Much of the discussion surrounding cell tracking, cell phone GPS and cell phone tracker software could be helped by a GPS Satellite primer.
GPS satellites broadcast signals from space that GPS receivers use to determine three-dimensional location (latitude, longitude, and altitude) plus precise time. GPS stands for Global Positioning System and is a network that is composed of 3 main segments: Space Segment, Control Segment and User Segment.
The GPS Space Segment incorporates twenty-four to thirty-two satellites that orbit the earth at a height of about 12,000 miles. These satellites are also known as as the GPS Constellation, and they are orbiting twice a day. They are not parked over one spot, they travel at over 7,000 mph. GPS satellites are solar powered but have battery backup for when they are on the dark side of the earth. They are placed so that there are at least 4 satellites ?visible? from any point on earth. Small rocket boosters on each satellite keep them properly positioned. The satellites last about ten years until all their fuel runs out.
GPS Satellites are not communications satellites. Geostationary or communications satellites are at a much higher orbit of about 22,300 miles above the equator. These satellites are used for weather forecasting, satellite TV, satellite radio and most other types of global communications. At exactly 22,000 miles above the equator, the earth’s force of gravity and centrifugal forces are offset and are in balance. This is the ideal location to position a stationary satellite. The earth rotates at about 1,000 miles an hour, and because of their high earth orbit the earth-synchronous satellites need to travel at about 7,000 mph to sustain position. This is just about the same speed as GPS satellites, but since geostationary satellites are 10,000 miles further away they don?t move relative to the earth.
The GPS Control Segment consists of Master Control Station, an Alternate Master Control Station, and a host of dedicated and shared Ground Antennas and Monitor Stations that work together to ensure the satellites are working correctly and the information they send to earth is accurate.
The GPS User Segment consists of of GPS receivers taking the shape of devices and , laptops, in-car navigation devices and hand-held tracking units along with the people that use them, and the software applications that make them work.
GPS receivers often take a long time to become ready to use after it’s turned on because it must acquire some basic information in addition to finding GPS satellite signals. This delay can be caused when the GPS cell phone has been unused for days or weeks, or has been transported a far distance while unused for. The GPS must update its almanac and ephemeris data and store it in memory. The GPS almanac is a set of data that every GPS satellite transmits. When a GPS receiver has current almanac data in memory, it can capture satellite signals and calculate initial location more quickly.
In the event that satellite signals are not available, or precision is less important than battery life, making use of Cell-ID is a useful alternative to GPS mobile phone location. The position of the mobile phone can be computed by the cell network cell id, which determines the cell tower the cellphone is using. By understanding the location of this tower, then you can know approximately the spot where the handset might be. Still, a tower can cover an enormous area, from a few hundred meters, in high populationdensity regions, to a few kilometers in lower density areas. For this reason location CellID precision is less than than GPS accuracy. Nonetheless tracking using CellID still presents a truly viable substitute.