Page 25 - Integrated Wireless Propagation Models

I n t r o d u c t i o n t o M o d e l i n g M o bi l e S i g n a l s i n W i r e l e s s C o m m u n i c a t i o n s 3

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50,000 1 scale topographic maps. Each map size was roughly 5 x 8 square miles. The
contour lines were in 20-ft increments. The maps were purchased from local map
stores in Morristown, New Jersey. The verification project was carried out in a joint
effort with Bell Labs and the TriState Team (New York Bell, New Jersey Bell, and
New England Bell). First, to make an elevation-grid map from a 5 x 8-sequence-mile
topographic map, the map was divided into 18 x 24 grids. Each grid is about one-half
square kilometer. Because several terrain elevation contour lines run through each
grid, an eyeball average of the terrain elevation lines in each grid representing the
elevation of that grid was proposed. Then the elevation-grid maps were generated.
The project team members were responsible for providing the elevation-grid maps in
their selective geographical area with the measurement data available in such corre­
sponding areas. Bell Labs took the elevation-grid maps received from the team mem­
bers and applied them to the Lee model, then the predicted signal strengths on
any particular streets on the maps were obtained. Use of the predicted outcome to
compare with the measured data showed a good match between the measured and
predicted data. The eyeball average values turned out to be good enough to be used
for the Lee model prediction. Nevertheless, the eyeball average process for getting the
grid maps and the hand calculation of the Lee model were labor intensive. The alter­
native was to purchase the 1 o x 1 o map tape of the DMATC (Defense Map Agency
Topographic Center). It had 1200 x 1200 data grids. The size of each grid was 3 arc­
second x 3 arc-second. The altitude value in each grid was stored in the tape from a
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250,000 1 digitized map. Bell Labs took an average of 30 altitudes from the surround­
ing 30 grids (5 x 6 grids) to get an average altitude for each grid. Using this average
altitude at each grid to compare with the value obtained from the eyeball average at the
same grid, the result was that the differences were very small. Therefore, the average
altitudes from DMA 1 ox 1 o tape were accepted to make the process less labor intensive.
Bell Labs programmed the Lee model and stored the DMA tapes into the computer. The
implementation of the Lee model using computer computation was called ACE
(Advanced Coverage Estimate) in 1978. The name of ACE has changed to ADMS (Area
Deployment of Mobile System). All the Baby Bells deploying their cellular systems in
1983 were using the ADMS tool. The Lee model9 went through many phases of revision
at PacTel and AirTouch. The Prediction Tool called Phoenix was based on the Lee model
and was used internally in all the Pactel and, later, AirTouch markets, both domestic
and international, such as in Germany, the United Kingdom, Italy, Portugal, Romania,
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Spain, Korea, and Japan. Lee's books A,s described the model very briefly. In 1985, some
portion of Ericsson's early internal prediction model used the Lee model.
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There are many commercial prediction tools that also used the Lee modeP- 3 In
2008, the Federal Communications Commission (FCC) and the International Telecom­
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munication Union (ITU) paid a lot of attention to the Lee model.l4• 5 This model has not
been patented. Therefore, it is worthwhile to be documented in this book.

1.5 Basic System Operations16
In every wireless system, an antenna is used to radiate and receive electromagnetic
energy. The antenna acts as a transducer between the system and free space is referred to
as the air interface. While a comprehensive treatment of the subject of antennas is beyond
the scope of this book, it is helpful to understand how they operate and how they can
affect mobile signal strength. For many types of antennas, we can estimate the gain from
the physical dimensions (size and shape) or from knowledge of the antenna beam widths.