GPS Midterm

GPS

is a satellite-based navigation system composed of a network of satellites placed into orbit by the United States Department of Defense (DOD)

1978

The Global Positioning System (GPS) was developed in

GPS

is a satellite-based navigation system composed of a network of satellites placed into orbit by the United States Department of Defense (DOD)

1978

The Global Positioning System (GPS) was developed in

Global Navigation Satellite System

is a blanket term that includes GPS, and all other forms of satellite navigation systems

1100 - 1600 MHz

Bandwith of the L-Band

1980s

When was GPS made available for civilian use

24 and 5

How many satellites are in the satellite constellation and how many satellites are visible at any time

3

How many satellites does a receiver require for two-dimensional positioning

4

How many satellites does a receiver require for three-dimensional positioning

Department of Defense

oversees the satellite constellation and monitors satellite operations.

World Geodetic System 1984 (WGS-84)

The GPS coordinate system is based on the

GPS

is the fastest growing type of navigation in aviation. It is accomplished through the use of NAVSTAR satellites set and maintained in orbit around the earth.

• Space Segment

• Control Segment

• User Segment

What are the segments of GPS

Space Segment

The spatial segment is composed of a constellation of 24 satellites.

55 inclination to the equator

What is the inclination of the orbit of the satellites

approximately 20,200 km with an orbital period of 12 sidereal hours

What is the altitude of the orbit of satellites

L1 channel at 1575.42 MHz

What frequency is used in civilian aviation

L2 channel 1227.60 MHz

What channel is used by the military

P (Y) or Precision Code and C/A or Carrier Acquisition Code

What are the two ranging codes of the signals L1 and L2

The L5 signal

is a significant upgrade, designed for improved accuracy, reliability, and signal robustness. It operates at 1176.45 MHz. It is designed to be more resistant to interference and provide better performance in challenging environments. It is also designed for safety of life applications, like aviation.

L1 (1575.42 MHz):

Key Features:

-          Primary civilian frequency.

-          Carries the C/A code (public) and P(Y) code (military).

-          Transmits the navigation message containing essential data (time, satellite health, ephemeris, almanac).

-          The almanac is crucial for initial satellite acquisition.

Military Advantage:

-          P(Y) code offers superior interference rejection.

L2 (1227.60 MHz):

Key Features:

-          Lower frequency, better penetration.

-          Originally military, now includes civilian L2C code on newer satellites.

-          Used for ionospheric error correction in dual-frequency receivers.

-          Provides redundancy. Benefits:

-          Improves accuracy in high-precision applications.

L5 (1176.45 MHz):

Key Features:

-          Newest civilian frequency.

-          Higher transmission power and advanced signal design.

-          Improved accuracy, reliability, and robustness.

-          Designed for safety-of-life applications (aviation).

-          Wider bandwidth, and longer spreading codes, which improves processing gain.

using the CDMA or Code Division Multiple Access

How is the GPS signal transmitted

CDMA (Code Division Multiple Access)

GPS receivers use these codes to identify and decode signals, allowing them to pinpoint the source and extract the necessary information, even when the signals are weak.

The control segment of the GPS

monitors each satellite to ensure its location and time are precise. This control is accomplished with five ground-based receiving stations, a master control station, and three transmitting antenna.

USER SEGMENT

This segment is constituted by the GPS receiver and allows:

-          signal acquisition,

-          distance calculation,

-          navigation computation (Satellite choice, positioning, propagation corrections),

-          detection and isolation of failed satellites.

TRILATERATION

-          This method uses distances to determine a location.

-          It involves measuring distances from known points.

The GPS receiver

measures the time it takes for a signal to arrive from three transmitting satellites.

186,000 miles per second

How fast does radio waves travel

20 meters horizontal

How far horizontal is the range of current GPS accuracy

WIDE AREA AUGMENTATION SYSTEM (WAAS)

It consists of approximately 25 precisely surveyed ground stations that receive GPS signals and ultimately transmit correction information to the aircraft.

1-3 meters laterally and vertically

What is the range of position errors that the WAAS system can reduce

7.6 meters

How much range does the WAAS improve the accuracy of the GPS

TSO-129A

What standard should GPS receivers be built to