of each tower, the base elevation had to be established first.  Base elevations were derived using ArcGIS to extract elevations from United States Geological Survey (USGS) Digital Elevation Model (DEM) 10 meter data.  The base elevation height was then added to the tower height to determine the elevation for the top of each tower.

Complete Listing of SPRINT PCS Towers in the Sarpy County Area

HGL = Ground elevation at Base of the tower      AGL = Height of tower

AMSL = Above Mean Sea Level       M = Meters       Note:  Tower elevations are in meters

 Table 2.  Sprint PCS cellular tower locations in the Sarpy county region of eastern Nebraska.  Data provided by Sprint PCS.  Extraction date:  November 2003.

     The digital elevation data, as well as land cover was derived from the USGS Seamless National Database http://seamless.usgs.gov/.  Other GIS sources of information included the following:

n      Vector Data (Census TIGER/Line data)  http://www.census.gov

                 To include: roads, drainage, city, county, and census tract boundaries.

n      Population Data (1990 U.S. Census)    http://www.ciesin.org.

3.0 GIS Line of Site Analysis Process

Fig. 9.  Line of Site Process Flow Diagram

     Fig. 9 reflects the steps taken to complete the line of site analysis for this project.  The Albers equal area projection was selected since area analysis was being performed. 

The Albers equal area projection parameters: 

            Latitude of Origin  37.5, False Easting  0, False Northing  0, Prime Meridian   0

            Central Meridian  -096.0, Standard Parallels  40.75 &  41.50

GCS North American 1983, Datum  NAD83.

      Projections were modified using functions in the ArcGIS Toolbox.  Both the vector and the raster data were clipped to the project extent to reduce file/project size and decrease processing time to create the TIN model.  Vector data was clipped using the ArcGIS GeoProcessing Wizard.  Raster data was clipped using ERDAS Imagine 8.5.

     Viewshed analysis was performed using ArcGIS 8.3 ArcMAP and the 3D Analyst extension. The Sprint PCS tower line of site coverage area was established using the 3D Analyst viewshed.

4.0  GIS Line of Site Analysis Results

     Using GIS to establish line of site coverage of the Sarpy county Sprint PCS cellular tower network verifies that the most significant coverage corresponds to the populous region of the county (reference Fig. 2).  The only significantly populated area not covered by the cellular network line of site coverage is Springfield in the south central region of the county.  The southern region, as a whole, does not have significant line of site coverage. 

     Fig 10.  Sarpy County Sprint PCS Line of Site Analysis

5.0  Field Validation

     To validate actual Sprint PCS signal coverage, field readings were taken. 

Fig. 11.  SPRINT PCS Signal Intensity Field Validation Locations

 Signal intensities were measured throughout the county using capabilities available through the personal cell phone debug screen.  Signal intensities were measured in decibels.  Optimum signal reception ranges were provided by

 Sprint PCS:

·                < -85 db   Good

·        -85 to   -95 db  Marginal

·        -95 to -105 db  Poor

·               > -105 db  Potential loss of Signal  

Field Validation locations were recorded as geographic coordinates (latitude/longitude) using a Global Positioning System (GPS) device.           

Fig. 12.  SPRINT PCS Signal Validation Graphic

     The final Sprint PCS Signal Intensity Graphic was created using ArcGIS Spatial Analyst.  Interpolation of the surface model was established using inverse distance weighted computations.  Fig. 12 reflects a much greater area coverage then what was

represented by the by of line of site analysis (Fig.10) due to the attenuation of the cellular signal as a result of interaction with land cover elements.  This phenomenon tends to extend reduced signal reception beyond the limits of the line of site buffer.  The signal eventually becomes so weak that it is undetectable by cellular phone. 

     The Field Validation graphic shows Springfield as an area void of optimum signal coverage.  Southern Sarpy county, between Louisville and Schramm State Park is also a significant void area.  Loss of signal in this region is mostly due to significant changes in topography, as well as tree coverage.  Of particular interest is the attenuation of signal strength due to trees and buildings in the downtown Papillion area and the loess hills area in the northeastern corner of the county. 

6.0  Conclusion

    Cellular maps that are available on line are very generic in their representation of coverages. Of the on line coverage maps reviewed, Verizon has

 the most extensive.  To precisely define the cellular coverage extent, GIS provides a platform for performing detailed analysis.

     The positioning of the Sprint PCS tower network is directly related to the populous areas of Sarpy county.  The populated area of note that is lacking optimum signal coverage is Springfield.  This is an area that would benefit greatly from the addition of a cellular tower.  It’s apparent though GIS analysis performed that void areas exist in Sprint PCS signal coverage over Sarpy county.   Graphics generated from this analysis could serve several uses; as a reference to Sprint PCS users in Sarpy county to identify limited use areas, and as an aid in determining future tower placement in Sarpy county.

                                                        Listing of Figures

Fig. 1  Location of Sarpy County in Nebraska. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0

Fig. 2  Sarpy County Population Density by Census Tract. . . . . . . . . . . . . . . . . . . . . . . 1.1

Fig. 3  Sarpy County Land Cover Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.1

Fig. 4  Nextel Coverage Graphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3

Fig. 5  SPRINT PCS Coverage Graphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3

Fig. 6  Verizon Wireless Local Coverage Graphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3

Fig. 7  Verizon Wireless National Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3

Fig. 8  Cricket Cellular Local Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3

Fig. 9  Line of Site Process Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0

Fig. 10  Sarpy County SPRINT PCS Line of Site Analysis . . . . . . . . . . . . . . . . . . . . . . 4.0

Fig. 11  SPRINT PCS Signal Intensity Field Validation Locations. . . . . . . . . . . . . . . . . 5.0

Fig. 12  SPRINT PCS Signal Validation Graphic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.0

                                                        Listing of Tables

Table 1  FCC SPRINT PCS Cellular Tower Locations in Douglas/Sarpy County. . . . . .2.0

Table 2  Complete Listing of SPRINT PCS Towers in The Sarpy County Area . . . . . . .2.0