GNSS Basics

Question 1

The process of finding your way from your current location to your desired destination is known as…

Answer 1

Navigation

Question 2

What were the 3 early methods of navigation?

Answer 2

1) Piloting (maps/landmarks)
2) Dead reckoning (straight line)
3) Celestial (stars)

Question 3

What is GNSS?

Answer 3

Global Navigation Satellite System

Question 4

What are the 2 methods of electronic navigation?

Answer 4

Radio navigation & GNSS

Question 5

What is the overarching term for satellite systems that provide global geospatial positioning?

Answer 5

GNSS

Question 6

What are the 2 GNSS systems for position determination?

Answer 6

Triangulation & trilateration

Question 7

Which GNSS system uses angles/azimuths from known landmarks to figure out your location?

Answer 7

Triangulation

Question 8

Which GNSS system uses intersecting spheres to determine location?

Answer 8

Trilateration

Question 9

The ~ range from an SV to a user’s receiver is known as…

Answer 9

Pseudorange

Question 10

What do receivers use as the pseudorange?

Answer 10

The radius of a sphere, centered on the satellite’s location

Question 11

How many circles are required to pinpoint a location in triangulation?

Answer 11

3

Question 12

How many spheres are required to pinpoint a location in trilateration?

Answer 12

4

Question 13

Errors in GPS signals that affect trilateration are collectively known as…

Answer 13

User Equivalent Range Error (UERE)

Question 14

What are the 2 types of UERE?

Answer 14

1) User Range Error (URE)
2) User Equipment Error (UEE)

Question 15

What 2 errors contribute to URE?

Answer 15

1) Satellite clock error
2) Satellite ephemeris error

Question 16

What causes satellite clock error?

Answer 16

The drift of the SV clock from actual GPS time

Question 17

How do satellite clock errors affect different users?

Answer 17

Equally, regardless of their distance from the SV

Question 18

What causes satellite ephemeris errors?

Answer 18

The difference between actual SV location and the position predicted by SV orbital data in NAV message. Also, perturbations.

Question 19

How do ephemeris errors affect different users?

Answer 19

Differently, based on their distance from the SV

Question 20

What are the 4 contributors to UEE?

Answer 20

1) Ionosphere
2) Troposphere
3) Receiver noise
4) Multipath

Question 21

What are the 3 ways the ionosphere causes UEE?

Answer 21

1) Scintillation
2) Refraction
3) Group delay

Question 22

How does the troposphere cause UEE?

Answer 22

Refraction

Question 23

How does receiver noise cause UEE?

Answer 23

Interferes w/receiver performance (larger pseudoranges)

Question 24

How does multipath cause UEE?

Answer 24

Delays reception of reflected GPS signals

Question 25

What is DOP?

Answer 25

Dilution of Precision

Question 26

What would cause a poor (high) DOP?

Answer 26

Satellites being too close together

Question 27

What are the 4 essential elements of GNSS?

Answer 27

1) Timestamp 2) Ionospheric data 3) Clock correction 4) Satellite ephemeris (location)

Question 28

Which essential element is required to calculate pseudorange?

Answer 28

Timestamp

Question 29

Which access scheme is used in GNSS?

Answer 29

CDMA (Code Division Multiple Access)

Question 30

An SV's signal is identified from many others in the same BW by use of what?

Answer 30

PRN codes

Question 31

What are the 3 scintillation effects that can impact GNSS signals?

Answer 31

1) Refraction 2) Group delay 3) Diffraction/scattering

Question 32

What are the 5 GPS channels and their uses?

Answer 32

1) C/A for civilian use 2) P/Y for military use 3) L3 for NUDET (nuclear detection) data 4) L4 for ??? 5) L5 for safety of life

Question 33

Why can we obtain only pseudoranges and not precise ranges?

Answer 33

Because of clock errors and atmospheric refraction

Question 34

In what band does GPS operate?

Answer 34

L-band, which is heavily affected by scintillation

Question 35

Which countries are associated with the following GNSS systems? 1) GPS 2) GLONASS 3) Galileo 4) BeiDou 5) QZSS 6) IRNSS

Answer 35

1) USA 2) Russia 3) Europe (EU) 4) China 5) Japan 6) India