Global Positioning System Reference
In-Depth Information
Table 9.5
Environments Characterized for L-Band Signal Transmission
Median Signal
Attenuations in
Decibels for Mobile/
Portable/In-Vehicle
1
Environment
Description
Open
Almost no trees or buildings
2.5/0.0/12.0
Rural light
Moderate to large number of trees, very few buildings 3.0/3.5/12.0
Rural moderate
Moderate to large number of trees, very few buildings 8.0/7.0/16.0
Rural heavy
Light to moderate forested area
16.0/10.0/18.0
Scattered trees and building structures (e.g., homes far
from mobile receiver or new residential areas with
little vegetation)
Suburban light
2.0/1.5/14.0
Suburban area with one- and two-story homes with
moderate amount of trees
Suburban moderate
3.5/6.5/13.5
Older suburban areas with large numbers of trees and
homes close to roads (e.g., older subdivisions in a city
like Chicago)
Suburban heavy
7.0/2.5/11.0
Small, sparse urban areas (e.g., urban areas of smaller
cities)
Urban light
2.0/2.0/16.0
Urban moderate
Urban areas from moderate-sized cities (e.g., Phoenix) 4.0/4.0/15.5
Urban heavy
Steel canyons (e.g., downtown Chicago)
5.0/15.0/16.0
In-building
residential
Buildings made of wood or stucco (e.g., Phoenix and
California residences)
12.5
2
In-building
commercial
One- to three-story motels, airports, and commercial
buildings
24.0
2
In-building
high-rise
High-rise buildings
30.0
2
1. The numbers in the column correspond to decibels of attenuation for the indicated conditions. The mobile case corresponds to
the reception conditions in an automobile with an antenna installed on its roof, while, for the in-vehicle case, the antenna is used
inside the car. The portable case corresponds to an antenna from a transportable satellite receiver with a large quad helix
antenna, not typical of GPS antennas embedded into cell phones.
2. These numbers correspond to the “Portable” case.
It should be noted that due to the requirement for reasonable transmitter effi-
ciency “Portable” antennas used for the data collection experiments are fairly large
and mounted to minimize head blockage. The result is some attenuation numbers
that are similar to “Mobile” attenuations. Due to the size of these antennas, they are
not considered acceptable for the GPS needs of a cellular handset. Appropriately
sized GPS antennas for handsets have significantly less gain than any antennas used
in the collection of the data discussed from [71, 72] or, for that matter, than conven-
tional GPS antennas for mobile or automotive applications.
As cellular telephones continue to shrink, the problem of integrating ade-
quate-performing GPS antennas becomes even more difficult. To perform well, the
antenna needs to present uniform gain in the up direction covering the full hemi-
sphere where GPS signals emanate. Simple patch antennas are used in automotive
applications and can be hidden under the dash or under the rear deck with little
effort and provide the ideal RHCP to match the satellite transmitted signal. How-
ever, placement of a dedicated GPS antenna in a cell phone forces compromises in
performance with regard to antenna efficiency and gain pattern, especially when the
user can hold it in many different orientations (handheld next to head, in the dialing
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