RADIO BASED NAVIGATION SYSTEM

Radio-based navigation system developed by DOD initially operated in 1993 ,fully operated in 1995.

Trilateration intersection of spheresSV RangingTiming why consistent, accurate clocks are requiredDetermining Range of GPSDilution of precision

GPS involves THE FOLLOWING

Space segment of GPS satellites.

GPS Satellites Details.

2-Dimensional Example

Total number of satellites are 30,24 are under work,6 are extra satellites.

Each satellite has 6 orbits. 3 satellites works for GPS, 4th satellite work for accuracy. 3 satellites for 2d fix.

Satellite orbital distance 20,000km. Orbital speed is 14,000km/hr 60 degrees apart and 55 degrees with respect to equatorial plane. Use measurement of 4 satellites Distance=travel time*speed of light

Distance from two satellites defines 2 points (in 2 dimensional space.)

The distance from a third satellite narrows the location to an “error triangle.”

THREE SV RANGES KNOWN Satellite-1) 20,000km radius Satellite-2) 21,000km radius Satellite-3) 22,000km radius

Located at one of these 2 pointsHowever, one point can easily be Eliminated because it is either not on earth or moving at impossibleRate of speed.

CESIUM ATOMIC CLOCKS are used in GPS satellites

Due to general theory= 45 microseconds special theory= 7 microseconds overall effect= 38 microsecondsHence GPS satellite are slowed by 38

microseconds

If 1/100th of a second error occursit introduce error of 1,860 miles.

Receiver and satellite use same code GPS sync with each satellite by shifting the

timing of the start of an internally generated PRN code.

Compare incoming code with receiver generated code

From satellite

Measure time difference between the same part of code

From receiver

Series of ones and zeroes repeatingevery 1023 bits. So Complicated alternation of bits that pattern looks random thus called“pseudorandom code”.

Ionosphere(Charged Particles)

Troposphere

Technique used to correct some of these errors Referred to as “differential GPS” or DGPS In DGPS, two GPS receivers are used

One receiver is located at an accurately surveyed point referred to as the “base station”

A correction is calculated by comparing the known location to the location determined by the GPS satellites

The correction is then applied to the other receiver’s (known as the “rover”) calculated position

GPS system allows you to search the local area for nearby AMENITIES such as hotels, restaurants etc.

GPS is very useful during adventures. GPS devices are perfect for water

navigation. Since there are no landmarks in large

bodies of water.

www.slideshare.net/RishiAadi/GPS www.esf.edu/for/herrington/557/557pps/GPS

www.seminarslides.com/ppt/global-positioning-system

en.wikipedia.org/wiki/GPS www.nwcg.gov/pms/pubs/475/PMS475 www.pocketgpsworld.com/howgpsworks.ph

www.physics.org/article-questions.asp?id=55