Gps System

GPS SYSTEM if you want more information about GPS (or other related to electronics and telecommunication) you can feel free to mail me at [email protected] I assure you that I will help you if that possible. Department of Electronics and Telecommunication Engineering, College of Engineering and Emerging Technologies, University of the Punjab.

First GPS satellite was launched into space in 1978.It tells the position of its user. This system uses the grid of altitudes and longitudes of earth. Global Positioning System is composed of three segments. 1. Space segment 2. Control segment 3. User segment

SPACE Segment: It consists of total 28 satellites from which 24 are operative and 4 are spares. Each satellite is at the altitude of 20200km, orbiting the earth every 12 hours. Total orbits of GPS are 6 (6X4) 4 satellites in each orbit. Each traveling at a speed of 11500km/hr.GPS system has six orbital planes each inclined to the equator by 55 degree. Each satellite has atomic clock with fundamental frequency of 10.23 MHz from which signals are generated.

CONTROL Segment: Control segment contains one master station, four monitor stations and four ground antennas. These are not accessible to users but the team that controls the GPS. There may be possibility of satellites traveling slightly out of orbits so the ground monitor stations keep track of the satellite orbits, altitudes, location and speed. The ground stations send orbital data to the master control station which in turn send corrected data to the satellites. This corrected and exact position data is called the “Ephemeris” data which is valid for about six hours.

USER Segment: User segment consists of only GPS receivers. The users that have a GPS receiver can use this system.

APPLICATIONS: Typical applications of GPS are land navigation, marine navigation, surveying, aerial navigation. Others are not listed here.

WORKING PRINCIPLE OF GPS On back and play the following formula works: Distance (D) = velocity (V) x time (T) Where D is the distance from satellite to receiver, V is the velocity of radio signal which is equal to the speed of electromagnetic waves and T is the time taken by radio signal from satellite to receiver. 1. For the communication purpose the band used is L-band. The range of frequencies of L-band is from 390 MHz -to- 1550 MHz. 2. For modulation of information signals two carriers are used. “L1” and “L2”. 3. It is essential that the antenna of GPS receiver have a direct view of satellite because L1 and L2 carriers propagate in straight line. 4. The power of transmission from satellite is about 50W. 5. “L1” carrier is broadcasted at 1575.42 MHz (10.23x154) 6. “L2” carrier is broadcasted at 1227.60 MHz (10.23x120) 7. “L1” carrier has two codes modulated upon it: a) Course/Acquisition code (C/A) modulated at 1.023 MHz. b) Precision code (P-code) modulated at 10.23 MHz. 8. “L2” carrier has only one code modulate upon it: a) ‘L2 P-code’ modulated at 10.23 MHz.

NAVIGATION MESSAGE Navigation message is information that satellite transmits to receiver. It contains… • satellite orbital and clock information • general system status message • Ionospheric delay model Navigation code has a low frequency of 50Hz modulated both on the carriers L1 and L2.