Global Positioning System Reference
In-Depth Information
Cell phone
transmitter
Cell phone user in building
Information from
base to cell phone
GPS
base
station
FIGURE 12.28
Concept of a cell phone GPS system.
coherent integration longer than 10 to 20 ms. This way, one can create a long
local signal based on the cell phone received GPS information from the base
station and perform correlation with received weak signals to acquire it. The
satellite positions can also be obtained from the cell phone information. The
GPS receiver with the cell phone unit is not required to decode the navigation
data, and this limits the sensitivity of a GPS receiver. The only information
required to find the cell phone operator position is the pseudorange. With the aid
from the cell phone information, the sensitivity can be improved at least another
10 dB such that a
C/N
0
=
14 dB can be achieved
(
13
,
14
)
.
The concept of such a GPS cell phone system is illustrated in Figure 12.28.
Under this arrangement, when the GPS signal at the cell phone is strong, it can
determine the user position very rapidly, such as in a few ms because the receiver
does not need to decode the signal. When the input signal is weak, the receiver
can acquire the signal and determine the required pseudorange.
A software GPS receiver can have many other applications that are difficult
for a hardware receiver to achieve. It is possible for a software GPS receiver
to perform additional functions besides user position determination by using the
same hardware but different software. As the processing speed improves, the
bandwidth of a software receiver could be increased to process more wideband
signals. It is likely that in the near future, there will be built several different
types of receivers using different software but only one set of hardware.
REFERENCES
1. Braasch, M., Professor at Ohio University, has provided the Matlab program.
2. Lin, D., Tsui, J., “Direct Y(P)-code acquisition algorithm for software GPS receivers,”
ION GPS-99, pp. 363 - 367, Nashville, TN, September 14 - 17, 1999.
3. Kaplan, E. D.,
Understanding GPS Principles and Applications
, Artech House, Nor-
wood, MA, 1996.
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