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For the avid readers who might want the answer key, here goes........
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2h. Review questions
Question 1 of 7
If the distance to your satellite is 20,135,196.834 meters, how long does it take the signal to reach you? (Speed of light = 299,792,458 m/s)
Time = Distance ÷ Speed of Light
Time = 20,135,196.834 m ÷ 299,792,458 m/s
Time = 0.067 s
Question 2 of 7
What is the name given to the unique code assigned to each GPS satellite? (Choose the best answer.)
a) Pseudorandom noise (PRN) code
b) Unique identity designation (UID) code
c) Identity confirmation code (ICC)
d) Digital satellite identity (DSI) code
Pseudorandom code (or PRN code) is the unique code assigned to each GPS satellite.
Question 3 of 7
To estimate the travel time of a GPS signal from a satellite to your GPS receiver, a copy of the PRN code is generated by the -- receiver satellite satellite tracking station and then compared to the code received from the -- receiver satellite satellite tracking station .
receiver, satellite
To estimate the travel time of a GPS signal from a satellite to your GPS receiver, a copy of the PRN code is generated by the receiver, and is compared to the code received from the satellite.
Question 4 of 7
To estimate the travel time of the signal from the satellite to the receiver, the code produced by the receiver is -- delayed stopped amplified until the correlation between two signals jumps to its -- minimum maximum end point .
delayed, maximum
To estimate the time of travel of the signal from the satellite to the receiver, the code produced by the receiver is delayed until the correlation between the receiver-generated code and the code received from the satellite jumps to its maximum.
Question 5 of 7
Pseudorange:
(Choose all that apply.)
a) is an approximate distance between a GPS satellite and the GPS receiver
b) is contained in the ephemeris
c) may be accurate to within a few centimeters
d) is based on the travel time of the radio signal
Pseudorange is an approximate distance between a GPS satellite and the GPS receiver antenna, based on the travel time of the radio signal. The ephemeris contains information on the exact position of the satellite at a given time, but not the distance to the receiver. Pseudorange is not accurate beyond a few hundred meters. Additional ranging methods are needed to refine the accuracy to within a few centimeters.
Question 6 of 7
In its most fundamental form, what are the knowns and unknowns in the basic trilateration system of equations for computing a GPS satellite-based position?
Satellite positions (xS,yS,zS) is -- known unknown .
known
Satellite clock bias (TS) is -- known unknown .
known
Receiver position (xR,yR,zR) is -- known unknown .
unknown
Receiver clock bias (TR) is -- known unknown .
unknown
In GPS positioning, the satellite positions are considered known (they are provided as part of the broadcast ephemeris) as is the satellite clock bias (also provided in the broadcast ephemeris). The receiver position is unknown, as is the receiver clock bias.
Question 7 of 7
Why is the solution of a position approximate? (Choose the best answer.)
a) We never really know where the satellites are in space
b) There are always more “unknowns” than “knowns” in our mathematical solutions
c) Measuring distance at the speed of light requires extremely precise timing, which is hard to achieve perfectly
The solution of a basic GPS-based position is approximate because the signal being used to measure the distance between the satellite and a point on Earth is travelling at the speed of light. For this to work, we need extremely precise timing. Even a millisecond of error can cause hundreds of meters of positional error. Although there are numerous “unknowns” in our positional equations, there are typically enough “knowns” (given signal reception from at least four satellites) to approximate a mathematical solution. GPS positioning requires us to know where the satellites are in space at the time of GPS signal transmission.