GPS

Question 1

Five requirements for GPS:

Answer 1

. Location - determining position
. Navigation - from one location to another
. Tracking - monitoring object or personal movement
. Mapping - creating maps of the world
. Timing - bringing precise timing to the world

Question 2

Characteristics:

Answer 2

. US owned utility
. Satellite based radio system - provides positioning, navigation, and timing
. Useful tool for civilian and military use
. US AF develops, maintains and operates the space and control segments

Question 3

Three segments of GPS:

Answer 3

. Space segments - the satellites
. Control segment - the ground stations
. User segments - the user GPS receiver

Question 4

Space segment:

Answer 4

. 24 - 32 satellites, orbiting in MEO
. 32 satellites consist of:
- six orbital planes with 4 satellites each:
- 24 satellites make up core constellation
- orbits arranged so at least six sats are always within line of sight
- any satellites after the 24 will improve the precision of GPS by providing redundant measurements
With an expanded constellation, nine satellites are usually visable

Question 5

Control Segment:

Answer 5

Current operational control segment:
. Master control station (MCS)
. And alternate MCS
. 11 command and control ground antennas
. 16 monitoring sites

Question 6

User segment:

Answer 6

GPS receivers and the user community.

The typical receiver is composed of:
. Antenna and pre-amplifier
. Radio signal microprocessor
. Control and display device
. Data recording unit
. Power supply

4 satellites are required to compute the four dimensions of position and time.

Question 7

GPS Frequencies:

Answer 7

L1 - L5
1575.42MHz - 1176.45MHz

Question 8

L1

Answer 8

1575.42MHz

Question 9

L2

Answer 9

1227.60MHz

Question 10

L3

Answer 10

1381.05MHz

Question 11

L4

Answer 11

1379.913MHz

Question 12

L5

Answer 12

1176.45MHz

Question 13

GPS signals:

Answer 13

2 low-power radio signals
They travel by line of sight
3 different types of information:
. Pseudorandom code - ID code
. Ephemeris data - satellites position, health of satellite, current date and time
. Almanac data - tells GPS receiver where the satellite should be, orbital information for all satellites in the system

Question 14

GPS accuracy:

Answer 14

Coarse acquisition C/A
Precise P(Y)

Crypto loading provides more reliable position, and also ensures it is more resistant to jamming and interference

Question 15

Coarse acquisition:

Answer 15

Civilian and military GPS receivers without crypto loaded.

Question 16

Precise:

Answer 16

Only available to military GPS receivers, only available if the receiver is loaded with crypto.

Question 17

Tactical utility of GPS:

Answer 17

. Enhance the ability of commanders to track and navigate
. Pinpoint precision
. Picture of the location of friendly and enemy forces

Question 18

Bowman use of GPS:

Answer 18

. 24 GPS satellites (21 active, 3 spare) in orbit, 20,200km above Earth
. 4 satellites can be accessed
. Weather and terrain can be influencing factors
. 3 satellites can give 2D fix,
. 4 satellites can give 3D fix including altitude

Question 19

Vehicle Appliqué GPS Receiver (VAGR):

Answer 19

. BCIP - Bowman Combat Infrastructure Platform require precise timing and positional information. Positional information is used by ComBAT.
. Central source for GPS information within bowman platforms - benefits of situational awareness
. Accepts crypto for increased security

Question 20

Reacher use of GPS:

Answer 20

. Visible satellites - has to be over 4 to be enabled

Question 21

Telecoms utility of GPS:

Answer 21

. Timing source for multiple devices and multiple networks
. GPS source provides network frequency verification and time of day
. 3 satellites for 2D positional fix - positioning, nav, timing
. 4 satellites for 3D positional fix - plan and height

Question 22

8 GPS vulnerabilities:

Answer 22

1. Atmospheric delays
2. Signal multipath
3. Receiver clock errors
4. Orbital errors
5. Number of satellites visible
6. Radio interference or jamming
7. Faulty mapping software
8. Major solar storms

Question 23

How GPS knows where you are? 4 steps:

Answer 23

1. Satellites broadcast radio signals providing information.
2. GPS signal travels through space at the speed of light
3. GPS receiver receives the signal, uses the information provided to calculate distance from each satellite
4. Once I had the distance of 4 satellites it can use geometry to calculate the location on earth.